ML20024H210
| ML20024H210 | |
| Person / Time | |
|---|---|
| Site: | Mcguire, Catawba, McGuire  |
| Issue date: | 05/24/1991 |
| From: | Tucker H DUKE POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9105300196 | |
| Download: ML20024H210 (4) | |
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" t ', l DUKE POWER May 24, 1991 U. S. Nuclear Regulatory Commissicii ATTN:
Document Control ncsk washington, D.C.
20d55 Gubject:
Catawba Nuclear Station, Units 1 and 2 McGuire Nuclear Station, Units 1 and 2 Docket Nos. 50-413, 414 and 50-369, 50-370 NRC Inspection Report No. 50-413, 414/91-07 and 50-369, 370/91-06 Violations 50-413, 414/91-07-02 and 50-369, 370/91-06-06 Reply to a Notice of Vio]ation Gentlemen:
Enclosed is the response tc the Notice of Violation issued April 26, 1991 concerning Catawba and McGuire Nuclear Station Control Room Area Ventilation Systems.
Very truly yours,
[
Hal B. Tucker' WRC/lcs Attachment xc: W/ Attachment Mr. S. D. Ebneter Regional Administrator, Region II U. S. Nuclear Regulatory Commission 101 Marietta St., NW., Suite 2900 Atlanta, Georgia 30323 Mr. W. T. Orders NRC Resident Inspector Catawba Nuclear Station Mr. R. E. Martin Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission OWFN, Mail Stop 9113 Washington, D.C.
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4 DUKE POWER COMPANY REPLY TO A NOTICE OF VIOLATION Technical Specification 3,7,6 requires that two independent Control Room Area Ventilation Systems be OPERABLE in all modes. System operability includes (TS 4.7.6.e.3) the capability to maintain the control room at a positive pressure of greater than or equal to 1/8 inch water gauge during normal operation and accident conditions.
10 CFR 50 Appendix B, Criterion Ill, Design Control, requires in part that measures be established to assure that applicab!c regulatory requirements and the design basis as specified in the license application for structures, systems, and components are correctly translated into specifications, drawings, procedures, and instructions. Further, design control measures shall provide for verifying the adequacy of design, such as by the performance of design reviews, the use of alternate or simplified calculational methods, or the performance of a suitable testing
- program, Contrary to the above, design control measures were inadequate, in that, the original design of the control room ventilation system was such that the system could not meet its function of maintaining at least 1/8 inch water gauge positive pressure in the ccntrol room under all assumed accident conditions.
FESPONSE
- 1. Erasons for Violation Evaluation of control room doses following a postulated Design Basis Accident did not consider that failure of non-safety chlorine / radiation monitors (McGuire) or smokr/ radiation monitors (Catawba) would isolate the control room pressurization intakes. Although operator actions to restore the intakes were available, this action could not be accomplished within the time constraints imposed by an instantaneous release of the design basis source term.
Initial design of the McGuire and Catawba control room ventilation systems (VC) considered isolation of air intakes to be desirable in order to prevent intrusion of chloiine or radioactive contamination into the control room.
Since non-safety radiation monitors (McGuire and Catawba) and non-safety chlorine detectors (McGuire only) were the state-of-the-art equipment at the time, a failure mode had to be cnosen in which a non-safety monitor was assumed to fail.
It was considered preferable to isolate the air intakes in this case to prevent unmonitored air from being drawn into the control room, The intakes could later be reopened at the discretion of the operators.
The dose calculations considered a delay in control room pressurization due to a loss of offsite power concurrent with the Design Basis Accident and a subsequent diesel start, However, no
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s abditional delay was considered due to a postulated failure of the non safety monitors and the required operator action.
- 2. Currective Action 111thetumLRc5tthdddered McGuire The automatie isolation functions have been deleted from the control room air intakes.
Operating annunciator resixmse procedures have been revised so that control room operators will itolate an air intake if a radiation or chlorine alarm is recciwd. If chlorine alarms are present on both intakes, then both will be isolated as appropriatey, if radiation alarms are present on both intakes, then the least contaminated intake will be selected to remain open so that pressorization of tbc control room with filtered air is assured for radiological events.
The control room dose calculations have also been revised to assume that one intake is isolated for the first four hours of a Design 11 asis Accident in the event that a radiation monitor is inoperable. In the case of an inoperable radiation monitor the Technical Specifications require that the affected control room intake be isolated. The operatiag procedures require the operator to determine which intake should be open in the event of an accident where one intake is already isolated due to an inoperable monitor and the other monitor alarms. If a determination can not be made, then both intakes will be opened. These actions ensure that control room doses will remain below the GDC 19 limits.
The McGuire VC system is now in compliance with the single failure requirements and operator doses are calculated to be less than the limits of GDC 19 for the Design liasis Accident.
Catawba A Technical Specification change was submitted and approved deleting the requirement to automatically isolate the control room ventilation intakes upon radiation or smoke alarms.
Operator action will bc relied upon to take the appropriate actior.s, if necessary.
l Automatic isolation was preserved for the safety-related chlorine detectors since a single failure of one safety-related detector will still maintain one intake available for pressurization.
Emergency procedures have been revised to require surveillance every 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> to confirm that an intake has not been isolated due to a chlorine detector failure. Operator action to initiate the surveillance is specified after the diagnosis of a high energy line break inside containment.
Termination of the surveillance is a Technical Support Center function based on plant conditions and recovery options. The dose calculations have been revised to acknowledge that one intake can be isolated for up to 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> due to a chlorine detector failure (8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> for detection and 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> for repair).
The Catawba VC system is now in compliance with the single failure requirements and operator doses are calculated to be less than the limits of GDC 19 for the Design liasis Accident.
3*, Corrective Actions to be Taken to Avoid further Violations No further corrective actions will be taken.
- 4. Date of Full Compliance McGuire and Catawba are both currently in full compliance.
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