During the '70-'80s, nitride fuel had been a candidate advanced fuel for fast
breeder reactors because of its high thermal conductivity and high melting point.
Recently nitride fuel is being globally reevaluated for future innovative nuclear
systems following a decade-long fundamental study by JAERI.
JAERI has proposed the sub-critical accelerator driven system (ADS) for transmutation of long-lived minor actinides (MAs) in high-level radioactive waste. A mononitride solid solution containing MAs is the primary component chosen for dedicated ADS fuel. Actinide mononitride offers mutual solubility for MAs, which provides the fuel with phase stability and flexibility of composition. Nitride fuel for a Pu burning fast reactor was proposed by France in the mid-90s. Fig. 2-9 shows an example of nitride fuel developed for widespread applications.
JAERI has established a fabrication procedure for nitride fuel using carbothermic reduction and has obtained data on thermal conductivity and phase stability with various compositions of nitride fuel. Following research on U and Pu nitride, the scope of research has been extended to MA nitrides such as NpN, AmN, CmN, and their solid solutions. Irradiation performance of nitride fuel under high-power conditions was demonstrated by an irradiation test of (U, Pu)N fuel at JMTR and the fast test reactor, JOYO; the JOYO test was performed as joint research with JNC. Further, an irradiation test of MA simulated nitride fuel for transmutation was begun at JMTR this year. Research on the pyrochemical reprocessing of nitride fuel based on chloride molten salt electrorefining is also in progress.
However, nitride fuel has a few drawbacks. One is that it produces radioactive C-14 by the 14N(n,p)14C reaction when using natural nitrogen. Enriched nitrogen, N-15, can be used, but that is costly. Also, there are few irradiation databases compared with oxide or metal fuels. JAERI will continue R&D to resolve these issues. |
