ML14184A991
| ML14184A991 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 09/29/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML14184A990 | List: |
| References | |
| REF-GTECI-048, REF-GTECI-049, REF-GTECI-NI, TASK-048, TASK-049, TASK-48, TASK-49, TASK-OR GL-91-11, NUDOCS 9210070078 | |
| Download: ML14184A991 (2) | |
Text
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10 "oUNITED STATES 4'
NUCLEAR REGULATORY COMMISSION C
WASHINGTON, D. C. 20555 ENCLOSURE 1 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE LICENSEE'S RESPONSE TO GENERIC LETTER 91-11 CAROLINA POWER & LIGHT COMPANY H. B. ROBINSON STEAM ELECTRIC PLANT, UNIT NO. 2 DOCKET NO. 50-261
1.0 INTRODUCTION
By letter dated July 19, 1991, pursuant to 10 CFR 50.54(f), the Nuclear Regulatory Commission (NRC) issued Generic Letter (GL) 91-11, Resolution of Generic Issue (GI) 48, "LCOs for Class 1E Vital Instrument Buses," and GI 49, "Interlocks and LCOs for Class 1E tie breakers."
The NRC staff has concluded that concerns raised within GI 48 and GI 49 can be resolved by verifying or implementing appropriate administrative controls that include time limitations and surveillance requirements for vital instrument buses (VIBs), Inverters, other on-site power sources to the VIBs, and tie breakers that connect redundant Class 1E buses at one unit or that can connect Class 1E buses between units at the same site. The Carolina Power & Light Company, by letter dated January 31, 1992, certifies that with three exceptions the H. B.
Robinson Steam Electric Plant, Unit No. 2 (HBR2) is in substantial agreement with the technical and schedular requirements of GL 91-11. The licensee stated that the exceptions deal with revisions to the procedures which were expected to be implemented by June 10, 1992.
The staff has reviewed the licensee's response and provided the following evaluation.
2.0 EVALUATION GI 48 (LCOs for Class 1E Vital Instrument Buses)
At the HBR2, there are eight Class 1E VIBs (IB1 through IB4 and IB6 through IB9) that provide power for instrumentation and controls of the engineered safeguards features systems and the reactor protection systems. Each of the VIBs IB1 through IB4 has a normal and an alternate power supply with its supply breakers mechanically interlocked so only one breaker can be closed for the incoming feed. Buses IB1 and IB2 ultimately receive power from 480 vac emergency bus El and buses IB3 and IB4 from 480 vac emergency bus E2.
Buses IB1 and IB4 receive power via intermediate motor control centers (MCCs) 5 and 6, respectively, and constant voltage transformers. Bus IB2 receives power from MCC-5 via battery charger A (or Al), and from station battery A via 125 vdc MCC-A and inverter A. Bus IB3, similarly receives power via MCC-6 and equivalent B train components. The alternate power supply for VIBs IB1 through IB4 is 120 vac non-safety MCC-8. Buses IB6 through IB9 receive power via VI8 IB1 through IB4, respectively.
9210)070078-920929 PDR ADOCK 05000261 P _
-2 The VIBs are in service continuously and loss of a VIB is discernable in the control room. Abnormal Operating Procedure A0P-024, "Loss of Instrument Bus",
is in place to restore.either normal or alternate power to VIB in the shortest possible time. Further, if power is lost to IB2 or IB3 and not restored within two hours, AOP-024 requires that the plant be in hot shutdown within the following six hours and in cold shutdown within the following thirty hours. The procedure AOP-024 limits the amount of time that IB2 or IB3 can be powered from alternate supply (MCC-8); however, IBI and IB4 were not addressed. The licensee committed to revise AOP-24 to address these buses.
The licensee has indicated that AOP-024 was revised in June 1992, to extend operating limitation to IB1 and IB4 as well.
This limitation consists of allowing only one bus at a time (unless nuclear safety considerations dictate otherwise) to be powered from MCC-8 for no more than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> without commencing plant shutdown, i.e., be in hot shutdown within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in cold shutdown within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. HBR2 also added requirements to perform a weekly check of the output voltage from the inverters. MCC-5 can also be powered from the dedicated shutdown bus during shutdowns, such as whenever the El bus is de-energized for maintenance or testing. Hence, plant operating procedures were revised to verify proper lineup of MCC-5, with independent verification, prior to reactor.start-up.
GI-49 (Interlocks and LCOs for Class 1E tie Breakers)
At HBR2, there are no tie breakers specifically designed to directly interconnect both energized safety trains. There are two sets of tie breakers which allow the B safety injection (SI) pump and 120 vac power panel 26 to be alternately powered from either safety bus.
Both interlocks and procedural controls on the selectivity of the power sources for SI pump B and Power Panel 26 prevent interconnection of energized safety buses.
3.0 CONCLUSION
The staff agrees that HBR2 has in place the appropriate administrative controls, mechanical devices, and plant procedures that satisfy the intent of GL 91-11.
Principal Contributor:
A. Pal Date: 9/29/92