Scenarios and analytical methods for UF/sub 6/ releases at NRC-licensed fuel cycle facilities

This report identifies and discusses potential scenarios for the accidental release of UF/sub 6/ at NRC-licensed UF/sub 6/ production and fuel fabrication facilities based on a literature review, site visits, and DOE enrichment plant experience. Analytical tools needed for evaluating source terms for such releases are discussed, and the applicability of existing methods is reviewed. Accident scenarios are discussed under the broad headings of cylinder failures, UF/sub 6/ process system failures, nuclear criticality events, and operator errors and are categorized by location, release source, phase of UF/sub 6/ prior to release, release flow characteristics, release causes, initiating events, and UF/sub 6/ inventory at risk. At least three types of releases are identified for further examination: (1) a release from a liquid-filled cylinder outdoors, (2) a release from a pigtail or cylinder in a steam chest, (3) an indoor release from either (a) a pigtail or liquid-filled cylinder or (b) other indoor source depending on facility design and operating procedures. Indoor release phenomena may be analyzed to determine input terms for a ventilation model by using a time-dependent homogeneous compartment model or a more complex hydrodynamic model if time-dependent, spatial variations in concentrations, temperature, and pressure are important. Analytical tools formore » modeling directed jets and explosive releases are discussed as well as some of the complex phenomena to be considered in analyzing UF/sub 6/ releases both indoors and outdoors.« less