Thermal Hydraulic Test of Advanced BWR Fuel Bundle With Spectral Shift Rod (SSR): Overview and Pre-Test Analysis by TRACG Code

Japanese national project of next generation light water reactor (LWR) development started in 2008. As one of its development items, the thermal-hydraulic test of spectral shift rod (SSR) is planned. A new component called SSR, which replaces conventional water rod (WR) of boiling water reactor (BWR) fuel bundle, was invented to enhance the BWR’s merit, spectral shift effect for uranium saving. In SSR, water boils by neutron and gamma-ray direct heating and water level is formed as a boundary of the upper steam region and the lower water region. This SSR water level can be controlled by core flow rate, which amplifies core void fraction change, resulting in the amplified spectral shift effect. In this paper, its test plan overview and pre-test analysis by TRACG code is presented. The test plan was developed with the purpose of evaluating SSR thermal-hydraulic characteristics at the actual BWR operating condition (7MPa), such as the controllability of SSR water level, and obtaining data for the validation of calculation method. In the test plan, several types of SSR simulation which covers SSR design in both next generation BWR and conventional BWR were designed. Also test operating conditions such as thermal-hydraulic parameters are determined. In order to evaluate these test specifications, pre-test analysis by TRACG code was conducted. Analysis results of each parameter’s effect on SSR characteristics are consistent with SSR mechanism, which shows that the actual operating condition for SSR fuel is simulated well.