Abstract
In boiling water reactors, the cooling water may takes place of boiling phenomenon in the core. At low flow and high power conditions, it may easily induce instability by unstable power or flow oscillation. It’s coupled mechanisms of neutronic and two-phase flow thermal-hydraulic behaviors. In order to fit in with the newest fuel designs, we import a new version of frequency domain stability program, LAPUR6.0. Based on the LAPUR5.2 methodology, the main subjects of this paper are to establish a methodology and analytic mode of LAPUR6.0 and to update the auto search program DRASM. At first, this paper illustrates the new input cards and its setting process, and introduces the current analytical procedures of LAPUR6.0. Then compare the results between new version and old version. Finally, this paper uses LAPUR6.0 to see the differences of decay ratio at the following situations, the use of part length rods, using different method to calculate local loss and choosing different friction models. From the results of CS2C25 reload design, it can found that decay ratios by LAPUR6.0 are smaller than LAPUR5.2, especially the regional mode decay ratios. Except for the influence of program calculation variation, the other reasons are those three situations. The use of friction model II cause the greatest impact in stability, results in smaller decay ratio. The use of part length rods also reduce the decay ratio, but not as big as friction model II. As for local loss, there is no apparent difference by adding the calculation of local loss.