Criticality Analysis of Burnup Effect on Multiplication Factor

• Main Author: 陳君柔
• Other Authors: Jiang, Shiang-Huei
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/10346858534087785055

碩士 === 國立清華大學 === 核子工程與科學研究所 === 99 === During all process of nuclear fuel cycle, criticality safety analysis is indispensable. Burnup effect dominates the result of criticality analysis. In this study, we evaluated the effect of burnup credit on the k-eff of a spent fuel dry storage transfer cask system, and performed core neutronics analysis for a generation IV lead-cooled fast reactor SSTAR(Small Secure Transportable Autonomous Reactor). The computer software systems SCALE 5.1 and 6.0 were used in this thesis. We modeled complex geometries by taking advantage of the 3D Monte Carlo code KENO, which is a functional module for criticality evaluation in SCALE. Several sequences consisting of cross section processing, depletion modules and KENO were used to complete the assessments. We consider a transfer cask loaded with 24 PWR fuel assemblies with 4.2 % 235U enrichment. For fresh fuels, k-eff was calculated to be 0.9227. For fuel assemblies with 45,000MWD/MTU burnup, k-eff kept decreasing as actinides and fission products being added into the fuel batch by batch. When all available actinides and fission products are included, k-eff was reduced to 0.6270. The SSTAR lead-cooled fast reactor is characterized by its long core life. The fuel composition is transuranium nitride, and the specific power is 21.19 MW/MTHM. The calculated result shows that the reactor can last for 20 years without refueling. During operation, the total flux of each core region varies from 5.07×1014 neutrons/cm2-sec to 1.70×1015 neutrons/cm2-sec. The average energy of low-enriched fuel region is about 3.35×105 eV to 4.41×105 eV, and the trend is increasing or fixed; in high-enriched fuel region the average energy decreases from 6.00 × 105 eV to 4.80 × 105 eV. The amount of U-235 and U-238 consumed with time; Pu-239 is bred in low-enriched region but consumed in high-enriched region with time.