Saturday, April 26, 2008

RBMK Reactors and Weapons-Grade Plutonium Production

As a student of the Soviet nuclear weapons complex, I have long been mystified by the near-universal belief in the west that the Soviet RBMK reactor design was chosen in order to produce weapons-grade plutonium for the Soviet military. Although it's possible that experiments were done at the first RBMKs in the 1970s to see if it was possible for these reactors to produce weapons-grade material, the fact of the matter is that the RBMK design was chosen for other reasons, and that they are not used for plutonium production. In fact, RBMK fuel is generally not reprocessed.

The basic rationale behind the RBMK was the desire of the Soviet government to produce large nuclear power plants as inexpensively as possible. The RBMK met this goal well, but sacrificed safety in order to do so. One of the main attractions of the RBMK was that it was built out of modular components that could be produced by existing Soviet industry. At the time the first RBMK-1000 was being built at Leningrad in the late 1960s, the Soviet Union had extreme difficulty manufacturing the forgings needed for large pressurized water reactors. The RBMK could also operate using low-enriched uranium oxide fuel- 2.0-2.4% U-235. This served as another cost-saving measure. The 2.0% fuel generally has a burnup of around 30,000 Megawatt-days per metric ton of heavy metal.

So what becomes of spent RBMK fuel? According to End Points for Spent Nuclear Fuel and High-Level Radioactive Waste in Russia and the United States (2003):

More than 8,700 MTHM of RBMK SNF with total radioactivity of 3.1 billion curies are stored in cooling pools at the power plants and at separate wet-storage facilities onsite. At the Leningrad Nuclear Power Station, for example, fuel is stored for three to five years in the cooling pool adjacent to the reactor building, then is loaded into a cask full of water and moved to a storage building nearby on the site (NAS 1990). Approximately 3,000 fuel assemblies are breached, which complicates handling and storage.

Dry storage is expected to replace pool storage for all of the fuel in coming years. It is anticipated that the roughly 8-meter-long RBMK fuel assemblies will have to be cut in two to fit inside the dry storage casks. Russia does not currently ship any RBMK SNF, with the exception of transportation of half-assemblies for post-reactor tests in hot cells.

The decision on the long-term plan for RBMK fuel management has not been made yet. Several approaches are possible and are now under consideration. Although accumulation of RBMK SNF at the power plant site can lead to difficulties when the plant is to be decommissioned, this spent fuel is not seen as a proliferation or an immediate health hazard, so it is the committee’s judgment that leaving it in place is a reasonable allocation of scarce resources. Nevertheless, to prevent theft for possible use in a radiological weapon, this spent fuel must be protected at the sites.

Also see this article from the antinuclear group Bellona, which states that as of six years ago, the wet storage facility at the Leningrad AES contained fuel assemblies dating back to 1975, which were then on the verge of being moved into dry storage. Given that the LAES was the first RBMK reactor, going into service in 1973, this indicates that it was never standard practice to remove spent fuel from the plants- and thus, making it impossible for the spent fuel to be reprocessed into weapons material. So even though the RBMK design is a descendant of plutonium-production reactors, it is inaccurate to characterize it in this category itself.


DV8 2XL said...

I was one of those that were under the impression the RBMK's were selected to facilitate the production of weapons-grade plutonium. It was one of thoses 'facts' that we heard over and over again and never questioned. Makes one wonder how many other 'facts' I may have wrong, and I'm pro-nuclear power and pro-nuclear weapons; (in general, you know what I mean) just goes to show you can't sit on your laurels.

Thanks for setting us straight.

Charles Barton said...

Excellent research. You put to rest a long held assumption. Incidentally you also demonstrated that the Soviets ignored the possibility of using reactor grade plutonium plutonium in nuclear weapons, demonstrating once again that the notion that electrical generation reactors represent a proliferation is a myth.

Alexandra Prokopenko said...

RBMK as a weapon plutonium producing device - sounds like a myth invented by US intelligence services for demonization of Soviet nuclear industry and Soviet Union itself (even their peaceful reactors are actually aimed at producing plutonium).
Recently my colleague Robert Margolis came across a video made by US intelligence on a Syrian reactor suspected to be a planned plutonium production:

Wavefunction said...

In fact many people in the West think that most, if not all of Soviet industry was built in such a way that it would always switch from civilian production to weapons and military production at a moment's notice. But I have also heard some prominent historians such as Rhodes say this. There must be some gray here. What's the truth?

Sovietologist said...

As a rule, the Soviet economy prioritized defense expenditure. In fact, this is the area in which the Soviets excelled. Despite their severe economic disadvantages, by the 1970s the Soviet Union could actually match NATO strategically. Many Soviet technologies were intended for dual use- their airliners, for instance, included some features that increased their utility as troop transports. The Vostok space capsule and the early Soviet spy satellites shared a lot of hardware. But not everything they built was like that. Sometimes a spade is just a spade. And because the Soviets had enough plutonium by the mid-1970s to match the US in weapons, it wasn't necessary to build dual-use reactors.

As for the question of how quickly the Soviet economy could mobilize for war, I think this changed between the 1950s and the 1980s. In some sense the Stalinist economic policy was always on a war footing. But under Brezhnev there were many more consumer goods produced- Ladas, TVs, that sort of thing- and nuclear weapons put the kibbosh on the idea of the kind of economic mobilization seen during WWII.

Alexandra Prokopenko said...

Actually, the fact the the USSR economy was military-oriented, was true to a certain extent. If we look at planning the way productions of civil goods were located, for example, assembly of heavy machinery like tractors and high tech electronics, oil refineries and so on are found in the Western part, Belarus in particular. Belarusian Tractor Plant that produced tractors for the entire USSR, could as well produce tanks, and the 3 large oil processing plants (Mozyr, Rechytsa, Nowopolotsk) could produce enough fuel close enough to the border in case of war. The economy was planned in such a way that is was civil-oriented with an option to go over to military production quick enough.

Sovietologist said...

Ah yes! I have a bunch of Soviet electronics made in those factories in Minsk/Pinsk.

I've been told that sometimes the consumer electronics industry got components that were intended for military production but then failed to pass quality control. Apparently this is why there are people who go around looking for old Soviet electronics to scrap- the components contain a very high content of valuable materials compared to western ones.

Alexandra Prokopenko said...

Yes, indeed, I know several Swedish businessmen who were buying old Soviet electronic scrap in huge amounts and selling it afterwards in Western Europe.

pwshafer said...

Production reactors. These are used to make plutonium (and often tritium) efficiently. Production reactors are frequently graphite-moderated and either air-, CO 2 -, or helium-cooled. The longer a given sample of fuel is irradiated, the greater the build-up of 240 Pu, an isotope which decays by spontaneous fission and which should be minimized in weapon fuel. Consequently, plutonium production reactors usually are designed to be refueled while operating (on-line refueling) so that relatively little 240 Pu is found in the “spent” fuel. The A-D production reactors and the N-reactor plant used a graphite moderator with light water as the coolant which passes through stainless steel tubes containing aluminum or titanium-vanadium alloy cladded Uranium metal fuel. The fuel has less than 1% U-235 to start or essentially natural uranium. In the case of the N-reactor, the tubes are pressure tubes of stainless steel which allow for steam production to produce electricity in a conventional turbine – generator. All of these reactors are now shutdown and are being dismantled.
The first Soviet production reactor was at Obninsk. It operated from 1954 to 1975. It was similar in design to the Hanford B reactor. Since the 1970s, the Soviets have built additional graphite moderated-light water cooled production reactors in Siberia. The RBMK reactor designed to produce electricity (and plutonium) is a scaled-up version of these reactors
The Soviet RBMK dual purpose reactors (ex. Chernobyl), similar to the US N-reactor are capable of efficiently producing both reactor grade and weapons grade plutonium in vast quantities since they are able to be refueled during operation and have blanket capabilities in their huge graphite moderators (more on this in Part 2). There are currently 13 large RBMKs in Russia and former Soviet states. These reactors nominally start with very low enriched Uranium oxide fuel (<2% U-235) but are capable of accommodating cladded Uranium metal fuel rods to facilitate weapons grade plutonium production.