Lesson Learned Statement:An Unreviewed Safety Question (USQ) was declared at the Waste Encapsulation and Storage Facility (WESF) because the hot cell shield windows contain more oil than is assumed in the WESF Basis for Interim Operations (BIO). The incorrect amount of oil was obtained from the fire hazard analysis (FHA) but was not verified by the BIO authors before using it in calculations of combustible loading.
Discussion:An accident analysis in the WESF BIO assumes that the shielding windows fail during a fire involving cells B through E. Such a failure would allow the mineral oil in the windows to leak into the hot cells, adding fuel to the fire. Accident analysis shows that a hot cell fire involving more than 24 kg of combustible material could plug exhaust HEPA filters resulting in a radiological release greater than permissible guidelines. Therefore, the BIO requires a control to limit the amount of combustible material in a hot cell. The amount of mineral oil in the window must be included in the allowable combustible material load because the oil could leak into the cell.
The BIO assumes two gallons of oil in each window based on a number taken from the WESF Fire Hazards Analysis (FHA). While updating the fire hazard analysis in June 2002, analysts realized that the amount of oil in each window is closer to 8 gallons than the 2 gallons assumed by the BIO. Because the amount of oil available to leak into the hot cell is greater than the amount assumed by the BIO, the control developed in the BIO is not adequate.
Analysis:An investigation identified that the two gallon value for the amount of oil in each window was originally determined for the FHA in 1998. At that time a review of the drawings and available vendor information found no clear documentation of the volume of oil contained in each window. The FHA author requested that the amount of oil in the window be measured by draining one of the windows but that task was not performed because of conflicting priorities. The two gallon value was obtained by calculating a volume from the drawing of the window. That estimate was acceptable at the time, even though not highly accurate, because the exact value was not important to the FHA analysis. The FHA included that estimated quantity of oil for information. The BIO authors used that number but did not recognize a need to verify it before using it as an integral part of a control. They trusted the number because it came from a released document that had been through a thorough review and approval process.
Recommended Actions:A separate review and verification of other critical values and parameters in the BIO identified a few errors but none that impact the accident analyses.
Facilities with oil filled hot cell windows should ensure that the volume of oil used in safety basis or fire hazard calculations is accurate. They should consider measuring the volume if accurate documentation is not available.
Everyone who performs calculations, especially those used in safety bases, should verify that all numbers on which those calculations are based have a degree of accuracy consistent with the application of the calculation.
Originator:Fluor Hanford, Inc.
Submitted by Jan Pennock; (509) 373-7210
Contact:Project Hanford Lessons Learned Coordinator; (509) 373-7664; FAX 372-3950;
Name Of Authorized Derivative Classifier:Not required
Name Of Reviewing Official:John Bickford
Priority Descriptor:Blue / Information
Keywords:hot cell window, mineral oil, basis for interim operations, fire hazard analysis
References:HNF-SD-WM-BIO-002, Rev 1B, section 22.214.171.124.1.4, WESF Basis for Interim Operations
HNF-SD-WM-FHA-019, WESF Fire Hazards Analysis
Occurrence report RL—PHMC-WESF-2002-0003
NTS report NTS-RL—PHMC-WESF-2002-0001
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DOE Function / Work Categories:Authorization Basis
ISM Category:Develop / Implement Controls
Hazard:Fire / Smoke / NFPA
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