Sensitivity of Physics Parameters for Establishment of a Burned CANDU Full-Core Model for Decommissioning Waste Characterization

Abstract

The sensitivity of parameters related with reactor physics on the source terms of decommissioning wastes from a CANDU reactor was investigated in order to find a viable, simplified burned core model of a Monte Carlo simulation for decommissioning waste characterization. First, a sensitivity study was performed for the level of nuclide consideration in an irradiated fuel and implicit geometry modeling, the effects of side structural components of the core, and structural supporters for reactive devices. The overall effects for computation memory, calculation time, and accuracy were then investigated with a full-core model. From the results, it was revealed that the level of nuclide consideration and geometry homogenization are not important factors when the ratio of macroscopic neutron absorption cross section (MNAC) relative to a total value exceeded 0.95. The most important factor affecting the neutron flux of the pressure tube was shown to be the structural supporters for reactivity devices, showing an 10% difference. Finally, it was concluded that a bundle-average homogeneous model considering a MNAC of 0.95, which is the simplest model in this study, could be a viable approximate model, with about 25% lower computation memory, 40% faster simulation time, and reasonable engineering accuracy compared with a model with an explicit geometry employing an MNAC of 0.99.

Verification of Source Term Estimation Method against Measured Data for Decommissioning Waste from a CANDU Reactor

“…In the previous paper, 7) a modeling method was proposed with a snapshot full-core model. The snapshot full-core model denotes the reactor core model describing the irradiation condition at an arbitrary time t. Because the neutron flux continuously fluctuates as the reactor operates, 7) it is certain that the time-average full-core model represents a more reliable average neutron flux in the structural component than a snapshot full-core model.…”

“…In this study, the modeling method for the reference burned full-core proposed in the previous paper 7) and nuclide buildup calculation method proposed in this paper for the source term characterization of the decommissioning waste from CANDU reactors were verified by comparing the estimated nuclide inventory with the measured nuclide inventory in an irradiated pressure tube discharged from Wolsong Unit 1.…”

“…7), Cho et al described the establishment of a burned full-core model, for a Monte Carlo simulation, as a neutron source that is needed to activate the structural components in the inner and outer core to calculate the source terms of the waste decommissioning from a CANDU reactor. A simple burned full-core model with reasonable calculation accuracy and short computer runtime compared with the explicit model is proposed from an engineering viewpoint in the previous paper.…”

“…A simple burned full-core model with reasonable calculation accuracy and short computer runtime compared with the explicit model is proposed from an engineering viewpoint in the previous paper. 7) However, the established model and overall source term estimation method were not verified by comparing the estimated nuclide inventory from the analysis system with the measured inventory in the structural components.…”

Radiological Characteristics of Decommissioning Waste From a Candu Reactor

“…Because the neutron flux of the structural component continuously fluctuates as the reactor operates, the timeaverage full-core model definitely generates a more reliable average neutron flux in the structural component than the snapshot full-core model, which describes the reactor condition at arbitrary time t and results in a neutron flux and cross-sections at time t [7]. It is important to use the average neutron flux of the component in the activation calculation, because it is very difficult to consider a varying neutron flux as a function of operation time.…”