Abstract
This study presents the time-dependent analyses of transmutations of long-lived fission products (LLFPs) and medium-lived fission products (MLFPs) occurring in thermal reactors in a conceptual helium gas-cooled accelerator-driven system (ADS). In accordance with this purpose, the CANDU-37 and PWR 15 × 15 spent fuels are separately considered. The ADS consists of LBE-spallation neutron target, subcritical fuel zone, and graphite reflector zone. While the considered ADS is fueled with the spent nuclear fuels extracted from each thermal reactor without the use of additional fuel, fission products extracted from same thermal reactor are also placed into transmutation zone in graphite reflector zone. The LLFP transmutation performance of the modified ADS is analyzed by considering three different spent fuels extracted from the thermal reactors. Spent fuels are extracted from CANDU-37 in case A, from PWR-15 × 15 in case B, and from CANDU-37 fueled with mixture of PWR 15 × 15 spent fuel and 46% ThO2 in case C. The LBE target is bombard with protons of 1000 MeV. The proton beam power is assumed as 20 MW, which corresponds to 1.24828·1017 protons per second. MCNPX 2.7 and CINDER 90 computer codes are used for the time-dependent burn calculations. The ADS is operated under subcritical mode until the value of keff increases to 0.984, and the maximum operation times are obtained as 3400, 3270, and 5040 days according to the spent fuel cases of A, B, and C, respectively. The calculations bring out that in the modified ADS, LLFPs and MLFPs, which are extracted from thermal reactors, can be transformed to stable isotopes in significant amounts along with energy production.
Highlights
Introduction eCANDU reactors, firstly developed in Canada, are commercial thermal reactors that mainly use natural uranium as fuel. eir cooler and moderator are highpressured liquid heavy water (D2O). e CANDU reactors do not use control rods that regulate the neutron numbers in the reactor
While the considered accelerator-driven systems (ADSs) is fueled with the spent nuclear fuels extracted from each thermal reactor without the use of additional fuel, fission products extracted from same thermal reactor are placed into transmutation zone in graphite reflector zone. e long-lived fission products (LLFPs) transmutation performance of the modified ADS is analyzed by considering three different spent fuels extracted from the thermal reactors
MCNPX 2.7 and CINDER 90 computer codes are used for the time-dependent burn calculations. e ADS is operated under subcritical mode until the value of keff increases to 0.984, and the maximum operation times are obtained as 3400, 3270, and 5040 days according to the spent fuel cases of A, B, and C, respectively. e calculations bring out that in the modified ADS, LLFPs and medium-lived fission products (MLFPs), which are extracted from thermal reactors, can be transformed to stable isotopes in significant amounts along with energy production
Summary
Received 12 July 2019; Revised 29 August 2019; Accepted 17 September 2019; Published 20 October 2019. Is study presents the time-dependent analyses of transmutations of long-lived fission products (LLFPs) and medium-lived fission products (MLFPs) occurring in thermal reactors in a conceptual helium gas-cooled accelerator-driven system (ADS). In accordance with this purpose, the CANDU-37 and PWR 15 × 15 spent fuels are separately considered. While the considered ADS is fueled with the spent nuclear fuels extracted from each thermal reactor without the use of additional fuel, fission products extracted from same thermal reactor are placed into transmutation zone in graphite reflector zone. E calculations bring out that in the modified ADS, LLFPs and MLFPs, which are extracted from thermal reactors, can be transformed to stable isotopes in significant amounts along with energy production. In order to solve these spent fuel problems, a new and innovative approach, instead of deep geological storages of nuclear waste and LLFPs, is presented where nuclear waste is transmuted into stable isotopes in ADSs
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