Evaluation of distortion of wall stored energy in core make-up tank test facility

Scaled-down thermal-hydraulic tests are widely used in nuclear reactor safety analysis. The wall stored energy is one of the inherent problems in a scaled-down test facility, which will cause distortions in the simulation of the transients or local thermal-hydraulic phenomena. In a scaled-down test facility for simulating the Core Make-up Tank (CMT) system, which is adopted as the passive safety system in AP series power plant, the cold wall functions as heat sink and absorbs heat from the hot liquid, thus affects energy balance. To study the influence of the wall stored energy on the CMT test facility, distortion evaluation on the CMT in the natural-circulation mode and drainage mode with H2TS method was analyzed. Then, numerical simulation model of CMT test facility was established using RELAP5/MOD 3.4, and sensitivity study of wall stored energy distortion was conducted. The distortion evaluation results show that even if the model wall thickness employs the geometric-similarity principle, there are distortions of the non-dimensional parameters because of the higher rate of heat transfer from the fluid to the wall and the smaller thermal inertia in the model. However, the evaluation of the wall stored energy distortion shows that in a certain range, the influence of the wall stored energy distortion can be neglected or is conservative. Therefore, through reasonable design and arrangement, the scaled-down CMT test facility can properly simulate the thermal-hydraulic phenomena of the prototype. The results provide a theoretical basis and guidance for the design and operation of the tests and lay the foundation for the construction of the test facility.