ML17157A263
| ML17157A263 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 07/26/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17157A262 | List: |
| References | |
| NUDOCS 9008060103 | |
| Download: ML17157A263 (3) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY OFFICE OF NUCLEAR REACTOR REGULATION SUS UEHANNA STEAN ELECTRIC STATION UNITS 1 AND 2 DIESEL GENERATORS'NLET AIR MODIFICATION PENNSYLVANIA POWER AND LIGHT COMPANY DOCKET NOS. 50-387/50-388 INTRODUCTION By letter dated June 7, 1990, Pennsylvania Power
& Light Company (PP&L or licensee) requested NRC approval to install a modification at the Susquehanna Steam Electric Station (SSES) to correct the combustion air temperature for each diesel generator.
The valves being installed in the modification are safety related and fully qualified.
- However, two portions of the control equipment are non-qualified (non-'g')
items and are being installed temporarily until the qualified ('g') components become available.
The licensee estimates that by the end of 1990 the 'g'omponents would be installed.
Installation of the valves and the non-'9'omponents creates a
new failure mechanism.
The valves themselves could fail.
The use of commercial grade components increases the probability that the components will fail.
Therefore, the proposed modification involves some unreviewed safety concerns and requires NRC approval prior to installation of the proposed modificati on.
EVALUATION An evaluation of the impact of the new valves failing as well as the failure of the associated commercial grade components indicates that the modification will not impact plant safety.
The modification was designed in light of potential failure modes of the new equipment and the need to preserve the design basis of the plant.
If the controller fails, the most serious effect is closure of the valve, which will reduce the flow of emergency service water (ESW) to the intercooler to a nominal
- amount, causing intake air temperature to rise.
Test data from the engine manufacturer (Cooper-Bessemer) shows that full load can be maintained even with intake air temperatures of 165'F - 175'F.
In the event the intake air temperature continues to rise, the modification is designed with a high-high alarm at 160'F which terminates power to the valve causing it to fail safe (full open. position).
Once this high-high alarm is activated, the valve remains open until a manual reset action is initiated.
The engines are currently configured to -allow full ESW flow through the intercooler whenever ESW is running and have shown distress only after repeated starts.
Since the failed component will be expeditiously replaced, distress of the engines is not likely to occur.
9008060103 900726 PDR ADOCK 05000387
If the controller fails and results in the valve failing in-position the same arguments apply.
This failure mode is probably less severe and the time period over which the intake air temperature will rise is longer.
If the valve fails at a conservative setting the temperature may not rise at all.
The controller module and dual indicator module for this modification are identical to those used in other non-g applications at Susquehanna.
The equipment is highly reliable and risk being introduced is not significant.
- Also, the 'g'omponents are being procured in parallel and will be installed by the end of 1990.
CONCLUSION The worst case
- scenario, associated with the modification to correct the combustion air temperature, is failure of the controller and valves.
Based on a review of the arguments provided by the licensee the staff concludes that the safety function of the diesel generator power system is not compromised.
The installation of the proposed modification is therefore acceptable.
Dated:
July 26, 199Q
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