Fuel conditioning facility inert gas filled reprocessing hot cell leak rate measurement

Abstract

The Idaho National Laboratory Fuel Conditioning Facility conducts treatment of U.S. Department of Energy owned metallic fast reactor spent fuel using pyro-processing. Certain steps in pyro-processing generate pyrophoric metal laden with radioactive material. Therefore, the process is conducted within an inert atmosphere to prevent ignition. The Fuel Conditioning Facility uses a 60,000ft3 (1700m3) shielded hot cell environment with a purified argon gas atmosphere. Significant leakage of air into the hot cell can raise the oxygen concentration to the point where exposed pyrophoric metal will burn, which can subsequently result in release of radioactive material through the air in-leakage point. Additionally, limited air in-leakage can cause exposed metal to oxidize, rendering it unfit for pyro-processing. To ensure hot cell confinement boundary integrity, the Fuel Conditioning Facility executes periodic surveillance of the confinement boundary leak rate. This paper describes the leak rate surveillance techniques associated with this large inert-gas-filled hot cell.Two methods have been developed to determine the cell leak rate. One method uses the cell atmosphere oxygen concentration change over time. The other method uses the cell pressure and temperature change over time. The oxygen rate increase method is a very accurate method of determining the air leak rate during many types of operating conditions. However, the data observation period must be sufficiently long to obtain an accurate value. The pressure-temperature method is not as time consuming but is significantly less accurate than the oxygen concentration method.The cell leak rate is extremely small, less than 0.01cfm, given the very large cell size. The oxygen concentration method is accurate to approximately ±0.002cfm. The pressure-temperature method is accurate to about ±1cfm. The pressure-temperature leak rate method can be used as a confirmation of the oxygen method results or as a backup if the oxygen monitors are not working.