In-vessel thermohydraulic analysis of MONJU with AQUA (IV); Natural circulation analysis from a Full-power operation at the power ascension test period

Muramatsu, Toshiharu; *

PNC TN9410 92-106, 354 Pages, 1992/04

PNC-TN9410-92-106.pdf:26.19MB

A natural circulation analysis in the upper plenum of the MONJU reactor was conducted for transient simulating a pump coast down and reactor scram to a full-power operation condition using a multi-dimensional code AQUA. In the analysis, full options of the AQUA code (higher-order differencing schemes, an algebraic stress turbulence model, an adaptive Fuzzy control system, etc.) were used to obtain a refined numerical result. From the analysis, the following results have been obtained. (1)In a steady-state calculation simulating the full-power operation condition, maximum axial temperature gradient 154C/m was calculated at the region between the upper and the lower flow holes. Therefore detailed measurements are necessary for thermal stress evaluation of internal components due to the axial temperature gradient at various power operation conditions. (2)In a transient caluculation simulating a natural circulation phenomenon, it was confirmed that a rising speed of the thermal stratification interface is delayed due to the decrease of a effective mixing volume in the upper plenum region. And the AQUA code calculated a discontinuity temperature transient (a hot shock continued from a cold shock) at the outlet nozzle of the reactor vessel due to the change of locally flow patterns in the upper plenum. Therefore it was concluded that detailed investigation is necessary using experimental data in various power operation conditions. (3)A gentle temperature transient was calculated with the AQUA code in comparison with a one-dimensional code. It is concluded that the one-dimensional code yields a conservative numerical result.