ML19351A281
| ML19351A281 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 10/10/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19351A279 | List: |
| References | |
| NUDOCS 8910190204 | |
| Download: ML19351A281 (2) | |
Text
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NUCLEAR REGULATORY COMMISSION r.
w^sHINoToN. o. c. rosss y *,.. +,f SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION TELATEDTOFACILITYOPERATINGLICENSENO.DPR-73 GPU NUCLEAR CORPORATION THREE MILE ISLAND NUCLEAR STATION, UNIT NO. 2 DOCKET NO. 50-320
. INTRODUCTION I
On July 26,1989, the 480 volt AC bus 2-46 transformer failed. The bus was re-energized by cross tieing it to bus 2-36. GPUNuclearCorporation(licensee) 1
- was unable to restore bus 2-46 transformer within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> which placed the plant in an action statement of Technical Specification (TS) 3.8.2.1.1 and Recovery Operations Plan section 4.8.2.1.1.
Thefailurewascausedbydegraded insulation on the primary side windings of the transformer. The licensee s maintenance organization estimated that it would take them 12 to 16 weeks to refurbish the transformer and up to a year to acquire a new transformer and install-the replacement. The licensee's engineering staff evaluated the safety significance of cross tieing bus pairs 2-35/2-45 and 2-36/2-46 for the remainder of the TMI-2 defueling. The licensee's safety evaluation found the proposal i
acceptable.
EVALUATION The NRC staff reviewed the loads of the unit substation (USS) busses, the L
current status of the plant, and the nuclear safety related (NSR) and important to safety (ITS) functions performed by loads supplied by these busses. The i
staff and licensee also reviewed the ability of a single transformer to carry the loads imposed by the two cross tied busses.
The THI-2 reactor is in the final stages of defueling and cleanup following the i
March 28, 1979 accident. Decay heat is less than one kilowatt. Many safety l
systems (i.e., decay heat removal and core flood tanks) are no longer required for plant safety and have been removed from the Technical Specifications and i
I the Recovery Operations Plan. Due to a combination of reduced loads due to i
cleanup operations and conservative design of the original system there remains j
i significant excess capacity of the transformers. The maximum load with both
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L bus pairs cross tied is less than 30% of capacity for either transformer.
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2-The Nuclear Safety Related/Important to Safety (NSR/ITS) loads supported by the f
subject busses include fuel handling building and auxiliary building ventilation exhaust systems, one train of reactor building purge exhaust, and reactor building power receptacles.
Even with both pairs of busses cross tied, independence of power supply to the above NSR/ITS loads would be maintained. The 2-36/2-46 couple would power one pair of auxiliary building exhaust fans and the 2-35/2-45 couple would power the other redundant pair of auxiliary building exhaust fans.
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CONCLUSION The transformers have more than twice the capacity to carry the loads imposed by cross tieing bus pairs 2-35/2-45 and 2-36/2-46. The cross tieing of the bus pairs will not result in a loss of redundancy. Based on the above evaluation, the proposed change is acceptable.
It does not reduce safety margins or result in increased effluents to the environment. The impact of the proposed change falls within the s: ope of acti' ities previously considered in the March 1981 Programmatic Environmental Impact Statement as supplemented.
DATED: October 10, 1989 i
Principal Contributor: Lee H. Thonus l
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