Gennadi Pshakin

The Soviet Union’s fast-neutron reactor program began at the end of 1949 when physicist Alexander Leypunsky presented a special report to the Government on the idea of creating nuclear reactors that could produce more fissile material than they consumed. The rationale offered was that in the future, as the Soviet nuclear industry expanded rapidly, there would be a shortage of uranium. In November 1949, the Government decided to launch a fast-reactor development program. Leypunsky was designated as the program’s scientific leader and the State Scientific Centre of Russian Federation, Institute of Physics and Power Engineering (IPPE) in Obninsk became the lead research institute.1

The program contended with inadequate knowledge in many areas, including the behavior of the candidate reactor, core and coolant materials under irradiation and the information required to design the steam generators, where the reactor coolant and water would be separated only by a thin layer of material.2

It is important to note that the program started only four years after the most destructive war the country had ever faced. There were shortages of both special materials and personnel with relevant expertise.3

The first decade, 1949-59

The first decade of the Soviet breeder program was exploratory. In May 1955, a fast critical assembly BR-1 (in Russian "Bystry Reactor-1," i. e. Fast Reactor-1) started operation at IPPE. It was fueled with metallic plutonium and without a coolant.4 The compact plutonium core and uranium blanket allowed a breeding coefficient of approximately 1.8, which lent great support to the breeding idea.

The following year, the fast reactor, BR-2 began operation. Both gaseous and liquid-metal coolants were considered during the design stage.5 Mercury was chosen but the metal plutonium fuel was not stable under irradiation even at low temperatures and mercury leaked from pipe joints and corroded the steel cladding.6

The BR-2 was replaced with the BR-5 (5 MWt),7 and commenced operations in 1959. It was cooled with liquid sodium and fueled with plutonium dioxide to allow higher fuel temperatures and power densities (up to 500 kilowatts/liter) in the core.8 The BR-5’s power was subsequently increased to 10 megawatt thermal (MWt) and it operated until 2004. In addition to reactor research and development, the BR-5 was used for medical-isotope production and even medical treatment (neutron-capture therapy of throat cancer using neutron beams from the reactor).