05000413/LER-2007-002
| Catawba Nuclear Station | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4132007002R00 - NRC Website | |
BACKGROUND
These events are being reported under the following criteria:
10 CFR 50.36(c)(2)(i), Limiting Condition for Operation not met; and 10 CFR 50.73(a)(2)(i)(B), any operation or condition which was prohibited by the plant's Technical Specifications.
Catawba Nuclear Station Units 1 and 2 each is a Westinghouse four-loop Pressurized Water Reactor (PWR) [EIIS: RCT].
The divider barrier consists of the operating deck and associated seals, personnel access doors, and equipment hatches that separate the upper and lower containment [EIIS: NH] compartments. Divider barrier integrity is necessary to minimize bypassing of the ice condenser [EIIS: BC] by the hot steam and air mixture released into the lower compartment during a Design Basis Accident (DBA). This ensures that most of the gases pass through the ice bed, which condenses the steam and limits pressure and temperature during the accident transient.
Limiting the pressure and temperature reduces the release of fission product radioactivity from containment to the environment in the event of a DBA.
The emergency personnel hatch, also known as the submarine hatch, is used as an emergency egress for personnel between the lower and upper containment compartments. The submarine hatch functions as part of the divider barrier.
The submarine hatch is operated by a handwheel that activates four latching arms. When the handwheel is aligned with the latching arms disengaged, the hatch cover may be forced open during a DBA due to the pressure increase in lower containment. The submarine hatch is therefore considered inoperable when it is unlatched. A protective cage is installed over the handwheel to prevent personnel from inadvertently bumping it when walking nearby. A wire seal is installed on the handwheel for configuration control. The wire seal consists of a twisted pair of copper wires threaded through one hole drilled into a lug welded to the hatch cover, and through another hole drilled into one of the handwheel spokes. The wire is secured by crimping into a lead disc. This wire seal design is easily broken in order to allow personnel egress in an emergency.
� The wire seal is not required by Technical Specifications.
Technical Specification 3.6.14 governs divider barrier integrity, including the submarine hatch. Limiting Condition for Operation 3.6.14 requires divider barrier integrity to be maintained in Modes 1, 2, 3, and 4. Condition A states that with one or more personnel access doors or equipment hatches other than the pressurizer enclosure hatch open or inoperable, other than for personnel transit entry, the personnel access doors and equipment hatches must be restored to operable status and closed positions within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. If this is not accomplished, Condition D requires the unit to be in Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. Surveillance Requirement 3.6.14.2 requires a verification, by visual inspection, that the seals and sealing surfaces of each personnel access door and equipment hatch have no detrimental misalignments; no cracks or defects in the sealing surfaces; and no apparent deterioration of the seal material. This surveillance is required to be performed prior to final closure after each opening and every 10 years for seals made of resilient materials. Surveillance Requirement 3.6.14.3 requires a verification, by visual inspection, that each personnel access door or equipment hatch that has been opened for personnel transit entry is closed. This surveillance is required to be performed after each opening.
On June 9, 2007, Unit 2 was in Mode 1 at 73% power at the time of discovery of this event. On June 10, 2007, Unit 1 was in Mode 1 at 100% power at the time of discovery of this event. During this event, no structures, systems, or components were out of service that had any effect on divider barrier integrity.
EVENT DESCRIPTION
(Certain event times are approximate.) Date/Time �Event Description June 9, 2007/2155�Two non-licensed operators (NLOs) were making rounds inside the Unit 2 containment. While observing the submarine hatch from upper containment, one of the NLOs noted that the wire seal appeared to be intact. The holes in the lug and in the handwheel spoke were noted to be out of alignment. The NLO checked the wire seal again from the other side and noted that the wire was broken. He then attempted to lift the hatch cover and the hatch opened.
Technical Specification 3.6.14 Condition A was entered. Maintenance personnel were immediately requested to re-seal the hatch as required by Surveillance Requirement 3.6.14.2 and to install a new wire seal.
June 9,2007/2250 The Unit 2 submarine hatch was secured.
Technical Specification 3.6.14 Condition A was exited.
containment.� While observing the submarine hatch from upper containment, one of the NLOs noted that the holes in the lug and in the handwheel spoke were also out of alignment.
The wire seal was observed to be intact all the way around; however, it was observed to be loose.
� The NLO pulled up on the hatch cover and the hatch opened.
�Technical Specification 3.6.14 Condition A was entered.
June 10, 2007/0130 The Unit 1 submarine hatch was secured.
Technical Specification 3.6.14 Condition A was exited.�it was subsequently However,� determined that Technical Specification 3.6.14 Condition A was prematurely exited before Maintenance personnel re-sealed the hatch as required by Surveillance Requirement 3.6.14.2 and installed a new wire seal.
June 10, 2007/ hatch as required by Surveillance Requirement was now in full compliance with Technical Specification 3.6.14.
June 10-15, 2007� Catawba site management evaluated these events from a sabotage perspective. Conference calls were held with NRC management on June 10 and on June 13 to provide information. On June 15, site management determined that heightened security was no longer required.
CAUSAL FACTORS
The root cause of the submarine hatches becoming unsecured was determined to be a deficient design. The specific events and dates/times associated with the hatches becoming unsecured could not be established. The Unit 1 hatch was last opened and re-sealed on December 25, 2006. The Unit 2 hatch was last opened and re- sealed on March 24, 2003. It was determined that general design deficiencies make these hatches susceptible to inadvertent opening.
When the hatches are fully secured, there is 5/8 inch to 3/4 inch of engagement of the hatch latching arms with the underside of the opening. This results in a condition where only 30 degrees of handwheel rotation is required in order to move the latching arms from maximum to zero engagement. Also, the hatches are difficult to close and there are no travel stops present to indicate when the hatch latching arms are fully engaged. These deficiencies result in the hatches being susceptible to inadvertent opening by personnel coming into contact with the handwheels. They also introduce uncertainties in the determination of whether the hatches are actually fully secured.
CORRECTIVE ACTIONS
Immediate:
1. The NLOs secured the submarine hatch on each unit.
Subsequent:
1 Maintenance personnel re-sealed the submarine hatch on each unit as required by Surveillance Requirement 3.6.14.2 and installed a new wire seal.
2.NLO rounds were revised to require a physical pull on the submarine hatch in addition to a visual verification of the wire seal in order to verify that the hatch is closed and secured.
Planned:
1. At the next available outage opportunity of sufficient duration, the Unit 1 and Unit 2 submarine hatches will be re-configured or re-designed to ensure a more reliable means of hatch closure.
There are no NRC commitments contained in this LER.
SAFETY ANALYSIS
Divider barrier integrity ensures the functioning of the ice condenser to the limiting containment pressure and temperature that could be experienced following a DBA.
T The limiting DBAs considered relative to containment temperature and pressure are the loss of coolant accident (LOCA) and the steam line break (SLB).
T The LOCA and the SLB are analyzed using computer codes designed to predict the resultant containment pressure and temperature transients.
TDBAs are assumed not to occur simultaneously or consecutively.
The primary safety concern with having the submarine hatch open during plant operations is the additional open area presented for steam bypass flow.
Should a LOCA or a SLB occur, some volume of steam which would normally pass through the ice condenser would proceed through the submarine hatch area and increase pressure in upper containment.
Calculations exist to demonstrate that the increased peak containment pressure would still remain well below the containment design pressure and that the divider barrier would still perform its intended safety function.
T Therefore, there would be no effect on either core damage frequency or large early release frequency.
TDivider barrier bypass leakage has no effect on other DBAs.
The health and safety of the public were not adversely affected by these events.
ADDITIONAL INFORMATION
Within the previous three years, there were no LER events of a similar nature. Therefore, these events are considered to be non-recurring.
Energy Industry Identification System (EIIS) Tcodes are identified in the text as These events are not considered reportable to [EIIS: XX].
the Equipment Performance and Information Exchange (EPIX) program.
These events are not considered to constitute Safety System Functional Failures. There were no releases of radioactive materials, radiation overexposures, or personnel injuries associated with the events described in this LER.