Event Notification Report for February 20, 2001

NRC BULLETIN 91-01 24 HOUR REPORT

The following is a portion of a faxed report:

On 02/20/01 at 0848 hours the Plant Shift Superintendent's office was informed that a Nuclear Criticality Safety Analysis (NCSA) was deficient. NCSA-PLANT088, Storage of Abandoned Equipment, utilizes the NCS calculation document NCS-CALC-98-029, which contains the following non-conservative assumptions:

The KENO model used a radius of 6.35 cm to model the inner diameter of a 5-inch pipe. This does not bound all nominal 5-inch diameter pipe. Standard 5-inch pipe can have an inner diameter of 5.345 inches (13.5763 cm) which would require a radius of 6.7882 cm.

This document modeled a UO2F2 - H2O mixture with an H/U ratio of 4. The use of this H/U ratio is acceptable for cascade piping due to the way the cascade is operated. It is not acceptable for use in other buildings (i.e. X-705, X-700, and X710) if the pipe is filled with fissile material. An H/U ratio of at least 16 should have been used to bound pipes in the other buildings.

NCS-CALC-98-029 provides part of the basis for defining what a safe geometry is in NCSA-PLANT088.A00 (Storage of Abandoned Equipment). The calculation models a spacing violation between two 5.0-inch diameter 10-ft long pipes containing 100% enriched UO2F2 at an H/U of 4. Each pipe modeled in the calculation contains approximately 125,000 grams of U-235 at 100% enrichment. The USEC possession limit for HEU outside of shutdown cascade equipment is 1000 grams U-235.

Control 1a in NCSA-PLANT088.A00 defines a safe geometry based on having a nominal pipe diameter of 5-inches or less, as well as limiting the length of the pipe to less than 10-feet and specifying that the pipe has not been exposed to oily material. Since 'nominal' 5-inch diameter pipes may have diameters slightly larger than 5.0-inches, control 1a is not consistent with the assumption in calculation NCS-CALC-98-029 of exactly 5.0-inch diameter. Therefore, NCSA-PLANT088.A00 is technically deficient, NCSA-PLANT088.A00 is currently active in various buildings on plant site. None of the equipment currently regulated by NCSA-PLANT088.A00 used the definition of safe geometry (as defined in control 1A in NCSA-PLANT088.A00) to show double contingency. Rather, all equipment currently under NCSA-PLANT088 is controlled based on being below a safe mass, which the NCSA allows as an alternative to controlling the geometry. Therefore, double contingency can still be shown for all equipment currently regulated by NCSA-PLANT088.A00 (based on spacing and mass controls).

As part of the response to this incident, other NCSAs were investigated which referenced either NCS-CALC-098-029 or NCSA-PLANT008 as part of their safety basis, It was determined that NCSA-PLANT062.A04 (Cascade Maintenance Equipment Removal and Storage) has the same problem as NCSA-PLANT088.A00. In addition, NCSA-0705_ 041.A01 (Material Handling and Storage in X-705) and NCSA-PLANT048.A04 (Contaminated Metal) also reference either calculation NCS-CALC-98-029, NCSA-PLANT088.A00, or PLANT062.A04 as part of their safety basis for storage of favorable geometry equipment. While there may be items stored under these NCSAs based on the controls defining favorable geometry, none of these items individually can contain greater than a safe mass because of the requirements of TSRs 2.2.3.16 and 2.7.3.15. These TSRs require any removed cascade equipment containing greater than a safe mass under optimum moderation conditions to be decontaminated within 72 hours. Since there can be no equipment stored under any of the affected NCSAs containing greater than a safe mass, this incident is being reported to the NRC as a 24-hour event report.

SAFETY SIGNIFICANCE OF EVENTS:

The non-conservative assumption in NCS-CALC-98-029 has a low safety significance for the following reasons:

The calculation assumed two 5-inch 10 foot long pipes completely filled with a UO2F2-H2O mixture (H/U ratio of 4) containing approximately 125,000 grams of 100% enriched U-235. This case bounds the entire operating history of the plant. Current plant requirements limit the production of enriched uranium to 10 wt% U-235. Any material greater than 10% is currently contained within shutdown cascade piping (which is covered by other NCSAs not affected by this incident), or is limited to 1000 grams U-235 by the USEC possession limits.

There is no equipment currently controlled by NCSA-PLANT088.A00 that uses a safe geometry as one control for double contingency.

While there may be equipment covered under NCSAs PLANT062, PLANT048, or 0705_041 that use safe geometry as a control, TSRs 2.2.3.16 and 2.7.3.15 (Removed Equipment with Deposits) ensure that any such equipment containing greater than a safe mass is decontaminated to less than or equal to a safe mass within 72 hours of removal. The safe mass required by these TSRs is based on optimum moderation conditions. As a result of these TSRs and their implementing procedures, there is no removed equipment currently stored on plant site under any of the affected NCSAs which contains greater than a safe mass. Since the safe mass is defined as less than half of the minimum credible critical mass, a criticality would not have occurred even if a spacing violation had occurred.

The calculation in question was intended to demonstrate subcriticality in the event of a spacing violation between two favorable geometry pipes. Since there are no known spacing violations between such equipment, there remains at least one control in place to prevent criticality (spacing) in all cases. The normal storage of favorable geometry equipment in a properly spaced configuration was not affected by this discovery.

POTENTIAL CRITICALITY PATHWAYS INVOLVED (BRIEF SCENARIO[S] OF HOW CRITICALITY COULD OCCUR):

Two 10 foot long 5 inch pipes containing a mixture of UO2F2-H2O mixture (H/U ratio of 16) containing I00 wt% U-235 placed adjacent to each other could achieve criticality.

CONTROLLED PARAMETERS (MASS, MODERATION, GEOMETRY, CONCENTRATION, ETC.):

The controlled parameters for equipment which could be affected by this event are spacing and geometry.

ESTIMATED AMOUNT, ENRICHMENT, FORM OF LICENSED MATERIAL (INCLUDE PROCESS LIMIT AND % WORST CASE OF CRITICAL MASS):

No specific equipment was identified as being out of compliance. Therefore, the amount, enrichment or form is not known. However, it is known that no individual piece of equipment stored under the affected NCSAs contains greater than a safe mass, due to the TSR requirements.

NUCLEAR CRITICALITY SAFETY CONTROL(S) OR CONTROL SYSTEM(S) AND DESCRIPTION OF THE FAILURES OR DEFICIENCIES:

The calculation document for a spacing violation between two favorable geometry components contained a non-conservative assumption which was not properly flown into the NCSA controls. The spacing control remained in place. Thus, one control used for double contingency was rendered invalid. The deficiency will be corrected by revising the NCSA controls to be consistent with the calculation.

CORRECTIVE ACTIONS TO RESTORE SAFETY SYSTEM AND WHEN EACH WAS IMPLEMENTED:

Daily Operating Instructions (DOI) stating "No further equipment shall be implemented under NCSA-PLANT088 until the deficiency Is corrected."

The licensee has notified the NRC Resident Inspection and DOE.

UNIT 1 SHIFT SUPERVISOR TESTED POSITIVE FOR ALCOHOL DURING A RANDOM FITNESS FOR DUTY TEST.

"On February 20, 2001, after reporting for a non-scheduled work shift at about 1800 PST, the supervisor was informed he had been selected for a random fitness for duty (FFD) test. As allowed by plant procedures, the supervisor entered the protected area (PA) at about 1820 PST, but not any vital areas, before reporting for FFD testing at about 2000 PST. At 2109, breathalyzer test results were positive for alcohol. The supervisor requested that a blood sample be used for confirmatory testing. Pending blood sample testing results, the supervisor's PA access was immediately terminated and he was placed on investigatory suspension.

"On February 23, 2001, during an NRC inspection exit interview, NRC inspectors commented that SCE should not wait on blood testing results to determine reportability of this occurrence. Consequently, even though evaluation of the blood sample test results by the Medical Review Officer (MRO) have not been completed, SCE is reporting this occurrence . SCE will implement appropriate disciplinary actions if completion of the blood sample test result evaluation by the MRO confirms the initial test results."

The NRC Resident Inspector will be notified of this event report.

***** UPDATE AT 1130 EST ON 02/26/01 FROM CLAY WILLIAMS TO LEIGH TROCINE *****

The licensee called to provide a time correction. The breathalyzer test results were positive for alcohol at 2109 PST in lieu of 2019 PST.

The licensee plans to notify the NRC resident inspector. The NRC operations officer notified the R4DO (Linda Howell).