underground can be utilized for nuclear weapons and can cause public dose in the
very far future over several tens of thousands of years. Instead of direct disposal,
transmutation of Pu and MAs (TRU, trans-uranic) has been studied in many
countries for the purpose of eliminating them from the waste.
Transmutation can be performed by a “transmuter” that is dedicated for transmutation with the lesser role of electricity generation. It contains a fast reactor
(FR) and an accelerator-driven system (ADS), which are fast neutron systems with
metal coolant. FRs have been mainly developed as breeder reactors but they act as a
burner reactor in the phase-out scenario. The burner reactor has no blanket region
for breeding, larger Pu content, and shorter operation-cycle length [1]. The ADS has
been designed as an MA transmuter with a smaller amount of Pu but changes to a Pu
transmuter in this scenario.
In the present study, an ADS for Pu transmutation (Pu-ADS) is designed by
neutronics calculation based on the ADS for MA transmutation (MA-ADS). In the
original design for MA transmutation, drop of criticality during depletion is very
small, and a long operation cycle is achieved because MAs behave as fertile
material. In the Pu-ADS, criticality decreases much more rapidly and design
modification is necessary.
After the design of the Pu-ADS, a scenario study is performed by a nuclear
material balance (NMB) code that was developed by the authors. The following
items are revealed by the study: accumulation of TRU in the LWR SFs, necessary
number of transmuters, reduction of TRU, reduction of repository footprint, and
radiotoxicity by transmuters.
In Sect. 19.2, calculation methods for neutronics design and scenario code
are introduced. Section 19.3 provides the neutronics design and resulting ADS.
Section 19.4 discusses assumptions and results of the scenario study. The results are
concluded in Sect. 19.5.
19.2 Methodology
19.2.1 Neutronics Calculation
Several codes were combined for ADS design (Fig. 19.1) containing proton
transport, neutron transport, cross-section preparation, and depletion. The PHITS
code [2] was used for transportation of protons and neutrons above the energy
boundary of 20 MeV. Transportation of neutrons slowing down less than 20 MeV is
interrupted, and position, direction, and energy are stored in a cutoff file. This file is
processed as to be readable by the PARTISN code [3], which is a neutron transport
code with multi-group theory. A 73-group cross section is prepared by SLAROM
[4] code with the JENDL4.0 [5] nuclear data library. A 1-group micro-cross section
is calculated by multiplying the 73-group cross section to the 73-group flux from
PARTISN. One-group micro-cross section and total flux is used in the ORIGEN2
208
K. Nishihara et al.
very far future over several tens of thousands of years. Instead of direct disposal,
transmutation of Pu and MAs (TRU, trans-uranic) has been studied in many
countries for the purpose of eliminating them from the waste.
Transmutation can be performed by a “transmuter” that is dedicated for transmutation with the lesser role of electricity generation. It contains a fast reactor
(FR) and an accelerator-driven system (ADS), which are fast neutron systems with
metal coolant. FRs have been mainly developed as breeder reactors but they act as a
burner reactor in the phase-out scenario. The burner reactor has no blanket region
for breeding, larger Pu content, and shorter operation-cycle length [1]. The ADS has
been designed as an MA transmuter with a smaller amount of Pu but changes to a Pu
transmuter in this scenario.
In the present study, an ADS for Pu transmutation (Pu-ADS) is designed by
neutronics calculation based on the ADS for MA transmutation (MA-ADS). In the
original design for MA transmutation, drop of criticality during depletion is very
small, and a long operation cycle is achieved because MAs behave as fertile
material. In the Pu-ADS, criticality decreases much more rapidly and design
modification is necessary.
After the design of the Pu-ADS, a scenario study is performed by a nuclear
material balance (NMB) code that was developed by the authors. The following
items are revealed by the study: accumulation of TRU in the LWR SFs, necessary
number of transmuters, reduction of TRU, reduction of repository footprint, and
radiotoxicity by transmuters.
In Sect. 19.2, calculation methods for neutronics design and scenario code
are introduced. Section 19.3 provides the neutronics design and resulting ADS.
Section 19.4 discusses assumptions and results of the scenario study. The results are
concluded in Sect. 19.5.
19.2 Methodology
19.2.1 Neutronics Calculation
Several codes were combined for ADS design (Fig. 19.1) containing proton
transport, neutron transport, cross-section preparation, and depletion. The PHITS
code [2] was used for transportation of protons and neutrons above the energy
boundary of 20 MeV. Transportation of neutrons slowing down less than 20 MeV is
interrupted, and position, direction, and energy are stored in a cutoff file. This file is
processed as to be readable by the PARTISN code [3], which is a neutron transport
code with multi-group theory. A 73-group cross section is prepared by SLAROM
[4] code with the JENDL4.0 [5] nuclear data library. A 1-group micro-cross section
is calculated by multiplying the 73-group cross section to the 73-group flux from
PARTISN. One-group micro-cross section and total flux is used in the ORIGEN2
208
K. Nishihara et al.