Session: 15-06

Paper Number: 134875

134875 - Neutronics Design of Molten Salt Reactor for Transmutation of Various Radioactive Nuclides 

Abstract: 

The radioactivity of radioactive waste originating from nuclear reactor operation consists of minor actinides (MA) and fission products (FP). A lot of studies have been performed on the partitioning and transmutation of MA to reduce the long-term high radioactivity and heat generation, and some have been focused on the transmutation of long-lived fission products (LLFP) such as Tc-99 and I-129. Few studies have been performed for the transmutation study of the short-lived FPs such as Sr-90 and Cs-137 despite their large heat generation dominating for the early 150 years.

 

A molten salt reactor (MSR) has been in the spotlight as one of the Generation IV reactors. An MSR is operated by circulating liquid fuel, in which fissile nuclides are melted into the molten salt. An MSR has attracted attention for its safety features such as small excess reactivity and negative temperature feedback. The employment of liquid fuel enables an MSR to reduce some complicated fuel fabrication processes and reprocess the existing fuel salt sequentially.

 

There have been many studies on the MA transmutation in MSRs, and good transmutation capabilities have been reported. For the transmutation of FPs, a few studies have been carried out, confirming the possibility of the transmutation of some LLFPs such as Tc-99, I-129, and Cs-135. However, there are few studies on the transmutation of short-life FP and the simultaneous transmutation of MA and FP in an MSR.

 

The objective of the present study is to investigate the feasibility of the simultaneous transmutation of MA and FP in a single MSR core. The MSR designed in this study adopts a graphite moderator in the MSR core, and a fluoride salt containing MA nuclides on the basis of past studies about the MA transmutation in an MSR core. For the FP transmutation, the FP salt flow channels, which are independent of the fuel salt, are introduced into the graphite reflector region surrounding the core because a thermal-to-epithermal neutron field is suitable for the transmutations due to their large capture cross sections in a thermal energy region and the existence of the resonance structures in an epithermal region for many FP nuclides. The FP nuclides are partitioned into several groups on the basis of their chemical properties and cross section properties, and the FP salts are arranged into their own flow channels. The neutronics analyses are conducted by using Serpent2 with nuclear data library JEFF-3.3 to investigate the criticality and transmutation ability of the MSR.

Presenting Author: Koji Fujikura Tohoku University

Presenting Author Biography: Koji Fujikura is a master's student at Tohoku University working on the transmutation of radioactive nuclides in molten salt reactors.

Authors:

Koji Fujikura Tohoku University
Naoto Aizawa Tohoku University