ML20070S604
| ML20070S604 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 03/28/1991 |
| From: | Withers B WOLF CREEK NUCLEAR OPERATING CORP. |
| To: | Lieberman J NRC OFFICE OF ENFORCEMENT (OE) |
| References | |
| EA-91-003, WM-91-0049, NUDOCS 9104020357 | |
| Download: ML20070S604 (6) | |
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W%F CREEK NUCLEAR OPERATING CORPORATION Bart D. Withers
@gm March 28, 1991 VM 91-0049 J. Lieberman, Director Office of Enforcement U. S. Nuclear Regulatory Commission Washington, D. C. 20555
Subject:
Docket No. 50-482:
Reply to Notice of Violation (EA 91-003)
Dear Mr. Lieberman:
The attachment to this letter provides Wolf Creek Nuclear Operating Corporation's (VCNOC) reply to the Notice of Violation (EA 91-003) concerning inoperable safety injection pumps because of e blocked minimum recirculation line to the refueling water storage tank.
Enclosed is a check (#075964) in the amount of $25,000 made payable to the Treasurer of the United States, i
If you have any questions concerning this matter, please contact me or Mr. H. K. Chernoff of my staff.
Very truly yours,
- y Bart D. Withers President and.
Chief Executive Officer BDW/jra Attachment Enclosure cci A. T. Howell (NRC), w/a R. D. Martin (NRC), w/a D. V. Pickett (NRC), w/a M. E. Skov (NRC), w/a iCh
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Attachment to WM 91-0049 Page 1 of 5 REPLY TO NOTICE OF VIOLATION Violation 9039-01: Failure te Satis #v a Technical Specification Reouirement i
fjndinn Wolf Creek Generati.ng Station Technical Specif;.L'; ion (TS) 3.5.2 requires that two independent emergency core cooling system sECCS) subsystems be operable in Modes 1,
2, and 3 with each subsystem comprised.
In part, of one operable 1
safety injection (SI) pump.
TS 3.0.3 requires that when a Limiting Condition for Operation is not met, that action be initiated within one hour to place the unit in at least hot standby within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, at least hot shutdown within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, and at least cold shutdown within the subsequent 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
Contrary to the above, on December 23, 1990, between at ' east 12:07 a.m. and 12:30 p.m., the reactor was operated in Mode 1 with both EI pumps inoperable.
Both SI pumps were rendered inoperable because they could not have performed their intended function for a limited range of loss of coolant accidents.
This resulted when the common recirculation line between the SI pumps and the refueling water storage tank became blocked with ice after the freeze protection system failed. With both SI pumps inoperable decing this period, the licensee failed to place the unit in at least hot ctandby within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
Admission or Denial of the Alleged Violationt 4
Wolf Creek Nuclear Operating Corporation (WCNOC) acknowledges this violation with regard to
'.e requirements of Technical Specification 3.0.3.
Based on WCNOC's further
- aluation, the event, although a significant operating occurrence, had significant safety impact on the operation of Wolf Creek Generating Ocatica (WCGS).
On December 20 and 21, 1990, the Control Room received freeze protection trouble alarms for the demineralized water storage tank and the condensate storage tank.
The freeze protection panel breakers were verified to be closed per alarm response procedure ALR 00-055F,
' Freeze Protection Trouble".
In addition, Electrical Maintenance personnel were directed to verify the current i
in the affected heat trece circuits to confirm proper operation.
On December 21, 1990, the Control Room received a freeze protection trouble alarm for the refueling water storage tank (RWST).
Control-Room personnel notified Electrical Maintenance personnel of the alarm on the RWST heat trace circuit.
On December 23, 1990 at 0007 CST, an attempt was made to add water to the RWST because of a low level alarm.
The RWST level was substantial.ly above the recNired technical specification minimum level.
The flow path utilized to add water involved the return line to the RWST, which also provides a flow path fe; safety injection (SI) pump recirculation flow. When this attempt to fill the RWST failed, an investigation was started to determine the cause.
It was l
learned that a work request existed to repair an isolation valve (BGV0195).
This valve isolates the Chemical and Volume Control System from the Refueling l
Water Storage System.
The problem description on t.ke work request indicated that the valve stem and diaphragm had separated.
Belleving that this l
l l
I
a Attachment to WM 91-0049 Page 2 of 5 condition would prevent flow through the valve, the faulty isolation valve was identified as the reason that flow could not be established to the RWST.
Because RWST level was still sutvtantially above minimum level, it was decided at that time to wait until dayst.ift to have the problem with BGV0195 further evaluated.
The dayshift crew attempted to fill the RWST using an alternate flow path and also requested that Electrical Maintenance personnel verify operation of the l
heat trace circuits.
Electrical Haintenance personnel determined that the l
heat trace was malfunctioning.
Following an unsuccessful attempt to fill the
- RWST, the dayshift crew recognized that the recirculation line was blocked with ice, rendering the SI pumps inoperable. Accordingly, entry was made into Technical Specification 3.0.3 at 1230 CST.
Reasons for Violation:
The SI pumps were rendered inoperable when the recirculation line became blocked with ice.
This condition developed because a faulty ambient temperature switch in the RWST heat trace circuit prevented proper operation of the circuit.
A review of this event has identified the following factors that hampered early detection of a developing problem and contributed to the delay in discovery of the ice lockage.
1.
Ineffecti e communications between Control Room personnel and Electrical Maintenance personnel prevented the RUST heat tracing from being thoroughly evaluated when its alarm was received. Control Room personnel were unaware that a crew change had occurred within the Electrical Maintenance organization since their previous discussions conc.rning troubleshooting of the freeze protection system.
Consequently, Control Room personnel were not explicit in their request for amperage measurements and the conversation was instead focused on the "reflash" capabilities of the alarm.
Electrical Maintenanct personnel did not adequately communicate among themselves or with Control Room personnel the status of individual heat trace circuits to ensure resolution of the problem.
2.
Administrative controls did not sufficiently recognize the safety significance of flow through the recirculation line and the need to ensure flow capability.
Corrective Steps Which Have Been Taken and Results Achieved:
Both SI pumps were placed in " pull-to-lock" at 1250 CST to prevent an automatic start and subsequent pump damage because of a potential shutoff head condition.
The Shift Supervisor assigned an operator to operate the SI pumps under appropriate operating conditions.
Subsequently, the Shift Supervisor dedicated an operator to perform this function and provided him ith written instructions. Activities were initiated to remove the ice blocking the RWST recirculation line in order to restore the SI pumps to operable status.
A jumper was installed across the ambient temperature switch to provide power to the heat trace. A temporary heat source was used on the
e Attachment to WM 91-0049 Page 3 of 5 blocked section of the pipe in conjunction with the Fuel Pool Cleanup Pumps providing internal pressure to remove the blockage. At 1600 CST, Control Room personnel declared a Notification of Unusual Event and began to reduce power in compliance with Technical Specification 3.0.3.
Subsequently, flow was established to the RWST and following verification of recirculation flow for both SI pumps Technical Specification 3.5.2 was exited.
The RWST was placed in continuous recirculation through its return line to assure minimum SI pump flow capability.
A review was conducted to determine if there were other cimilar pump arrangements in which a heat traced line could freeze and prevent recirculation capabilities of the pump.
No similar situations were found.
During the period of extrem;1y cold weather, Electrical Haintenance personnel verified the current in heat trace circuits every four hours to confirm proper operation.
The faulty ambient temperature switch was removed from service and bench tested satisfactorily.
Although corrosion was initially believed to be a factor in the switch failure, subsequent disassembly of the switch did not reveal corrosion or the root cause of the malfunction.
A new ambient temperature switch was installed at 1340 CST on December 24, 1990, thus restoring the RWST heat trace circuit to normal operation.
The functional requirements of the SI pumps to mitigate the consequences of design basis accidents were reviewed and the Updated Safety Analysis Report licensing bases analyses were evaluated to assess the safety significance of the blocked recirculation lina.
Specifically, the analyses associated with the postulat.ed primary and secondary system pipe ruptures were examined.
As discussed in Licensee Event Report (LER) 90-025-01, this review concluded that when required, the SI pumps would function as intended for all secondary side ruptures and primary side ruptures except for break sizes between 0.375 and 1.75 inches.
For break sizes in this range, a small increase in peak clad temperature would result from the potencial failure of the pumps.
Even with the small increase, peak clad temperature would have remained well below the limits of 10 CFR 50.46.
Based on this evaluation, the event, although a significant operat;ng occurrence, had no significant safety impact on the operation of WCCS.
Corrective Steps Which Will be Teken to Avoid Further Violations:
As discussed in LER 90-025-01, to ensure proper operation of the ambient temperature switches and the low temperature alarm
- switches, the Instrumentation and Controls Recalibration Schedule has been revised to require calibration of these switches in the fall of each year to ensure that the heat trace circuits and alarms activate at the proper temperature.
Alarm response procedures are intended to provide the actions necessary to respond to the most probable failure mode and to stabilize the situation so that further pursuit of the problem can occur as appropriate. Alarm response procedures are not written or intended to be used for troubleshooting activities.
Alarm response procedure ALR 00-055F instructed the operators to verify that the power supply breaker, the heater circuit breakers, and control circuit breaker for the affected Freeze Protection Panel are closed.
These actions are considered appropriate for this alarm, however, verification
Attachment to WM 91-0049 Page,4 of 5 that the desired result is obtained is always required.
In Operations Event Report (OER) 91-01, the Manager Operations discussed the need for all operators to aggressively and thoroughly pursue problems once identified.
This OER was placed in required reading for all licensed and non-licensed operators to ensure thorough dissemination of this guidance.
A review of this event and procedure ALR 00-055F by Operations personnel determined that the actions required by the procedure revealed the deficiency (i.e.,
a defective heat trace circuit).
Efforts to determine the reason for the defective heat trace circuit were in progress and ineffective communications resulted in the failure to identify the faulty ambient temperature switch in a timely manner. A review of other alarm response procedures is not necessary since procedure ALR 00-055F was determined to be adequate as evidenced by the successful verification of freeze protection circuit operation on the demineralized water storage tank and the condensate storage tank.
Procedure STN GP-001, " Plant Winterization",
has been revised to include provisions to put the RWST in continuous recirculation through its return line to assure minimum flow capability of the SI pump recirculation line. Procedure ALR 00-055F has been enhanced by providing additional instructions when a freeze protection trouble alarm is received in the Control Room.
These instructions include provisions to have Electrical Maintenance check heat trace current daily to verify proper operation when a freeze protection trouble alarm is activated.
Also, this procedure instructs the operators to put the RWST in recirculation if temperature control cannot be restored.
LER 90-025-00 was included in Operations Required Reading to ensure that all licensed personnel are cognizant of the details of this event. The need for effective communications was discussed in group meetings for Operations, Maintenance, and Instrumentation and Controls personnel.
These communication needs were also reiterated to plant personnel through a letter from the Director Plant Operations.
The details of this event will be provided as part of licensed requalification training to licensed personnel to reiterate the safety significance for flow through the recirculation line and emphasizing that immediate operator actions are necessary when freeze protection alarms are received.
This training will also reiterate the need for effective communications.
As stated in LER 90-025-01, this training will be completed by March 29, 1991.
This event has been included in the recurring training file for evaluation for inclusion in subsequent requalification training cycles.
Date When Full Compliance Will be Achieved 1 Full compliance will be achieved by March 29, 1991.
Design Review and Enhancements :
As discussed in LER 90-025-01, a review of the design adequacy of the heat trace circuits for the RWST by Nuclear Plant Engineering personnel concluded that the as-built design satisfies the applicable design standards and
Attachment to WM 91->049 Page,5 of 5 s d criteria.
- However, several design enhancements were identified that could.
Improve reliability of the system and plant personnel's ability to monitor the i
circuite for proper operation.
The following design enhancements will be implemented prior to startup from the fifth refueling outage:
1.
The addition of pilot lights at the ends of the heat tracing tape to positively verify that no discontinuities exist on the heat tracing tape.
2.
The addition of an auto-manual switch to allow bypassing the existing ambient temperature thermostat to establish power to the heat tracing tape.
Implementation of these enhancements is expected to improve reliability and maintainability of the RWST heat trace circuits, i
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