On December 8, 1995, a team of safety analysis experts working on a new Pantex Environmental Impact Statement notified the DOE Amarillo Area Office that the present analysis may not correctly postulate the plutonium dispersal for a highexplosive detonation because of the as-found configuration of the assembly cells. The team identified a scenario that could result in significantly higher radiation doses at the site boundary than previously calculated. The increased doses resulted from a different dispersal path than previously analyzed combined with large vent areas, consisting of penetrations and gaps, around personnel and equipment blast doors in the cells. The operating contractor determined that an unreviewed safety question existed and submitted a justification for continued operation while the issue is resolved. (ORPS Report ALO-AO-MHSM-PANTEX-1995-0216)
The 1983 Environmental Impact Statement analyzed the effect of a plutonium release from a high-explosive detonation in the assembly cells. During the detonation, the plutonium coverts to an aerosol in the cell, which is pressurized by the blast. The pressure is sufficient to raise the gravel roof on the bay allowing the airborne plutonium to disperse by interaction with the gravel. However, if the volume of high-explosive is less than the quantity needed to raise the roof, the resulting cell pressure would bleed down through the gaps. In this case, the dose release at the site boundary would exceed all previous projections. The authors expressed concern with the gaps around the personnel and equipment blast doors. The gaps were not repaired at that time.
The accident scenario with the highest potential for off-site release involves insufficient high-explosives to raise the gravel roof. In this scenario, dose at the site boundary could exceed previous analyzed projections. The Safety Analysis Report estimated the probability of this accident to be once every one hundred thousand years.
Between 1983 and 1994, engineers re-analyzed the problem several times to assess the impact of larger gap sizes than those stated in the environmental impact statement. As a result of a 1994 study of the analysis report, planners added a major repair item to fix the personnel door problems. This activity is still pending.
During preparation of safety documentation for the site-wide environmental impact statement, the group of analysts determined that the off-site dose at the site boundary would exceed previous analyzed projections. After quantifying their results, they notified the DOE Area Office on December 8 and provided a list of actions to reduce the offsite dose.
On December 9, 1995, the operating contractor assembled a team to accurately measure gaps and penetrations around the cell doors, identify short term options for reducing off-site dosage, and begin planning a long-term solution. They also limited plutonium loading in cells. These actions reduced the largest mean dose at the site boundary to less than 100 rem. On December 12, 1995, the operating contractor received approval for the justification for continued operation of the cells for 60 days allowing time to plug leakage paths and better assess the hazards.
This event underscores the importance of timely response to problems identified in the safety analysis. DOE 5480.21, Unreviewed Safety Questions, section 10.d, requires that a contractor must notify the appropriate DOE office upon discovery of a potential inadequacy in a safety analysis, perform a safety evaluation, keep the facility in a safe condition while the evaluation is performed, and submit the completed evaluation before removing any operational restrictions. Managers at DOE facilities should review their programs for compliance with this Order.