NRC Generic Letter 1987-05
| ML031140335 | |
| Person / Time | |
|---|---|
| Issue date: | 03/12/1987 |
| From: | Bernero R Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| GL-87-005, NUDOCS 8703120429 | |
| Download: ML031140335 (10) | |
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UNITED STATES
NUCLEAR REGULATORY COMMISSION
WASHINGTON, D.C. 20555 mAu 12 1987 TO ALL LICENSEES OF OPERATING REACTORS, APPLICANTS FOR OPERATING LICENSES, AND
HOLDERS OF CONSTRUCTION PERMITS FOR BOILING WATER REACTORS (BWRs) WITH MARK I
CONTAINMENTS
SUBJECT: REQUEST FOR ADDITIONAL INFORMATION-ASSESSMENT OF LICENSEE MEASURES
TO MITIGATE AND/OR IDENTIFY POTENTIAL DEGRADATION OF MARK I DRYWELLS
(GENERIC LETTER 87-05)
Gentlemen:
INTRODUCTION
In 1980 at the Oyster Creek Nuclear Generating Station GPU Nuclear Corporation (GPU) observed water coming fromwthe drains that are connected to the sand cushion located between the drywell wall and the surrounding concrete.. The licensee continued their investigations to locate and correct the source of.
leakage during the 1983 refueling outage. In the spring of 1986 during the
1986 refueling outage the licensee again noticed water coming from the drains.-
At that,time they decided to perform ultrasonic thickness measurements of the.
drywell shell plates adjacent to the sand cushion to determine if corrosion had occurred. On November 20, 1986, the licensee informed the NRC. of their initial ultrasonic examination findings. The staff issued Information Notice No. 86-99 on December 8, 1986-providing details on the source of eaIage, actions taken by the licensee to eliminate the leakage and preliminary information on the extent of corrosion that had occurred on the drywell shell In the.sand cushion location. From the results of further non-destructive examinations of the drywell shell, metallurgical analyses of samples removed from the drywell shell and chemical analyses of the sand and water obtained from the sand cushion region, the wall thinning appears to have resulted from general wastage of the carbon steel plates from corrosion caused by water containing aggressive anions. From the UT results it appears that general wastage of the shell', to a varying extent, has occurred in two localized regions of the drywell shell plates adjacent to the sand cushion. One localized region extends'about 35 feet circumferentially, the other region extends about 21 feet ci'rcumfer- entially. The drywell shell in these regions was reduced from a thickness of
1.115 inches to an average of about 0.850 inches with some local spots being reduced to about 0.750 inches. The staff issued a Safety Evaluation on this subject by letter to GPU dated December 29, 1986. The staff, through contacts with the BWR Owner's Group and various licensees has completed a survey to obtain additional information on the sand cushion details, the gap materials and the inspections performed at various facilities. A summary of the results are presented in Table 1.
Purpose
The purpose of this Generic Letter is to obtain information from BWR Owners regarding their intended actions to determine if drywells at their facilities have degraded by the corrosion mechanism described above and if the licensees have current and/or future plans to minimize the potential for this problem at their facility. The information provided will be utilized by the staff to determine, pursuant to 10CFR50.55a(g)(6)(ii),-if an augmented inservice inspection program is required for the Mark IXdrywell shell to assure its continued structural reliability.
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2- Discussion From the information obtained from the review of the Oyster Creek event, it appears one source of leakage that resulted in wetting the sand cushion was related to the deterioration of a drain line gasket at the drywell to cavity seal (see figure 1). There also is some question as to whether or not the drain line which serves to remove any leakage past the drywell to cavity seal was functioning properly.
Upon reviewing the details of the sand cushion design at the various Mark I
facilities, there appears to be a design feature that varies, dependent on the architect-engineer, that may be significant. In some designs, Figure 2, the sand cushion is covered with a galvanized steel plate which is sealed to the drywell shell and the surrounding concrete.- Further, drains are provided to remove-water which might collect on the plate from above. In other designs, Figure.3, the sand cushion is open to the gap between the drywell shell and the surrounding concrete and the only path for water to drain from the sand cushion is through the small drain lines at the bottom of the sand cushion. It appears from the Oyster Creek experience that, with the high permeability of the sand cushion and the small bottom drains, the likelihood of adequately drying the sand cushion is low if copious amounts of water have entered the sand cushion.
The staff has sufficient concern to initiate the collection of information pf the licensee's current or proposed action to assure the degradation of the drywell shell plates adjacent to the sand cushion has not occurred and to determine if augmented inspections above and beyond those planned by the licensee's are necessary.
Information Requested Pursuant to the provisions of 1OCFR50.54(f), licensees are requested to provide the following information under oath or affirmation to the Office of Nuclear Reactor Regulation:
All Mark I Owners
1) 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.
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2) 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.
3) Confirm the information listed in Table 1 Is correct with. regard to your facility.
Mark I Owners Whose Desions Are Such That The Sand Cushion I6-OpemnTo.Gap Between The Drywell Shell And Surrounding Concrete f.-5 Provide any plans for performing ultrasonic thickness measurements of the drywell shell plates adjacent to the sand cushion or nyi other proposed actions to ascertain if plate degradation has occurred. Since the degradation that has occurred at Qysterjlpek -
is localized, sufficient details should be included to show that0the ..
,-
sampling basis for ultrasonic thickness measurements is adequate-in terms of size and test location.
Licensees and applicants are requested to respond to this generic letter * -
within 60 days of the date of this letter. Our review of your submittal of information is not subject to fees under the provision of 1OCFR170. -
This request for information was approved by the Office of Management nd*.7 Budget under clearance number 3150-0011 which expires September 30, 1989 Comments on burden and duplication may be directed to the Office of Management and Budget, Reports Management Room 3208, New.Executive Office Building Washington, D.C. 20503.
Sincerely, I . ,I
Robert M. Bernero, Director Division of BWR Licensing Office of Nuclear Reactor Regulation I X Enclosure:
As stated er&YPIZ_ 4 J f .C4'4-'
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- 4- STATUS 01/06/87 TABLE 1 RE-IJET~rf MARK I CONTAINMENRT SURVEY
SAND WALL METHOD/ WAS
GAP THICK RESULTS THE
DETAIL UT SENT GAP
PLANT NAME DRW. PER- TO GAP MATERIAL
(AWE) AVAIL. FORMED NRC MATERIAL REMOVED COMMENTS
Oyster Creek yes yes yes Firebar D & no Gap not sealed (Burns & Roe) Fiberglass Cooper - yes yes yes Urethane no Gap not sealed, (Burns & Roe) Foam UT not meaningful Duane Arnold yes no no Polyurethane yes Gap sealed (Bechtel) - Foam and drains I
Hatch 1 yes no no Ethafoam yes Gap sealed & drains Hatch 2 yes no no Ethafoam yes Gap sealed & drains (Bechtel)
Peach Bottom 2 no no no Polyethylene no Gap sealed & drains (Bechtel). Strips Peach Bottom 3 no no no Polyethylene no Gap sealed & drains (Bechtel) Strips Pilgrim yes yes no Etha Foam yes Gap sealed & drains (Bechtel)
Browns Ferry 1 yes no no Polyurethane no Gap not sealed Browns Ferry 2 yes no no Polyurethane no Gap not sealed Browns Ferry 3 yes no no Polyurethane no Gap not sealed (TVA)
Hope Creek na no no Fiberglass no (Bechtel)
Millstone 1 yes yes no yes No thinning noted (Ebasco) Gap not sealed Monticello yes yes yes Polyethylene yes Gap sealed & drains (Bechtel) Strips Quad Cities 1 yes no no Polyurethane foam no Gap not sealed Quad Cities 2 yes yes yes Polyurethane foam no UT not meaningful (S&L) Gap not sealed Dresden 2 yes* yes yes Polyurethane no UT not meaningful Dresden 3 yes* yes yes Foam (burned up) Gap not sealed (S&L)
Nine Hile Pt 1 yes no no Fiberglass Form Gap sealed & drains (Utility)
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Fitzpatrick yes no no Etha Foam yes Caps sealed, drains n (S&W) shown Vermont Yankee yes* no no Styrofoam no Probably not sealed (EBasco)
Brunswick 1 na na na na na Concrete reinforced Brunswick 2 containment (UERC)
Fermi 2 yes no Foam no Gap not sealed (S&L)
- Not detailed enough NA - Not Applicatle
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Figure 3
I- /, 3iv LISTYOF RECENTLY ISSUED GENERI&L<ETTERS I
- ,. . i, Generic Date of Letter No. SubJec.t Issuance II 3suad To GL 87-04 TEMPORARY EXEMPTION FROM 03/06/87 ALL POWER
PROVISIONS OF THE FBI CRIMINAL REACTOR
HISTORY RULE FOR TEMPORARY LICENCES
WORKERS
GL 87-03 VERIFICATION OF SEISMIC 02/26/87 ALL LICENSEES
ADEQUACY OF MECHANICAL AND NOT SUBJECT TO
ELECTRICAL EQUIPTMENT IN USI A-46 OPERATING REACTORS, USI A-46 REQUIREMENTS
GL B7-02 VERIFICATION OF SEISMIC 02/19/87 ALL HOLDERS OF
ADEQUACY OF MECHANICAL AND OPERATING
ELECTRICAL EQUIPMENT IN LICENSES NOT
OPERATING REACTORS CUSI A-46) REVIEWED TO
CURRENT
LICENSING
CRITERIA ON
SEISMIC
QUALIFICATION
OF EQUIPMENT
GL 87-01 PUBLIC AVAILABILITY OF THE NRC 01/08/87 ALL POWER
OPERATOR LICENSING EXAMINATION REACTOR
QUESTION BANK LICENSEES AND
APPLICANTS FOR
AN OPERATING
LICENSE
GL 86-17 AVAILABILITY OF NUREG-1169, 10/17/B6 ALL LICENSEES
"TECHNICAL FINDINGS RELATED TO OF BOILING
GENERIC ISSUE C-8 WATER REACTORS
BWR MSIC LEAKAGE AND LEAKAGE
CONTROL SYSTEM
GL B6-16 WESTINGHOUSE ECCS EVALUATION 10/22/B6 ALL
MODELS PRESSURIZED
WATER REACTOR
APPLICANTS AND
LICENSEES
GL 86-15 INFORMATION RELATING TO 09/22/B6 ALL LICENSEES
COMPLIANCE WITH 10 CFR 50.49, AND HOLDERS OF
"ED OF ELECTRICAL EQUIPMENT AN APPLICATION
IMPORTANT TO SAFETY" FOR AN
OPERATING
LICENSE
GL 86-14 OPERATOR LICENSING 06/20/86 ALL POWER
EXAMINATIONS REACTOR
LICENSEES AND
APPLICANTS
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2) 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.
3) Confirm the information listed in Table 1 is correct with regard to your facility.
Mark I Owners Whose Designs Are Such That The Sand Cushion Is Open To Gap Between The Drywell Shell And Surrounding Concrete Provide any plans for performing ultrasonic thickness measurements of the drywell shell plates adjacent to the sand cushion or any other proposed actions to ascertain if plate degradation has occurred. Since the degradation that has occurred at Oyster Creek is localized, sufficient details should be included to show that the sampling basis for ultrasonic thickness measurements is adequate in terms of size and test location.
Licensees and applicants are requested to respond to this generic letter within 60 days of the date of this letter. Our review of your submittal of information is not subject to fees under the provision of 1OCFR17O.
This request for information was approved by the Office of Management and Budget under clearance number 3150-0011 which expires September 30, 1989 Comments on burden and duplication may be directed to the Office of Management and Budget, Reports Management Room 3208, New Executive Office Building Washington, D.C. 20503.
Sincerely, Robert M. Bernero, Director Division of BWR Licensing Office of Nuclear Reactor Regulation Enclosure:
As stated DBL:E- "Laia DO
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