Analysis of Core Physics Experiments on Fresh and Irradiated BR3 MOX Fuel in REBUS Program

Abstract

As part of an international experimental program REBUS, core physics experiments have been implemented on a UO 2 core, which consists of 3.3 and 4.0 wt% UO 2 fuel rods in a square pitch of 1.26 cm, and two partial MOX cores, which replace 7 Â 7 UO 2 fuel rods in the center of the UO 2 core by fuel bundles made of fresh BR3 MOX fuel or irradiated BR3 MOX fuel with an average burnup of 20 GWd/t. Burnup calculations of the BR3 MOX fuel were performed using a general-purpose neutronic calculation code SRAC, and core calculations of the three critical cores were carried out using SRAC, a transport calculation code THREEDANT, and a continuous-energy Monte Carlo code MVP. The measured inventories of major U and Pu isotopes on a sample taken from the BR3 MOX fuel agree with the results of the burnup calculations within 3% deviation. The k eff 's of the three cores are from 0.985 to 1.002. The measured burnup reactivity of the irradiated BR3 MOX fuel was well reproduced by the three types of core calculations. The influence of the accuracy of the inventory calculations on burnup reactivity was studied by comparing between the calculated and measured inventories. The result indicates that the biases in the inventory and reactivity calculations compensate each other, and it makes the total biases of the burnup reactivity small.

Analysis of Measured Isotopic Compositions of High-Burnup BWR MOX Fuel

“…Neutronics analysis of the data have been reported by the organizations participating in the programs. 1,[3][4][5][6][7][8][9][10] Alander et al 6) and Yamamoto et al, 7) who analyzed the measured isotopic compositions of the high-burnup BWR MOX fuel in the REBUS program, observed that the burnup calculations based on an infinite assembly model overestimated fissile isotopes of U and Pu. They attributed it to harder neutron energy spectra in the assembly calculations than those under actual irradiation conditions, where the MOX assembly was burnt surrounded by UO 2 assemblies.…”

Analysis of core physics experiments on irradiated BWR MOX fuel in the REBUS program

“…[6] and has been confirmed to be relatively reliable except for some nuclides though the comparison with isotopic inventories measured by different organizations in some of international programs. The measured inventories provided the burnup of the measured fuel sample by applying Neodymium-148 Method [12].…”

“…The core characteristics of the irradiated MOX core are summarized in Table 4. Table 4 also shows those of the fresh MOX core (hereafter, referred to as 'fresh BR3 MOX core'), where a 7 6 7 test bundle consisting of 24 fresh BR3 MOX rods was loaded [6]. Since the core loaded with a fresh MOX bundle consisting of fresh MOX rods of 5.52 wt% (Pu-fissile) corresponding to the 9 6 9 MOX assembly were not performed, we used the core characteristics of the fresh BR3 MOX core as a substitute to evaluate burnup reactivity as mentioned in Section 4.3.…”

“…same as that for the other irradiated fuel rods in the REBUS program and was described in Ref. [6]. The total fission distributions were converted to the burnup distributions by applying an average energy release per fission (MeV/fission) during irradiation, which was calculated as part of burnup calculations of the 9 6 9 MOX assemblies shown in the Section 4.1.2.…”

Multigroup Scattering Matrix Generation Method Using Weight-to-Flux Ratio Based on a Continuous Energy Monte Carlo Technique

“…The underestimation of the diffusion calculations with the SRAC code has been reported for some critical experiment analyses. 9,10) The diffusion coefficient determination method using the present method will be improved in the next step. P1 transport calculations were more accurate than P0 transport calculations; 2D transport calculations with axial buckling correction were sufficiently accurate as well.…”