随着电力市场的改革与新能源的不断发展，核电面临着市场竞争的严峻挑战。在保障安全性的前提下，采取改进措施以提高核电经济性具有重要意义。无源启动在反应堆启动过程中不使用外中子源，因此不需要对外中子源进行采购及全过程管理，降低了核电建设运营的成本，可以提高核电的经济性。但启动前期由于中子通量低存在探测盲区，需要理论计算给出盲区阶段的情况。本课题基于蒙特卡罗程序RMC对反应堆无源启动盲区阶段进行模拟研究。课题首先针对RMC的直接模拟法功能进行优化完善。根据直接模拟法计算瞬态的流程，研究了瞬态初始时刻中子与缓发中子先驱核分布的计算方法、缓发中子先驱核的强制衰变处理方法、控制粒子数的梳子法、多项式拟合降噪处理等方法，实现了直接模拟法用于三维复杂模型的瞬态计算。课题对无源启动前期随机中子动力学阶段进行研究，具体研究了中子裂变多重性模型扩展、中子符合计数功能、反应性随时间变化的功能、动态系统存活概率POS计算方法、蒙卡转折时间点计算方法，提出了更适用于确定指定时刻中子通量的计数统计方法：速度估计法。从而实现了针对弱中子场随机中子动力学阶段模拟。课题对蒙卡直接模拟法与预估修正准静态方法的衔接计算进行研究，解决了衔接计算所需要的时间吸收源、缓发中子源、反应性、有效缓发中子份额、中子代时间的求解方法。实现了三维的基于弱中子场中随机中子动力学的直接模拟法与基于强中子场中含时玻尔兹曼方程的预估修正准静态方法的衔接计算模拟。课题针对特定小型反应堆进行无源启动模拟计算分析，详细研究了无源启动的自发裂变源设置，针对多种反应性变化的算例进行计算分析。研究了各算例中转折时间点的概率分布与堆芯内指定时刻最大通量所在位置的空间概率分布，为无源启动中的盲区阶段提供有效信息。本课题在反应堆无源启动盲区阶段模拟研究方面所取得的成果与创新，使RMC具备了计算反应堆无源启动的功能，能够描述盲区阶段的物理图像，为无源启动的实际应用模拟提供了分析工具与方法，具有实际的学术价值与工程应用价值。

With the reform of electric power market and the continuous development of new energy, nuclear power is facing the severe challenge of market competition. In addition to ensuring the absolute safety of the reactor, it is of great significance to take improvement measures to improve the economy of nuclear power. Startup without external neutron source does not use external neutron source in the process of reactor start-up, so there is no need to purchase external neutron source and manage the whole process, which reduces the cost of nuclear power construction and operation and improve the overall economics of nuclear power. However, due to the low neutron flux, there is a detection blind area in the early stage of startup, so the situation of the blind area should be calculated theoretically. Based on the Monte Carlo code RMC, this subject conducts a simulation study on the blind zone stage of the reactor startup without external neutron source. The subject firstly optimizes the function of direct simulation method of RMC. According to the process of calculating the transient by the direct simulation method, the calculation method of the distribution of neutrons and delayed neutron precursor at the initial moment of the transient, the forced decay processing method of the precursor, the comb method to control the number of particles and the polynomial method for controlling the number of particles are studied. Finally, the direct simulation method is realized for transient calculation of 3D complex models.The subject conducts research on the stochastic kinetics stage in the early stage of startup without an external neutron source. The specific research contents include the expansion of the neutron fission multiplicity model, the function of neutron coincidence counting, the function of reactivity changing with time, and the calculation of the POS of dynamic system. At the same time, the calculation method of Monte Carlo turning time point is studied, and a counting and statistical method more suitable for determining the neutron flux at a specified time is proposed: the velocity tally method. Finally, the stochastic kinetics simulation for weak neutron field is realized.The subject studies the connection calculation between the Monte Carlo direct simulation method and the predictor-corrector quasi-static (PCQS) method, and solves the time absorption source, delayed neutron source, reactivity, effective delayed neutron fraction and neutron generation time required for the connection calculation. The three dimensional connection simulation between the direct simulation method based on stochastic kinetics in weak neutron field and the PCQS method based on time-dependent Boltzmann equation in strong neutron field is realized.The subject conducts a simulation calculation and analysis of the specific small reactor without an external neutron source, in which the spontaneous fission source setting of the fuel is studied in detail, and studies various examples of reactivity changes. The probability distribution of the turning point in each case and the spatial probability distribution of the position of the maximum flux at the specified time in the core are studied, which can provide effective information for the blind zone stage in the startup without external neutron source.The achievements and innovations in the simulation research of the blind zone stage of reactor startup without external neutron source have enabled RMC to have the function of calculating reactor startup without external neutron source, and can describe the physical image of the blind zone stage. It provides analysis tools and methods for the practical application simulation of the reactor startup with no external neutron source, and has practical academic value and engineering application value.