A Nuclear Reactor By Any Other Name…

All nuclear reactors do the same thing – create heat from the decay and fission of radioactive materials. However, there are six different types of reactors used to generate electricity, differentiated by fuel, coolant and moderator.

Reactor Type	Locations	Number	Fuel	Coolant	Moderator
Pressurized Water	US, France, Japan, Russia, China	265	Enriched UO2	Water	Water
Boiling Water	US, Japan, Sweden	94	Enriched UO2	Water	Water
Pressurized Heavy Water	Canada	44	Natural UO2	Heavy Water	Heavy Water
Gas-cooled	UK	18	Enriched & Natural UO2	CO	Graphite
Light Water Graphite	Russia	12	Enriched UO2	Water	Graphite
Fast Neutron	Japan, France, Russia	2	PuO2, UO2	Liquid Sodium	None
Other	Russia	2	Enriched UO2	Water	Graphite

Source: World Nuclear Association

The fuel is usually uranium oxide (UO₂) in cylindrical pellets placed end-to-end in long tubes. Most reactors use enriched uranium which contains from 3.5 to 5.0 per cent U-235 (the really active ingredient) and from 95.0 to 96.5 U-238. A few reactors use natural uranium which consists of 0.7 per cent U-235 and more than 99.2 per cent U-238. In Fast Neutron reactors, plutonium oxide (PuO₂) is used

The moderator slows neutrons released during fission so that there is more chance they will collide with uranium atoms in the reactor core, releasing more neutrons and heat energy and sustaining a chain reaction.

The coolant is what carries the heat from the core to the either a steam generator or the turbines.

All reactors operate in the same basic way. The fuel is induced into a fission reaction wherein unstable U-235 atoms release neutrons and heat. The released neutrons are slowed by the moderator and collide with other atoms and more neutrons are released and a self-sustaining chain reaction develops. The coolant, contained in separate pipes running through the reactor core, absorbs the heat and, in all reactors but Boiling Water Reactors, carries it to a steam generator. The steam generator is a separate circuit in which water is turned to steam that turns the turbine that turns the generator. After passing through the turbine, the steam is condensed into water and continues the cycle. All this is housed in a containment structure designed to contain any material or vapour that could escape from the reactor in the event of a nuclear mishap.

With Pressurized Water Reactors, the water used as coolant is kept at very high pressure, and consequently, very high temperatures without boiling.

In Boiling Water Reactors, the coolant water is allowed to boil and become steam and that steam drives the turbine. There is no secondary steam circuit.

Pressurized Heavy Water Reactors operate are identical to Pressurized Water Reactors except they use heavy water as both coolant and moderator. Heavy water consists of deuterium oxide. Deuterium is an isotope of hydrogen with two neutrons instead of one. Heavy water slows neutrons so efficiently that the uranium fuel doesn’t need to be enriched, and natural uranium can be used. The primary Pressurized Heavy Water Reactor is the CANDU reactor, developed in Canada, hence the name – CANada DUterium.

Graphite-moderated reactors sit in a solid block of graphite and use either light water or carbon monoxide as coolant.

Fast neutron reactors use neutrons from plutonium derived from U-238 surrounding the plutonium. They are sometimes called Breeder Reactors.

All of the reactors generating electricity in Canada are Pressurized Heavy Water CANDU Reactors. The reactors at Fukushima Dai-ichi are Boiling Water Reactors. The Chernobyl reactor was a Light Water Graphite Reactor with no containment structure. Three Mile Island was a Pressurized Water Reactor.

Rating Nuclear Accidents

Graphic: International Atomic Energy Agency

Earthquakes have the Richter Scale; nuclear mishaps have the INES – International Nuclear and Radiological Event Scale.

The purpose of INES is to provide a means of “communicating to the public in a consistent way the safety significance of nuclear and radiological events.” There are seven levels to the scale which are applied to three “areas of impact”:

• People and the Environment considers the radiation doses to people close to the location of the event and the widespread, unplanned release of radioactive material from an installation.
• Radiological Barriers and Control covers events without any direct impact on people or the environment and only applies inside major facilities. It covers unplanned high radiation levels and spread of significant quantities of radioactive materials confined within the installation.
• Defence-in-Depth also covers events without any direct impact on people or the environment, but for which the range of measures put in place to prevent accidents did not function as intended.

The seven levels are defined such that each level is ten times more severe than the previous level. Unlike the Richter Scale, where intensity of an earthquake is determined by a mathematical formula, the INES is based on a series of definitions. For example, under People and the Environment, Level 2 is defined as “exposure of a member of the public in excess of 10 millisieverts or exposure of a worker in excess of the statutory annual limits.” Level 3 is defined as “exposure in excess of 10 times the statutory annual limit for workers and non-lethal deterministic health effects from radiation (e.g. burns).”

Similarly, a Level 6 event is defined as a significant release of radioactive material likely to require implementation of planned countermeasures, whereas a Level 7 event is defined as a major release of radioactive material with widespread health and environmental effects requiring implementation of planned and extended countermeasures.

Fukushima Dai-ichi is currently considered a Level 6 event while Chernobyl is considered a Level 7 event.

While this may seem somewhat subjective, there is a very comprehensive, 218-page INES Users Manual developed by the International Atomic Energy Agency in cooperation with the Organization for Economic Co-operation and Development and the Nuclear Energy Agency. The manual removes a lot of ambiguity. Media reporting on a nuclear accident should consult the manual.

Where is My Electricity Coming From at This Hour?

If you live in Ontario and want to know where your electricity is coming from at this hour, the Canadian Nuclear Society hosts a website called Where is My Electricity Coming From at this Hour?

All you have to do is go to the website and it not only tells you from whence your electricity comes, but also how many tonnes of CO₂ have been avoided by not burning coal, the number of homes being supplied by each electricity source, from whence your electricity came in past 48 hours and the capabilities and output of pretty much every generating unit in Ontario, be it nuclear, coal, natural gas, hydro, wind or other. The source for the generation data is Ontario’s Independent Electricity System Operator.

We’re pretty excited about this service, not only because of the transparency it provides, but also of its false-impression-busting capabilities. For example, the amount of CO₂ Ontario’s coal-fired generating plants emit gets a lot of coverage, and from this we get the impression that coal is one of the major sources of Ontario’s electricity, but in consulting Where is My Electricity Coming From at this Hour, we find that currently only four per cent is coming from coal. Forty-nine per cent is coming from nuclear power, 23 is coming from hydro, 18 from natural gas, five from wind and one from other, chiefly wood biomass.

And 16 hours ago, 4.6 per cent was coming from coal, and that was about as high as it got in the last 48 hours.

In fact, the website points out that 13,210 tonnes of CO2 that would have been emitted in the past hour if all the electricity in Ontario was coal-fired, have been avoided due to the use of other energy sources.

We wonder how many Canadians coast to coast know and understand where their electricity comes from, not only by the hour, but in general. Knowing where our electricity comes from may be useful in deciding how much we’re going to use and how we’re going to use it.

Wednesday Update – Japan

The Canadian Nuclear Association, which is monitoring events in Japan closely, reports the situation is fluid. International reaction regarding domestic nuclear programs is mixed, with some countries calling for temporary halts to new construction pending assessments of existing facilities.

Updates are also provided by the Canadian Nuclear Safety Commission.

Seawater continues to be pumped into Fukushima Dai-ichi Units 1, 2, and 3. Partial melting of the reactor cores at Units 1 and 3 is feared as is potential meltdown at Unit 2. It is now thought that damage to the containment structures is likely at Units 2 and 3.

High levels of radiation from Unit 3 forced workers to retreat temporarily to a safe area of the complex, but work continued one the radiation spike subsided.

The Canadian government reports that radiation from the disaster poses no threat to Canadians.

Nuclear Energy and the Japan Earthquake

Japan generates about 30 per cent of its electricity from 55 nuclear reactors operating in 18 nuclear power plants. Because Japan is in a region with a large amount of seismic activity, all nuclear plants are constructed to exacting safety standards. One aspect of these standards is systems that automatically shut down reactors in the event of an earthquake.

The problem is we can shut down a reactor, but we can’t completely shut down the reaction.

Part of the reaction is fission, which occurs when a uranium 235 (U235) atom collides with a stray neutron. The atom splits into smaller atoms and releases more neutrons and heat energy. The new neutrons collide with more atoms and the process becomes self sustaining – a nuclear chain reaction.

Another part of the reaction is radioactive decay, which is the random and spontaneous decay of an unstable nucleus. Radioactive decay cannot be controlled.

Fission can be regulated by raising or lowering control rods in the reactor. Control rods are made of substances that inhibit fission by absorbing neutrons. To shut down a reactor, the control rods are lowered completely into the reactor core which effectively stops nuclear fission.

However, the core of the reactor is still hot, and radioactive decay is still ongoing, so it must be cooled, usually by circulating cold water through it.

The Fukushima-Dai-ichi nuclear power plant survived both the earthquake of March 11 and the subsequent tsunami without suffering major damage. The local electricity system, however, was severely damaged and put out of commission, as were back-up systems at the power plant. Although the control rods at the plant were lowered and the reactors automatically shut down, the lack of electricity prevented the water circulation necessary to cool the cores of Units 1, 2 and 3. Auxiliary diesel pumps were brought in and the containment structures were flooded with sea water. Units 4, 5, and 6 were under maintenance at the time of the earthquake.

All four units at the nearby Fukushima Dai-ni nuclear power plant were shut down safely following similar cooling problems.

However, at each of Fukushima Dai-ichi, Units 1, 2, and 3, the heat of the core vapourized the water almost as fast as it could be pumped in. The increasing amount of vapour raised the internal pressure to the point where some of the steam had to be vented to prevent damage to the containment structure. The released steam contained hydrogen that exploded when it came in contact with oxygen in the atmosphere. At Units 1 and 3, the explosions damaged the reactor buildings, but left the containment structures intact. The explosion Tuesday at Unit 2 damaged the suppression pool within the Unit 2 containment structure.

Under normal circumstances, venting radioactive steam is avoided; however, in this case, it was the lesser of two evils. A rupture of the containment structures would have had catastrophic results.

As of Tuesday, there are fears that the cores of the three units have suffered partial meltdown.

Wind is dispersing radiation from the three units out over the Pacific Ocean, reducing the immediate danger in the area. The Canadian Federal government does not expect the dispersed radiation to pose a health threat to Canadians living on the west coast.

While the situation is still critical, there is little danger of a Chernobyl-scale disaster. While the reactors, containment structures and reactor buildings survived the earthquake and tsunami, the backup systems and emergency power systems proved inadequate.

Kapow! Nuclear fusion with a bullet

If John Woo had decided to get into the energy sector instead of bullet-ridden action movies, he might have proposed something like this: firing a diamond bullet into a chunk of solid methane to produce nuclear fusion. And you thought nuclear energy was already exciting.

Of course, the idea of using a high-speed projectile as an energy source is just a theory at the moment, proposed by a group of Chinese researchers at Beijing University in a pair of papers (“Hypervelocity Macroscopic Particle Impact Fusion with DT Methane” and “Fast Ignition Impact Fusion with DT methane”). Even though the energy required to fire a millimetre-sized bullet at 1,000 km/s is considerable, the papers’ authors believe there would still be a net energy gain.

According to the Popular Science article linked above:
The collision’s peak energy is 4 petawatts, at a rate of 1.5 petawatts over 40 nanoseconds. That’s four quadrillion watts. About 80 percent of that energy is wasted in the form of scattered neutrons, but the remaining electrons and radiation are enough to heat things up to fusion temperatures.

Novel alternatives to the current model of nuclear generation are cropping up every day, from alternative fuel sources like uranium nitride to DIY enthusiasts (link to DIY nuclear). But when it comes to exciting alternatives, it’s going to be hard to beat a diamond bullet. Unless, somehow, they can also include a golden gun.

Via Popular Science

Nuclear in New Brunswick

AREVA, a France-based multinational nuclear energy company, recently announced that it would be examining the feasibility of building a second nuclear reactor in New Brunswick in addition to the Point Lepreau facility.

Canada currently has 22 nuclear reactors. Eighteen are currently operational, in five generating facilities: Bruce, Pickering and Darlington in Ontario; Gentilly 2 in Quebec and Point Lepreau in New Brunswick. Nuclear power provides about 12 per cent of the electricity generated in Canada.

At this point, AREVA has only announced a letter of intent for this new light-water reactor, with a more substantive agreement with the province to be inked by the end of 2010. And if nothing ultimately came of the letter, it certainly wouldn’t be the first aborted nuclear project in recent years.

In July 2009, Bruce Power pulled the plug on two additional reactors in Bruce County, focusing instead on refurbishing its existing reactors. The plants had been slated to be built at Nanticoke on Lake Erie, but the rising costs of nuclear production, and the long-term construction period required for a new reactor were likely mitigating factors.

Another important recent development to Canada’s nuclear energy sector has been the federal government’s omnibus bill (Bill C-9), which among other provisions aims to sell off the nuclear power division of Atomic Energy of Canada Limited (AECL), the crown corporation responsible for the CANDU line of reactors. The recent failure of the National Research Universal (NRU) reactor at Chalk River, which provides radioactive isotopes for diagnostic procedures, was the likely catalyst for the sale. (AREVA’s letter of intent is not coincidental: NB Power recently rejected AECL’s proposal to build a new CANDU reactor, in favour of AREVA).

If New Brunswick successfully commissions a new reactor, it would be the first new reactor built in Canada since the MAPLE II reactor, which, like Chalk River’s NRU reactor, was built to provide medical isotopes. MAPLE II began operating in 2003 but has been subsequently terminated due to technical issues.

Given the volatile fate of recent attempts to build nuclear facilities, it’s worth noting again how early on in the process this letter of intent comes. In any case, it all goes to show that when it comes to nuclear power, things always run a little hot.

Cutaway your Christmas list

BibliOdyssey has the perfect gift idea for those impossible-to-buy-for people on your Christmas list. We bet they don’t have these.

Nuclear reactor wall charts.

Beautiful cutaway illustrations of the Super Phénix, the Snupps, the Fulton, a Canadian classic the Candu 3, the Douglas Point BRW/6, the Grand Gulf, the Guangdong and last but not least the Oskarshamn.

With this much choice, there is no excuse for not wrapping up you Christmas gift shopping today.

Image: UNM CSEL Nuclear Engineering Wall Chart Collection

Is nuclear green?

The nuclear industry is billing itself as a viable green and environmentally-friendly energy source. Its detractors say otherwise.

According to the Canadian Nuclear Association, Canada’s reactors avoid 100 million tonnes that would be emitted by fossil fuel-burning plants. That constitutes a reduction of 10 to 15 per cent. The federal government agrees, and has incorporated nuclear energy as part of its environmental initiative.

As a high-density energy source, nuclear power has a small environmental footprint. One kilogram of uranium creates 400,000 kilowatts (KWh) per hour of energy compared to three KWh from the same amount of coal.

That said, nuclear energy doesn’t enjoy universal acceptance as a “green” energy source. Radioactive nuclear waste is hazardous, and stays hazardous for hundreds of thousands of years. Opponents say there’s simply no way to find, plan, or build storage to last that long.

The Alberta government recently commissioned a $250,000 report on nuclear energy. It concluded nuclear power is a “safe energy alternative” and offers a smaller footprint than hydroelectric and wind power. The nuclear industry says it has developed completely safe methods and places to store waste.

Nuclear opponents also dispute the claim that it’s greenhouse gas-free. Mining uranium ore, refining and enriching fuel, building the plant, and operating it all produce carbon dioxide in relatively large quantities. A 1,250 megawatt plant produces the equivalent of 250,000 tons of CO2 annually.

But that’s still much, much less than coal-fired power plants and natural-gas turbines. It’s almost impossible to find 100 per cent clean energy.

So why wouldn’t we look for the cleanest possible?

Nuclear waste management

The legacy of more than 40 years of nuclear electricity generation in Canada is a stockpile of just over two million spent reactor fuel bundles. Projected to top 2.3 million by 2011, it presents a considerable and costly challenge for governments and utilities.

Each bundle is about the size and shape of a fireplace log, weighs about 24 kilograms and if the entire inventory could be stacked like cordwood, it would fill five hockey rinks to the top of the boards. But it can’t be stacked like that because it is fissile material.

The current inventory is stored in “swimming pools” at the reactor sites where the waste was generated, in Ontario, Quebec and New Brunswick and at Atomic Energy of Canada Limited’s (AECL) research facility in Manitoba. It stay in the pools for 7-10 years while heat and radioactivity decreases and is eventually removed to dry storage.

But Canada has yet to answer the question of where best to store the fuel bundles in the long term. Deep geologic disposal in the geologically-stable Canadian Shield was identified by AECL as the preferred option in the 1970s. While it has been researched exhaustively, it was not until 2002, under the auspices of the Nuclear Fuel Waste Act, that a new Nuclear Waste Management Organization (NWMO) was tasked with ensuring that the bundles and other irradiated waste will be isolated from people and the environment –most likely for centuries.

The NWMO expects to publish its disposal site selection process this spring and after a public comment period, hopes to finalize the selection process by year’s end and have the repository operating by 2035.

In its latest annual report, NWMO Chairman Gary Kugler, who has a doctorate in nuclear physics from McMaster University and is a former senior vice-president of nuclear products and services at AECL, acknowledges that the challenge is as much social as technical.

“The prevailing view of Canadians continues to be that the generation enjoying the benefits of nuclear power has the responsibility of managing its used fuel,” Dr. Kugler said, summarizing one of the key outcomes of a series of public discussions that took place last year.

To ensure that the cost of managing spent fuel doesn’t become a burden for future generations, the NWMO has updated its original $5-6 billion estimate for building and operating a repository as well as securely transporting waste. Its latest estimate is $7-8 billion, an amount which is certain to increase again when the next estimates are prepared no later than 2012.

The current reactor operators, Ontario Power Generation, New Brunswick Power, Hydro-Quebec and AECL, have so far put $1.51 billion into a trust fund, which is expected to top $2 billion in 2011. The fund will keep growing as the final repository site moves from concept to reality – which is inevitable as various provinces contemplate adding to or joining the country’s nuclear power club.

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