Scenario Analysis

Based on the ADS design in Sect. 19.3 and FR design in Wakabayashi et al. [1], the impact of introducing transmutation is evaluated by mass-flow analysis. Table 19.9 lists analyzed scenarios in which two conventional scenarios and three transmutations are included. In the conventional once-through scenario identified as “LWROT,” Pu and MA exist in spent fuel and are directly disposed of in an underground repository. The second conventional scenario identified as “LWR-PuT” is Pu utilization in a LWR. The spent uranium fuels from an LWR are reprocessed, and, separated Pu is fabricated as MOX and burned in the LWR. Spent MOX fuel is directly disposed.

In the FR scenario, both Pu and MA are mixed or co-extracted and transmuted in FR without any limit of MA content in the fuel. In the ADS scenario, Pu is transmuted in the present design (Pu-ADS) and MA are transmuted in the reference ADS (MA-ADS). In the FR+ADS scenario, MA content in FR is limited to less than 5 % and the remaining MA are transmuted in the ADS.

Characteristics of transmutation systems are listed in Table 19.10. FR has a twice larger thermal output than ADSs, although the specific heat is smaller. Therefore, initial inventory involving fuels in the core and in the fuel cycle of FR is much larger than Pu-ADS even if uranium is excluded; thus, the number of FR that can be introduced is limited. As a result, the transmutation half-life of FR is longer than ADSs by a factor of two.

Result of LWR-OT

Figure 19.5 illustrates a result of the LWR-OT scenario where time evolution of electricity generation, Pu inventory, and MA inventory are shown. The peak of 50 GWe appears in 2010 and decreases because of the Fukushima accident and closure after 40-year operations. All LWRs will be shut down in 2055. The Rokkasho reprocessing plant (RRP) will not be operated, but 7,100 tHM spent fuel has been reprocessed, mainly overseas. The year of reprocessing is not clear

Table 19.9 Scenarios

Table 19.10 Characteristics of transmutation systems

aInitial inventory involves fuel in core and in fuel cycle (cooling, reprocessing, and fabrication)

but assumed to be in the 1990s. A small amount of MOX fuel from this reprocessing will be utilized in LWRs.

Pu inventory mainly exists in UO2-SF. “Pu” in the figure is not “separated” Pu, but Pu in MOX fresh fuel in this scenario. The total of plutonium is 350 t that is gradually disposed of to a repository from 2043 until 2105. The trend of MA inventory is almost the same, but it continues to increase after 2040 because 241Pu becomes 241Am with a half-life of 14.35 years.