Thursday, June 4, 2015

Demand Response - The Not so Holy Grail of Renewable Energy

The variability (i.e. the sun isn't always shining and the wind isn't always blowing) of wind and solar is a big problem, which is why cheap, scalable and efficient energy storage is often called the holy grail of renewable energy, and with good reason.

Que the inspiring music.

Indeed if such a thing existed I wouldn't feel so concerned about the future and as a consequence would probably not be writing blog posts about energy, but I'm not going to be talking about energy storage with this post.  Instead I'm going to be talking about demand response the... well lets call it the not so holy grail of renewable energy.

It comes with one of those little umbrellas.  How bad could it be?
Perhaps I'm being a tad over dramatic here. Demand response just means for people or businesses to stop using electricity when the utilities want them to. I'm not against demand response on principle. It could help save a lot of money. My problem is that the people pushing for this the most are wind and solar advocates who want to help match demand to the wind and sun. If they want to use this to make our demand match in that way they are going to have get control over large part of people's lives.

As I see it there are two major issues that need to be considered. One is that demand response for households creates the risk of electricity rationing which would likely have a larger effect on poor people. This both posses an issue of social justice, and an issue over a reduction in the benefit that people get from 24/7/365 electricity. Being able to flip a switch to create light wherever you need it is one of the best things about modern life. Losing such utility is not something that should be taken lightly. I mean do we really want to live our lives at the mercy of the weather and seasons?

I'd love to turn up the thermostat, but today isn't very windy or sunny.  As a ration consumer I have to respond to price signals.   
Another issues has to do with manufacturing and the price of stuff.  Some of the cost of manufacturing is in the form of costs that don't vary by the amount that is made.  These costs are refereed to as fixed costs.  An example of fixed cost for a factory would be machinery or the building.  These are things that have to get paid for regardless of how much the factory produces.   If you produces a lot then the fixed cost gets divided up between all the stuff you've made and fixed costs becomes less per unit produced.

Imagination that you had a fixed cost of 5,000,000.  If you produced only a single item then the fixed cost for that product would be 5,000,000.   If you produced 5,000,000 items then the fixed cost for each of those items would be one dollar.

It's easy to see that  the effect fixed costs have on the cost of producing an item can vary a great deal.  With that in mind imagine that you had two identical factories.  The only difference is that one factor operates 24 hours a day and the other factory is solar power so it only operates when it's sunny enough.  Let's say the solar power factory operates 20 percent of the time.  From this we can tell that the fixed cost for items produced by the solar powered factory will be 5 times more than the fixed cost for items from the factor that runs 24 hours a day.   Depending on what's being made that could be a substantial difference.   Also, some manufacturing processes can't be stopped in the middle and taken up again whenever it's convenient because doing so would damage machinery and/or wasted materials, time and other resources.

After reading all this you might think I'm against demand response, but that isn't true.  Demand response could be useful, just not for matching electricity use to the wind and sun.  The best use of the technology would be to make up for small seasonal, and peak electric use, variations.  For example it would make a lot more sense to shut down a factory (one that can take that kind of start and stop) for 5 hours a year then it would be to build a natural gas plant (and all it's required pipelines and power lines) that is only needed for 5 hours a year.    At any rate weather this article changes you mind about anything I hope it at least makes you think.

Until next article.

Wednesday, March 11, 2015

Just how Safe are Fossil Fuels, Wind, Solar and Nuclear Power?

This article I'm going to compare safety for different form of electric generation.  Lets start with the energy deathprints.

Energy’s Deathprint

Energy's deathprint is a rarely talked about measure of the number of deaths per unit of energy produced for different power sources.  Here are the results from two studies on it.

From page 168 Sustainable energy without the hot air

As you can see coal, oil and biomass are particularly bad.  This is because of small particles released while burning thing (i.e. ash or fly ash).   These don't agree with people very much.  Not only do these particles cause deaths, but they also cause other health problems.  Some countries do a better job of filtering them out then others.  With a bit of searching you can find info for a variety of similar studies.   Here is another one.  I thought this review of it was particularly insightful. 

Carbon Footprints

Global Warming is a serious issue.  One study projects that...
Worldwide, upward of 20,000 air-pollution-related deaths per year per degree Celsius may be due to this greenhouse gas.
That's rather extrema considering how long the temperature changes are projected to last.  Here is a graph that shows the carbon footprint for various forms of electric generation. 

From Carbon footprint of electricity generation by Stephanie Baldwin
 The units for the graph are gCO^2eq /kwh.

From page 8 of Carbon footprint of electric generation.  I suggest reading the whole PDF.  It's not very long, and definitely worth it. 

Ranges in each electricity generation technology are due to
  1. Differences between individual plants – some older and/or less efficient
  2. Different technologies – e.g. run-of-river vs. reservoir storage
  3. Different LCA input (boundary definition) parameters
  4. Different studies – some studies older, so had older data (2000 was cutoff date)

In regards to the difference for nuclear power.  From page 18 of Carbon footprint of electric generation.
  1. Nuclear also has a very small carbon footprint 
  2. Most CO 2 emitted during uranium mining (40% of life cycle CO2) 
  3. Global uranium reserves – lower grades may cause footprint to rise in future 
  4. 3 studies: AEA ( to 6.8g), Öko ( to 30-60g), Storm van Leeuwin ( 60 to 120g)
I would like to add to this that there are two important issues for understand nuclear power's carbon footprint.  One is the method of fuel enrichment.  Some have a bigger carbon footprint than others.  The other is the type of reactor.  Some reactors are able to use much more of the natural uranium mined then other which reduces their carbon footprint.  I'm really hopping we will start making more breeder reactors so we can use all of it. 

Radioisotopes Released into the Environment

I'll just give a brief description for coal, natural gas and nuclear power that will hopefully give you some idea about the radioisotopes (i.e. the stuff that produces radiation) they release into the environment.   For your information sometimes when people in the news talk about radiation they are talking about radioisotopes and sometimes they are talking about ionizing radiation.  If you’re not familiar with these concepts you may wish to read my post Some Basic Information Useful for Understanding Nuclear Power Safety.

Radioisotopes and fossil fuels 

There are radioisotopes mixed into almost everything.  This includes fossil fuels.  When you burn the fossil fuels these radioisotopes become more concentrated (in the ash) then they are in the natural environment.   This can result in people having more radiation exposure then they would otherwise. 

Radioisotopes Released by Coal

The main radiation release from coal  is in the form of fly ash.  In order to give you some idea about what this entails let me start out with a few quotes.

From the USGSRadioactive Elements in Coal and Fly Ash: Abundance, Forms, and Environmental Significance

Coal is largely composed of organic matter, but it is the inorganic matter in coal—minerals and trace elements— that have been cited as possible causes of health, environmental, and technological problems associated with the use of coal. Some trace elements in coal are naturally radioactive. These radioactive elements include uranium (U), thorium (Th), and their numerous decay products, including radium (Ra) and radon (Rn). Although these elements are less chemically toxic than other coal constituents such as arsenic, selenium, or mercury, questions have been raised concerning possible risk from radiation. In order to accurately address these questions and to predict the mobility of radioactive elements during the coal fuel-cycle, it is important to determine the concentration, distribution, and form of radioactive elements in coal and fly ash.
Emphasis Added

10-30 ppm uranium in fly ash

10-30 ppm thorium in fly ash

From the EPA - Coal Fly Ash, Bottom Ash and Boiler Slag

In 2012, 59 percent of the coal consumed by electric utilities and independent power producers in the United States resulted in the generation of about 68 million tons of fly ash, bottom ash and boiler slag. An additional 42 million tons of other residuals were generated from flue gas desulfurization and fluidized bed combustion.

Fly ash is carried up with hot flue gases and trapped by stack filters. It is the largest of the coal combustion residuals (about half) by weight.

Stack filtration devices, such as electrostatic precipitators, baghouses and scrubbers are routinely used to reduce the emission of fly ash. They are about 99 percent effective. Only about one percent is released into the air.
Emphasis Added 
Now lets do a little math with these numbers.

68,000,000 tons * 50%  * 1% = 340,000 tons

So, in 2012, 59 percent of the coal consumed by electric utilities resulted in 340,000 tons of fly ash being released into the air.

((340,000 tons * 10ppm) / 1,000,000) * 2,000 lb./tons = 6,800 pounds*

((340,000 tons * 30 ppm) / 1,000,000) * 2,000 lb./ton = 20,400 pounds*

*assuming tons is short tons and ppm is a mass fraction.

Extrapolating for the other 41% we get...

6,800 lb / .59 ≃ 12,000 pounds
20,400 lb / .59 ≃ 35,000 pounds

So in 2012, we had roughly between 12,000 and 35,000 pounds of radioactive uranium and roughly between 12,000 and 35,000 pounds of radioactive Thorium being released into the air by  electric utilities resulted. If it wasn’t for the consumption of coal in production electricity this Thorium and Uranium would have remained under ground where it couldn’t possibly hurt anyone. Instead it was released into the air in the form of small particles which often end up the the lungs of people and animals.

Now lets talk about Radon 

Radon is a colourless odorless gas that is responsible for a large part of people's yearly radiation dose from natural sources.  So let try and figure out how much radon is release from a years worth of coal.

In the Us 858,000,000 Short tons of coal a burnt each year.  There is around 1 to 3 parts per million uranium in Us coal.   So there is between 858 and 2574 tons of uranium in a years worth of coal.  

Assuming that the amount of uranium has stayed basically constant over the years, that none of the decay chain products have left the coal and that the decay products move through the chain at roughly the same speed (all fairly safe assumption to make), then the Radon produced each year by the coal equals the uranium 238 that decays each year.

So between...

  (9,600 Gd/sec   X  3.15569e7 sec. / 6.02214129×1023) X 222 ≃ .11Grams
   decays a sec         in a year                 1 Mole                   mass Rn-222

  (29,000 Gd/sec  X  3.15569e7 sec. / 6.02214129×1023 ) X 222 ≃ .23 Grams
     decays a sec       in  a year                  1 Mole                   mass Rn-222

So a years worth of coal in America creates around .11 to .23 grams or 590 to 1,800 TBq of radioactive gas. Of course this says nothing about where it's released, and it also says nothing about the addition Rn-222 that it will continue to released from the coal ash ponds for years to come.

So should we all panic and run for the hills? 

Probably not.

According to the first source.
The radiation hazard from airborne emissions of coal-fired power plants was evaluated in a series of studies conducted from 1975–1985. These studies concluded that the maximum radiation dose to an individual living within 1 km of a modern power plant is equivalent to a minor, perhaps 1 to 5 percent.
 From a more recent study.

McBride and his co-authors estimated that individuals living near coal-fired installations are exposed to a maximum of 1.9 millirems of fly ash radiation yearly. To put these numbers in perspective, the average person encounters 360 millirems of annual "background radiation" from natural and man-made sources, including substances in Earth's crust, cosmic rays, residue from nuclear tests and smoke detectors.

There are a lot of radioisotopes in the coal all the Us burns each year, but not all of it ever reaches the public (Most fly ash is captured and stored),  Radon-222 has a half life of only 3.8 days so it's unlikely to get to far plus it will quickly be diluted in as it spreads out from the plant and also the radio isotopes in coal aren't that concentrated to begin with although burning it makes them  somewhat more so. 

Radioisotopes Released by Natural Gas

I know what you're thinking.  They couldn't possible pump radioactive gas into our homes right?  Well...
It has been known for over 40 years that radon, a radioactive gas, is present in natural gas. Reports by R.H. Johnson 7 and C.V. Gogolak 8 calculate the health effects due to burning natural gas in kitchen stoves and space heaters. In an US Environmental Protection Agency report, Raymond Johnson calculate s the number of lung cancer deaths due to inhalation of radon in homes throughout the U.S. as 95 due to radon concentrations in the pipeline of 37 pCi/L.

Yikes. By the way that quote came from this study that estimates the problem is much worse in New York because of gas from the Marcellus shale.  It estimates that the gas from the Marcellus shale raises the death toll by 1,182 to 30,448 a year.  That is a significant number.  Here is a blog post contesting that study. Unfortunately neither the study or the blog post that contests it have actual measurements from the Marcellus shale well heads.  Something you would think someone would want to take.

While this all sounds scary it should be noted that there is controversy in regards to the effect of low level radiation. 

Radioisotopes Released by Nuclear Power

Here is an awesome graphic that explains it all.



There isn't one really.  I hope learned something and you enjoyed it.

Tuesday, March 10, 2015

The Impending Solar Energy Bubble and What can be Done to Stop it

The compensation people receive for their excess electricity should not be allowed to cause other people's rates to go up.  If it does the situation will be inequitable and will in essence be a tax on the poor to the benefit of the better off.  In order to insure this doesn’t happen the amount people receive for excess electricity must not exceed the reduction in the total electric system costs that their excess electricity results in. 

The system needed to deliver us power 24 hours a day 365 day a year is composed of a number of different parts. All of those parts have costs that need to be paid in order to keep the lights on.   So logically if solar electricity is lowering the cost of power for other people then it must reduce the need for some of those parts or reduce maintenance costs.  The real question is how much does it really do this.  Solar panels can only really be counted on for the amount of power they produced on a cloudy day on the winter solstice.  Some places have snow so even less than that.   Basically in many parts of the world solar panels don’t reduce the need for other equipment at all (it depends a lot on how close the the equator you are).   

Some people argue that solar reduces wear on equipment other argue it damages and increases wear on equipment because of its sporadic nature, and it requires costly upgrades to the grid.  Who know weather overall it decreases or increases the system costs from wear.  It probably varies by circumstance.  A lot more work needs to be done studying this.  

Basically the way I see it in places like Germany (i.e. places that get almost no energy from solar for part of the year) solar only reduces the need for coal and natural gas so people should only be compensated for the amount of coal and natural gas not burned because of the electricity they produced, but I imagine that few people would take the word of a random person on the internet for this.  That is why there is the need for a competent impartial independent third party to look at all the evidence and reach a decision they feel is in the best interest of all electric customers.

If this isn’t done right there is the potential for a huge bubble.  People doing all kinds of creative things financially in regards to solar and net metering.   If I am correct and people are just shuffling the costs around then things will become strained as more and more people are forced to get solar because of the increasing electric rate.  Obviously this is unsustainable.  Everyone cannot pass the costs off onto someone else and the poor can’t shoulder the entire burden themselves.  Something has to give eventually. 

Friday, March 6, 2015

The Problem with Net Metering

In the better off parts of the world most people enjoy the benefits of electricity on demand 24 hour a day 365 days a year.  If you are reading this you most likely do as well.  Pretty much all of us (us being the lucky ones) are customers, but not all of us are producers.  In the past producing your own electricity was rarely practical.  Now day thing are different.    Now solar systems exists at prices in many people's reach.   This has created a new issue that needs to be addressed.   That issue is what compensation should people receive for putting their excess electric production on the grid.

In the Us right now a policy (or rather a series of similar policies) called net metering determines what they get.   Net metering basically means they can sell electricity back to the grid for the same price they would buy it for.   Currently it exists in 42 states although there are policy differences.  Here is a map from which lists the states that have it along with a grade for how good they think the net metering laws are in that state.

With net metering it's possible for people to bring their electric bill down to zero with only a small grid connection fee needing to be paid each year.

It's pretty easy to see what the problem is here.  Imagine what would happen if everyone did it.    If everyone brought their electric bill down to zero who would pay for the electric service they would all still be using during the night time, when it cloudy or a times during winter.  They would all essentially be using service without paying for it which obviously wouldn't work.  Now imagine if half the people did it.   Half the people aren't paying for the electric service leading the other half to foot the bill.   This is inequitable and it gets worse if you think about little more.  The half of the people able to afford the solar system and having to space to install them will be the better off people.  The poor people living in apartments would end up footing a larger part of the bill.  This is simply not right.

People putting solar on their roof is a choice and the amount of money they receive for their excess electricity should not increase or decrease other people electric bill.  In order to make this happen I propose that their needs to be an impartial independent regulatory body that examines all the evidence and determines what the proper compensation should be. 

Tuesday, February 10, 2015

I'm Going to go Tour Diablo Canyon Nuclear Power Plant Tomorrow

I'm going to go tour Diablo Canyon nuclear power plant tomorrow.   Looking up things about nuclear power I found out tours are available, and I thought it would be kind of cool to see a nuclear power plant with my own eyes.   When I get back I'll edit this post adding how it went... 

I had a lot of  fun. I got there a little early.  Waited about 20 minutes until it opened.  I started of at a visitor center called the  PG&E Energy Education Center.  I started by looking around at the exhibits.  Here is a replica fuel assembly that I thought was neat.

Unfortunately I'm not so great a photography.  After I looked around a little they had a lecture.  Most of it stuff I already know, but one interesting fact is that Fukushima was only 20 feet above sea level, while Diablo Canyon is 85 feet above sea level.  Quit the difference.  The lecture left me with a nifty souvenir.

Its a plastic replica fuel pellet.   On it is written that it is the equivalent of 149 gallons of oil, one ton of coal or 17,000 cubic feet of natural gas.  Rather nicely done I thought.

After that we drove to the plant.  They didn't let me take any pictures inside the plant, but I was allowed to take this one outside it.

Security was really tight.  I didn't know nuclear power plants had so much security.  Inside the plant was fairly normal looking for the most part.  I got the see the turbine rooms which was really impressive.  It was amazing to sit there and think about how much power is flowing through such a small area.  I also got to look into the control room through a small window in the door.  The dry cask waste storage was a lot smaller then I thought it would be.  I was impressed by the number of things they changed in response to Fukushima.

 Over all I would have to say I was very happy with the tour, and impressed by the whole operation. Also, it's nice to now be able say I've seen a nuclear power plant with my own eyes. 

Friday, February 6, 2015

Comment Donation Bank

A comment donation bank would be a website where people donate their comments with the understanding that other people will copy and past them various places on the Internet.

This is an idea I've been thinking about for a while.  There is a lot of work involved in responding to the repeated bad ideas put forth by people who choose to remain ignorant.  This website would exist to help reduce that work of fighting those bad ideas and misinformation by allowing people to keep repeating the same responses every time. 

How I picture it working

Anyone will be able to make comment pages.  Comment pages will have tags attached to them which help organize them.  Tags will be for what the comment can be used to respond to.  Some possible tags might be for things like nuclear waste, and nuclear proliferation threats, or responses to individual papers and websites.  People can make their own tags or use tags that other people made.  Comment pages will have their own comment section, a way to flag inappropriate or inaccurate comments, and a way to rate the usefulness of the comments to give feedback about how effective individual comments are in practice.   

Some Costs Matter More than Others

In any in depth discussion about energy invariably costs get brought up at some point.  Cost are very important, but I would argue that some costs matter than others though.  

Costs of raw material and production costs are the most important because these cost can give you some idea of the EROEI.  The cost of raw materials give you some idea of the energy needed in order to gather and refine them.  The cost of production gives you an idea of how much energy is needed in order to assemble the raw materials. 

Labour costs are much less important because people have to work doing something anyway.  Also, the amount of labour needed matters more than the  the dollar amount because it can give you some idea of how much labour will be available for other pursuits if the energy source in question became more prevalent. 

Costs imposed by governments are also much less important, because they often correlate mostly to labour costs, and because they can be changed at some future date. 

Thursday, February 5, 2015

My Week Long Trip to China

My sister decided to go to China and she was kind enough to take me with her.   I decided to take a break from the usual topics to talk about my trip. 

First Stop Beijing

Beautify city.  While there I say the great wall, the forbidden city and a number of temples.  The city has a great subway system.  It was the first time I've ever used a subway.  I was impressed.  Every major city should have one.  Also impressive to me was the electric tram system, and the rent a bike stations all over the place.  There was also a lot of small vehicles which I'm guessing were fuel efficient.

Traffic was insane.  Traffic lanes and lights were more like suggestions then rules.   Seat belts and turn signals were not widely used.    Instead people seemed to rely mostly on their horns for telling other cars what they were doing.

The air quality was a bit bad.  There were some evergreen trees I saw which were decidedly lacking in the green part.

Second Stop Xi'an

After a few days in Beijing I took a sleeper train to Xi'an.  As the name implies a sleeper train is a train with beds.  There were four beds to a room.  Lucky my sister got the same room as me.  Her bed was above mine.  It was a bit hard to figure out what to do at the train stop since no one seemed to speak English there.  Lucky by following the crowed we figured it out eventually.  It is a good thing we didn't have to buy the tickets ourselves or we would really have been lost. 

When we got there we saw the Terracotta army.  They were rather impressive.  We also saw a temple and the cities wall.  Unfortunately there was no subways in this city so we were a bit limited in what we could do. 

Third Stop Shanghai

We took a sleeper train to Shanghai.  It was an impressive city.  Unfortunately my sister was a bit sick so we didn't do much there.  We saw the museum and the people's square then went back to our hotel.  I went out and got some food by myself latter.  It was only 15 yuan (Around $2.40 US) which was pretty amazing for the amount of food I got.  The less touristy places in China are a lot cheaper.  The next day we left.  I went home, and my sister went to New Zealand.  She'll be back in about a month.  

Wednesday, January 14, 2015

Why I'm not Worried about Nuclear Power

Growing up in California left me with a negative impression of nuclear power without any real knowledge of it.  I remember being scared of it as a child. Especially the nuclear waste.  I used to think they should shoot it all into space.  Now such an idea seems ridiculous to me.  I can't imagine why you would need to go so far when the problem is easily manageable here on earth.   Nuclear power has moved way far down on the list of things to be afraid of.   With this article I'd like to explain why.

I'd just like to start by saying that radiation can be harmful. Everyone seems to agree with that.  What people can't always agree about is the finer details such as if harm was done, how much harm was done and how much harm could be done by any particular event or potential event.

Also, if you don't have a basic understand of radiation and radioisotopes you may wish to read this first.   

So, you may be wondering why I'm not particularly worried about nuclear power given that radiation can be harmful.  Well for starters radiation is all around us, and it always has been.

Radiation is all Around Us, and Always has Been

Radiation is constantly bombarding us from space.  It's in the oceans, the soil and the food we eat.  It's even in the air we breath.  It's a bit harder to be afraid of it when you realize it's all around us, and always has been.  The first ape that walked on two legs was being bombarded by radiation.  The first animal that crawled up out of the sea was being bombarded by radiation.  Even when the first cells came about and life as we know it began there was radiation everywhere. 

In fact even fission was happening on earth before humanity was a thing.  In the Oklo uranium deposit (located in the country of Gabon in equatorial Africa) it was discovered that a nuclear chain reaction caused by natural processes took place millions of years ago. Here is a time line.

The history of the Oklo fossil reactors spans almost the entire history of the earth. ‘Oklotime’ can be divided into four stages:
  1. U mobilization phase: Commenced ~3500 million years ago.
  2. U ore/reactor formation: Started ~2800 million years ago.
  3. Reactor operation: Commenced 2000 million years ago (for about a million years).
  4. Waste movement: The last 2000 million years.

Yet despite this nuclear reaction happening on earth uncontrolled by man, and unreported on by an media outlets, life on earth survived.  In fact there is not evidence that it was hampered in any way.  If that isn't enough for you there is something called spontaneous fission where heavy atoms undergo fission well... spontaneously.   Also, there a certain number of neutrons (around 14 neutrons/cm2/hour) constantly bombarding the earth as a result of  cosmic ray spallation.  When these neutrons encounter uranium they can induce fission just like in a nuclear reactor, but despite these two thing releasing small amounts of fission products directly into the environment since the earth began life goes on undeterred. 

Learning more About Science has Made me Less Afraid

I find learning more about science is a fun and rewarding activity.  Which is why it shocks me when I encounter articles like this one and realize that some people know almost nothing about science at all. 

All radioactivity is man-made (True/False)

Percent that got it right

It amazes me how many people don't even know about natural sources of radiation.  I'm not a scientist, I'm never going to be a scientist, but I've found certain basic information about science incredibly useful for understanding the world around me.  Without it I'm not sure how I would judge the endless barrage of claims that I encounter every day.  Let me share with you some of the things I've learned about science that have made me less afraid.

Half Lives

Half-life: Introduction to half-life

Half lives describes how long until half of any given type of radioisotope has decayed into something else.  This is important because it's during the decaying part where the radiation gets produced.   In terms of safety there are good and bad things about any half life length.  For example things with short half lives are more dangerous because they produce more radiation, but because they have short half lives they don't stick around as long which is good.  Things with long half lives stick around for a long time, but they are less dangerous because they don't produce as much radiation.  Learning about half lives made me realize that the really dangerous stuff will be gone before too long.   As for the longed lived stuff, the world is fulled of long lived radioisotopes (uranium, thorium, C-14 etc.).   It doesn't seem to hamper us much, if any.

Diffusion and Dilution 

Diffusion is a natural process where random collisions between particles in fluids or gasses cause them to travel around randomly becoming more intermingled within the medium. You can observe this process by placing a drop of red food coloring in a cup of water. Over time you can watch the red coloring spread out until the water is of uniform color. Here is a video that explains diffusion if you want to know more.

Radioisotopes mixed into air and water diffuse outward in all direction becoming diluted in the process. Picture the place where the radioisotopes starts out at as one side of the radius of a sphere and the distance they have diffused out to as the other side.  In order to better illustrate this Here is the volume of a sphere.

As you can see radius is taken to the third power.  As you can imagine this means that volume increases very quickly as radius gets bigger.  This is something called exponential growth. Exponential growth means the rate at which things grow also grows.  Here is a graph showing the growth of the volume of a sphere.

As you can see with exponential growth thing get large very quickly.  Even if things like the earth block some paths of diffusion it is still easy to see that the volume in which radioisotopes are diluted becomes large really fast, and dilution matters.  Things that are very dangerous in concentrated forums are basically harmless if diluted enough.  

You may be wondering about solid particles right now,  but if you are worried small particles like dust undergo diffusion as well although it's different than the diffusion for liquids and gasses. One difference is that dust consolidates on the ground which is two dimensional, but the area of a circle circle also grows exponentially.

Although things like wind also needs to be considered there are definitely limits to the concentration of small dust particles faraway from an accident.  As for larger particles I'm not sure what their means of locomotion would be. 


This kind of thinking might not be much consolation to people close to a serious nuclear power incident where concentrations of radioisotopes are greater, but it definitely shows that there limits to the scope of nuclear accidents, and history has shown even residents close to serious nuclear power accidents don't die from radiation poisoning.    Radioisotopes with short half lives are dangerous in concentration, but diluted over a large volume they aren't that dangerous at all, and because they have a short half life what danger they do pose will soon pass. 

The World is full of Dangerous Stuff

Another reason why I'm not particularly worried is that that life is filled with harmful and potentially harmful things.  Heck, In 2014 761 people died on commercial airlines world wide while a staggering 33,783 people died in automotive accidents in the US alone.  For me nuclear power is pretty far down on the list of things to worry about.

One example of something potentially very hazardous is water.  If inhaled the content of a single swimming pool could kill hundred if not thousands of people.  Such a situation may seem ridiculous to you, but it's no more ridiculous than arguments that single nuclear reactor can kill us all (which ignores basic laws of physics like diffusion). 

At any rate here is some information about drowning:
Every day, about ten people die from unintentional drowning. Of these, two are children aged 14 or younger. Drowning ranks fifth among the leading causes of unintentional injury death in the United States
That's quite a few people.  Certainly more then die each day from nuclear energy.   I'm sure we could cut down this number by banned all the swimming pools and putting guards around all the rivers and lakes, but people aren't willing to do that because not only would it cost to much but swimming is fun.  I wonder why we are so rational when it comes to swimming but irrational when it comes to nuclear power.  After all affordable reliable energy is more than just fun, it a necessity of modern life.

To Much Fear and Hyperbole not Enough Facts

Of the two sides the anti nuclear side is by far the largest purveyor of bull crap. I've learned to take everything they say with a grain of salt.

Hey, I call it like I see it

I tend to believe that everyone has a little bit of bull crap in them, but the anti nuclear activists often take it to the extreme.  They are given to outrage with little in the way of facts, rampant  paranoia and dismissing anything that disagrees with their preconceived notions.    One example of anti nuclear bull crap can be seen below. 

Maps like these are complete bull.  You could take a piss in the ocean and draw an equally scary map showing how your piss is slowly contaminating all the seas of the world, and it would about as meaningful as this map.  Let me give a quote that shows what they are talking about.
An estimated 538,100 terabecquerels (TBq) of iodine-131, caesium-134 and caesium-137 was released. 520,000 TBq was released into the atmosphere between 12 to 31 March 2011 and 18,100 TBq into the ocean from 26 March to 30 September 2011. 
Admittedly worse then urine, but not nearly as bad as they are making it out to be.   A think a good comparison for putting it into context would be to compare what has gone into the ocean to what was already in the ocean.
  1. The oceans have Uranium in them. In the pacific ocean the radiation from Uranium is 22 EBq or 22,000,000 trillion becquerels.
  2. The oceans have Potassium 40 in them. In the pacific ocean the radiation from Potassium 40 is 7,400 EBq or 7,400,000,000 trillion becquerels.
  3. The oceans have Carbon 14 in them. In the pacific ocean the radiation from Carbon 14 is 3 EBq or 3,000,000 trillion becquerels.
  4. The oceans have Rubidium 87 in them. In the pacific ocean the radiation from Rubidium 87 is 700 EBq or 700,000,000 trillion becquerels.
  5. The oceans have Tritium in them. In the pacific ocean the radiation from Tritium is 370 PBq or 370,000 trillion becquerels.
So we have…
Uranium                      22,000,000 trillion becquerels
Potassium-40         7,400,000,000 trillion becquerels
Carbon-14                     3,000,000 trillion becquerels
Rubidium-87            700,000,000 trillion becquerels
Tritium                              370,000 trillion becquerels
Total            8,125,370,000 trillion becquerels
So we have 8,125,370,000 trillion becquerels of radiation in the pacific ocean from natural sources and the anti nuclear activists don’t seem to care, but when the fifth most powerful earthquake ever recorded results in 18,100 TBq of radiation being released into the oceans and they start drawing scary maps and acting like we are all doomed.    The logic in this position escapes me and it only gets worse...

Uranium 238 (99.284% of natural uranium) has a half life of 4.468 billion years, and uranium 235 (0.72% of natural uranium) has a half life of 703,800,000 years, so it's going to be producing those becquerels for a long long time.   If that still isn't enough for you rivers wash more uranium into the ocean at a rate of 32,000 tons (page 165) a year, and carbon-14 is only one of the radioisotope continuously showering us as a result of cosmic rays.   Still not enough for you... There's more.  Here is the decay chain for both naturally occurring forms of uranium.


That is an awful large number of radioisotopes continuously being produced in the oceans naturally, but anti nuclear activists don't seem to know or care at all. They seem only to care about radiation has to do with their agenda against safe clean nuclear power. This has made me lose a lot of trust in them.

There  are some people who think that Fukushima should mean the end of nuclear power, but their fears seem way overblown to me.  As I learned more about the different types of energy I've come to favour nuclear power strongly.  None of the other energy sources can do what it can.  Wind and solar are intermittent, have lower power density and scaling.  Fossil fuels are increasing hard to get at, and of course there is climate change to worry about.  Nuclear power gives me hope for the future which is why I think it's worth defending

Tuesday, January 13, 2015

Is this What They Mean by Clean Energy?

Germany is destroying whole towns in order to power their country.

Wind and solar require other power sources when the wind isn't blowing or the sun isn't shining.

If those other sources are coal then they bear part of the responsibility.

Monday, January 5, 2015

Both Low EROEI and Low Power Density is a Serious Problem - Wind Addition

In my last post I talked about how having both low EROEI and low power density is a serious problem.  I used solar as an example.  In the comment section someone mentioned something about 80% of our power coming from wind, but wind isn't much better. It has a higher EROEI, but it's power density is terrible.  I'll explain below. 

If you haven't read the last article you might want to do so now.

First I'll start with the sources.

Source One - Catch 22 of energy storage.

EROEI for wind with storage is 3.9. 

Source Two - Sustainable Energy — without the hot air

The red stack (i.e. energy consumption) in figure 18.1 adds up to 195 kWh per day per person (page 103).

4,000 m^2 land per person in UK.  

Source Three - Rethinking wind power
Keith’s research has shown that the generating capacity of very large wind power installations (larger than 100 square kilometers) may peak at between 0.5 and 1 watts per square meter.
Now lets think about it a little.

Lets start by talking a bit about EROEI.   The comment that inspired this post gave me a link that says EROEI is meaningless.  I disagree.  EROEI is very important when it gets close to one.  I'll explain but first let start with this definition from Wikipedia for anyone unfamiliar with the term.
In physics, energy economics and ecological energetics, energy returned on energy invested (EROEI or ERoEI); or energy return on investment (EROI), is the ratio of the amount of usable energy acquired from a particular energy resource to the amount of energy expended to obtain that energy resource.

EROEI is important because it creates a multiplier effect for other quantities.  Other quantities include things like space, different material and man power.   The closer EROEI gets to one the closer the need for those other quantities get's to infinity.

For example:

Imagine that you had a some solar panels that had a EROEI of 2. One meter square of them produces let say 5 watts average. For simplicity's sake lets stick with only this one kind of power source for now.

If you wanted to get 5 watts from these panels you would need both the one meter squared, plus another half a meter squared to maintain the one meter squared, plus another quarter meter square to maintain the half meter square and so forth.  This goes on endlessly, and when you sum up the results you get the multiplier.


Thanks to Mark44 on physics forums for this!

Now lets talk about the multiplier

The multiplier works for all quantities not just area.

For example:

if it take 5 people to maintain some generation that produces 5 watts and the multiplier is 3 then that 5 watts really needs 15 people (5 X 3 =15).

Here is the formula you need to figgure out the multiplier for any given EROEIs.

Where X = EROEI
This doesn't only apply to a one power source systems.  Any power source that with EROEI close to one would require outrageous amounts of different resources in order to contribute significantly to our total energy supply.  

Now for Wind

The multiplier for wind isn't that bad, but the power density is crap.  At between 0.5 and 1 watts per square meter even if you covered the whole of the UK with wind turbines the yield would still kind of suck.

Here's the math

4,000 m^2 is space in uk for each person.

1.34 is the multiplier for wind


4000 / 1.34 ≃ 3,000

Around 3,000 is how much possible space for wind for each person when you minus the space for wind turbines needed to maintain the system.

So between...

           (3,000 * .5 * 24)/1,000   ≃ 36  kWh per day per person

           (3,000 * 1 *  24)/1,000   ≃ 72  kWh per day per person

So maybe you can get close to 80% if you cover the whole of the UK with wind farms (assuming the EROEI doesn't drop because of diminishing returns).  Do you think people can really cover so much of the UK with renewable energy?  What about space they need for other things like energy storage.  It's really hard for me to believe, and even if you could I think it would be pretty horrible.  

Both Low EROEI and Low Power Density is a Serious Problem - Solar PV Addition

Taking information from two sources I'm going to show that a combination of low EROEI, and low power density is a huge problem.   Here is the first source which talks about EROEI with energy storage.  It's called catch 22 of energy storage.  Here is the second that talk about power density among other thing.  It's called Sustainable Energy — without the hot air.  Both of them are a good reads if you haven't read them already. 

From the First Source

The EROEI for solar pv with energy storage is listed at 1.6.

From the Second Source

If we covered 5% of the UK with 10%-efficient panels, we’d have

10% × 100 W/m2 × 200 m2 per person = 50 kWh/day/person. (page 41)

The red stack (i.e. energy consumption) in figure 18.1 adds up to 195 kWh per day per person (page 103).

Now lets think about this a little

EROEI describes the energy that is needed to be invested (i.e. used) in order to get more energy. If the EROEI is 2 then one unit (of some unit of energy) invested will get you 2 (of that unit). If solar is to become a permanent thing then maintaining any given area of it will take energy. The amount of energy is determined by it's EROEI. Lets say that the EROEI is 2. Then maintaining 1m2 of it would take 1/2m2. That 1/2m2 would need 1/4m2 and so on. The sum of all these works out to some finite number.   In order to work it out you need something called the Geometric series.

Here's the equation where X = EROEI

Using the formula I get 2.67(1/(1-(1/x))) using solar PV's EROEI. The number 2.67 is a multiplier we can use to figure out the total area needed.  That means instead of 5% of the uk's land providing 50 kWh/day/person it would take 13.3 % (5 X 2.67 = 13.3) when taking EROEI into account.   In order to get 195 kWh/day/person it would take 51.87 % (13.3 X (195/50)) or 207,480 m2 per person.

That doesn't even count the area of land used by the energy storage.  Pump hydro for the source given.   Here's a good source that talks about that.  Guess what it take a lot of space, and don't forget that there are other land uses as well. 

Source Two Page 41

And don't think you can do without most of the storage because of demand response, management, whatever you want to call it.   Solar power manufacturing facilities cost a lot.  In order to keep the prices down they need to be run 24/7, so at most you can only ration 37.5 % (1 / 2.67 = 37.5) percent of that power. 

This is simply madness, or more like a fantasy.  It's time people came to terms that they have two choices.  Fossil fuel, or nuclear power.   Fossil fuel's give us a few short years in exchange for our climate and our children's future while nuclear power gives us hope and a better life for countless millions.   I know which one I'm rooting for. 

Update:  I changed a lot.  Credit to my brother Jeremy for helping me with the math.  I also added another post that talks about the same thing for wind.

Sunday, January 4, 2015

Some Basic Information Useful for Understanding Nuclear Power Safety

When people talk about nuclear power safety they often don't explain certain basic information that you need to know in order to really understand the the subject.  This is probably for the best because repeating the same information over and over again would grow old really fast, but unfortunately this leaves people new to the subject unable to fully understand the arguments.  The goal of this article is to hopefully be helpful to anyone who doesn't understand the basics. Basically I tried to write something that I think would have been helpful to me when I was starting out. 

The Very Basic

A drawing of a Lithium atom. In the middle is the nucleus, which in this case has four neutrons (blue) and three protons (red). Orbiting it are its three electrons.
Lithium atom model
Lets start with the very basic, all the stuff on earth is made up of tiny building blocks called atoms (you can see all types on the periodic table of the elements).  Atoms are made up of three things.  Those three things are electrons, protons and neutrons.  Protons and neutron exist in the middle of the atom clumped together in what is called the nucleus.  The electrons exist around that. Atoms can form molecules (i.e. groups of atoms) by sharing electrons. 

The type of atom (i.e. the element) is determined by the number of protons in it's nucleus.  For example atoms that have one proton are hydrogen atoms, and atoms that have 92 protons are uranium atoms.

Unlike protons and neutrons, the number of electrons an atom has can change fairly easily.  The default position for atoms is having the same number of electrons as protons.  When atoms don't have an equal numbers of protons and electrons they are called ions.  Knowing what ion you're dealing is important because different ions (even of the same element) behave very differently chemically which is why they came up with Equivalent notations for writing it down.
Example of Equivalent Notations
Every proton is +1, and every electron is -1, simple subtraction tells you what ion you've got.  For example iron (Symbol Fe) has 26 protons.  If an atom of Iron has 24 electrons then its ionic state is 2+ (26 - 24 = +2), and if it has 28 electrons its ionic state 2- (26 - 28 = -2).

The number of neutrons an atom has determines what type of isotope it is.  All atoms are some type of isotope even though it's not usually that important because different isotopes of the same element (i.e. type of atom) behave the same chemically for most intents purposes and thus it is often not mentioned or thought about.

Isotopes are identified by their atomic mass.  The atomic mass includes both protons and neutrons (electrons are very light so they don't count).  So for example there are three naturally occurring isotopes of carbon on earth.  They are called carbon-12, carbon-13 and Carbon-14.  Carbon has 6 protons so Carbon-12 has 6 neutrons (12 - 6 = 6), Carbon-13 has 7 neutrons (13 - 6 = 7) and Carbon-14 has has 8 neutrons (14 - 6 = 8).

Ionizing Radiation and Radioisotopes

Not all isotopes are stable.  Unstable isotopes eventually decay into different types of atoms releasing radiation in the process.  For example Carbon-12 and Carbon-13 are stable while Cabron-14 eventually decays into Nitrogen-14 (which is stable).

The unstable isotopes are called radioisotopes (also known as radionuclide, radioactive nuclide, or radioactive isotopes), and the radiation released is know as ionizing radiation although most people just call it radiation.

When an unstable isotope decays is random while the probability of it decaying over any period time is fixed.  This probability is understood through something called a half-life.  A half-life is the time it takes for half of a given amount of a radioisotope to transmute (i.e. decay) into something else

It's a bit like rolling a dice. Every time you roll a dice the chance of getting a one is the same.  If you replace "time you roll a dice" with "fixed period of time" and "getting a one" with "a type radioisotope decaying" it's exactly the same. 

You can also use the dice analogy to understand half-lives.  Picture that you were rolling a group of six sided dice.  Every time you rolled them you remove any dice that lands on a one.  The half life of these dice would be three rolls because after three rolls half the dice should be gone.  You might be thinking to yourself that half lives aren't very precise because of the random element, but you have to remember that atoms come in large numbers.   There are something like 78,000,000,000,000,000,000 atoms in a grain of sand.  If you rolled six dice then at the end maybe half would be gone or maybe not, but if you are rolling trillions of dice pretty darn close to half of them would be gone. 

In fact half lives are so precise that people use it for dating stuff.   There is something called Radiocarbon dating that uses the half life of Carbon-14 in order to tell how old things are.  Carbon-14 is constantly being created in the earth's atmosphere by nitrogen being bombarded by cosmic radiation.  Because it's being created at a constant rate it's also being absorbed by plants at a constant rate and from plants it moves to animals.  When something dies it stop taking in Carbon-14 so by using it's half life researches can tell how long ago something died based off the amount of carbon-14 left in it's remains.   

Some radioisotopes decay into other radioisotopes.  When that happens you have what is called a decay chain.  The decay chain is used to describe how radioisotopes decay until they eventually reach a stable state.  Here is the decay chain for Thorium a common naturally occurring radioisotope. 

You may be wondering at this point where all the radioisotopes on earth come from.   Well some (34 types) are primordial (i.e. they came about before the earth was formed).  This includes Uranium, Thorium and Potassium-40.  Some of them are caused by cosmic radiation such as Carbon-14.  A small minority are created as a result of human activity, the most common of these activities involves the breaking down of larger radioisotopes into smaller radioisotopes in order to produce energy.  Here is a really good link about radioactivity in the environment if you're interested in learning more about it.

Types of Radiation 

The types of radiation produced by radioisotopes include both Electromagnetic radiation and Particle radiation.  Electromagnetic radiation plays a big part in our lives.  Depending on the frequency it has many different applications and also names.  The most familiar form is the visitable spectrum, or more commonly just called light.  It's also useful for microwaves ovens, cell phones, radio, x-rays etc.

But for our purposes we are only interested in electromagnetic radiation that is ionizing radiation. Ionizing radiation is radiation that has enough energy to knock electrons off atoms (or molecules) thus ionizing them.   This is important because as we talked about before different ions behave much differently chemically.  This can cause problems.  In most cases a few atoms (or molecules) being ionized doesn't matter much, but in some cases it does.  For example ionizing radiation can cause harm to living tissue.  You've probably noticed such harm yourself if you've ever spent too much time in the sun and got sunburned.  

Some atoms (and molecules) hold their electrons better than others so what types of radiation are ionizing isn't so clear cut, but really what we care most about is the effect of ionizing on human beings so I would say ultraviolet (sun burn) rang and higher (higher frequency that is, the higher the frequency the more energetic the more able to knock of electrons) is ionizing radiation.

Usually when we are talking about radioisotopes decaying we are talking about gamma rays (i.e. y-rays), not X-rays or ultraviolet. Lower wave length ionizing radiation can be created as secondary radiation (i.e. ionizing radiation created by other ionizing radiation) though. 

Particle radiation is simply particles that are moving very quickly.  The two types of particles that matter for what we are talking about are Alpha particles and Beta particles.

Alpha particles are helium-4 atoms without any electron.  The ones created by radioactive decay have a strong ability to ionize things, but they have little ability to penetrate shielding and can be stopped by a piece of paper or the thin layer of dead skin all of us have. 

Beta particles are electrons or sometimes positrons.  Positrons are the antimatter equivalent of electrons.  When electrons and positrons meat they destroy each other releasing some gamma rays in the process.

Metric Prefixes

Now that we've covered what radiation is and where it comes from lets talk about how it's measured.  Well before that we have to talk about something call metric prefixes.  If you spend time reading about this subject you're going to encounter these things a lot.

For Micro it's usually abbreviated μ or mc

Metric prefixes are used for writing really large or really small numbers without having to write all the zeros.  It's very similar to scientific notations in that regards.  The prefix goes before the unit abbreviation.  For example with 10 cm the c is the metric prefix (centi) and the m is the abbreviated unit types (meter). 

It's fairly easy to convert a number to a different prefix or know the number in it's entirety (i.e. what the number is without prefixes). Look at the table above to the left of prefix you want to convert from.  The number to the right of the 10 is the one we're interested in.  Take that number and subtract the number next to the 10 of the prefix you want to convert to.  If you want to convert to no prefixes then subtract zero.    If the number you get is negative move the decimal point that many spaces to left, if it's positive move the decimal point that many places to the right. 

For example 1,000 nm (-9 - (-6) = -3) = 1 µm ,  1,000 µm (-6 - (-3) = -3) = 1 mm, 1,000 mm (-3 - 0 = -3) = 1 m, and 1,000 m (0 - 3 = -3 ) = 1 km.  Where m stands for meters.

Measuring Radiation

There are a lot of different ways of measuring radiation.  I'll try and go over the most common ones.

Activity (A)

Activity measures the number of nucleus decays.  It's calculated using amounts of radioisotopes and knowledge of there half lives.  The two main units for this are Becquerel, and Curie. 

The becquerel (symbol Bq) it is the SI derived unit of radioactivity.  One Bq is defined as the activity of a quantity of radioactive material (i.e. radioisotopes) in which one nucleus decays per second. Basically it's a unit used to describe the amount of radiation produced by some amount of radioisotopes.

The curie (symbol Ci) is a non-SI unit of radioactivity, named after Marie and Pierre Curie. It is defined as 1 Ci = 3.7 × 1010 decays per second.

Conversion factors:
1 GBq = 0.027 Ci
Absorbed dose (D)

Absorbed dose measures the energy (from ionizing radiation) absorbed by a mass.  This is important because it takes energy to ionize things so knowing how much energy is going towards ionizing things help you know how much stuff is getting ionized.  This in turn can help give you some idea of the effect.  Most Geiger counters measure this. The two main unit types for this are Rad and Grey.

The SI unit for absorbed dose is the gray (Gy).  One gray is the absorption of one joule of energy, in the form of ionizing radiation, per kilogram of matter.

The other unit is called the Rad.  The rad is a non-SI CGS unit that is sometimes also used, predominantly in the USA.

Conversion factor:
1 rad = 0.01 Gy 
Dose equivalent (H)

Dose equivalent is a measure of the health effect of low levels of ionizing radiation on the human body.   The two main unit types for this are Roentgen and Sievert.  Quantities that are measured in roentgens or sieverts are intended to represent the stochastic health risk, which for radiation dose assessment is defined as the probability of cancer induction and genetic damage.  There is no way to directly measure equivalent dose.  Instead other measurements are used to arrive at equivalent dose using various conventions.  For example with X-rays and gamma rays the gray is numerically the same value when expressed as the sievert (Sv), but for alpha particles one gray is equivalent to twenty sieverts because of the radiation weighting factor that is applied.

Conversion factor:
1 rem = 0.01 Sv

Radiation Inside the Body

Internal doses can be worse than external one's (depends on amounts and other factors).   For example alpha particles can be stopped by a thin layer of dead skin making them fairly harmless outside the body, but more dangerous than other types of radiation inside it.  In fact a large part of people's average annual doses comes from alpha particles produced by the decay of Radon (symbol Rn).  Radon is an odourless, colourless, gas that exists in small amounts all around us.  Radon is constantly being created as part of the decay chain of all the naturally occurring isotopes of uranium and thorium.

At any rate predicting internal doses is important.  An important thing to remember when internal doses are concerned is that different isotopes behave the same chemically.  This can be both a good thing and a bad thing.  For example Iodine-131 is a radioactive isotope of iodine that is produced a lot in nuclear reactors.  It has a half life of about 8 days.   Like all iodine it's utilized by the thyroid which means if it gets released into the environment it can be a problem.   Luckily by taking potassium-iodide pill you can flood your body with non radioactive iodine so Iodine-131 wont get absorbed, and because it's half life is so short it will be gone in short order.  Because they behave the same chemically radioisotopes also have many beneficial uses such as Radiopharmacology a branch of medicine which uses radioisotopes for medical imaging and in therapy for many diseases (for example, brachytherapy).  Ironically Iodine-131 is also one of the radioisotope used in medicine.

Internal Dosimetry 

Internal dosimetry is the science and art of internal ionizing radiation dose assessment due to radioisotopes incorporated inside the human body.  Radioisotopes deposited within a body will irradiate tissues and organs and give rise to committed dose until they are excreted from the body or the radionuclide is completely decayed.  The internal doses for workers or members of the public exposed to the intake of radioactive particulates can be estimated using bioassay data such as lung and body counter measurements, urine or faecal radioisotope concentration, etc.

Man-Made Radiation Exposure Breakdown 

This kind of depends on what you think of as man made exposure.  For example is Radon pumped into people's houses along with natural gas man made or natural exposure?  At any rate, not counting stuff like Radon most man made radiation exposure is a result of various medical procedures (such as x-ray).  This accounts for around 20% of exposure worldwide and up to 50% of exposure in  industrialized countries.  Here is a pie chart.


Linear no threshold model

The most widely accepted model for determining harm for low doses is known as the Linear no threshold model  (LNT).  For this model it doesn't matter how much radiation you receive.  All radiation can cause harm, all radiation has an equal chance of causing harm.  Here is a nifty online calculator for it applying it. 

Organizations That Support LNT

 United States National Research Council
"The assumption that any stimulatory hormetic effects from low doses of ionizing radiation will have a significant health benefit to humans that exceeds potential detrimental effects from the radiation exposure is unwarranted at this time."
United States National Academies
"The scientific research base shows that there is no threshold of exposure below which low levels of ionizing radiation can be demonstrated to be harmless or beneficial."
 National Council on Radiation Protection and Measurements

United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR)
Until the [...] uncertainties on low-dose response are resolved, the Committee believes that an increase in the risk of tumour induction proportionate to the radiation dose is consistent with developing knowledge and that it remains, accordingly, the most scientifically defensible approximation of low-dose response. However, a strictly linear dose response should not be expected in all circumstances
The Controversy

Radiation can be harmful. Everyone seems to agree with that.  What people can't always agree about is the effect of very small doses of radiation.  Anyway Here is a page that does a good job of describing the controversy.  If you want to understand this subject better this is worth reading. 

Living things evolved in a world full of radiation.  Various biological defence mechanisms have come about in order to protect organisms from it and other sources of harm.  Here is a list of some of our bodies defences. 

  1. Defences against the metabolically induced reactive oxygen species (i.e. defence against things that have been ionized),  
  2. DNA repair, and  
  3. Elimination of damaged cells. 
The big disagreement is low levels of radiation, where it is difficult to show statistically what is going on.  There are several different models that describe the effects of radiation at low doses. 

Another model is the threshold model

This model says that only radiation over a certain dose is harmful.

Organizations that support this model

French Academy of Sciences (Académie des Sciences) and the National Academy of Medicine (Académie nationale de Médecine).

In conclusion, this report raises doubts on the validity of using LNT for evaluating the carcinogenic risk of low doses (< 100 mSv) and even more for very low doses (< 10 mSv). The LNT concept can be a useful pragmatic tool for assessing rules in radioprotection for doses above 10 mSv; however since it is not based on biological concepts of our current knowledge, it should not be used without precaution for assessing by extrapolation the risks associated with low and even more so, with very low doses (< 10 mSv), especially for benefit-risk assessments imposed on radiologists by the European directive 97-43.
Hormesis Model

Another model is the  is the hormesis model which postulates that a certain amount of radiation actually decreases your chance of getting cancer a little because it stimulates your body's natural defences.

What People agree About

At any rate pretty much everyone agree about larger doses so Here are a few facts I think anyone would agree with. 

  • 100 rem received in a short time can cause observable health effects from which your body will likely recover, and will increase your chances of getting cancer.
  • 1,000 rem in a short or long period of time will cause immediately observable health effects and is likely to cause death.


As for conclusions there isn't one really.  Hope this was helpful to someone.

Update:  I've made a lot of changes in order to make it more complete.  Also, changes some things to make it more balanced.