gi neer ing, En gi neer ing Faculty, Erciyes Uni ver sity, Kayseri, Tur key Sci en tific pa per
This study presents the power flattening and time-dependent neutronic analysis of a conceptual helium gas cooled Accelerator Driven System (ADS) loaded with TRISO (tristructural-isotropic) fuel particles. Target material is lead-bismuth eutectic (LBE). ThO2, UO2, PuO2, and CmO2TRISO particles are used as fuel. PuO2and CmO2fuels are extracted from PWR-MOX spent fuel. Subcritical core is radially divided into 10 equidistant subzones in order to flatten the power produced in the core. Tens of thousands of these TRISO fuel particles are embedded in the carbon matrix fuel pebbles as five different cases. The high-energy Monte Carlo code MCNPX 2.7 with the LA150 library is used for the neutronic calculations. Time-dependent burnup calculations are carried out for thermal fission power (Pth) of 1000 MW using the BURN card. The energy gain of the ADS is in the range of 99.98–148.64 at the beginning of a cycle. Furthermore, the peak-to-average fission power density ratio is obtained between 1.021 and 1.029 at the beginning of the cycle. These ratios show a good quasi-uniform power density for each case. Furthermore, up to 155.1 g233U and 103.6 g239Pu per day can be produced. The considered system has a high neutronic capability in terms of energy multiplication, fissile breeding, and spent fuel transmutation with thorium utilization.
This paper presents analyses of enrichments of uranium taken out from Canada Deuterium Uranium and pressurized water reactors spent fuels and fissile fuel breeding from thorium in two different helium cooled-accelerator driven system designs, DESIGN A and DESIGN B. In the beginning, the 235U percentages in the uranium fuels taken out from the reactors spent fuels are 0.17% and 0.91%, respectively. Both system cores are fuelled with two different minor actinides compositions extracted from PWR-MOX spent fuels. The DESIGN A has one transmutation zone (enrichment zone) surrounding the fuel core and containing thorium or spent uranium fuels, while DESIGN B has a second transmutation zone (fissile fuel breeding zone) surrounding the first transmutation zone and containing only thorium fuel. In brief, a total of ten cases formed by the combinations of accelerator driven system designs, minor actinides components, and spent uranium with thorium fuels are analysed, which are six in DESIGN A containing one transmutation zone and four in DESIGN B containing two transmutation zones. Lead-bismuth eutectic alloy, a liquid heavy metal, consisting of 45% lead and 55 % bismuth is used as target material in the investigated accelerator driven system. It is assumed that the target is bombarded with 1.2383?1017 protons per second and that the energy of each proton is 1000 MeV. This means a proton beam power of 20 MW. The 3-D and time-dependent neutronic analyses are conducted by using the MCNPX 2.7 and CINDER 90 nuclear code. Both accelerator driven system designs are operated until the values of keff rise to 0.985 to determine the longest operation times that are the effective burn times in all cases. Depending on the design, minor actinide composition, and fuel type (spent UO2 and ThO2), the results obtained at the end of cycle exhibit the effective burn times vary from 300 days to 2050 days, the fuel enrichments can reach up to 2.49-4.23% and the values of gain reach up to 10.8-25.1.
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.
This study presents the neutronic performances of fissile breeding and energy production of a gas cooled accelerator-driven system with LBE-uranium dioxide (UO2) spallation target. The accelerator-driven system is designed and optimized by considering various target materials, in terms of neutronic. Two different materials, LBE + natural UO2 and LBE + 15% enrichment UO2 are selected as target materials. The target zone is divided into two parts, one within the other; the outer part is pure LBE target part, and the inner part is UO2 target part cooled with the helium gas. Tristructural-isotropic (TRISO)-coated fuel particles, containing UO2 fuel, are embedded in a carbon matrix pebble with the packing fraction of a 29%, and the pebbles are placed in the UO2 target part and in the fuel core with the packing fraction of a 60%. The fuel core is cooled with helium that is a high-temperature coolant. The target is bombarded with the continuous beams of a 1 GeV protons to produce high-flux neutrons that enter the fuel core. The fuel core is surrounded with a graphite reflector zone serving as both effective moderation and reflection of these neutrons. Furthermore, the whole system is enclosed by boron carbide, B4C (shielding zone), to prevent the neutrons leakage out of the accelerator-driven system. The highenergy Monte Carlo code MCNPX along with the LA150 library is used for neutronic calculations. The numerical results bring out that the investigated accelerator-driven system has a high neutronic performance, from the energy production and fissile breeding points of view. Namely, it can be obtained over the thermal power of a 350 MW and produced over the fissile breeding of a 300 g/day.
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