19.4.5 Result of FR+ADS
In the FR+ADS scenario, MA content in FR is limited below 5 % with respect to
design limit and the remaining MA is transmuted in the ADS. In the first generation
of transmutation from 2050 to 2110, six FRs and three ADSs are deployed, then
three FRs and two ADSs in the second generation, and two FRs and one ADS in the
third generation are built (Fig. 19.9). In the fourth generation, only ADS is utilized
as to reduce TRU rapidly. The total amount of Pu and MA is reduced to 20 and 10 t,
respectively, excepting MA in vitrified waste.
19.4.6 Impact on the Repository
One of the impacts on the repository by transmutation is reduction of potential
radiotoxicity, which is defined as total ingestion dose of the waste. Because waste is
isolated from the public in the underground in reality, such direct ingestion never
occurs and it is considered to be hypothetical, but it can represent the potential
danger of waste. This toxicity of waste can be compared to that of uranium ore
consumed for electricity generation causing radioactive wastes. Figure 19.10 illustrates those toxicities corresponding to whole operation of LWRs and transmuters.
Consumed natural uranium is 370,000 t.
When wastes are generated, the toxicity becomes higher than corresponding
uranium ore by three orders of magnitude. Fission products such as Sr and Cs are
dominant in the early several hundreds of years, although actinides contribute to
toxicity after that. Toxicity in the LWR-OT scenario decays to the level of uranium
ore after 100,000 years. By reducing Pu in the LWR-PuT scenario, the decay time
becomes shorter, to 70,000 years. In the transmutation scenarios, shortening of
decay time depends on the remaining amount of TRU. The decay time is about
10,000 years in the ADS scenario in which the remaining TRU is approximately
30 t, including vitrified wastes. In comparison between the LWR-OT scenario and
the ADS scenario, the amount of TRU is reduced by one order of magnitude, so
toxicity is also reduced by same order. If MA in the vitrified wastes is retrievable,
the amount of TRU will be reduced to around 10 t, which implies toxicity is reduced
to 1/30 and the decay time is around 2,000 years. Thus, the impact on toxicity by
transmutation is significantly affected by MA in the vitrified wastes. Early introduction of MA partitioning to the RRP and R&D for retrievability from the glass
wastes is of importance in this aspect.
Another impact on the repository is reduction of repository size by partitioning
and transmutation of heat-generating nuclides in the wastes. Repository size is
represented by a repository footprint, which is defined as an area devoted for waste
excluding aisles, ducts, utility area, surface facility, and other.
In the LWR-OT scenario, the footprint corresponding to 45,000 t spent fuel
reaches almost 4 km
2 , which is double the typical repository design for the glass
224
K. Nishihara et al.
In the FR+ADS scenario, MA content in FR is limited below 5 % with respect to
design limit and the remaining MA is transmuted in the ADS. In the first generation
of transmutation from 2050 to 2110, six FRs and three ADSs are deployed, then
three FRs and two ADSs in the second generation, and two FRs and one ADS in the
third generation are built (Fig. 19.9). In the fourth generation, only ADS is utilized
as to reduce TRU rapidly. The total amount of Pu and MA is reduced to 20 and 10 t,
respectively, excepting MA in vitrified waste.
19.4.6 Impact on the Repository
One of the impacts on the repository by transmutation is reduction of potential
radiotoxicity, which is defined as total ingestion dose of the waste. Because waste is
isolated from the public in the underground in reality, such direct ingestion never
occurs and it is considered to be hypothetical, but it can represent the potential
danger of waste. This toxicity of waste can be compared to that of uranium ore
consumed for electricity generation causing radioactive wastes. Figure 19.10 illustrates those toxicities corresponding to whole operation of LWRs and transmuters.
Consumed natural uranium is 370,000 t.
When wastes are generated, the toxicity becomes higher than corresponding
uranium ore by three orders of magnitude. Fission products such as Sr and Cs are
dominant in the early several hundreds of years, although actinides contribute to
toxicity after that. Toxicity in the LWR-OT scenario decays to the level of uranium
ore after 100,000 years. By reducing Pu in the LWR-PuT scenario, the decay time
becomes shorter, to 70,000 years. In the transmutation scenarios, shortening of
decay time depends on the remaining amount of TRU. The decay time is about
10,000 years in the ADS scenario in which the remaining TRU is approximately
30 t, including vitrified wastes. In comparison between the LWR-OT scenario and
the ADS scenario, the amount of TRU is reduced by one order of magnitude, so
toxicity is also reduced by same order. If MA in the vitrified wastes is retrievable,
the amount of TRU will be reduced to around 10 t, which implies toxicity is reduced
to 1/30 and the decay time is around 2,000 years. Thus, the impact on toxicity by
transmutation is significantly affected by MA in the vitrified wastes. Early introduction of MA partitioning to the RRP and R&D for retrievability from the glass
wastes is of importance in this aspect.
Another impact on the repository is reduction of repository size by partitioning
and transmutation of heat-generating nuclides in the wastes. Repository size is
represented by a repository footprint, which is defined as an area devoted for waste
excluding aisles, ducts, utility area, surface facility, and other.
In the LWR-OT scenario, the footprint corresponding to 45,000 t spent fuel
reaches almost 4 km
2 , which is double the typical repository design for the glass
224
K. Nishihara et al.