Technical basis in support of the conversion of the University of Missouri Research Reactor (MURR) core from highly-enriched to low-enriched uranium - core neutron physics

Abstract

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Preliminary Accident Analyses for Conversion of the University of Missouri Research Reactor (MURR) from Highly-Enriched to Low-Enriched Uranium Prepared by

“…Since the modeling considered only the highest heat flux element of a fresh HEU core and the corresponding element of the LEU core, future analysis may need to be expanded to include at least other LEU core cases prescribed in the neutron physics analysis [1]. Consideration must also be given to whether including only a single element in the RELAP5 model is sufficient.…”

“…A very short restart input file was produced for each transient. The power generation values of the 96 fuel meat nodes, i.e., 24 fuel plate × 4 axial level nodes, were set to represent the full power of element 7 of the HEU core power distribution 1B1, as provided by the neutron physics analysis [1]. This element has the highest heat flux in core 1B1, which is a fresh core.…”

“…limit on the reactivity insertion from control bank withdrawal. For the proposed LEU-fueled core, previous studies have shown [1] that in order to maintain the neutron flux and current levels at various crucial experimental locations within the reactor at the same level after the fuel conversion from the HEU to LEU, the steady-state operating power level must be increased from 10 MW to 12 MW. Hence the accidental positive reactivity insertions for the LEU core were initiated from an initial steady-state power level of 12 MW.…”

“…Then an LEU element model was substituted for the HEU one. The power distributions for both elements were taken from recent neutron physics analysis [1].…”

“…In the neutron physics analysis [1], detailed power distributions were predicted for a set of 24 potentially limiting HEU core states and the analogous 24 LEU core states. For the current Phase I accident analysis only the highest heat flux HEU core and the highest heat flux LEU core, 1B1 and 5B1, respectively, were modeled.…”