EPRI Advanced Ultrasonic Fuel Cleaning Technology

摘要

Corrosion product transport in the primary coolant results in deposition and activation of iron and nickel based oxides that are responsible for system dose rates when these get redistributed during power transients, startup, and shutdown. In addition, excessive core deposition may result in fuel failures in both PWRs and BWRs. Excessive corrosion product deposition is identified as part of the root cause of axial offset anomaly (AOA) in PWRs. As fuel economic concerns continue to demand longer cycle lengths and higher core thermal duties, AOA has become particularly costly to PWRs. As a measure to mitigate AOA, the EPRI Robust Fuel Program developed an advanced fuel cleaning system based on novel ultrasonic technology. The idea of fuel cleaning for AOA is to first remove a likely source of metal oxide deposit on the hottest feed fuel assemblies by cleaning corrosion product from the second cycle fuel before reloading it; and, second to eliminate the risk of AOA developing early in the next cycle on aggressively driven reload fuel. From a radiation management perspective, the idea of cleaning reload fuel is to eliminate from the primary circuit a large fraction of the activated, particulate material that can cause increased personnel dose exposure by redistributing onto ex-core surfaces or depositing in sample taps, drains, filters, and low flow areas. Development and applications of EPRI fuel cleaning technology in PWRs and BWRs are described in this paper. Last year, jointly sponsored by AmerenUE, this technology was successfully demonstrated on spent fuel at Callaway Plant. Callaway subsequently cleaned and reloaded sixteen assemblies during their October 1999 refuel. These assemblies are currently undergoing re-irradiation and are being monitored for any signs of anomalous flux depression, with no anomalies seen to date. Also in 1999, under Entergy sponsorship, EPRI completed laboratory and mock-up feasibility studies showing that the technology is capable of cleaning BWR type fuel deposit as well.