Monday, January 08, 2007

The Nuclear Question

Recently, over on Pete's site, the subject of nuclear power came up with regard to terrorism. It got me (us?) thinking about the debate over its use.

Several years ago at university I wrote a paper on the basics of nuclear energy. It included information on the structure of atoms, and radioactivity, and also a description of nuclear reactors designed and built here in Canada. I'm a firm believer that this is a great alternative to coal and other fossil fuel burning power generation souces. There has even been an extremely safe, viable, disposal method developed for depleted materials, and yet people are still terrified.

Anyway, in the interest of education, I'd thought I'd put up here some of the information I pulled together on reactors and such.


A nuclear reactor is a device in which a fission chain reaction can be initiated, maintained, and controlled to produce heat. Its essential components are fissionable fuel, moderator, shielding, control rods, and coolant. This paper will focus on Canadian deuterium-uranium (CANDU) reactors.

An atom's nucleus can be split apart by nuclear fission. When this is done, a tremendous amount of energy is released. The energy is both heat and light energy. This energy, when let out slowly, can be harnessed to generate electricity.

A CANDU nuclear power plant uses natural uranium (0.7% U-235, unenriched) as fissionable fuel. It is processed into tiny pellets that are loaded into rods that are then placed in bundles in the power plant's reactor. Inside the reactor, the uranium atoms are bombarded with neutrons at the right energy level and split apart in a controlled, continuous fission reaction thus releasing energy. Approximately 200 MeV is released by the decay of one Uranium-235 atom. This energy is used to boil water in the core of the reactor.

The bundles are placed in several hundred pressure tubes which penetrate the reactor vessel. A moderator of heavy water (deuterium) fills the reactor vessel and acts as a coolant. In order to keep the uranium from overheating, control rods containing cadmium are raised and lowered into the bundle as needed. Light water can also be introduced into the core to act as a neutron absorber.

This heavy water from around the nuclear core is sent through a series of pipes to another section of the plant where it heats light water to make steam. The steam in turn powers a turbine to generate electricity. The steam is then condensed and placed in a cooling tower until the water is at a temperature where it can be used again.

The safety systems of the CANDU reactor take into account human error, equipment failure and natural risks such as earthquakes. In the event that an accident should occur, CANDU reactors are designed to contain radioactive emissions within reactor buildings. There has never been an accident in a CANDU reactor where a worker has received radiation exposure which required medical treatment.

In the event of an emergency in a CANDU reactor, the first thing which happens is that the reactor is shut down. This is accomplished by dropping the control rods completely into the reactor. If the rods cannot be inserted, a system quickly injects gadolinium (64Gd) into the moderator.

If the cooling system ruptures and coolant is lost, valves will close to isolate the intact system and light water from storage tanks is injected into the ruptured system. The water is recovered from the bottom of the reactor, passes through the heat exchange system, and is injected once again into the ruptured system. Since there are independent cooling systems in the reactor, chance of a coolant loss from both at the same time is minimal. Since CANDU reactors are designed with such a large amount of pressure tubes, a failure of the pressure vessel is not possible. If all the coolant was lost and the emergency core cooling system failed then the heavy water moderator would carry off enough heat to prevent major melting.

The structure containing the reactor and its components is made of stressed concrete with a plastic liner. It also includes a spray system and air coolers for reducing the pressure in the building.

Spent nuclear fuel is kept at the individual nuclear plants. It is stored underwater or dry in concrete canisters. Water keeps the fuel bundles cool and absorbs the energy from the bundle, providing a radiation shield. The used fuel can be stored under water for long periods of time, or it can be transferred to dry concrete storage canisters on site. According to Atomic Energy of Canada Limited (AECL) there is enough space at each nuclear plant to store all of its used fuel for the operating life of the reactor.

(You can find here information on a (very sound, safe) proposed method of waste disposal.)

Nuclear reactors do release radioactive material into the environment, however, at a very low rate. The radiation from reactors can add 0.01 mSv per year to the average human exposure of approximately 2 mSv. It would take 10,000 mSv in a short_term dose to cause immediate illness and subsequent death within a few weeks. A short term dose of 1,000 mSv would probably cause (temporary) illness such as nausea and decreased white blood cell count, but not death. In comparison, in order to receive even mild radiation sickness, the average human requires a whole-body dose of 300 mSv. [Toon, 363] This demonstrates that nuclear power generates only a fraction of the amount of radiation which could cause illness and even quite an amount less than humans are normally exposed to from day to day.

As well, nuclear reactors do not release carbon dioxide into the environment as do coal and hydrocarbon burning facilities. This is a huge advantage with the current need to reduce green house gas emissions, smog, and pollution.

Anyway... that's enough. Everyone knows the "against" arguements, I just have a serious pet peeve with people who form opinions that aren't educated ones. Don't argue unless you know the facts. The risk from nuclear waste is negligible comapred to the current risk of climate change. Nuclear power is a way to eliminate enormous amounts of GHG emissions. If we don't curb that, its not going to matter if a little radiation leaks out of the Canadian Shield in a few hundred thousand years because there'll be no one here to care.

13 Comments:

At 5:18 AM, Anonymous Anonymous said...

Regarding "The Nuclear Question" (2007-01-08), it is surprising to read that anyone should be considering building new nuclear power plants in the US when there is a simple mature technology available that can deliver huge amounts of clean energy without any of the headaches of nuclear power.

I refer to 'concentrating solar power' (CSP), the technique of concentrating sunlight using mirrors to create heat, and then using the heat to raise steam and drive turbines and generators, just like a conventional power station. It is possible to store solar heat in melted salts so that electricity generation may continue through the night or on cloudy days. This technology has been generating electricity successfully in California since 1985 and half a million Californians currently get their electricity from this source. CSP plants are now being planned or built in many parts of the world.

CSP works best in hot deserts and, of course, these are not always nearby! But it is feasible and economic to transmit solar electricity over very long distances using highly-efficient 'HVDC' transmission lines. With transmission losses at about 3% per 1000 km, solar electricity may be transmitted to anywhere in the US. A portion of the Mojave desert would be sufficient to meet the entire current US demand for electricity.

In the recent 'TRANS-CSP' report commissioned by the German government, it is estimated that CSP electricity, imported from North Africa and the Middle East, could become one of the cheapest sources of electricity in Europe, including the cost of transmission. A large-scale HVDC transmission grid has also been proposed by Airtricity as a means of optimising the use of wind power throughout Europe.

Further information about CSP may be found at www.trec-uk.org.uk and www.trecers.net. Copies of the TRANS-CSP report may be downloaded from www.trec-uk.org.uk/reports.htm. The many problems associated with nuclear power are summarised at www.mng.org.uk/green_house/no_nukes.htm.

 
At 8:09 AM, Blogger Boo said...

Thanks for the comment gerry...

Not sure if you noticed, but I'm talking about Canada (specifically Ontario) - where hot deserts are unheard of.

Clean coal tech has been developped in Canada, but the gov't seems reluctant to implement it.

Building nuclear plants is what the premier whats to do and imho its not necessarily a bad idea.

 
At 5:17 PM, Blogger roman said...

Why do I have this nagging feeling that Gerry Wolff's CSP initiative sounds too good to be true. If, indeed, this could be done, why is there absolutely no publicity about this? If the promise of supplying the electrical needs of the US by placing solar collectors in the Mojave desert is tenable, I am very much surprised that this scheme is not heavily promoted by the environmental people everywhere. Am I missing something?

 
At 11:13 PM, Blogger billie said...

are you saying that you don't want to have a battle of wits with unarmed people? :) great post- very informative.

 
At 12:36 PM, Blogger Boo said...

thanks Roman, Betmo

Roman, I dont get it either - I've heard about great clean coal tech but its not being implemented.

I dont think our Premier is so political that he wouldn't take up a worthwhile new scheme.

So does that mean its not as great as all the hype?

Bet - uninformed opinions are a huge pet peeve of mine... but you knew that

:)

 
At 9:06 AM, Blogger Pete said...

Boo

Thanks for the details (and of course the plug ;-)

Interesting the discussion on what politicians mention (nuclear) and what they don't (clean coal and concentrated solar). It could be that particular industries have influence on politicials or Cabinets out of sync with the environmental merits of a particular power source.

Another factor with nuclear, with especial relevance to middle ranking powers, like Canada and Australia is the potential value of the civilian nuclear power as a transition stage towards ownership of nuclear weapons.

Expertise in handling uranium safely and more particularly the production of necessary quantities of enriched uranium or plutonium must come from somewhere. Allies cannot always be relied on to provide these materials, nuclear devices or a nuclear shield against countries further down the weapons trial (Iran, North Korea, China, Russia etc).

So weapons are a unmentionable, but perhaps a useful hidden genie in the civilian nuclear bottle.

Pete

 
At 9:56 AM, Blogger Pete said...

Doesn't anyone disagree with my arguable arguments favouring nuclear weapons for deserving countries like Canada and Australia?

Some may see there is a long trail from nuclear power stations to weapons - one aspect is techical complexity another is gradually persuading public opinion. But power generation and weapons of the same dimension. Probably a major argument aganist nuclear power stations in the first place for many.

Pete

 
At 2:17 PM, Blogger Boo said...

"But power generation and weapons of the same dimension. Probably a major argument aganist nuclear power stations in the first place for many."

this is exactly what I was arguing with this post Pete - that there IS a huge trail from one to the other. And that nuclear power DOES NOT have be a prequel to weapons.

I wanted people to understand that nuclear plants ARE NOT just big nuclear bombs. That they DONT explode - its impossible.

That link is whats holding everybody up.

 
At 6:00 PM, Blogger SadButTrue said...

One thing being left out of this discussion is that there are a number of different designs that nuclear power generating stations may take. The heavy water moderated CANDU design used in Canada is inherently non-proliferating. Without extensive modification, it cannot be used to produce weapons-grade materials. Canada originally produced this design in hopes of being able to export a power generating technology within international non-proliferation agreements.

Countries that do have nuclear weapons programs naturally tend towards dual-purpose nuclear generators; so-called breeder and fast breeder reactors that produce enriched uranium and plutonium along with the electricity. The most dangerous of these primarily military facilities include the now-defunct Chernobyl reactor, and the US facility near Hanford, WA. The latter is considered by anyone with any knowledge of the issue as a ticking time bomb environmentally. This ancient and decaying complex produced the materials for Fat Boy and Little Man, the bombs dropped on Hiroshima and Nagasaki.

 
At 8:43 AM, Blogger Pete said...

Thanks Boo and SadButTrue

You're both filling yawning gaps in my knowledge about the technical side of reactors.

The sudden pro-nuclear energy campaign initiated by my (Australia's) Prime Minister appears only partially a means of cutting greenhouse gas emissions.

In Australia's case it is much more isolated from friendly powers than Canada. Australia is largely surrounded by Asian countries which we have occasionally fought. So this means the dual use path for at least one or two future Australian nuclear reactors is quite conceivable.

Basically I don't think we can 100% rely on the US to fully protect us or sell us nukes if China starts coveting Australia's vast coal, gas and uranium reserves. China is steadily becoming an ever more crucial trade partner to the US - perhaps forcing the US to choose.

Pete

 
At 9:09 AM, Blogger Boo said...

Sad - you've basically said, in clearer terms, what I've been trying to get across here about CANDU reactors... they're not a threat to anyone. Nuclear power can be used "peacefully" - so to speak.

Unfortunately, as you also mentioned - many want the dual use capability. Maybe the UN should instruct Iran that having nuclear power is fine but force them to build a "safe" reactor - like a CANDU. I know its ridiculous... but a good thought.

Same for you Pete, maybe CANDU reactors in Australia? Of course, you do make it sound as though Aust. needs the weapons capability... sheesh. I hope not.

 
At 12:16 AM, Blogger Pete said...

Boo

You're right about Iran. Many countries are suggesting Iran stick to safe reactors and that any enriched uranium needed by Iran not be enriched in Iran. Reason is the west (and Russia) don't want Iran to enrich uranium to weapons grade on the side.

In Australia I think we'll probably build 5-6 safe CANDU type reactors in the next 25 years and perhaps one dual use.

In 25 years there are likely to be 6 or so additional nuclear weapons states. Ausstralia does not have the strong nuclear umbrella alliances with the US that Canada has - I'm talking about NATO and NORAD etc. Our weak ANZUS alliance and isolated position will make it essential that Australia has a self-sufficient nuclear capability within 25 years.

I'm mainly talking off topic here so I'll carry this issue on my blog sometime.

Pete

 
At 9:08 AM, Anonymous Anonymous said...

Check out Google Earth - every one can. Out in NB they have spent fuel stored above ground in concrete tube?? Who's bight idea was that? If there was an explosion by them it would send crap into the bay of fundy and all over the east coast. Now they want to rebuild the place and put all the hot old crap in similar containers??

 

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