物理-热工耦合对超临界水堆系统特性的影响分析

物理-热工耦合是超临界水堆系统分析的关键问题之一。以日本超临界水冷热堆Super LWR的堆芯设计为例，借助Dragon编制中子截面数据库，建立双群中子扩散方程计算模块，联系同时建立的热工计算模块，得到超临界水堆的物理-热工耦合计算模型。通过对比稳态与瞬态工况下耦合前、后的热工工况，分析物理-热工耦合条件下的超临界水堆系统热工特性。结果表明：在稳态工况下，物理-热工耦合将导致内、外组件堆芯功率峰值沿轴向发生明显偏移，使得部分节点的包壳温度升高，但包壳最高温度降低；在瞬态工况下，物理-热工耦合将导致堆芯包壳最高温度的发生位置有所改变。发生给水加热丧失瞬态后，在某一时刻，外部组件的包壳最高温度将转而超过内部组件的包壳最高温度。可见，物理-热工耦合对包壳最高温度的大小和发生位置均可能产生明显影响。计算分析可为超临界水堆瞬态及安全分析提供相应理论参考。

Influence Analysis of Coupled Neutronics and Thermal-Hydraulics on Characteristics of Supercritical Water-Cooled Reactor System

Coupled neutronics and thermal-hydraulics is one of the key issues of supercritical water-cooled reactor system analysis. Taking the Super LWR concept proposed by Japan as example, the neutron cross-section library for supercritical water-cooled reactor was made by Dragon code, and then a two-group neutron diffusion calculation module was created. By combining with the thermal-hydraulic calculation module, the coupled neutronic and thermal-hydraulic calculation module of supercritical water-cooled reactor was finally obtained. By comparing the thermal-hydraulic behavior under the uncoupling calculation condition with that under the coupling calculation condition for both steady-state and transient analyses, thermal-hydraulic characteristics of supercritical water-cooled reactor under coupled neutronic and thermal-hydraulic condition was analyzed. The results show that, in steady-state case, the neutronic and thermal hydraulic coupling will lead to the axial core power peak factor shifting along axial direction for both the inner and outer assemblies. It makes part of the cladding temperature rising but the maximum cladding temperature decreasing. In transient case, the neutronic and thermal-hydraulic coupling may cause the position changed of maximum cladding temperature. When the loss of feed-water heating occurs, the cladding temperature in the outer fuel assembly will become even higher than that in the inner fuel assembly at a certain time. Thus, the neutronic and thermal-hydraulic coupling has a significant impact on both the value and the location of the maximum cladding temperature. The calculation analysis can provide a theoretical reference for transient and safety analyses of supercritical water-cooled reactor.