Source term evaluation for postulated UF(sub 6) release accidents in gaseous diffusion plants -- Summer ventilation mode (non-seismic cases)

摘要

Computer models have been developed to simulate the transient behavior of aerosols and vapors as a result of a postulated accident involving the release of uranium hexafluoride (UF(sub 6)) into the process building of a gaseous diffusion plant. For the current study, gaseous UF(sub 6) is assumed to get released in the cell housing atmosphere through B-line break at 58.97 kg/s for 10 min and 30 min duration at the Paducah and Portsmouth Gaseous Diffusion Plants. The released UF(sub 6) undergoes an exothermic chemical reaction with moisture (H(sub 2)O) in the air to form hydrogen fluoride (HF) and radioactive uranyl fluoride (UO(sub 2)F(sub 2)) while it disperses throughout the process building. As part of a facility-wide safety evaluation, this study evaluated source terms consisting of UO(sub 2)F(sub 2) as well as HF during a postulated UF(sub 6) release accident in a process building. UO(sub 2)F(sub 2) mainly remains as airborne-solid particles (aerosols), and HF is in a vapor form. Some UO(sub 2)F(sub 2) aerosols are removed from the air flow due to gravitational settling. The HF and the remaining UO(sub 2)F(sub 2) are mixed with air and exhausted through the building ventilation system. The MELCOR computer code was selected for simulating aerosols and vapor transport in the process building. To characterize leakage flow through the cell housing wall, 3-D CFD tool (CFDS- FLOW3D) was used. About 57% of UO(sub 2)F(sub 2) was predicted to be released into the environment. Since HF was treated as vapor, close to 100% was estimated to get released into the environment.