In preparation for the conversion of the University of Missouri Research Reactor (MURR) from the use of highly enriched uranium to low-enriched uranium fuel, MURR plans to upgrade primary coolant pumps. MURR currently operates with two parallel pumps in the primary loop, each providing half of the total core flow. The upgrades will involve replacing them with double capacity pumps, with only one pump operating at a time during normal operation. A duplicate pump will serve as a backup in case one of the two primary pumps is out. Due to these upgrades, one of the postulated loss-of-flow accident scenarios – a locked rotor in one of the two primary coolant pumps – is expected to be significantly impacted. For the current two-pump operation, about 60% of the steady-state core flow is maintained with a locked rotor of one of the two pumps whereas, for the planned one-pump operation, a locked rotor of the only operating pump is expected to significantly reduce the core flow. Due to an absence of full pump performance data – especially with varying pump velocity down to zero, the locked rotor pump behavior cannot be accurately determined solely based on the available data. This article proposes a methodology to characterize the locked rotor pump behavior based on extrapolation of available data, sensitivity analysis, and insights from known orifice flow resistances. The results show that sufficient safety margins are still maintained for the one-pump operation with the upgrades. • Accident scenarios give reactor response to transients, such as a locked rotor. • Research reactor pump system upgrade evaluated system transients. • Safety margins are maintained with one pump, including with low-enriched uranium fuel.
Yoon et al. (Mon,) studied this question.