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ACCESSION NBR:FAC IL: 50-275

r 50-323AUTH. NAHE

CRANEI P. A.REClP. MANE

NIRAQLIAe F. J.

REGULATORY ORN*TION DISTRIBUTION SY N (RIDS )

8207060181 DOC. DATE: 82/07/01 NOTARIZED: NO DOCI ¹Diablo Canyon Nuclear Power Planta Unit il Pacific QaDiablo Canyon Nuclear Power Planta Unit 2i Pacific Qa 5000323

AUTHOR AFFILIATIONPacific Qas h Electric Co.

REC IP IENT AFFILI ATIONLicensing Branch 3

SUBJECT: Forwards "Breakwater Damage bg Severe Storm Waves h TsunamiWavesi " "Evaluation of Seismic Stability of Breakwaters atDiablo Canton Nuclear Power Station "

8< "Height LimitingEffect of Sea Floor Terrain Features 5 of Hypothetical lg... "

DISTRIBUTION CODE: SOOIS COPIES RECEIVED: LTR j ENCL ~ SIZE: (S f/'~~TITLE: PBAR/FSAR ANDTS and Related Correspondence

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PACIFIC GAS 8 ND ELECTRIC COMPA.NY77 BEALE STREET, SAN FRANCISCO, CALIFORNIA 94106

P. O. BOX 7442, SAN FRANCISCO, CALIFORNIA 94120TELEPHONE (415) 781-4211

TELECOPIER (415) 543.7813

ROBERT OHLBACHVICC PRCSIOCNt AHD OERCRAL A'IIORNCY

CHARLES T. VAN CEU8 EN

PHILIP A cRANel JRHENRv J. LSPLANTe

JOHN B. 8 IBSCNARTHUR L ~ HILLMAN,JR.

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July 1, 1982

Mr. Frank J. Miraglia, Jr., ChiefLicensing Branch No. 3Division of LicensingOffice of Nuclear Reactor RegulationU.S. Nuclear Regulatory CommissionWashington, DC 20555

Re: Docket No. 50-275, OL-DPR-76Docket No. 50-323Diablo Canyon Units 1 and 2

Dear Mr. Miraglia:

Enclosed is a report titled "Pacific Gas and Electric Company'sInterim Report On Its Investigation of Breakwater Damage at Diablo Canyon".This report provides the current status of work that has been performed byPGandE to address the full power licensing requirements of Section 2.4 ofSupplenent 13 of NUREG-0675 (Safety Evaluation Report for Diablo Canyon, Units1 and 2) as discussed with the NRC Staff at the September 25, 1981 meeting.In addition, the report also provides the status of investigations andanalyses concerning the consequences of a breakwater degraded to nean lowerlow water. Finally, the report concludes with a discussion of the status ofthe breakwater repair program. Also enclosed are the following threeconsultants'eports referenced in the PGandE report:

1. "Breakwater Damage by Severe Storm Waves and Tsunami Waves," byRobert L. Wiegel, March 5, 1982.

2. "Evaluation of Seismic Stability of Breakwaters of Diablo NPS,"by H. Bolton Seed, September 22, 1981. (Revised April 6, 1982)

3. "The Height Limiting Effect of Sea Floor Terrain Features and ofHypothetically) Extensively Reduced Breakwaters on Wave Action atDiablo Canyon Sea Water Intake," by Omar J. Lillevang,Fredric Raichlen, Jack C. Cox, March 15, 1982.

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82070b0181 820701PDR *DOCK 05000275P '..PDR

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t1r. Frank J. Miraglia, Jr. July 1, 1982Page 2

PGandE requests that the Staff schedule a meeting within several weeksto discuss the material submitted. Since we are currently conducting physicalmodel experiments, we suggest that this meetng take place at the OffshoreTechnology Corporation s facilities in Escondido, California.

Kindly acknowledge receipt of this material on the enclosed copy ofthis letter and return it in the enclosed addressed envelope.

Enclosures

cc (w/encl.): Service List

Philip A. Crane, Jr.

~ I WE4A I ~ i" r„v

Pacific Gas and Electric Company'sInterim Report On Its Investigation

ofBreakwater Damage at Diablo Canyon

Introduction

This report gives the current status of work that has been performedby PGandE to address the full power licensing requirements of Section 2.4 ofSupplement 13 of NUREG-0675 (Safety Evaluation Report for Diablo Canyon, Units1 and 2) as discussed with the NRC staff at the September 25, 1981 meeting("Meeting" ). In addition, this report also provides the status ofinvestigations and analyses concerning the consequences of a breakwaterdegraded to mean lower low water ("MLLW"). Finally, this report concludeswith a discussion of the status of the breakwater repair program.

Consultant Reports

The following reports attached to this submittal detail theinvestigation and analyses which have been completed to date:

1. "Breakwater Damage by Severe Storm Waves and Tsunami Waves," byRobert L. Wiegel, March 5, 1982. ("Wiegel Report" )

2. "Evaluation of Seismic Stability of Breakwaters of Diablo NPS,"

by H. Bolton Seed, September 22, 1981. (Revised April 6, 1982)("Seed Report" )

3. "The Height Limiting Effect of Sea Floor Terrain Features and ofhypothetically Extensively Reduced Breakwaters on Wave Action atDiablo Canyon Sea Water Intake," by Omar J. Lillevang,Fredric Raichlen, Jack C. Cox, March 15, 1982.("Lillevang Report" )

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Wiegel Re ort

The Wiegel Report provides a compilation of worldwide reports on

breakwater damage investigations gathered through an exhaustive literaturesearch. Based upon the documented cases in the report, the author concludesthat -the observed crest elevations of breakwaters sustaining storm damage tendto stabilize at approximately the low water level and that the displacedmaterial remains as part of the reshaped breakwater structure continuing toperform a useful part of the function for which the breakwater was built.

The Wiegel Report further concludes that the Diablo Canyon breakwaterwould not likely be damaged by a tsunami, and that occasional damage tobreakwaters from great storm waves should be planned for as it is usually noteconomically feasible to design breakwaters to resist damage by the mostextreme case waves.

It is inferred from the historical storm damage data in the WiegelReport that an entire breakwater is unlikely to be damaged by a single storm.Rather, damage is likely to be initiated by a great storm and to progress inseparate stages during subsequent storms. This pattern has also beendemonstrated at the Diablo Canyon breakwater where damage did not progress ,

from the initial damage in January 1981 until November 1981 when anothersevere wave attack caused additional damage.

The Wiegel Report indicates that in general breakwaters do notcompletely erode but would rather degrade, if unrepaired, to approximatelyMLLW at which the crest elevation would tend to stabilize. This condition wasassumed by PGandE for physical model testing in its investigations of theconsequences of breakwater damage at Diablo Canyon.

Seed Report

The Seed Report evaluates the effects of the SSE (Hosgri) upon thebreakwater. The report concludes that following an SSE, subsidence of thecrest elevation of an undamaged breakwater due to surficial sliding andcompaction would be less than three feet. The conclusions indicate that theoverall cross section configuration would be unlikely to change significantlyenough to impair its wave attenuating capacity. Similarly, if the breakwateris assumed to be degraded through wave damage to MLLW at the time the SSE

occurs, the cross section would not change significantly as a result of groundshaking.

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Lillevang Report

The Lillevang Report describes the physical model exper iments-andtheir results. The report describes the construction and operation of the3-dimensional hydraulic model at Offshore Technology Corporation's facilitiesin Escondido, California and documents the results of wave effects in theintake basin and at the intake structure during tests simulating a range ofwave conditions. The experiments were run with the objective of determiningthe inundation effects and forces of two design flooding events at theAuxiliary Saltwater ("ASW") pump ventilation structures located at the rear ofthe intake structure during: 1) a probable maximum tsunami event combinedwith a storm wave of annual severity and a high tide with anomaly; and 2) a

maximum credible wave event combined with a high tide with anomaly.

Model Experiments

As proposed at the Meeting, the model study evaluated the effects on

the intake structure of the two different design flooding events assumed tooccur with the breakwaters degraded to MLLW. The model testing determinedthat the maximum heights of waves in front of the intake structure, resultingfrom the two design flooding events, were physically limited due to theoffshore terrain features and the presence of the breakwater degraded toMLLW. Once the waves reached the limited height, further increases in theoffshore wave heights did not increase the height of waves in the intakebasin. However, it was observed that when the waves reached their limitedheight within the basin, the existing air ventilation openings for the ASW

pumps would be subject to inundation. This finding led to further experimentsto evaluate the feasibility of a proposed design modification which wouldincrease the elevation of the ventilation openings by the use of extendedrisers to prevent inundation.

These experiments were conducted to determine the hydraulic forces on

the proposed modification to the ventilation structures along with the heightof the splash run-up associated with the two design flooding events. The

forces were determined to be substantially less than the structural capacityof the modified ventilation structures.

The design flooding events tested in the model are described below.The water level references can be observed in Figure 1. This figure providesa schematic representation of the intake structure and the breakwater degradedto MLLW.

a) "Probable Maximum Tsunami" combined with storm waves of annualseverity and high tide with anomaly.

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This design flooding event is defined by Supplement 5 to theSafety Evaluation Report ("SER 5") as a Hosgri tsunami with a.maximum wave height of 9.2 feet, an astronomical andmeteorological tidal height of 6.3 feet for a water elevation of

.15.5 feet above MLLW not including storm wave effects. The

storm wave considered was an 18-foot wave height outside thebreakwater with a period of 15 seconds.

In the model testing a still 'water height of +17 feet MLLW was

used with waves ranging to 45 feet high and periods of 12, 16and 20 seconds. The maximum wave response heights inside thebreakwater were measured and found to be limited to a maximum of21 feet with the crest of these waves reaching a maximumelevation of A2 feet MLLW. Overtopping waves spilling into thebasin between the breakwater and the intake structure raised thestillwater level above 17 feet MLLW.

b) "Maximum Credible Wave Event" combined with high tide withanomaly.

Model tests for this design flooding event were run with a

simulated tide level at +7.5 feet MLLW which is greater than the6.3 feet assumed in SER 5 as representing a high tide withanomaly. Results for the higher 7.5 feet still water level arebelieved to be conservative as both model tests and computationsshow that the response wave height in the basin increases withincreased still water level. Therefore, the response wave

heights are higher than would have occurred with the SER 5

approved design flooding event. The tests were conducted withwaves ranging to 45 feet in height and periods of 12, 16 and 20seconds.

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The results of the model tests indicate that determination ofthe "Maximum Credible Wave Event" would have no significance fordetermination of the wave effects at the intake structure. Thetests found that the response wave within the intake basin

.reached a limiting maximum height which did not increase furtherin response to increases in the offshore wave height. This isdue to the effects of the natural terrain and the presence of a

breakwater at elevation -0- MLLW. Therefore, it is the limitingmaximum response wave height in the basin in combination withthe still water level in the basin that is of interest forassessing the maximum inundating effects and wave forces at theintake structure rather than some undetermined "Maximum CredibleWave Event" offshore.

The limited maximum response wave height for a tide level of+7.5 feet MLLW was measured in the model to be approximately 14

feet, and the crest of the waves in the basin reached a maximum

elevation of 36 feet MLLW. Maximum wave heights and crestelevations in the basin were less than those recorded for thetests with the still water level at +17 feet MLLW.

Water was observed to be on the deck of the intake structure duringmodel tests of both design flooding events with the breakwater degraded toMLLW. These tests indicated the vent openings at the ASW pump air ventstructures would be frequently wetted by the localized splash run-up caused by

the concrete vent structures themselves and occasionally inundated.Therefore, design modifications were determined to be necessary to assure thatthe vents would not ingest unacceptable quantities of water that would impairthe safety related function of the ASW pumps.

Tubular "snorkel" extensions of the vents were proposed andincorporated into the model for feasibility testing. The testing confirmedthat the vent extensions remained free of the upward splashed water, sincethey are set back from the edge of the concrete vent structure. Under some

conditions, the height of the splash was observed to exceed the elevations ofthe vent extension height of +52 feet MLLW, as shown in Figures 2 and 3.These figures, which were extracted and modified from the Lillevang Report(Figures 42 and 41 respectively), summarize the range and the average ofobserved splash run-up at each ventilation structure caused by a wave from thesoutherly direction (203 degrees). This wave angle produced the highestsplash run-up. The other waves tested were from the westerly direction (258degrees).

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As shown in Figure 1, the ventilation structure is setback 81 feetand the openings of the vent extensions have been faced away from the Sea. Byfacing the vent openings in this direction, the effects of splash run-up areminimized. Because the splash run-up exceeding the snorkel height does notcontact the snorkel, ingestion of water would be limited to wind borne spray.The resulting potential ingestion is considered minor and acceptable.Therefore, if Diablo Canyon were subject to either of the Design Flooding ,

Events with a breakwater degraded to HLLW and with the air vent modificationsshown in Figures 1 and A-1 installed, the operation of the ASW pumps would notbe adversely affected due to water ingestion. For details of the design, seeAppendix A to this report. Figure A-1 in Appendix A provides schematicdetails of the ventilation structure modifications. These modifications willbe installed prior to power ascension.

Other Consequences of Breakwater Degraded to MLLW

In addition to the concerns regarding the flooding of the ASW pumps,

the Staff expressed other concerns regarding the intake structure. In thatregard, the Staff requested that PGandE address the potential for Tribars fromthe degraded breakwater impacting upon the intake structure and the potentialof ship collisions with the intake. The Staff also requested that wave forceson the intake be addressed.

In response to the first concern, the Tribars and armor stones were

observed to be repeatedly deposited in a debris pile on the leeward slope ofthe breakwater after wave action had caused damage to both the actualbreakwater structure and to the physical model. These results confirm that itis not feasible for the reformed wave in the basin to car ry massive denseobjects such as Tribar fragments or armor stones across the deep water of thecove to impact the intake structure. The observations documented by theWiegel Report further substantiate that breakwater materials displaced duringdamaging storms would remain part of the breakwater and would not be carriedacross the cove to impact the intake structure.

As for the concern regarding wave forces upon the intake structure,only the forces upon the existing ventilation shafts and the extended airvents were measured in the model program covered by the Lillevang report.PGandE is continuing its investigation of the potential wave forces on theintake structure and will provide these results in a future report. Thisportion of the overall investigation is scheduled to begin in July 1982 and we

anticipate submitting a report of these investigations by November 1982.

As for the potential for ship collisions at the intake structure as a

result of the breakwater being degraded, a study is being conducted and a

report addressing the probability of ships impacting the intake structure isexpected to be complete by September 1982.

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Breakwater Repair

Although PGandE believes that the studies summarized in this reportdemonstrate that a breakwater degraded to MLLM affords adequate protection forthe design flooding event, it also believes that repair of the breakwater iseconomically prudent to assure reliable ope0ation of the plant.

PGandE's repair program includes investigation of the cause of thebreakwater damage, investigation of the frequency and magnitude of severestorms, and the evaluation of methods to enhance the breakwater's resistanceto storm damage. 0. J. Lillevang, the consulting engineer who originallydesigned the breakwater, was retained by PGandE to investigate the causes ofthe damage and to recommend appropriate repairs. Lillevang, with approvalfrom PGandE, implemented construction of a 3-dimensional hydraulic scale modelas the best method of studying the problem situation.

Lillevang employed Dr. Fredric Raichlen of California Institute ofTechnology to assist with the design and testing of the model constructed atOffshore Technology Corporation's facilities in Escondido, California.Meteorologists R. Rea Strange and Dr. Donald Resio were retained by Lillevangto make independent but similar hindcast studies of historical storms thathave impacted the Diablo Canyon coastline. Professor Leon E. Borgman of theUniversity of Wyoming was retained to review the results of Strange and Resioto assess probabilities of severe storm waves impinging upon Diablo Canyon,.including analysis of the likely storm return period. In addition, Dr. RobertKoh of California Institute of Technology provided Lillevang with waverefraction analyses and data for input to the model study.

Following completion of the design flood event studies in January1982, the modeling study focused on determining the mechanism which causedstorm damage to the breakwater and evaluating the resistance of proposedrepair schemes to the worst historical storms. This phase of the model studywas completed in May 1982 and a report is being prepared to present theresults. Based on the results of the stuQ, repair recommendations for thebreakwater were provided to PGandE. The recommended repairs call for theinstallation of larger Tribars (37 tons versus 21.5 tons) and placement ofpumped concrete at selected locations which were shown by the model study toincrease the resistance to wave damage.

Analysis of historical storm data is continuing and reports arescheduled to be submitted to PGandE by July 1982. Preliminary results fromthese studies were used in developing the repair design. The January 1981storm that caused the present damage was determined to be less intense thanseveral of the storms hindcast, though more intense than the storm used in theoriginal design of the breakwater. The most intense storm hindcast occurredin 1905. This storm had a significant wave height of more than 30 feet and areturn frequency estimated to be approximately 88 years. This contrasts withthe significant wave height of 18 feet considered in the original design ofthe breakwater.

The breakwater repair design, developed in the modeling program, hasbeen tested using the simulated 1905 storm spectrum from four differentdirections in the southwest quadrant. This design was found to be capable ofresisting such intense wave attack with only minor, limited damage resultingin dislocation and removal of only a few Tribars. The breakwater repair willincorporate the design features that enabled the model to resist the mostintense storm conditions of record.

PGandE is proceeding with implementing the recommended repairs duringthe 1982 summer and fall season when wave c'onditions will be calm enough topermit construction. The repair contract has been awarded and work isexpected to begin during early July, 1982.

Conc Iusi on

The results of the investigations and analyses performed to datedemonstrate that adequate protection is provided to the safety relatedequipment within the intake structure with the breakwater degraded to MLLMwhen the ASW pump air vents are extended to 52 feet MLLW. PGandE's analysesto date address:

1. The degradation effects of waves upon a breakwater;

2. The degradation effects of the SSE (Hosgri) upon the breakwater;

3. The inundation effects of two design flooding events on theintake with the breakwater degraded to MLLM; and

4. The forces on the ASW pump ventilation structures during the twodesign flooding events with the breakwater degraded to tILLW.

Work continues on the potential consequences of a breakwater degradedto MLLM. A study is being initiated to determine the wave forces on theintake as a result of the two postulated design flooding events. This studyis expected to be completed by November 1982. Additionally, a study is beingundertaken to determine the potential for ship collisions at the intakestructure. This report is expected to be completed by September 1982.

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SCHEMATIC OF INTAKE STRUCTUREAND A BREAKWATER DEGRADED TOMEAN LOWER LOW WATER (MLLW)

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RESULTS FROM PHYSICAL MODELSPLASH RUNUP WHICH EXCEEDS TOP OF VENT DUE TO WAVES FROM SOUTH

FOR WAVE PERIODS WITH CONCURRENT MAXIMUMTIDE,TSUNAMI AND METEOROLOGICALSURGE (+17 FEET)

MODIFIED FROM LILLEVANGREPORT-FIGURE 42

MLLWEL.52.0'AVE ANGLE ~ 203 DEGREES

WATER DEPTH ~ 117 FT

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TO WAVES FROM SOUTH FOR WAVE PERIODSAT MAXIMUMASTRONOMICALTIDE LEVEL (+7.5 FEET)

MODIFIED FROM LILLEVANGREPORT-FIGURE 41

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APPENDIX A

The following is a description of the vent extension discussed in thebody of the report.

A schematic of the vent extension is shown in Figure A-l. It willhave co-axial pipes extending above the roof of the existing concrete ventshaft. The modified system is being designed to meet the same ventilationrequirements as the existing system. The inner pipe, 26" diametertransitioning to 28" at the top, will be the exhaust and the outer pipe, 40"

diameter transitioning to 46" diameter at the top, will be the intake. The

inner pipe will tie into the existing exhaust duct and fan below the top deckof the intake structure.

The existing ventilation louvers in the concrete vent shaft will be

removed and sealed. The top of 46" diameter pipe shall be at elevation +52

MLLM- This will provide vertical clearance to operate the intake gantry crane.

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