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在相对速度空间建立中子引发裂变链概率所满足的与时间相关的微分-积分方程,基于多群SN方法开发动态数值程序(Dynamic Segment Number Probability,DSNP),分析了动态计算的收敛性,并对动态系统的裂变链概率演化过程进行数值模拟。模拟计算表明,DSNP程序与Partisn程序的计算结果均一致;临界状态附近存在大量的有限裂变链,使得引发概率的动态演化结果高于稳态计算结果,在Baker动态流场模型上,第一临界点后1μs的范围内计算结果最大差异约为300%。随着裂变系统反应性增加,有限裂变链的贡献逐渐减弱,持续裂变链占优,引发概率的动态演化曲线与稳态结果逐渐重合,差别小于5%,表明系统中子引发自持裂变的能力趋于稳定,此时动态引发概率的时间积分结果比稳态结果高5%-35%。高浓铀模型上的数值模拟验证了DSNP程序的准确性,该程序可定量计算动态系统的引发概率,相对于稳态方法,DSNP程序能够更为准确地描述裂变系统点火概率的演化过程。
Time-dependent differential-integral equation satisfied by the probability of neutron induced fission chain in the relative velocity space, the Dynamic Segment Number Probability (DSNP) is developed based on multi-group SN method, and the convergence of dynamic calculation is analyzed. The dynamic evolution of fission chain in a dynamic system is numerically simulated. The simulation results show that the DSNP program is consistent with the Partisn program. There are a large number of finite fission chains near the critical state, which leads to higher dynamic evolution of the initiation probability than the steady-state calculation. In the Baker dynamic flow model, the first critical The biggest discrepancy in the calculated results over a 1 μs point is about 300%. As the reactivity of the fission system increased, the contribution of the finite fission chains gradually weakened, and the persistent fission chains dominated. The dynamic evolution curves of the initiation probability and the steady state results gradually coincided with the difference of less than 5%, indicating that the ability of system neutron to initiate self-sustained fission In the steady state, the time integral result of the dynamic induced probability is 5% -35% higher than the steady state result. The numerical simulation of HEO model verifies the accuracy of DSNP program, which can quantitatively calculate the probability of initiation of dynamic system. Compared with steady state method, DSNP program can describe the evolution of ignition probability of fission system more accurately.