Minor Actinide Transmutation in GFR600

Within the Generation IV initiative, the gas-cooled fast reactor (GFR) is one of the reactors dedicated to minor actinide (MA) transmutation. This paper summarizes the research performed with the GFR600 reference design in order to assess its MA burning capabilities. For the study, modules of the SCALE program system were used.

Single-cycle parametric studies were performed with cores having different MA content and spatial distribution. It was shown that the addition of MAs to the fuel greatly reduced the reactivity loss during burnup. Moreover, the higher the MA content of the core, the higher the fraction of it that was fissioned; however, the more the delayed neutron fraction and the fuel temperature coefficient degraded. Significant reduction can be achieved in the amounts of neptunium and americium, while curium isotopes accumulate.

The study of multiple consecutive cycles showed that by adding only depleted uranium (DU) to the reprocessed actinides in fuel fabrication (pure DU feed strategy), up to 70% of the initially loaded MAs can be fissioned in the first five cycles. Moreover, the reactor can be made critical during that time if the initial MA content is higher than 3%. By feeding MAs as well (constant MA content strategy), the reactivity has a steady increase from cycle to cycle, predominantly due to ²³⁸Pu breeding from ²³⁷Np.

The effects of the isotopic composition of the plutonium and MAs were also examined by performing calculations with data specific to the spent fuel of traditional western pressure water reactors and Russian type VVER440 reactors. Despite the considerably different MA vectors, no significant deviation was found in their overall transmutation. However, the Pu composition had a strong effect on the reactivity and the delayed neutron fraction in the first cycles.

Finally, cores having nonuniform MA content were investigated. It was found that though the MA destruction efficiency was significantly higher in the middle of the core than at the edge, moving some of the MAs from the outer regions to the center resulted in only minor improvement in their destruction. However, the spectral changes caused by the rearrangement increased the k-effective, which allowed higher burnups and increased MA destruction. Unfortunately, some of the safety parameters of the reactor degraded.