ML20012G480
| ML20012G480 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 02/24/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20012G479 | List: |
| References | |
| NUDOCS 9303030149 | |
| Download: ML20012G480 (3) | |
Text
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGUtATION RELATED TO DUKE POWER COMPANY MCGUIRE NUCLEAR STATION. UNITS 1 AND 2 DOCKET NOS. 50-369 AND 50-370
1.0 INTRODUCTION
The Duke Power Company (DPC) letters of July 29, 1992 and February 17, 1993, requested NRC approval of a limitation of 20,000 square feet of unqualified coatings inside containment.
In support of that request, DPC provided a technical justification that assumes all the unqualified containment coatings (20,000 square feet) fail following a postulated loss-of-coolant accident.
This technical evaluation assessed the impact of the postulated coatings failure on the performance of the emergency core cooling system during recirculation from the containment sump following a postulated loss-of-coolant.
accident.
McGuire Nuclear Station adopted Regulatory Guide (RG) 1.54 (Quality Assurance Requirements for Protective Coatings Applied to Water-Cooled Nuclear Power Plants) for all civil components with the exception that the provisions of ANSI N45.2-1971 were not applied. Original mechanical and electrical equipment was procured prior to issuance of the RG 1.54 and as a result does not comply with the RG.
In an effort to enhance the McGuire coatings program, DPC performed an inventory of unqualified coatings inside containment and established a maximum allowable limit of 20,000 square feet of unqualified coatings.
The safety evaluation regarding the acceptability of this limit follows.
2.0 EVALUATION In support of the position that the 20,000 square feet of unqualified coatings will not degrade ECCS/ containment sump performance, the licensee makes the following arguments:
(1)
Lighter debris floating in water collected in the lower containment compartments should not reach the sump since this water travels to the sump through spare penetrations located near floor level.
Floating debris should not pass through these penetrations since they are located below surface level.
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Heavier particles that settle to the containment floor should not reach the containment sump due to the low water velocities not being sufficient to transport such particles to the sump screens.
(Estimated velocity of water approaching the sump is approximately
.24 ft/sec versus a required velocity of greater than 2 ft/sec to transport this debris.)
(3)
Following a loss-of-coolant accident, there is approximately 20 minutes (while the RWST empties) until ECCS suction must be switched to the containment sump. During this time period, sump water levels will rise above the coverplate making it more unlikely that floating debris will be drawn into the sump suction.
In addition, Alden Research Laboratory (ARL) sump model tests indicate that air entrainment and vortex formation are unlikely in the containment sump.
Floating debris in the sump should not be drawn into the sump suction.
(4)
There is an insignificant amount of unqualified coatings in the near vicinity of the containment sump.
Therefore, given the difficulty for debris to travel to the sump and the small amount of potential f ailed coatings in the near vicinity of the sump, sump screen blockage should not be significant due to failed unqualified coatings.
The licensee concludes, from the above qualitative arguments, that sump screen blockage resulting from failed coatings should not be significant.
Previous ARL sump model tests indicate that up to 50% sump screen blockge does not degrade ECCS performance.
As a result, the ECCS and containment spray (NS) systems' performance should not be degraded due to failed unqualified coatings.
In addition to the above arguments, the licensee performed a conservative calculation assuming all 20,000 square feet of unqualified coatings fail and are drawn into the sump structure. The licensee assessed the impact of the failed coatings on the performance of the ECCS and NS systems following a postulated large or small break loss-of-coolant accident.
The licensee concludes from this analysis that ECCS performance would not be significantly degraded based on a low debris / water ratio, input from equipment suppliers, and engineering judgement.
The licensee stated that overall amount of debris that is postulated to reach the sump during a design basis event is not significantly increased even if all 20,000 square feet of unqualified coatings i
were to fail.
In addition, the licensee states that the original conclusions l
reached in evaluation of the impact cf debris on the McGuire sump during licensing have not changed.
The NRC staff has reviewed the licensee's arguments and agrees that the new 20,000 square feet limit for unqualified coatings is unlikely to result in either significant sump screen blockage or degraded ECCS and NS performance.
The licensee has committed to maintain accurate records of unqualified coatings inside containment and to thereby ensure that the 20,000 square feet limit is not exceeded.
In addition, during the upcoming Unit I refueling outage, the unqualified coatings being applied (due to inaccessibility of the
=
7 surface areas),are not in the vicinity of high energy lines and are, therefore, not susceptible to the high energy line direct impingement effects.
Therefore, the staff finds the proposed 20,000 square feet limit for unqualified coatings to be acceptable.
Sate:
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