ML20214A109
| ML20214A109 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 05/11/1987 |
| From: | Gucwa L GEORGIA POWER CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| GL-87-05, GL-87-5, SL-2429, TAC-66615, TAC-66616, NUDOCS 8705190264 | |
| Download: ML20214A109 (6) | |
Text
Georgia Powtr Company 333 Piedmont Avenue Atlanta, Georgia 30308 i
Telephone 404 5264526.
Mailing Address-Post Office Box 4545 Atlanta, Georgta 30302 Georgia Power L T. Gucwa tr e couttwn Mctrc sys,vm Manager Nuclear Safety SL-2429 and ucensin9 0241U X7GJ17-H210 May 11, 1987 U. S. Nuclear Regulatory Commission ATTN:
Document Control Desk Hashington, D. C. 2055 PLANT HATCH - UNITS 1, 2 NRC 00CKETS 50-321, 50-366 OPERATING LICENSES DPR-57, NPF-5 RESPONSE TO NRC GENERIC LETTER 87-05 REQUEST FOR ADDITIONAL INFORMATION-ASSESSMENT OF LICENSEE MEASURES TO MITIGATE AND/0R LDENTIFY POTENTIAL DEGRADATION OF MARK I DRYHELLS Gentlemen:
By the subject generic letter dated March 12, 1987, response to three specific questions relative to the removal of water that could potentially enter the air gap between the drywell and surrounding concrete or the sand cushion was requested.
The Georgia Power Company response to the three requests for additional information is provided in the Enclosure to this letter.
Sincerely, f & $_=
L. T. Gucwa KHH:jhu Enclosure - Response to Request for Additional Information -
Assessment of Licensee Measures to Mitigate and/or Identify Potential Degradation of Mark I Drywells (Generic Letter 87-05).
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May 11, 1987 Page Two
.c: Georaia Power Company Mr. J. P. O'Reilly Mr. J. T. Beckham, Jr.
GO-NORMS U. S. Nuclear Reaulatory Commission. Washinaton Mr. L. P. Crocker, Licensing Project Manager - Hatch U. S. Nuclear Reaulatory Commission. Reaion II Dr. J. N. Grace, Regional Administrator Mr. P. Holmes-Ray, Senior Resident Inspector - Hatch 0241U 6
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Georgia Power d ENCLOSURE RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION -
ASSESSMENT OF LICENSEE MEASURES TO MITIGATE AND/0R IDENTIFY POTENTIAL DEGRADATION OF MARK I DRYNELLS (GENERIC LETTER 87-051 1.
OUESTION:
Provide a discussion of your current program and any future plans for determining if the drain lines that were provided at your facility for removing any leakage that may result from refueling or from spillage of water into the gap between the drywell and the surrounding concrete or from the sand cushion itself are unplugged and functioning as designed.
RESPONSE
Hatch Units 1 and 2 containments were designed with multiple drain and leak detection systems to assure that water does not enter and remain in the air gap between the drywell and the surrounding concrete or in the sand cushion.
The most credible path for water to enter into the air gap and sand cushion is leakage from the reactor well near the top of the containment which is normally filled with water during refueling operations.
A brief review of Figure 1 will show that four sets of drains consisting of seventeen individual drain lines have been installed to remove any water entering the reactor well or the air gap area below the reactor well.
Five drains have been provided to drain the reactor well following refueling operations (See detail A of Figure 1).
The reactor well is visually checked to assure complete drainage of trapped water.
This visual check assures that the reactor well is dry and eliminates the source of water to the air gap.
Successful drainage of the reactor well following each refueling also verifies satisfactory operation of the drain system.
The drain lines are all of welded construction and embedded in concrete.
A bellows has been installed between the concrete and the reactor well to provide a seal and to accommodate any possible differential movement between the concrete and the drywell shell (See detail A of Figure 1).
In order for water to flow beyond the reactor well, a failure of this bellows or a pipe failure would be required.
In the 0241U E-1 May 11. 1987 SL-2429
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Georgia Power d ENCLOSURE (Continued)
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION -
ASSESSMENT OF LICENSEE MEASURES TO MITIGATE AND/0R IDENTIFY POTENTIAL DEGRADATION OF HARK I DRYHELLS (GENERIC LETTER 87-.051 event of such a failure water could flow to a weir under the bellows.
If the water failed to drain from the weir through a set of four drain lines, it would accumulate in the weir and a level switch would initiate an alarm in the control room indicating the presence of water.
This would be an indication of plugged seal rupture drain lines and corrective action would be initiated.
The seal rupture drain lines are also of welded construction and embedded in concrete.
It is possible that the weir could overflow and water could enter the air gap.
The water would then flow to the top of the sand cushion which is sealed by a ring of 18 gauge sheet metal running between the drywell and into the surrounding concrete (See detail B of Figure 1).
The water would be removed from this area by another set of four drain lines and transferred to the radwaste system through the torus room floor drains.
Such a condition would be alarmed in the control room by the leak detection system and corrective action would be taken.
In the unlikely event that water accumulated on top of the sand cushion and the seal was penetrated, water would finally enter into the sand and would be removed by still another set of drain lines.
The sand cushion drains would also direct the water to the radwaste system and an alarm would be sounded in the control room.
As can be seen, multiple failures would be required before water could enter the sand cushion, and still more failures would be required before water would be allowed to remain in the sand cushion.
Because of the many methods available for prevention and detection of water leakage into the sand cushion, the drain lines are not tested for blockage at Plant Hatch Units 1 and 2, except for the functional check of the reactor well drain lines through their use in draining the reactor well following each refueling.
2.
QUESTION:
Provide a discussion of preventive maintenance and inspection activities that are currently performed or are planned to minimize the possibility of leakage from the refueling cavity past the various seals and gaskets that might be present.
0241U E-2 May 11, 1987 SL-2429
Georgia Power d ENCLOSURE (Continued)
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION -
ASSESSMENT OF LICENSEE MEASURES TO MITIGATE AND/0R IDENTIFY POTENTIAL DEGRADATION OF MARK I DRYHELLS (GENERIC LETTER 87-05)-
RESPONSE
As stated in the response to question number 1 above, Plant Hatch Units 1 and 2 design does not have seals and gaskets in the drainage system in the refueling cavity which could potentially leak.
The drain system is constructed of welded piping.
Failure of the bellows would cause leakage into the weir, and possibly into the air gap.
However, this bellows seal has no gaskets associated with it and a leakage detection system would alarm in the control room before water entered the air gap.
Therefore, no current preventive maintenance or inspections are required or planned.to minimize the possibility of leakage from such equipment.
3.
00ESTION:
Confirm the information listed in Table 1 is correct with regard to your facility.
RESPONSE
The information contained in Table 1 of the generic letter for Plant Hatch Units 1 and 2 is correct as shown.
0241U E-3 May 11, 1987 SL-2429
ENCLOSURE (Continued)
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION -
ASSESSMENT OF LICENSEE MEASURES TO MITIGATE AND/OR IDENTIFY POTENTIAL DEGRADATION OF MARK I DRYWELLS (GENERIC LETTER 87-05) ftPLACCAttf SUtfM 7 k (n". DASIN CAVITY DRAINS (TYR 4 plt,)
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