Analysis of Rod-by-Rod FP Inventory Distributions in BWR 8×8 UO2 Assemblies Using Lattice Physics Method

Abstract

Fuel rod gamma-ray spectrometry was performed for one-, two-, three-, and five-cycle irradiated BWR 8 Â 8-4 fuel assembles, and relative rod-by-rod FP inventory distributions of 137 Cs, 134 Cs, 106 Ru, and 95 Zr were obtained for the upper and lower axial height nodes of the assemblies. The measured data was corrected for the difference in gamma-ray transmission between UO 2 and Gd 2 O 3 -UO 2 rods. These distributions were compared with those calculated using the collision probability method, Pij, of the SRAC code system with an infinite lattice model of the fuel assembly. The calculated results generally well reproduce the measured distributions, and the accuracy of the analysis method of the present study was evaluated to be 1 to 2% for the inventory distributions of 137 Cs, 2 to 3% for 134 Cs, 2 to 3% for 106 Ru, and 2 to 3% for 95 Zr, which represent the distributions of the burn-up, the thermal flux multiplied by the burn-up, the buildup of 239 Pu, and the fission rate at the end of the fuel discharge cycle, respectively. One of the notable results of the analysis of this study is that the FP inventories for the Gd 2 O 3 -UO 2 rods were underestimated in most cases.

Nuclear Analysis of PIE Data of Irradiated BWR 8×8-2 and 8×8-4 UO2 Fuel Assemblies

“…In the theoretical analysis of the pellet average data, an interpolation analysis 14) was mainly adopted taking into account the irradiation history of the samples, which consist of the following processes: (i) implementing burnup calculations in a constant power density corresponding to the rated power of the plant and constant in-channel void histories, 0, 40 and 70% in-channel void fractions, where cooling periods in outages between operating cycles were neglected, and this treatment would affect inventories of daughter nuclides of relatively short-life nuclides such as 241 Pu, (ii) compiling tables of pellet average data such as isotopic inventories as a function of two variables, the pellet exposures or the node average exposures, and the in-channel void fractions, (iii) interpolations of the values in the tables of the pellet exposures and in-channel void fractions were made for the analysis of the data of the 8Â8-2 assembly, and interpolations of the values in the tables of the node average exposures and in-channel void fractions were made for the 8Â8-4 assemblies.…”

“…Similar results are also indicated by the other study 12) on burnup calculations of three-and five-cycle irradiation 9Â9-9 fuel assemblies. Yamamoto et al 14) have studied lattice analyses of relative rod-by-rod inventory distributions of 137 Cs (a burnup indicator) obtained by fuel rod gamma scanning for the BWR 8Â8-4 fuel assemblies, and reported that the relative inventories of 137 Cs of the Gd 2 O 3 -UO 2 rods in burnup calculations by SRAC show underestimations by a few percent compared with the measurements. The present results on the comparison between MVP and SRAC would partly explain these underestimations of the measured inventories of 137 Cs.…”

“…One of them is isotopic inventories of irradiated fuels, and there are a large number of studies [2][3][4][5][6][7][8][9][10][11][12] on the nuclear analysis of the measurement data. The other field is the analysis 13,14) of rod-by-rod FP inventory distributions measured by fuel rod gamma scanning.…”

“…The other measured data are on four BWR 8Â8-4 UO 2 assemblies, which were irradiated as lead use assemblies of the second-step high-burnup fuels and discharged after one, two, three and five cycles of irradiations, and are referred to as 2F2D1, 2F2D2, 2F2D3, and 2F2D8, respectively. 16) Yamamoto et al 14) have reported the analysis results of the rod-by-rod FP inventory distributions in the assembly radial planes that have been measured as part of the nondestructive irradiation tests of the BWR 8Â8-4 UO 2 assemblies.…”