Safety Analysis of the Mo-99 Production Upgrade to the University of Missouri Research Reactor (MURR) with Highly-Enriched and Low-Enriched Uranium Fuel

Abstract

The University of Missouri (MU) has been working in conjunction with Argonne National Laboratory (ANL) in the National Nuclear Security Administration (NNSA) Material Management and Minimization (M3) Reactor Conversion Program to support conversion of the University of Missouri-Columbia Research Reactor (MURR®) from highly enriched uranium (HEU) to low-enriched uranium (LEU) fuel. MURR is one of five U.S. High Performance Research Reactors (USHPRR) plus a critical facility that plans to convert to the use of LEU fuel. ANL/RTR/TM-18/16 Safety Analysis of the Mo-99 Production Upgrade to the University of Missouri Research Reactor (MURR) with Highly Enriched and Low-Enriched Uranium Fuel ii ANL/RTR/TM-18/16 Safety Analysis of the Mo-99 Production Upgrade to the University of Missouri Research Reactor (MURR) with Highly Enriched and Low-Enriched Uranium Fuel iv installed. Thus, the upgrade causes a change in the location of the maximum HEU fuel temperature resulting from the limiting LOFA, which is consistent with the shift in the core power distribution that occurs due to the upgrade. For the LEU core, the minimum margin to the fuel temperature safety limit for the limiting LOFA with the 2017-RBM-99 upgrade is 232 °C and occurs in an EOL fuel plate. This is the same margin as was predicted for the limiting LOFA for the PSAR analysis. The location of the minimum margin moves from plate 23 of the fuel element in core position 8 in the PSAR analysis to plate 23 of the fuel element in core position 4 with the upgrade. With more margin than the other scenarios, all LOFA transient results are considered to have very adequate margins to the burnupdependent fuel temperature safety limit. Because there is no change to the HEU or LEU nominal fuel element loadings and an overall negligible effect on the fuel burnup as a result of the 2017-RBM-99 upgrade, the radiological consequences of the maximum hypothetical accident and fuel handling accident were not evaluated in this work. As found in the PSAR analysis, for any event where a release is considered in the current HEU SAR, the radiological consequences after conversion remain lower than the regulatory limits. In summary, the Mo-99 production upgrade to MURR with the 2017-RBM-99 device has been found to cause a shift in the core power distribution for both HEU and LEU cores relative to the PSAR analysis. The predicted steady-state margins to flow instability with the upgrade are adequate for both HEU and LEU cores. The margins with the upgrade are lower than those predicted in the PSAR analysis for both HEU and LEU, but the margin for LEU is larger than that for HEU. For postulated transient accidents, the upgrade causes a slight decrease in the minimum margin to a fuel temperature safety limit based on the fuel blister threshold temperature. There is a 9 °C reduction in the safety margin for HEU for the most limiting accident evaluated under conditions specified in NUREG-1537. For a reference LEU core, the minimum safety margin for the most limiting transient accident with ...

Transition Core Planning and Safety Analyses in Support of LEU Fuel Conversion of the University of Missouri Research Reactor (MURR)

“…Safety margin evaluations for selected cores in the transition sequence up to and including the equilibrium LEU core are provided in Sections 4 and 5. It was confirmed in previous work that for a prototypic equilibrium LEU core using elements with a mixture of burnup levels and operating at 12 MW, the experimental performance meets or exceeds the performance for a typical HEU core at 10 MW [5,7]. For the LEU core transition cycles, however, experimental performance that will enable MURR to maintain current irradiation services is expected to be a key challenge.…”

“…Consequently, a power uprate to 12 MW for LEU, along with changes to the reactor limiting safety systems settings (LSSS) for the minimum core coolant flow rate and maximum coolant inlet temperature, was assumed for safety analyses with the preliminary LEU fuel element design [6]. These analyses confirmed that for equilibrium operations with the proposed LEU fuel design, a core power increase, and changes to the MURR Technical Specifications, MURR will maintain sufficient safety margins during steady-state and transient conditions, operating cycle length, and level and spectrum of key neutron fluxes and reaction rates to meet the scientific mission of the facility [5,7,12,13].…”

“…The estimated core burnup at BOC is shown to generally increase from 0 MWd for the first fresh core to near the target core LEU core burnup of 687 MWd. Based upon results obtained from previous work with LEU equilibrium cores [5,7], it is expected that cores at or near this burnup operating at 12 MW will yield experimental performance at all key locations that meets or exceeds the performance for typical HEU cores at 10 MW. The proposed sequence of transition cycles has cores within the target burnup band of 663 to 711 MWd beginning first in cycle 20.…”

“…This represents a substantial increase in detail relative to the 70 metrics evaluated in preliminary SAR work [5]. These metrics, which are identified in the reactor cross-section shown in Figure 2.1, are based on irradiation facilities and experiment loadings that were typical for operations at MURR in 2018 and used in previous analyses of equilibrium LEU operations following a major prospective facility upgrade [7]. In the current work these performance metrics provide an opportunity to evaluate LEU transition cycles and the LEU core after typical equilibrium operating conditions are reached relative to values calculated for a typical HEU core.…”

“…Working with the NNSA M 3 Conversion Program USHPRR Project Reactor Conversion (RC) Pillar led by Argonne National Laboratory, MURR has completed performance and safety analyses for prototypic equilibrium fuel cycle operations with the current HEU fuel and following conversion to this LEU fuel and a power uprate from 10 MW to 12 MW [5]. Performance and safety analyses have also been completed for HEU and for the preliminary LEU fuel element design [6] which demonstrate satisfactory experimental performance and margins to safety following a major facility upgrade [7].…”