Examination of criticality accident alarm coverage on the operating floors of Buildings X-333, X-330, and X-326 at the Portsmouth Gaseous Diffusion Plant. Revision 1

The diffusion cascade processing equipment at the Portsmouth Gaseous Diffusion Plant (PORTS) is located in Buildings X-333, X-330, and X-326. These buildings were referred to as the cascade buildings. Because enriched uranium operations are performed within the cascade buildings, the potential for a criticality accident in these buildings exists. A Criticality Accident Alarm System (CAAS) is in place to alarm in the event of a criticality accident. The CAAS is required to be designed to immediately detect the minimum accident-of-concern. A minimum accident-of-concern in an area with nominal shielding delivers the equivalent of an absorbed dose rate in free air of 20 rads per minute at a distance of 2 meters from the reacting material [Am86]. This report summarizes the analysis that was performed to evaluate the CAAS response to selected minimum accidents-of-concern on the operating floor of the cascade buildings. Selection of potential accident locations was based, in part, on the maximum distance to the closest CAAS detector. The other factor in selecting potential accident locations for analysis was the amount of intervening shielding between the accident location and CAAS detector. If the CAAS was predicted to alarm under conditions of significant shielding, then the system presumably would alarm in response to all accidents greater than the minimum accident-of-concern, at closer distances, and with less shielding