Comparison of BWR-stability measurements with calculations using the code LAPUR-IV

Abstract

A parametric study of stability characteristics in boiling water reactors (BWRs) was performed using the frequency domain code LAPUR-IV. Two different reactors, Peach Bottom Unit 2 and Vermont Yankee, were considered in a total of 17 different operating conditions that corresponded to three series of low-flow stability tests performed in these two reactors. Stability margins, in terms of decay ratio and natural frequency of the closed loop reactivity-to-power transfer function (T.F.), were calculated and then compared with the experimental results. In addition, a sensitivity analysis was performed to determine the changes in calculated results to be expected in response to alterations in the density reactivity coefficient (DRC), the recirculation loop pressure-to-flow T.F. parameters, and the fuel-to-cladding-gap heat conductance. This allows assessment of the effect of input data uncertainty on the calculated results. Satisfactory agreement was found between the stability margins calculated using LAPUR-IV and the experimental results. The sensitivity analysis shows that the DRC is the most critical of the parameters investigated for accurate stability calculations.