05000482/LER-2005-003
| Wolf Creek Generating Station | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4822005003R00 - NRC Website | |
PLANT CONDITIONS PRIOR TO EVENT
MODE — 6 Power — 0 Refueling operations in progress
EVENT DESCRIPTION:
Auxiliary Access Hatch Pathway During refueling outage 14, as allowed by Technial Specification (T/S) 3.9.4, a temporary closure device was in place on the auxiliary access hatch. On April 30, 2005 at 1530, an operator heard air blowing from containment through the exterior equalizing valve while walking by the auxiliary access hatch. An air flow path from containment through the auxiliary access hatch equalizing valve to the outside atmosphere was confirmed to exist and fuel movement was suspended. Administrative controls were placed on the equalizing valve and fuel movement was restarted.
In July of 1994, Amendment Number 74 to the Wolf Creek Generating Station (WCGS) T/S was issued by the NRC to allow the use of a temporary closure device on the auxiliary access hatch. The closure device is a steel plate that is bolted into the door opening. This plate has engineered, sealable penetrations to allow for cables to run through, and hose fittings on each side of the plate to allow for hose connections to be made.
Prior to installing the closure device, the doors of the auxiliary access hatch are opened. During the opening sequence of the doors, an equalizing valve opens to minimize the differential pressure across the doors. The evaluations and procedure reviews conducted for the closure device did not recognize that the equalizing valve remained open.
Steam Generator Pathway On April 27, 2005 at 1247, prior to commencing fuel movement to enter Mode 6, procedure STS GP-006, Containment Closure Verification, was performed.
To ensure that procedure STS GP-006 remains current the Containment Closure Trackers continually check clearance orders, check work being performed by all work groups, and check the various procedures to avoid having conflicts that would allow direct air-to-air pathways without appropriate controls in place.
On April 28, 2005 at 2346 hours0.0272 days <br />0.652 hours <br />0.00388 weeks <br />8.92653e-4 months <br /> clearance order (CO) R14 AB-B-0001D was placed by a Nuclear Station Operator.
The clearance order tagged valve ABV0070 open and valve ABV0071 open/uncapped. These valves are in series on the 'B' Main Steam line drain. The clearance order identified that the tag for valve ABV0070 affected containment closure.
On April 29, 2005 at 0037 hrs, Wolf Creek entered Mode 6 from defueled.
On April 30, 2005 at 1259 hours0.0146 days <br />0.35 hours <br />0.00208 weeks <br />4.790495e-4 months <br /> during a review of clearance orders, the Day Shift Containment Tracker notified the Control Room that penetration # 3, which contains valve ABV0070, had an air-to-air pathway. The 'B' Steam Generator manways had previously been removed which created a pathway to the containment atmosphere. Upon finding the penetration unisolated, immediate corrective action was put in place to have this penetration placed under administrative controls per STS GP-006.
BASIS FOR REPORTABILITY:
The air-to-air pathways via the equalizing vakie of the auxiliary access hatch and the open steam generator to the auxiliary building without administrative controls is contrary to T/S 3.9.4 which states, in part, 'An emergency personnel escape air lock temporary closure device is an acceptable replacement for an emergency air lock door' and 'Penetration flow path(s) providing direct access from the containment atmosphere to the outside atmosphere may be unisolated under administrative controls.' The events are reportable pursuant to 10 CFR 50.73(a)(2)(i)(B) for any operation or condition which was prohibited by the plant's T/S.
ROOT CAUSE:
Auxiliary Access Hatch Pathway The Safety Evaluation and No Significant Hazards Consideration Determination for T/S Amendment 74 failed to adequately assess the configuration change when using the closure device. The narrow focus of the evaluation also failed to identify the functionality of the door in relation to the equalizing valve. Multiple opportunities existed to identify the air-to-air flow path during the T/S Amendment, the procedure changes, and the Engineering Disposition.
However, the rigor of the various reviews and evaluations was not sufficient to identify the air-to-air flowpath through the equalizing valve.
Steam Generator Pathway The Shift Engineer, the Nuclear Station Operator, and the Containment Closure Tracker failed to close the communication loop with one another on the hanging of CO R14 AB-B-0001D and the documentation of the administrative controls in procedure STS GP-006. Not having the Containment Trackers as an integral part of the Work Controls Center during the Refueling Outages contributed to the miscommunication that occured.
CORRECTIVE ACTIONS:
Auxiliary Access Hatch Pathway Steps will be added to procedure CKL PE-352 to install and remove a blind flange to the exterior auxiliary access hatch equalizing valve. The exterior auxiliary access hatch equalizing valve will be added to procedure STS GP-006 as a containment penetration.
These changes will be completed by August 16, 2005.
Steam Generator Pathway STS GP-006 will be revised to have operations provide a dedicated computer and work station for the Containment Closure Trackers that will integrate the individuals performing this task into the Work Control Center during Refueling outages. This change will be completed by September 13, 2005.
Lessons learned from this event have been incorporated into Operating Experience for Licensed Operator Requalification training.
SAFETY SIGNIFICANCE:
During movement of irradiated fuel assemblies within Containment, the most severe radiological consequences result from a fuel handling accident. The fuel handling accident is a postulated event that involves damage to irradiated fuel. Fuel handling accidents include dropping a single irradiated fuel assembly and handling tool or a heavy object onto other irradiated fuel assemblies. In Mode 6, the potential for Containment pressurization as a result of a fuel handling accident is minimal.
Therefore, it is highly unlikely that there will be any significant release of radioactive material through the leakage path as described above. If a release were to take place through this path, the quantity of radioactive materials released to the outside environment would be insignificant. Even though the rate of leakage can not be determined, based on engineering judgment, the consequences of this release will be bounded by the fuel handling accident analysis performed for Amendment 95 to the WCGS T/S. The analysis assumes that the gaseous effluents escaping from the damaged fuel rods are released directly to the environment within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> through the open personnel airlock doors. The effluents do not mix with the surrounding air of the adjacent Auxiliary Building, and no credit is taken for any iodine removal by the atmosphere filtration system filters. The analysis results demonstrate that the potential dose consequences from a fuel handling accident with the personnel airlock doors remaining open will be well within the 10 CFR 100 limits.
OPERATING EXPERIENCE/PREVIOUS EVENTS:
flow path had been created between the Containment Building atmosphere and the Auxiliary Building during fuel movement. This event was caused by a series of personnel errors in the implementation of the work control process.
generators while core reload was underway. A dedicated non-licensed individual with the sole responsibility to close the valve upon direction from the Control Room was sufficient administrative controls. However, this was thought to be contrary to the T/S. LER 1996-005-00 was later retracted due to an evaluation that determined that a loop seal was adequate and Containment closure maintained.
flange installed on the Steam Generator "D" Main Steam Safety Valve. The corrective actions for this LER were directed toward instructions for installing blind flanges and would not have prevented this event.