Heavy Water Moderated, Molten Uranium Cooled Reactor MCNP Model

Journal Article · Sat Jul 01 04:00:00 EDT 2017 · Transactions of the American Nuclear Society

OSTI ID:23050321

Mann, Neal L. ^[1]

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1. 909 Massachusetts Ave NE, Washington, DC 20002 (United States)

Two of the major challenges facing the nuclear industry are the large amounts of nuclear waste produced by the current light water reactors and the risk of nuclear proliferation. Most proposed solutions for the waste problem involve fast breeder reactors, but that doesn't help with the nuclear proliferation problem. It is generally understood that a uranium fueled (U-238 + U-235) thermal reactor cannot be a breeder because there aren't enough neutrons. That analysis does not include the effects of fast fission of U-238. This is not surprising because the percentage of fast fissions in existing thermal reactor designs is low, around 3% (in Candu reactors) or less. Table I shows the neutrons involved in 1,000 fissions in a thermal reactor for a conversion ratio of 1.000 when the fuel is mostly U-238 and the fissile content is low enough so that most fast fissions are of U-238. The top section of the table is for U-235 in U-238, the bottom section is for Pu-239 in U-238. The bottom line in each section shows the number of neutrons available for all other losses (escape from the reactor, absorption in non fuel components, and absorption in xenon, samarium, and other fission products). If the percentage of fast fissions of U-238 is 10 or 15 % a thermal breeder may be feasible. This is largely independent of the percentage of fissile content of the fuel. If the reactor starting fissile content is mostly U-235, as the U-235 is replaced with Pu-239 the number of available neutrons increases even if the conversion ratio is only 1.000. The percentage of fast fissions in a reactor is a question of reactor geometry, as the minimum dimension of the fuel elements increases the average distance a fast neutron travels in the fuel before exiting increases and with it the probability of fast fission of U-238.

• OSTI ID: 23050321
• Journal Information: Transactions of the American Nuclear Society, Journal Name: Transactions of the American Nuclear Society Vol. 116; ISSN 0003-018X
• Country of Publication: United States
• Language: English

Related Subjects

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ABSORPTION
CANDU TYPE REACTORS
FAST FISSION
FAST NEUTRONS
FBR TYPE REACTORS
FISSION PRODUCTS
FUEL ELEMENTS
HEAVY WATER
NUCLEAR FUELS
NUCLEAR INDUSTRY
PLUTONIUM 239
RADIOACTIVE WASTES
REACTOR DESIGN
SAMARIUM
URANIUM
URANIUM 235
URANIUM 238
WATER COOLED REACTORS
WATER MODERATED REACTORS
XENON