Modeling and Simulations for the High Flux Isotope Reactor Cycle 400

Abstract

A concerted effort over the past few years has been focused on enhancing the core model for the High Flux Isotope Reactor (HFIR), as part of a comprehensive study for HFIR conversion from high-enriched uranium to low-enriched uranium (LEU) fuel. At this time, the core model used to perform analyses in support of HFIR operation is a Monte Carlo model with the MCNP code for the beginning of Cycle 400, which was documented in detail in a 2005 technical report. An updated HFIR core depletion model that is based on current state-of-the-art methods and nuclear data was needed to serve as reference for the design of an LEU fuel for HFIR.The recent enhancements in modeling and simulations for HFIR that are discussed in the present report include: (1) revision of the 2005 MCNP model for the beginning of Cycle 400 to improve the modeling data and assumptions as necessary based on appropriate primary reference sources-HFIR drawings and reports; (2) improvement of the fuel region model, including an explicit representation for the involute fuel plate geometry that is specific to HFIR fuel; and (3) revision of the Monte Carlo-based depletion model for HFIR, in use since 2009 but never documented in detail, with the development of a new depletion model for the HFIR explicit fuel plate representation.The new HFIR models for Cycle 400 are used to determine various metrics of relevance to reactor performance and safety assessments. The calculated metrics are compared, where possible, with measurement data from preconstruction critical experiments at HFIR, data included in the current HFIR safety analysis report, and/or data from previous calculations performed with different methods or codes. The results of the analyses show that the models presented in this report provide a robust and reliable basis for HFIR analyses.

Impact of fission neutron energies on reactor antineutrino spectra

“…MCNP5 was used due to extensive benchmarking of all MCNP5-based models used in this study. The list of reactor models investigated for this study are: a typical Westinghouse pressurized water reactor (PWR) [41], the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL) [42], and the National Bureau of Standards Reactor (NBSR) at the National Institute of Standards and Technology (NIST) [43]. The Westinghouse PWR operates with LEU fuel, while HFIR and NBSR operate with HEU fuel.…”

“…HFIR operates for approximately 24 days, after which a shutdown allows for a new core replacement. The HFIR MCNP full-core model [42] includes explicit geometry of the involute fuel plates with separate radial and axial fuel regions.…”

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

“…The purpose of the work described in this report was to develop and analyze a high-fidelity VESTA/MCNP model of HFIR with a representative experiment loading. MCNP models for HFIR Cycle 400 [3,4] have been used extensively for HFIR research-based and safety-based neutronics studies since 2005, with model improvements continuing over the years to take advantage of the available state-of-theart modeling and simulations methods and codes. The latest major revision of this MCNP model was completed in 2015 [4] and included a high-fidelity, explicit representation of the involute fuel plate geometry that is characteristic to HFIR, along with development and documentation of a new VESTA depletion model that is based on the explicit fuel model [4].…”

“…The work performed and documented in this report was driven by the HEU to LEU conversion project, which is sponsored by the US Department of Energy's (DOE) National Nuclear Security Administration Office of Material Management and Minimization. At this time, the primary objective of the HFIR LEU conversion project is to produce a safety basis documenting one or more acceptable LEU fuel designs based on combining recent alternate design studies [1] and up-to-date high fidelity models of the HFIR [4,5,6]. Following the conversion of HFIR from HEU to LEU fuel, (1) the ability of HFIR to perform its scientific missions must not be diminished, (2) the cycle length should be no shorter than that with the current HEU fuel, and (3) all safety requirements must be met.…”

“…Other than the fuel material and geometry, the primary difference between these models was the experiment loading in the flux trap target region. A recent, enhanced LEU depletion model for HFIR has been developed [6] with an explicit representation of the fuel plate geometry and similar to the new Cycle 400 model [4] in most aspects of the core configuration except for the experiment loading and a higher fidelity modeling of the fuel element side plates. However, the experiment loading for this new LEU model is not typical of current HFIR operation and needs to be improved.…”