【作者】 刘同先；

【导师】 曹欣荣；

【作者基本信息】 哈尔滨工程大学 ， 核能科学与工程， 2007， 硕士

【摘要】 随着MCNP在核科学和工程方面日益广泛的应用，MCNP计算中的影响因素分析近来受到越来越多的关注，例如在计算反应堆的物理状态发生微小变化所引起的反应性变化及反应堆压力容器快中子通量的校核计算方面。正是基于此目的，本文分析了MCNP计算结果的影响因素。通过了解程序中有关中子作用过程的物理模型和MCNP的使用方法，建立了两个典型的基准题的计算模型：MOX燃料试验研究堆的临界计算和反应堆压力容器通量计算，提出建模过程中一些技巧，进行了计算结果的影响因素分析：在MOX燃料试验研究堆的临界计算中，计算了实验堆的有效增殖系数和相对功率分布。通过更改初始裂变源(SRCTP)的方式，证明以不同的随机数序列重复计算问题，得到的计算结果总存在一定的涨落，并随着总迭代次数的增加逐渐减小；紧接着在统计涨落足够小的基础上，讨论了数据库的差异对计算结果的影响；指出采用S(α，β)热散射处理是得到合适的有效增殖系数计算值的必须条件。在压水堆压力容器通量计算中，进一步证实了计算结果的统计涨落和数据库对计算结果的影响，讨论了不同方差减小技巧下的计算结果间存在差异的原因，并分析了程序版本不同对计算结果的影响。最后通过和基准题中压力容器内表面快中子通量的相对分布比较，表明了计算过程的正确性。更多还原

【Abstract】 With MCNP applied increasingly and broadly in the aspects of the nuclear science and engineering, analyses of the influencing factors in the computed results using MCNP have recently received more attention from areas such as computations of reactivity changes caused by the minor changes of the reactor state and benchmark computations of the neutron flux of the reactor pressure vessel. To serve these needs, analyses of the influencing factors in the computed results using MCNP are present in the thesis.After comprehending the physics of neutron interaction being the essence of MCNP code and the method about how to use MCNP, this paper sets up computation model basing on two typical benchmark problems: the criticality computation of the MOX fuel research reactor and the flux computation of the reactor pressure vessel. During the process, there are the operative skills advanced in the paper. Finally, the most important work that analyzes the influencing factors in the computed results has been finished.The criticality computation of the MOX fuel research reactors firstly calculates the effective multiplication factors and the relative power distributions. And secondly it proves that the computed results rerunning the problems with a different random number sequence always have certain statistical fluctuation that reduces gradually along with the number of history increasing by the way of changing the initial fission source (SRCTP) from a previous MCNP criticality calculation. As following, under the condition of the statistical fluctuation weakly enough, the difference between the computed results using different data libraries is discussed, it pointed out that using S(α,β) thermal scatting treatment is the essential condition to obtain the appropriate effective multiplication factors.In the neutron flux computation of the reactor pressure vessel, the statistical fluctuation existing in computed results and the influence of the data libraries being on the computed result are further confirmed. There is the discussion about the reasons of difference between the computed results using different variance reduction techniques and the influence of procedure edition on the computed results. Finally, it indicates that the computation process is correctly according to the fast flux relative distribution of the pressure vessel internal surface presenting in the benchmark problem.更多还原