11 July 2014

Russia bets its energy future on waste-free fast breeder nuclear reactors

Russian fast breeder nuclear reactor, being assembled

Russian engineers began a fission reaction at the BN-800 fast breeder nuclear reactor in the Urals last week, marking the beginning of what the government hopes will be a new era of nuclear power for the country. It’s one of several such reactors operating in Russia, but represents a renewed push into nuclear energy even as the country bets big on natural gas production as a major source of national income. Fast breeder nuclear reactors do not require expensive heavy water moderator to begin the nuclear reaction, and they could even be run so they produce no net waste. Russian estimates say the 880-megawatt BN-800 reactor could provide power for more than 3 million families and construction of an even bigger cousin, BN-1200, is already underway.

To understand the major benefits of fast breeder reactors, we need to break down the name. “Fast,” in this case, refers to the neutrons that actually do the atom-smashing that triggers the nuclear fission. In normal (called “thermal”) nuclear reactors, neutrons must be slowed down as they travel from one sample of material to another, otherwise they will not impact fissile atoms and begin the nuclear reaction. “Fast” nuclear reactors get around this problem by using specialized or more enriched fuel samples that packs fissile atoms more closely together. This outsources most of the difficulty to the fuel production stage, rather than the fuel burning stage.

Note that the whole fission apparatus sits in a pool of liquid sodium
Note that the whole fission apparatus sits in a pool of liquid sodium.

Other reactor designs take the opposite approach, using ultra-expensive “heavy water” as the neutron-slowing moderator so they can used poorly enriched or even natural samples of uranium. Opinions vary over which strategy is best, but Russia spent the latter half of the twentieth century learning how to produce large amounts of nuclear material, while the country’s record with reactor maintenance is not nearly so stellar. A fast reactor seems like a good fit for the current Russian energy sector.

The other key word here, “breeder,” is even more important. Without going into too much detail, suffice to say that when a breeder reactor uses fuel, it actually produces enough neutrons to “breed” more fuel than it uses. This basically has to do with hitting enough atoms with neutrons that, some dependable portion of the time, the neutron will be added to the atom rather than blasting it apart. In modern designs, a “breeder blanket” of non-fissile uranium-238 surrounds the core to catch excess neutrons and become fissile plutonium-239, along with some of the uranium in the core.

interior of BN-800 reactor. It is still under assembly
he interior of BN-800 reactor. It is still under assembly in this picture.

You’ve probably already heard the downside of reprocessing and refissioning of nuclear fuel: it can produce weapons-grade uranium. It might seem odd to say it, but Russia is one country we really shouldn’t worry about too much in terms of nuclear tech if anything, the country has found its stockpiles of Soviet-era nuclear weapons to be a major burden. Russia also has too many complex relationships in the world’s most troubled areas to start selling nuclear-capable materials to insurgents or terrorist governments. While the proliferation argument is certainly not dead, relative to the global energy crisis it seems like a bit of a dead issue. Additionally, this is Russia we’re talking about literally all the griping in the world won’t change its government’s mind on an issue like this.

Leningrad nuclear power plant
Leningrad nuclear power plant

The BN-800 fast breeder reactor, like all modern fast breeder reactors, uses liquid sodium as its coolant. Water would have absorbed too many precious neutrons, and liquid sodium lets them pass without slowing them down. Liquid metal (remember, sodium is a metal) also has very high heat capacity, which makes it easier to avoid overheating. Best of all, it does not need to be pressurized to perform its function, so the whole reactor can be simpler and less dangerous. On the other hand, heated liquid sodium is also highly reactive with oxygen, among other things, and can cause fires if proper precautions aren’t taken. The sodium itself also becomes radioactive when neutrons are passed through it though this “activated sodium” has a half-life of less than a day.

Russia has big hopes for nuclear power. It is well on its way to achieving the goal first laid out in 2003, of doubling its use of nuclear power by 2020 and lessening domestic use of natural gas. This is partially to free up additional natural gas to sell around the world in the ongoing crisis in Ukraine, Russia’s ability to withhold Ukraine’s supply of energy has been of central importance. A total of eight BN-1200 reactors (1200MW) are planned to go live by 2030, making Russia one of the only countries truly betting on nuclear power in the future. We’ll see how well the gamble pays off, both domestically and in the world at large, over the next several years.

Courtesy Extremetech


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