ML18153B352
| ML18153B352 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 10/21/1993 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 93-674, NUDOCS 9310270261 | |
| Download: ML18153B352 (3) | |
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VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 October 21, 1993 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNIT 1 INOPERABLE BUT TRIPPABLE CONTROL RODS REQUEST FOR ENFORCEMENT DISCRETION Serial No.
NL&P/ETS Docket No.
License No.93-674 R
50-280 DPR-32 On October 21, 1993 during control rod exercising on Unit 1, a fault in the Control Rod Drive System rendered the control rod assemblies in Control Bank D immovable. In this faulted condition the control rod assemblies are immovable on demand by the Rod Control Drive System, but remain aligned, above the insertion limits, and trippable. The faulted condition does not affect the ability of the control rod assemblies to perform their intended safety function when a safety system setting is reached.
However, with immovable control rod assemblies the Unit is required to enter Technical Specification 3.12.C.3 which permits two hours for troubleshooting and repair prior to requiring that the unit be brought to hot shutdown in the next six hours.
The immovable control rod assemblies have been attributed to a power supply in a cabinet of the Control Rod Drive System. However, to effect thorough troubleshooting and repairs, a waiver of the two hour Action Statement in Technical Specification 3.12.C.3 is being requested. The Action Statement was entered at 0944 hours0.0109 days <br />0.262 hours <br />0.00156 weeks <br />3.59192e-4 months <br /> on October 21, 1993.
Consistent with our March 19, 1993 proposed Technical Specification changes, this enforcement disrcetion will permit continued operation for up to seventy-two hours to troubleshoot and repair the Control Rod Drive System with more than one control rod assembly immovable due to an external electrical problem, provided the affected control rod assemblies remain trippable. The seventy-two hours will expire at 0944 on October 24, 1993.
Our March 19, 1993 letter (Serial No.93-402) to the NRC proposed Technical Specification changes for control rod operability. In this submittal we provided the basis for plant operation for up to seventy-two hours with immovable but trippable controls rods below their insertion limit, and indefinite continued plant operation with immovable but trippable control rods that satisfy their insertion limits.
SAFETY IMPACT AND POTENTIAL CONSEQUENCES The operation of the unit with more than one control rod assembly being inoperable does not create any immediate threat to safety when these control rod assemblies are trippable. The control rod assemblies continue to be capable of performing their 9310270261_ 931021~-r~
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intended safety function to promptly shutdown the reactor when a safety system setting "is reached (i.e., reactor trip). Adequate core protection is maintained by maintaining insertion limits, bank overlap and shutdown margin. Power level will be maintained stable during the troubleshooting and repair activities. Additionally, shutting down a unit with immovable control rods is very complicated and could cause power distribution anomalies.
Our March 19, 1993 proposed Technical Specification changes provided the basis for limited plant operation (72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />) with an immovable but trippable controls rods below their insertion limit and indefinite continued operation with immovable but trippable control rods.
SIGNIFICANT HAZARDS CONSIDERATION The proposed enforcement disrcetion of the two hour Action Statement of the Technical Specification requirement in 3.12.C.3 for inoperable but trippable control rod assemblies does not result in a significant hazards consideration as defined in 1 O CFR 50.92.
Specifically, the proposed enforcement disrcetion does not:
Involve a significant increase in the probability or consequences of an accident previously evaluated. Allowing seventy-two hours for the diagnosis and repair associated with electronic or electrical malfunctions of the Control Rod Drive System is acceptable, since the primary safety function of the control rod assemblies (reactor trip) remains unaffected.
During the extended troubleshooting and maintenance period, the requirements for control rod assembly alignment, insertion limits, and shutdown margin are being maintained so that power and peaking distributions used in the safety analysis will remain unaffected. The proposed changes do not affect the ability of the control rod assemblies to perform their intended safety function when a safety system setting is reached. Therefore, the consequences of accidents related to or dependent on control rod assembly operation will remain unaffected.
Create the possibility of a new or different kind of accident from any previously evaluated. There are no new failure modes or mechanisms associated with plant operation during the extended period requested to perform maintenance on the Control Rod Drive System. Extended operation with inoperable but trippable control rod assemblies does not involve any modification in the operational limits or physical design of the involved systems.
There are no new accident precursors generated due to the extended maintenance period.
Involve a significant reduction in the margin of safety. Plant operation with the inoperable but trippable control rod assemblies does not affect the Technical Specification margin of safety. During the extended maintenance period the control rod assemblies maintain the ability to perform their primary safety function. Other Technical Specification limits for reactivity control, such as control rod assembly insertion limits, alignment and shutdown margin will remain in effect to assure that the safety margins are maintained.
ENVIRONMENTAL CONSEQUENCES This enforcement discretion will not change the types of any effluents that may be released offsite, nor create a significant increase in individual or cumulative occupational radiation exposure. The proposed changes do not affect the ability of the control rod assemblies to perform their intended safety function when a safety system setting is reached. Therefore, the consequences of accidents related to or dependent on control rod assembly operation will remain unaffected.
The enforcement discretion was reviewed by the Station Nuclear Safety and Operating Committee. It has been determined that no unreviewed safety question or significant hazards consideration exists.
In a October 21, 1993 telephone call between Mr. M. L. Bowling, of my staff and Mr. E.
W. Merschoff of the NRC, Region II office we requested and received verbal approval for discretionary enforcement to extend the two hour Action Statement of Technical Specification 3.12.C.3 to seventy-two hours to complete thorough troubleshooting and repair of the Control Rod Drive System.
Very truly yours, vZ<I ~~
Dar--
- w. L. Stewart Senior Vice President - Nuclear cc:
Mr. Stewart D. Ebneter Regional Administrator United States Nuclear Regulatory Commission Region II Suite 2900 101 Marietta Street, N. W.
Atlanta, Georgia 30323 Mr. M. W. Branch NRC Senior Resident Inspector Surry Power Station