Criticality safety analysis of spent fuel pool for a PWR using UO2, MOX, (Th-U)O2 and (TRU-Th)O2 fuels

Abstract

A spent fuel pool of a typical Pressurized Water Reactor (PWR) was evaluated for criticality studies when it uses reprocessed fuels. PWR nuclear fuel assemblies with four types of fuels were considered: standard PWR fuel, MOX fuel, thorium-uranium fuel and reprocessed transuranic fuel spiked with thorium. The MOX and UO2 benchmark model was evaluated using SCALE 6.0 code with KENO-V transport code and then, adopted as a reference for other fuels compositions. The four fuel assemblies were submitted to irradiation at normal operation conditions. The burnup calculations were obtained using the TRITON sequence in the SCALE 6.0 code package. The fuel assemblies modeled use a benchmark 17x17 PWR fuel assembly dimensions. After irradiation, the fuels were inserted in the pool. The criticality safety limits were performed using the KENO-V transport code in the CSAS5 sequence. It was shown that mixing a quarter of reprocessed fuel withUO2 fuel in the pool, it would not need to be resized

Long term comparison between reprocessed nuclear fuel cycles

“…MOX fuel contains 7.23% of plutonium and 92.77% of depleted uranium. This composition is equivalent to about 4.5% enriched UOX [16]. Nuclear power plants utilize one-third of MOX and two-thirds of UOX fuel in their core.…”

Water boiling time in a spent fuel pool with adiabatic and non-adiabatic boundary conditions

“…The heat sources in simulations are the SF and were derived from previous studies [6]. The main characteristics of SFs of interest in the present work, including the final amount of fissile material, the burnup and the operation time of the reactor were obtained from [6], and are listed in following: Each assembly of SF was modelled as a solid cylinder, and only a single UR is represented.…”

“…The heat sources in simulations are the SF and were derived from previous studies [6]. The main characteristics of SFs of interest in the present work, including the final amount of fissile material, the burnup and the operation time of the reactor were obtained from [6], and are listed in following: Each assembly of SF was modelled as a solid cylinder, and only a single UR is represented. To determine the volume of water in the model, the proportion SF/water in the real pool of the PWR from Angra II-Brazil fully filled with assemblies was adopted, i.e., 0.0508 [7], considering that the real pool has approximately 1,298 m 3 .…”

“…The water properties are from [9], at 298 K. The UO2 properties, at 673 K, are from [9,10]. The molar mass of MOX, (U-Th)O2, (TRU-Th)O2 and (U-Th)O2 were estimated from their chemical compositions from [6], at 298 K.…”

“…The (TRU-Th)O2 properties were estimated considering the most significant dioxides present in its composition, which are ThO2, PuO2 and UO2 [6]. The density, specific heat, conductivity, and thermal expansivity are represented by Q, and were estimated by the following expression:…”