弥散型燃料随机介质的蒙特卡罗中子输运计算方法研究

The dispersion fuel has advantages of high burnup, strong ability of containing fission products and good thermal conductivity. It is widely used as an advanced fuel element in next generation nuclear reactors, such as the High Temperature Gas Cooled Reactor and Fluoride Salt Cooled High Temperature Reactor. However, the dispersion fuel element in which the fuel particles statistically distributed in the background material presents some new challenges for the conventional neutronics methods. Based on the dispersion-fuel-based stochastic media, the Monte Carlo neutron transport simulation method will be studied in this research. Firstly, the mechanism of Non-Markovian effect will be studied and the method for fixing the effect for neutron transport in binary stochastic media will be proposed to get more accurate neutron transport simulation results. Secondly, the new fitting-based chord length distribution function accurately depicting the statistical distribution characteristics of fuel particles in the background material will be analyzed for neutron transport simulation in binary stochastic media. Thirdly, the Monte Carlo neutron transport simulation method in binary stochastic media will be expanded to applications in stochastic media with multi-type inclusions distributed in the background material. At last, an accurate and efficient Monte Carlo neutron transport simulation method is implemented for dispersion-fuel-based stochastic media with multi-type inclusions. The main goal of this research is to propose new methods for the challenges imposed by the dispersion fuel corresponding to its statistical distribution characteristics of fuel particles and provide some theoretical foundations for the development of the next generation reactor physics methods.

弥散型燃料因具有承受燃耗深、包容裂变产物能力强和导热性好等优点而被广泛应用在高温气冷堆、氟盐冷却高温堆等新型核能系统中。然而，弥散型燃料因其燃料颗粒在基体材料中的随机分布特性给传统中子学方法提出了新的挑战。本课题以弥散型燃料随机介质为研究对象，针对现有随机介质蒙特卡罗中子输运方法存在的问题和局限，首先开展二元随机介质中子输运的非马尔可夫效应机理与方法研究；其次，进行二元随机介质中子输运的拟合型基体弦长分布函数的计算方法研究；再次，将二元随机介质中子输运方法扩展到基体中填充多种燃料颗粒的多元随机介质应用中，给出多元随机介质中子输运计算的理论依据；最终，建立一套适用于弥散型燃料多元随机介质的蒙特卡罗中子输运计算方法与数值程序。本课题旨在解决新型核能系统中因弥散型燃料的随机分布特性给传统中子学方法带来的计算困境，提升蒙特卡罗中子输运方法在随机介质中的实用性，为发展新一代堆芯物理方法奠定理论基础。

弥散型燃料因具有承受燃耗深、包容裂变产物能力强和导热性好等优点而被广泛应用在高温气冷堆、氟盐冷却高温堆等新型核能系统中，同时近年来也被广泛应用在新型FCM弥散燃料压水堆设计中。然而，弥散型燃料因其燃料颗粒在基体材料中的随机分布特性给传统中子学方法提出了新的挑战。本课题以弥散型燃料随机介质为研究对象，针对现有随机介质蒙特卡罗中子输运方法存在的问题和局限，开展弥散燃料随机介质蒙特卡罗中子输运模拟计算方法研究。.首先，开展了基于OpenMC程序的弥散燃料蒙特卡罗中子输运模拟开发平台可行性研究。基于ICSBEP对OpenMC程序开展了临界基准验证，验证OpenMC程序用于弥散燃料蒙特卡罗中子输运模拟方法研究的可行性。其次，开展了二元随机介质中子输运的非马尔可夫效应机理研究，主要原因在于同一个中子在不同时刻在同一个位置看见的材料不一样，导致了中子输运历史的不自洽，提出了基于中子历史轨迹的修正方法。其次，进行了二元随机介质中子输运的拟合型基体弦长分布函数的计算方法研究，对典型几何弥散燃料模型的边界效应造成的弦长分布函数近似问题进行了改进，量化了传统弦长分布函数与改进弦长分布函数的差异；再次，将二元随机介质中子输运方法扩展到了基体中填充多种燃料颗粒的多元随机介质应用中，给出了多元随机介质蒙特卡罗中子输运模拟计算的理论依据。最终，建立了一套适用于弥散型燃料随机介质的蒙特卡罗中子输运计算方法与数值程序。.采用了板状、棒状、球状三种典型几何弥散燃料随机介质模型，构建了基于RSA模型的基准结果，通过数值基准例题验证，本课题临界计算结果与基准结果之间的误差均在300pcm以内，证明了本课题方法及程序的正确性与可靠性。通过本课题的研究，旨在解决新型核能系统中因弥散型燃料的随机分布特性给传统中子学方法带来的计算困境，提升蒙特卡罗中子输运方法在随机介质中的实用性，为发展新一代堆芯物理方法奠定一定的理论基础。