Design and Laboratory Evaluation of Future Elongation and Diameter Measurements at the Advanced Test Reactor

New materials are being considered for fuel, cladding, and structures in next-generation and existing nuclear reactors. Such materials can undergo significant dimensional and physical changes during high-temperature irradiation. To accurately predict these changes, real-time data must be obtained under prototypic irradiation conditions for model development and validation. To provide these data, programs such as the Advanced Test Reactor (ATR) National Scientific Users Facility (NSUF) have funded researchers at the Idaho National Laboratory (INL) High Temperature Test Laboratory (HTTL) to develop several instrumented test rigs to obtain data in real time from specimens irradiated in well-controlled pressurized water reactor (PWR) coolant conditions in ATR. This technical note reports the status of INL efforts to develop and evaluate prototype test rigs that rely on linear variable differential transformers (LVDTs) in laboratory settings. Although similar LVDT-based test rigs have been deployed in lower-flux materials testing reactors (MTRs), this effort is unique because it relies on robust LVDTs that can withstand higher temperatures and higher fluxes than often found in other MTR irradiations. Specifically, the test rigs are designed for detecting changes in the length and diameter of specimens irradiated in ATR PWR loops. Once implemented, these test rigs will provide ATR users with unique capabilities that are sorely needed to obtain measurements, such as elongation caused by thermal expansion and/or creep loading, and diameter changes associated with fuel and cladding swelling, pellet-cladding interaction, and crud buildup.