ML20215D909

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Sser Re Effect of Breakwater Damage on Saltwater Intake Structure
ML20215D909
Person / Time
Site: Diablo Canyon  Pacific Gas & Electric icon.png
Issue date: 02/15/1983
From:
NRC
To:
Shared Package
ML20197F583 List:
References
FOIA-86-679 NUDOCS 8610140358
Download: ML20215D909 (10)
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Supplement to Safety Evaluation Report Diablo Canyon Nuclear Power Plant Units 1 and 2 Docket Nos. 50-275 and 50-323 2.0 Site Characteristics 2.4 Ef fect of Breakwater Damage on Saltwater Intake Structure The plant obtains both its normal and emergency cooling water from the Category I Saltwater Intake Structure located on-the shoreline of a cove south of Units 1 and 2.

This cove is protected from storm waves by two breakwaters (east and west) with their crest constructed to elevation +20 feet Mean, Lower Low Water (MLLW). Although the breakwaters are not designated as safety-related structurese they do provide flood protection to the safety related Auxiliary Saltwater (ASW) pumps located within the Intake Structure. These ASW pumps are designed to remain functional during the design basis flood event.

As discussed in SER Supplement No.13, April 1981, during a winter storm on January 28r 1981, the West Breakwater was damaged by storm waves.

Approximately 120 feet of the seaward end of the breakwater sustained substantial damage consisting of displacement of concrete cap units, tribar armor units, and underlayer quarrystone to approximately 0 feet MLLW.

Subsequent storm waves in 1981 and 1982 extended this damage to a total length of about 240 feet (as of December 1982).

8610140358 861006 FOIA PDR PDR BISHOP 86-679 i

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' As a result of the January 1981 storm, which degraded a portion of the west breakwater to a level of about Elevation 0 feet MLLW, a breakwater configuration was presented that was more severe than any condition previous l

postulated for the Design Basis Flood event. Based on available information, neither the staff nor the applicant were in a position to evaluate:

I (a) the potential for and limits ofi further breakwater degradatione l

(b) the extent to which a significantly degraded breakwater would limit wave runup on the Intake Structure to a level below the design level of +30 feet MLLW during the design or lesser flooding events, and l

(c) the implications of this and associated events on operation of l

safety-related equipment.

l It was determined that if the wave ruoup on the Intake Structure exceeded the design level of +30 feet MLLW, the only safety-related equipment that might be affected are the Auxiliary Saltwater pumps located in the Intake Structure. The ASW pump motors are located approximately six feet (El 6.5 feet, MLLW) above the floor of the watertight ASW pump chambers.

These pumps are necessary for heat transfer from the component cooling heat exchangers. The water-tight ASW pump chambers are each provided with a ventilation stack which extends through the roof of the Intake Structure to Elevation +30 feet, MLLW.

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In order to preclude having to defend the safety of the plant in the future if the breakwaters wece to sustain further damage or be repaired and damaged agains the applicant proposed to reanalyze the ability of the Intake Structure to withstand the effects of the Design Basis Flood event with the breakwaters severely damaged. Based on studies by Wiegeli 1982 and I

Seeds 1982r the applicant selected elevation 0 feet, MLLW as the postu(ated minimum degraded level for be$h of the br,eakwaters and conducted hydraulic model tests of the effects of the Design Basis Flood evente i.e.i " Probable Maximum Tsunami" concurrent with annual storm waves (SER Supplement No. 5e September 1976). Additional model tests were conducted with " Maximum Credible Wave Events" combined with high tide and sea level anomaly.

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applicant also studied the probability of vessels impacting on the Intake Structure (Kirchere Monzon-Despang and Morris, 1982). The vessels were limited to those with sufficient draft to cross over the degraded breakwater 4

and sufficient displacement to infl/ct significant damage to the Intake Structure.

The hydraulic model studies utilized a laboratory testing facility measuring 80 feet by 120 feet by 4 feet deep which reproducede at a 1:45 model to prototype scaler the Intake Structurer the breakwaterse and the adjacent nearshore and offshore bathometry.

This represented a prototype area of 446 acres measuring 3600 by 5400 feet.

Detailed discussion of test procedures and results of the hydraulic model studies are reported by Lillevang, Raichtene and Caser 1982; Lillevange 1982 and Raichtene 1982. The application of the results of these studies on the ability of the ASW pumps to safely operate during these D8F events are reported by Matsudar 1983.

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. The applicant has concluded that the SW Intake Structurer with minor modificatione is capable of withstanding the effects, including wave forcess of the postulated Design Basis Flood events, thereby assuring continuous protection of the Auxiliary Saltwater (ASW) pumps. The Design Basis Flood events consist of the postulated degradation of both breakwaters to O feet MLLW combined with 1) the " Probable Maximum Tsunami" concurrent with storm waves of more than annual severity (estimated return period of about 41 years), or 2) the " Maximum Credible Wave Event" combined with high tide and sea level anomaly.

The SW Intake Structure modifications consist of:

a) extending and reinforcing the ventilation stack for each of the AWS pump chambers to El 52.0 feet MLLW:

b) modifying manholes that provide access to the SW intake structure forbay so as to reduce venting and to withstand pressures greater than 97 feet of seawater; and c) providing a concrete fill at the intersection of the underside of the deck slab and the rear of the curtain wall so as to mitigate slam or wave impact pressures.

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The applicant concluded that extending the ASW pump ventilation shafts (stacks) preclude the ingestion of seawater to the extent that the operation of the ASW pumps would not be impaired during the postulated Design Basis Flood events (Ryani 1982).

The applicant concluded that the probability of large vessels (i.e. gre,ater than 250 tons displacement) crossing the degraded breakwater and impacting

-6 the intake structure is acceptably low (storm-independent case is 6.7 x 10 events per yeari Kircherr Monzon-Despanze and Morrise 1982). With respect to the safety-related function of the ASW pumpse the impact of vessels displacing less than 250 tons on the intake structure would be inconsequential.

The applicant is in the process of reconstructing and strengthing the damaged portion of the west breakwater.

The staff and its consultante the U.S. Army Coastal Engineering Research Center (CERC)r were actively involved in the planninge monitoring and evaluation of the hydraulic model studies. The staff has determined that the licenseer during the progress of the physical hydraulic studiese has comphdwiththeguidanceprovidedinRegulatoryGuide1.125. Additionallyr X

.because the breakwaterse even in their assumed degraded condition, will provide a degree of wave protection to the Intake Structurer they are considered flood protection barriersi as defined in Regulatory Guide 1.102.

The staff, with the assistance of CERC have reviewed the applicant's reports and has drawn the following conclusions:

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Although. sufficient evidence has been provided to indicate that breakwater degradation below the level of 0 feet MLLW is rarer the information provided by the applicant does not substantiate the assumption that a rubble-mound breakwater cannot degrade below that level.

b.

The applicant has applied the most critical wave heights periode and direction of wave approach associated with both the " Probable Maximum Tsunami Annual Storm Wave Event" and the " Maximum Credible Wave Event".

The staff concludes that there are appropriate design basis and are in concordance sith Regulatory Guide 1.59.

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Extending the ventilation stack for each of the Auxiliary Saltwater c.

pump chambers on the Intake Structure to elevation +52 feet, MLLW will prevent significant ingestion of wave runup and spray and will allow unimpaired operation of the ASW pumps during the Design Basis Flood event.

d.

The applicant has conservatively determined the wave pressures on the Saltwater Intake Structure and the ventilation stacks associated with the Design Basis Flood event with both breakwaters degraded to O feet MLLW level. The structural ability of the SW Intake Structure and the ventilation stacks to resist impact forces associated with the DBF event 3.V and other design events is discussed in the Section 33 of this SSER.

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The applicant has conservatively determined the best estimate of the frequency of a vessel crossing the degraded breakwater and impacting on the Saltwater Intake Structure for the storm-independent case as

-6 6.7 x 10 per year. The analysis was limited to those types of vessels with a draft shallow enough to cross over the breakwater and displacing more than 250 tons. Vessels displacing less than 250 tons will not inflict significant damage to the Intake Structure.

The staff therefore concludes that the Auxiliary Saltwater pumps would be flood protectdd for events up to and including the " Probable Maximum Tsunami Event" and the " Maximum Credible Wave Event" even if the entire length of both breakwaters were degraded to the level of 0 feet MLLW. Because there is no assurance that the breakwater will not degrade below the level of o fee b NLLWe the staff will requirer and the licensee has agreed to, a technical specification to:

a) monitor the condition of the breakwater, b) implement timely corrective action when limited damage is sustainede and c) identify the limiting condition for operation relative to the 4Hdd+

configuration nf the breakwaters.

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Based on its review and analysis and the implementation of the technical 3

specifications the staff concludes that the plant meets the guidance of Regulatory Guides 1.59r 1.102 and 1.125. The staff further concludes that the plant meets the requirements of General Design Criteria 2 and 10 CFR Part 100r Appendix A with respect to tsunami and wave induced flooding.

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References i ht Lillevang, Omar J., Fredric Raichten, and Jack Cox "The He g 1.

h tically Limiting Effect of Sea Floor Terrain Features and of Hypot e Canyon Extensively Reduced Breakwaters on Wave Action at Diablo i

l Model Sea Water Intake" - Report on a Three-Dimensional Phys ca 982.

Study for Pacific Gas and Electric Company, March 15,1

" Breakwater Damage by Severe Storm Waves and 2.

Wiegeli Robert L.i Tsunami Waves," March Si 1982.

k ters at Seede H. Bolton, " Evaluation of Seismic Stability of Brea wa 3.

1981 (Revised April 6,1982).

Diablo Canyon NPS."

September 22r Interactions Raichten, Fredrice "The Investigation of Wave-Structure 4.

Nu lear for the Cooling Water Intake Structure of the Diablo Canyon Power Plant, December 1982.

and Richard J. Morrise Charles A., Hector Monzon-Despange 5.

Kircherr Intake

" Frequency of Vessel Impact with the Diablo Canyon December 10, 1982.

Structures, i

" Criteria for Selection of Critical Wave Direct ons Lillevang, Omar J.e 6.

November 2r 1982.

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Matsudar E. N., " Wave Effects on the Intake Structure at Diablo Canyon, Units 1 and 2," January 1983.

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Ryan, P.J., " Investigation of Seawater Ingestion into the Auxiliary Salt Water Pump Room Due to Splash Runup During the Design Flood Events at Diablo Canyon," Jan'uary 1983.

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