05000443/LER-1997-001, :on 970109,identified That Certain Obstructions to Flow of Flood Water Off Site May Produce Flood Levels Exceeding Elevations Specified in Fsar.Caused by Misapplication of Design Inputs

:on 970109,identified That Certain Obstructions to Flow of Flood Water Off Site May Produce Flood Levels Exceeding Elevations Specified in Fsar.Caused by Misapplication of Design Inputs

ML20134M270
Person / Time
Site:	Seabrook
Issue date:	02/10/1997
From:	Diprofio W, Legendre A NORTH ATLANTIC ENERGY SERVICE CORP. (NAESCO)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-97-001, LER-97-1, NYN-97015, NUDOCS 9702200170
Download: ML20134M270 (5)

LER-1997-001, on 970109,identified That Certain Obstructions to Flow of Flood Water Off Site May Produce Flood Levels Exceeding Elevations Specified in Fsar.Caused by Misapplication of Design Inputs

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)
4431997001R00 - NRC Website

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i North Nonh Atlantic Energy Service Corporation A-P.O. Box 300 Atlantic seatreet, Ni103874 I

(603) 474-9521 The Northeast Utilities System February 10,1997 Docket No. 50-443 NYN-97015 United States Nuclear Regulatory Commission Attn.: Document Control Desk Washington, D.C. 20555 Seabrook Station Licensee Event Report (LER) 97-001-00 Seabrook Station Design Basis Flooding Analysis Enclosed, please find Licensee Event Report (LER) No. 97-001-00 for Seabrook Station. This submittal documents a condition reported on January 9,1997, pursuant to 10CFR50.72(bXIXii)(B).

Should you require further infonnation regarding this matter, please contact Mr. Allen L. Legendre, Jr.,

Nuclear Licensing Supervisor, at (603) 773-7773.

Very truly yours, NORTH ATLANTIC ENERGY SERVICE CORP.

__. M' _ _

11 sam A. DiPr to Station Director L

cc:

II. J. Miller, Regional Administrator g

A. W. De Agazio, NRC Project Manager, Seabrook Station J. B. Macdonald, Senior Resident Inspector, Seabrook Station INPO I

Records Center 700 Galleria Parkway l

Atlanta, GA 30339 k

9702200170 970210 PDR ADOCK 05000443 s

PDR

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Seabrook Station 05000443 1 of 4 mum Seabrook Station Design Basis Flooding Analysis v

Eveni DATE (D)

LER NUMutn (5) ntruni DATE (7)

OTHER FACILilitt INVOLVED (5) t MONTH DAY YEAR YEAR SEQUENTIAL REVl510N MONTH DAY YEAR F AcluTY NAME DULui NUMBER NUMBER NUMBER i

01 09 97 97 001 00 02 10 97

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MODE (9) j l

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OTHER 20.2203(a)(2Hin) 50.35(c)(1) 50./3(a)(2)(v)

Specify en Abstract below or m NRC Form 366A 20.2203(a)(2)(sv) bO.35(cH2) 50.73(a)(2Hvu)

LIGthtm CONTACT POR THIS LER (12)

NAML TELEPHONE NUMBER (IfElude Ate #.,Odel Allen L. Legendre, Jr., Nuclear Licensing Supervisor (603) ~n3-7773 l

l COT tit ONE LINE FOR EACH COMPONENT FAILURE DE5uustu IN THIS MtPORT (13)

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1 AB iTRACT (Limit to 1400 spaces, i.e., approximately 1 b single-spaced typewntten lines) (15)

The Seabrook Station design basis flood analysis is documented in Section 2.4 of the Updated Safety Analysis R: port (UFSAR).

The UFSAR addresses two flooding scenarios: a probable maximum hurricane (PMH)/ Probable Maximum Flood (PMF) event and local intense probable maximum precipitation (PMP).

...a limiting event identified in the UFSAR is the PMH/PMF event which was analyzed to produce flood levels on the Se: brook Station site to an elevation of 21' mean sea level (msl) or less. Flooding associated with the PMH/PMF occurs primarily as a result of waves overtopping the vertical seawall. A critical assumption in the i

an: lysis is that the flood water will flow off the site via several flow paths that are specified in the UFSAR. North Atirntic has identified that certain obstructions to the flow of flood water off the site may produce site flood levels exceeding the elevations specified in the UFSAR. This condition was reported to the NRC on January 9,1997, pursuant to 10CFR50.72(b)(1)(ii)(B), as a condition that is outside the design basis of the plant. An operability d;t:rmination was performed to provide the basis for continued operation. Modifications to the flow obstructions will be implemented and the flooding analyses will be updated. The cause of this event has been determined to be e misapplication of design inputs and inadequate independent review, i

NRC FORM 366 (4-95)

'.U.S. NUCLEAR REGULATORY COMMISSION (4-95)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3) 05000443 YEAR SEQUENTIAL 3EVISION Seabrook Station NUMBER NUMDER 2 of 4 j

97 001 00 TEXT (11 more space is required, use additional copies of NRC Form 366A) (17) 1.

Descriotion of Event Tha Seabrook Station design basis flood analysis is documented in Section 2.4 of the Updated Safety An lysis Report (UFSAR). The UFSAR addresses two flooding scenarios: a probable maximum hurricane (PMH)/ Probable Maximum Flood (PMF) event and localintense probable maximum precipitation (PMP). The limiting event identified in the UFSAR is the PMH/PMF event which was analyzed to produce flood levels on th3 Seabrook Station site to an elevation of 21' mean sea level (msl) or less. Flooding associated with the PMH/PMF occurs primarily as a result of waves overtopping the vertical seawall. An important assumption in the analysis is that the flood water will flow off the site via several flow paths that are specified in the UFSAR. North Atlantic has identified as discussed below that certain obstructions to the flow of flood water off the site may produce site flood levels exceeding the elevations specified in the UFSAR. This condition w s reported to the NRC on January 9,1997, pursuant to 10CFR50.72(b)(1)(ii)(B), as a condition that is outside the design basis of the plant.

During a site walkdown conducted in support of the 10CFR50.54(f) review effort an engineer identified obs+ ructions to off site flow, in the form of concrete curbing and fence anchoring (steel plate) located around th3 site perimeter, especially on the east and south sides, which were not considered in the original PMH/PMF analysis. A new building, the Mechanical Maintenance Storage Facility, was also identified as pr:senting a minor obstruction to the flow of water off site. These obstructions could impede the floodwater flow off the site during the design PMH/PMF condition and could result in site water levels exceeding the 21' msl elevation and exceeding door elevations which are at 21.5' msl. Maintaining site water level below an clevation of 21.5' ensures that flood water ingress will not occur in any structures containing safety related systems and components.

Th3 PMP ana ysis is not affected by the obstructions.

I II.

Cause of Event

Tha cause of this event has been determined to be a misapplication of design inputs and inadequate ind: pendent review as discussed below. The flow obstructions were installed after the original flood analysis through several plant design change evolutions as follows:

Th3 security barrier plate, attached to the seawall fence, was on the original fence design detail provided on Dr wing 101056 revision 4 ( date of revision 5/2/84). This revision provided typical and specific details for tha installation of security fencing. The barrier plate was added since the fence fabric and bottom rail could not be embedded in the pavement as per typical fence detail. The location of the fence was considered in th3 site flood analysis which was completed on 11/4/82. The addition of the plate to the fence at the seawall is en original detail which was developed by the architect / engineer after the flood analysis was completed.

Tha engineer who performed the flood analysis was not aware at the time that special details would be j

NRC FORM 368A U.s. NUCLEAR REcVLAToRY CoMM2slON (4-95)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACluTY NAME (1)

DOCKET NUMBER (2)

LER NUMBER 16)

PAGE (3) 05000443 YEAR SEQUENTIAL REVISION Seabrook Station NUMBER NUMBER 3 of 4 97 001 00 TEXT (11more space is required, use additional copies of NRC Form 366A) (17) d:veloped for the fence at the seawall. It is not possible to interview the people involved in the development of f nce details but it is evident that no correlation was made to the FSAR flood analysis parameters.

Tha addition of the concrete curbing was the result ci the need for enhancement to the site security system.

Thn use of readily available concrete curbing allowed for a cost effective, timely and easily implemented modification. Design change, DCR 89-0078 CA 20, installed 8" high concrete curbing at various locations on ths plant perimeter. Review of DCR 89-0078 indicates that the effect on site flooding was not considered by th3 originator or the interdiscipline review groups.

Per discussion with applicable reviewers it was deti:rmined that the effects on flooding were not recognized, most likely because onsite drainage was not effseted, and the offsite drainage assumption for flooding due to the PMH/PMF were not well known.

Tha effect on PMH/PMF flooding flowpaths by the installation of the Mechanical Maintenance Storage Facility was not recognized by originator of minor modification MMOD 95-0585 or by interdiscipline rsviewers. The location of this facility has a very minor effect on the site flood analysis. The effects of on-sits drainage were factored into the building location and layout.

i 111. Analvsis of Event Tha PMH/PMF event is discussed in Section 2.4 of the Seabrook Station UFSAR. The design basis event discribed in the UFSAR represents a combination of limiting assumptions and conditions. It is highly improbable that these assumptions and conditions would manifest themselves and result in the design basis flood levels specified in the UFSAR. Seabrook Station is not currently susceptible to hurricane conditions as the hurricane season for the Northeastern United States falls between June and November.

IV Corrective Action An operability determination was performed to provide the basis for continued operation. The operability detarmination documented that Seabrook Station is not currently susceptible to a burricane or PMH/PMF conditions as the hurricane season for the Northeastern United States falls between June and November.

A design change will be implemr.nted to modify the barr:er plate attached to tha seawall fence and curbing cs deemed applicable by site flomi calculations. Ary required design changet, will be reflected in changes to tha UFSAR as required.

The site flooding analysis will be revised to include the effects of the Mechanical Maintenance Storage Fecility and to document the seawall barrier plate and security enhancements.

An item will be added to the Mechanical Engineering interdiscipline Review Evaluation, contained in the Design Change Manual (Fomi 4-1E), to evaluate the effect of plant changes, especially near the site perimeter, on the site flood analysis.

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.-U.S. NUCLEAR RE!ULATORY COMMISSION 14-9 5) a LICENSEE EVENT REPORT (LER)

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TEXT CONTINUATION FACluTY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3) 00000443 YEAR SEQUENTIAL REVISION Seabrook Station NUMBER NUMBER 4 of 4 97 001 00 TEXT (1f more space is required, use additional copies of NRC Fxm 366A) (17) i V,

Additional Information

i None l

Similar Events

1 i

Tha event has some elements in common with several recent Adverse Condition Reports (ACRs) concerning inTdequate 10CFR50.59 screenings and evaluations. The corrective actions for these ACRs include additional trrining on 10CFR50.59 evaluations, increased detail in the 10CFR50,59 evaluation process, and enhanced software tools to aid in UFSAR and licensing basis searches. These actions will minimize the potential for l

r:currence of this type of event.

Manuf acturer Data I

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