PNNL

Abstract

One widely discussed approach for mitigation of stainless steel spent fuel canisters (SFCs) is to coat the welds or even the full SFC surface with a thin nickel coating using a cold spray application method. The nickel material can also serve as a magnetostrictive interface between an electromagnetic acoustic transducer (EMAT) and the structural stainless steel plate material that encapsulates the nuclear waste material. The EMAT can send ultrasound waves into the canister and “listen” for reflections from chloride-initiated stress corrosion cracking (CISCC) damage or other mechanisms that may lead to through-wall leaks if undetected and unmitigated. This project outlines an approach for periodically monitoring the integrity of the SFCs using magnetostrictive EMAT sensors to emit shear horizontal waves and sense flaw-initiated reflections indicative of pits or cracks likely arising from CISCC. Flat 13-mm (1/2-in) stainless steel plates with welds similar to actual canister welds were prepared with 3-mm and 6-mm (0.25-in and 0.125-in) deep by 6-mm diameter flat-bottom holes placed within the weld heat-affected zone. The best sensor configurations could see critical flaws more than 2-m (79-in) away, thereby dictating that the weld heat-affected zone of the cylindrical plate can be monitored with a manageable 16 sensors.