Performance indices optimization of l ong‐lived fission products transmutation in fast reactors

Abstract

Summary An investigation on the nuclear transmutations of elemental long‐lived fission products (LLFPs) in a fast reactor is being conducted in Japan, focusing on the Se‐79, Zr‐93, Tc‐99, Pd‐107, I‐129, and Cs‐135, to reduce the environmental burden. With their high neutron flux and adequate excessive neutrons, fast reactors are considered strong candidates for transmuting those LLFPs into stable isotopes or shorter effective half‐lives under the partition and transmutation (P/T) strategy. In this investigation, the LLFP subassembly is assumed to be loaded into the radial blanket region of a Japanese MONJU class sodium‐cooled fast reactor (710 MWth). This work focuses on two LLFPs, namely, I‐129 and Tc‐99. The LLFPs are mixed with YD2 or YH2 moderator material to enhance the LLFP transmutation rate. The results include the optimal position of the LLFP assembly in the radial blanket and the optimal moderator volume fraction to optimize the transmutation performance indices, that is, the transmutation rate (TR, %/year), the support factor (SF is defined as the ratio of transmuted to produced LLFP), and the effective half‐life (T‐half) of the LLFPs. A countermeasure is also devised to resolve the expected higher power peak at the fuel assembly adjacent to the LLFP assembly. The neutronics and burnup analyses are conducted using the continuous‐energy Monte Carlo SERPENT2 code with the JENDL‐4.0 nuclear data library.

Transmutation of MAs and LLFPs with a lead-cooled fast reactor

“…As mentioned above, six radionuclides 79 Se, 93 Zr, 99 Tc, 107 Pd, 129 I and 135 Cs are selected as transmutation candidates. These LLFPs nuclides were mixed with the neutron moderator (70 at% LLFPs + 30 at% YD 2 ) and were loaded into the LLFPs assemblies to improve the transmutation performance since the feasibility of this moderator has been proven 9 , 11 , 29 . The moderator could soften the neutron at the LLFPs assembly region while having little effect on the neutron energy spectrum of the entire core, as it is loaded in the radial blanket region with a small loading mass.…”

Potential of transuranics transmutation in a thorium‐based chloride salt fast reactor

“…Previous research has revealed that both ADS and solid fuel critical fast reactors face technical challenges in transmuting TRUs to achieve a high transmutation rate (transmutation amount per unit time) within an accepted transmutation time. 13 First, in consideration of core critical and reactivity control, a transmutation system is equipped with fertile material in addition to the TRUs, and thus it is necessary to increase the TRUs loading and reduce the fertile material loading to enhance the transmutation rate. Meanwhile, a nuclide (e.g., thorium) with a relatively low TRUs yield should be chosen as the fertile material.…”