Modeling and Depletion Simulations for a High Flux Isotope Reactor Cycle with a Representative Experiment Loading

Abstract

The purpose of this report is to document a high-fidelity VESTA/MCNP High Flux Isotope Reactor (HFIR) core model that features a new, representative experiment loading. This model, which represents the current, high-enriched uranium fuel core, will serve as a reference for low-enriched uranium conversion studies, safety-basis calculations, and other research activities. A new experiment loading model was developed to better represent current, typical experiment loadings, in comparison to the experiment loading included in the model for Cycle 400 (operated in 2004). The new experiment loading model for the flux trap target region includes full length 252 Cf production targets, 75 Se production capsules, 63 Ni production capsules, a 188 W production capsule, and various materials irradiation targets. Fully loaded 238 Pu production targets are modeled in eleven vertical experiment facilities located in the beryllium reflector. Other changes compared to the Cycle 400 model are the high-fidelity modeling of the fuel element side plates and the material composition of the control elements. Results obtained from the depletion simulations with the new model are presented, with a focus on time-dependent isotopic composition of irradiated fuel and single cycle isotope production metrics.

Key metrics for HFIR HEU and LEU models

“…Cycle length is expressed in days, with a precision of 0.5 days. This precision is considered adequate for EOC estimations in HFIR depletion simulations [2,3].…”

“…The second model [3] considers an LEU interim design fuel [1] with a reactor power of 100 MW. Except for the fuel region, the two models are consistent and both include an explicit representation [2][3][4] of the HFIR's fuel plate involute geometry.…”

“…Each of these tables includes the flux and the flux per unit power for the HEU and LEU cores, as well as the LEU to HEU flux ratio, for each of the nine energy bins specified in Table 2.1. The EOC time was 26 days [2] for the HEU core and 34 days [3] for the LEU core, as further discussed in Section 3.4. The MOC state point was set as 14 days for the HEU and 18 days for the LEU core [2,3].…”

“…The models used to calculate these key metrics are documented in detail in previous publications [2][3][4]. This report presents a comparison of these key metrics, which were determined for two three-dimensional (3-D) high-fidelity HFIR models.…”

“…This report presents a comparison of these key metrics, which were determined for two three-dimensional (3-D) high-fidelity HFIR models. The first model [2] considers HEU fuel, an experiment loading representative of HFIR's current operation, and a reactor power of 85 MW. The second model [3] considers an LEU interim design fuel [1] with a reactor power of 100 MW.…”