基于等价理论的压水堆包壳材料共振计算方法研究

共振自屏效应的处理是影响压水堆组件程序反应性精度的主要因素之一,压水堆锆包壳材料同样具有共振自屏效应,忽略其影响会对反应性造成100～300 pcm(1 pcm=10^-5)的偏差。目前,主要通过提供经验上的参考稀释截面与包壳等价理论处理包壳材料的共振自屏效应,但并未对其适用性及精度进行完整的分析。因此,本文采用DRAGON程序,通过一系列压水堆算例对这2种方法进行测试,确定包壳共振自屏效应的主要影响因素以及这2种方法的适用性。结果表明,包壳材料的共振自屏效应仅仅与包壳区的原子核密度、厚度、慢化区的水铀比有关,并且参考稀释截面方法可以满足大部分典型压水堆系统的计算精度,但是对于包壳区尺寸、原子核密度、慢化区水铀比变化较大的系统计算精度较差,而包壳等价理论计算精度和普适性强,可用于不同类型压水堆系统包壳材料的共振自屏计算。

Investigation on Resonance Self-Shielding Calculation for PWR Cladding Materials Based on Equivalence Theory

The treatment of resonance self-shielding effect is one of the key factors for reactivity accuracy in PWR lattice code. The PWR cladding materials for zirconium isotopes also has the resonance self-shielding effect. Ignoring the influence of resonance self-shielding effect for cladding materials, it can cause 100~300 pcm errors in reactivity predictions. Now, the reference dilution cross section and cladding equivalence theory can be used in treating the resonance self-shielding effect for cladding material, but the applicability and accuracy of these methods has not been completely tested. Therefore, a series of PWR cases are used in testing the applicability of these methods computed by DRAGON code. The main impact factors for the resonance self-shielding effect in cladding material and the applicability of these two methods are determined. The results show that the resonance self-shielding effect in cladding material is only related to nuclide density, thickness and water/uranium ratio in the moderator region. The reference dilution cross section satisfies the typical PWR cases, however it can cause more errors in the great change of the above three factors. The new equivalence theory is more accurate and flexible, which can be used in different PWR cladding materials for the calculation of the resonance self-shielding effect.