ML20126H078

From kanterella
Jump to navigation Jump to search
Draft SER Supporting Return to Svc
ML20126H078
Person / Time
Site: San Onofre Southern California Edison icon.png
Issue date: 11/30/1984
From:
NRC
To:
Shared Package
ML20126G811 List:
References
FOIA-84-885 NUDOCS 8506180241
Download: ML20126H078 (39)
v • d • e


Text

. - . _ - _. ._ .

4 as NOV 091984 4

4

'l SAFETY EVALUATION REPORT RETURN TO SERVICE PLAN SAN ONOFRE flVCLE/P GENERATING STATION, UNIT 1 00CKET NO. 50-E06 A

8506180241 850326 PDR FOIA BELLS 4-885 PDR NOVEMBER 1984 1

l TABLE OF CONTENTS

1. INTRODUCTION
2. BACKGRCUNP
3. RETURN TO SERVICE PLAN
a.

SUMMARY

OF SEISMIC MODIFICATIONS 4.1 Structures 4.2 Piping Systems and Related Mechanical Components

, 4.3 Electrical Equipment '

1 i

5. EVALUATION 5.1 Structures i 5.2 Electrical Equipment and Cable Trays 5.3 Return to Service Scope j 5.4 Seismic Capability of Other Safety-Related Systems ano Components 5.5 Seismic Capability Summary i

j 6. OTHER SIGNIFICANT SAFETY ISSUES

7. CONCLUSIONS

-1 l

8. FEFERENCES a

l J

I

'I I

SAFETY EVALUATION OF THE RETURN TO SERVICE PLAN SAN ON0FRE NUCLEAR GENERATING STATION, UNIT 1 DOCKET NO. 50-206

1. INTRODUCTION The Southern California Edison Company (SCE), licensee for San Onofre Nuclear Generating Station Unit 1, has submitted reports (see references) describing seismic analyses and plant modifications which address the plant's capability to withstand a postulated seismic loading of a 0.679 modified-Housner ground response spectra earthquake. In a submittal dated December 23, 1983, the licensee proposed a program for returning the San Onofre Unit 1 to operation prior to completion of the seismic upgrade program and the related seismic review under the Systematic Evaluation Program (SEP).

This Safety Evaluation Report describes the staff's review and conclusions regarding the licensee's implementation of their December 23, 1983 " return to service" (RTS) plan and the overall status of the evaluation to establish the plant's capability to withstand postulated severe seismic .

, events.

2. BACKGROUND The San Onofre Nuclear Generating Station Unit No.1, is one of eleven older operating plants that are part of SEP. The purpose of the SEP is to evaluate these plants against current licensing criteria to provide

integrated and balanced decisions for backfitting. One of the SEP topics is the reevaluation of the capability of San Onofre Unit 1 to withstand seismic events.

San Onofre Unit I was granted an operating license by the Atomic Energy Commission on March 27, 1967. In the original seismic design, components, systems and structures which were determined to be important to the safety of the plant were designated Seismic Category A. Specifically, structures, systems and components associated with the reactor coolant system, boron injection, safety injection system, and residual heat removal were designated as Seismic Category A. The design basis used for Seismic Category A was what in today's terminology would be consistent with a 0.25g Housner spectra Operating Basis Earthquake (0BE) and a 0.5g Housner spectra Safe Shutdown EartSouake (SSE). The turbine-building extensions, which contain Seismic Category A systems and components, were designated Seismic Category B and designed to a maximum ground acceleration of 0.2g (static force criteria). Seismic Category B is a classification specified by the licensees for components, systems and structures that are important to the continuity of power generation or whose contained activity is such that release would not constitute a hazard.

During the construction permit application for San Onofre Units 2 and 3, more sophisticated tectonic information was developed for the site. As a result, SCE designe.d Units 2 and 3 to a 0.679 Housner spectra for all safety-related equipment and structures.

_ _ .~_

l

)

l Since Unit I was originally licensed, various structures and systems have been added to the plant. The licensee designed these to higher seismic levels consistent with the criteria being applied in the design of Units 2 and 3. Specifically, the sphere enclosure building and the diesel generators and associated structures, system and components were designed to a 0.67g modified-Newmark response spectra (more conservative than the Housnerspectra).

In 1973, the licensee initiated a program to reevaluate and modify as necessary the capability of San Onofre Unit 1 to withstand more severe seismic events. The design basis for this program was the 0.679 Pousner spectra. The first phase of this program consisted of reevaluating (1) systems and components to prevent a design-basis loss of coolant accident, including the main reactor coolant loops and Nuclear Steam Supply System (NSSS) components, and (2) the reactor building and the containment sphere. Based upon this reanalyses, the licensee concluded that the containment sphere, the reactor building and structural steel framing have resistance capacities in excess of those required to meet the 0.679 Housner spectra. Conseq'uently, the licensee concluded that modifications to these structures were not necessary. However, support modifications in the fonn of additional seismic restraints were required to meet allowable stresses for several of the larger NSSS components which were base-supported. These modifications were implemented during an outage in 1976-1977 along with the other major plant modifications.

4.

Following initiation of the SEP in 1978, subsequent phases of the seismic reevaluation program were incorporated into the SEP. This program proceeded in three additional phases: (1) reevaluation of balance-of-plant structures; (2) reevaluation of piping and mechanical equipment required to shut down the plant; and (3) reevaluation of piping and mechanical equipment required to mitigate the consequences of accidents. The earthquake input used for this program was also the 0.67g Housner response spectra.

The NRC staff issued letters dated August 4,1980 and April 24, 1981 (References and ) to the licensee requesting details of the seismic reevaluation program including the scope of review, the evaluation j criteria, the schedule for completion, and justification for continued operation in the interim until completion of the seismic reevaluation program. The' licensee responded by letters dated September 24, 1980, i

February 23, April 24, July 7, August 11, September 28, October 6, 1981 and October 19,1981(References to ). The NRC staff evaluated the

! licensee's responses and issued a Safety Evaluation Report concerning the Interim Seismic Adequacy for San Onofre Unit I dated November 16, 1981 (Reference ).

-That report addressed the licensee's conclusion that continued operation

[ would not pose an undue hazard until the seismic reevaluation and any i

necessary upgrading could be completed. The NRC staff agreed with the licensee's April 28, 1980 (Reference ) basis for continued operation for those-systems, structures and components which were originally designed

_. - _ _ . _ . ._ . - . _ _ _ _ . _ _ _ . ~ . _ _ . _ _ . . . _ _ . _ . _ ~ . , _ _

to meet the 0.5g Housner Spectra as ground motion input; however, the staff concluded that certain modifications were necessary, in the near term, to upgrade the North Turbine Building Extension and the West l Feedwater Heater Platform which were originally designed to 0.2g static.

The licensees completed the modifications to upgrade these structures during the current outage which began on February 27, 1982.

On September 16, 1982 and August 16, 1984 (References and ), the staff issued its evaluation and recommendation for the free field earthquake ground motion which should be used for the seismic reevaluation of the San Onofre Unit 1 facility. As recommended in these letters, the horizontal component of the postulated earthquake ground motion should be 0.679 Housner ground response spectrum with 10% exceedance in the 0.07 to 0.25 second period range and the vertical component should be 0.44g Housner ground response spectrum with 10% exceedance in the 0.05 to 0.15 second period range. This ground motion has been and is being used for both the seismic reevaluation of San Onofre 1 under SEP Topic III-6,

" Seismic Design Considerations," and for the " return to service" evaluation.

San Onofre Unit 1, like the other SEP facilities, was not designed ir accordance with current codes, standards, and NRC reouirements.

Consequently, the staff concluded that it would be more appropriate under the SEP seismic reevaluation program to perform "more realistic" or "best estimate" assessments. of the seismic capacity of the facility and to consider the conservatisms associated with original analysis methods and l

design criteria. As a result, a set of review criteria and guidelires was developed for the SEP plants. These review criteria and guidelines, as they apply to San Onofre Unit 1, are described in the following documents:

1. NUREG/CR-0098, " Development of Criteria for Seismic Review of Selected Nuclear Power Plants," by N. H. Newmark and W. J. Hall, May 1978.
2. "SEP Guidelines for Soil-Structure Interaction Review," by the SEP Senior Seismic Review Team (SSRT), December 8, 1980.
3. Letter from W. Paulson, NRC to R. Dietch, SCE, " Topic III-6, Seismic Design Considerations, Staff Guidelines for Seismic Evaluation Criteria for the SEP Group II Plants," July 26, 1982.
4. Letter from W. Paulson, NRC to R. Dietch, SCE, "SEP Topic III-6, Seismic Design Considerations, Staff Guidelines for Seismic Evaluation Criteria for the SEP Group II Plants - Revision 1," September 20, 1982.
5. Letter from W. Paulson, NRC to R. Dietch, SCE, " Systematic Evaluation Program Position Re: Consideration of Inelastic Response Using NPC NUREG/CR-0098 Ductility Factor Approach," June 23, 1982.

Any cases which are different from the criteria or guidelines presented above are either evaluated against the Standard Review Plan (SRP) and Regulatory Guides (RGs) or evaluated on a case-by-case basis.

At a meeting with the NRC staff on May 3, 1982, the licensee presented the results of their reevaluation,.using the 0.67g Housner Spectra, for the balance of plant mechanical equipment and piping required to shutdown the plant. The results of that evaluation, as documented in their April 30, 1982 submittal (Reference ), indicated excessive calculated stresses for certain equipment, piping and their supports. These high stress values caused the NRC staff to be concerned whether existing pipe, pipe supports and mechanical equipment including anchorage met the original licensing basis for San Onofre Unit 1. This concern was the subject of a meeting between the licensee and the NRC staff on May 20, 1982. At the end of this meeting, the NRC staff concluded that the licensees needed to provide information that demonstrates that the facility meets its licensed design basis before the plant could be permitted to restart from the current outage.

By letter dated June 15, 1982, as supplemented by letter dated June 24, 1982 (References and ), the licensee stated that they intended to complete the analyses and make modifications to the facility to meet the 0.679 Housner spectra ground motion rather than to expend the resources required to demonstrate that the facility meets its original 0.5g Housner spectra design-basis. The licensee committed to extend the present outage until the modifications were completed to upgrade San Onofre Unit Itothe0.6{gHousnerSpectragroundmotion. Based on those commitments, the NRC issued an order on August 11, 1982 (Reference ) to confirm that the licensee should maintain San Onofre 1 in the shutdown condition until the required modifications were completed and NRC approval obtained for restart.

1

3. RETURN TO SERVICE PLAN As the. licensee undertook these analyses and plant modifications, they concluded that the methods and criteria being used would not provide substanstial seismic protection for the cost of the modifications being l installed. Consequently, in mid-1983, they suspended the seismic upgrade program to reconsider the approach and scope. Subsequently, SCE initiated a series of meetings with the NRC management and staff to discuss alternative approaches.

On December 23, 1983, the licensee subnitted a program plan (Reference )

for returning the plant to service prior to completion of the seismic reevaluation program. The objective of their proposed " return to service" (RTS) plan was to demonstrate that all plant structures, systems and components whose failure could cause an accident and/or whose function is required to achieve and maintain a safe hot standby condition (Mode 3) condition would be capable of withstanding the postulated earthquake; i.e.,

a 0.679 modified-Housner ground response spectra. This plan also includes a set of interim evaluation criteria to be applied to the structures (or structural elements), systems and components necessary for achieving and maintaining " hot standby" conditions following the postulated earthquake. The staff's evaluation reports of these criteria was addressed in letters dated Februarv 8 and August 7, 1984 (References ). In those evaluations, the staff concluded that the criteria would, when implemented with the exceptions and clarifications noted by the staff, demonstrate the plant?s capability to achieve a " hot standby" condition following a design-basis earthquake.

Although the licensee had installed seismic modifications on most of the safety-related systems, these upgrades were generally designed on a piece-meal basis. Therefore, substantial additional analyses were necessary to demonstrate compliance with the applicable criteria and to identify any additional modifications that may be necessary to demonstrate overall system integrity.

The concept of the RTS plan is to ensure that complete seismic capability is demonstrated for those structures, systems and components which are necessary to achieve and maintain a hot standby condition. The seismic evaluation for the remaining structures, systems and components would be completed as part of the SEP integrated assessment so that related environmental and accident loading conditions could be considered collectively in designing any additional plant modifications ~ .

The staff's review of the proposed RTS plan is described in an evaluation dated February 8, 1984 (Reference ). In that evaluation, the staff concluded that the hot standby scope and related acceptance criteria, as modified by the staff's comments, would provide adequate assurance that the plant could safely shutdown following a design-basis earthquake, if properly implemented.

- 10 '

The following evaluation is based on the staff's review of the reports submitted by the licensee., audits of the RTS analyses, and site inspec-tions by the staff conducted in concert with the inspection program performed by Region V (see inspection reports 84-10, 84-13, 84-14, 84-16, and 84-21; References to ).

4

SUMMARY

OF SEISMIC MODIFICATIONS As a result of the San Onofre 1 seismic upgrading program and SEP seismic review (SEP Topic III-6 review), the capacity of many safety-related structures, systems and components have been upgraded to resist the postulated 0.67g modified-housner ground response spectra. It should be noted that most modifications to the structures as well as some of the system modifications were performed in accordance with the seismic reevaluation program (SEP) criteria while only a limited scope of plant modifications were evaluated against the " return to service" criteria.

Listed below are the summaries of the completed modifications:

4.1' Structures Turbine Building Including North, South, East, West Extensions (see report transmitted April 30, 1982) - The modifications to the bracings, foundations, structural element connections of the north, east and west extensions have been completed. Most modifications for the south extension have been completed but it is not yet completely upgraded. As discussed in the staff's November 16, 1981 evaluation (Reference ), failure of the south extension would not prevent the plant from reaching a safe shutdown condition.

I i

Reactor Auxiliary Building (see report transmitted December 8, 1981) -

l Modifications to connections of the masonry walls to the floor slab and the roof decking have been completed.

Ventilation Equipment Building (see report transmitted December 8, 1981) -

Modifications were completed to the roof ledger bolts and beams, and to insert plate bolts.

Intake Structure (see report transmitted December 8,1981) - The north, south and east pumpwell walls were modified. The licensee has recently added coated steel plates to the walls to restore structural capability because of excessive corrosion of the rebar, as discussed later.

l l

Fuel Storage Building (see report transmitted September 30, 1982) - The wall to roof diaphragm on the north and west walls was upgraded and a structural steel bracing was added to the east wall of the new fuel room.

Safety-Related Masonry Walls (see letter transmitted )

- In order to limit the large wall deflections, steel bracings were installed near the centerline of those walls for which the large deflections may affect the function of adjacent safety-related equipment.

Control Building (see report transmitted February 9,1982) - The control room ceiling was upgraded.

Sea Wall (see report transmitted December 8, 1981) - A new beach walk-way was built to raise the ground level on the. ocean side up to El. 14'-0.

This modification, completed in 1981, stablizes the sea wall to resist the postulated earthquake and tsunami loadings.

4.2 Piping Systems and Related Mechani al Components NSSS Supports - The supports of the pressurizer, reactor coolant pumps, and steam generators were upgraded to a 0.67g Housner spectra in 1977.

Piping Systems - All piping system supports (pipe supports and supporting structural elements) within the RTS scope were upgraded as required and new pipe supports were added where necessary to ensure integrity of the entire systems to 0.67g. .Some pipe supports have also been upgraded to 0.679 on parts of other safety-related systems.

Auxiliary Feedwater System - A new auxiliary feedwater tank and new suction piping froni the tank to the pumps have been installed. New discharge piping was installed in 1981.-

Auxiliary Feedwater Pump Foundation -: A reinforced concrete grade beam was installed underneath the pump foundation to span loose backfill soil. l Mectianical Components,- Supports were modified to all components within the RTS scope as required. Some mechanical supoorts have also been upgraded in other satety-related systents t- -

}

- 1? -

Containment Spray Ring - The supports for the containment spray header have been upgraded (this modification was not part of the RTS scope).

i 4.3 Electrical Equipment Electrical Equipment Anchorage - The anchorage for all safety-related electrical equipment was upgraded.

Electrical Raceways - Modifications were made to upgrade cable tray supports, conduits supports, tray tiedowns, and masonry wall expansion anchors, i

480 Volt Room Slab - New reinforced concrete grade-beams were installed in the floor slab to span loose backfill soil.

5. EVALUATION The overall seismic review of San Onofre Unit I has been performed based on the seismic reevaluation and modification reports submitted by the licensee, discussions at working-level review meetings with the licensee and their consultants, site inspections conducted by the staff and its consultants, and responses from the licensee to the issues raised during the course of the review. Included in this review are the criteria (analysis and performance), basic assumptions, modelling techniques, analysis methods and general appropriateness of the results. As a result

of this review, the criteria, modelling techniques, assumptions, analysis methods, and. results (analysis results, problem areas identified, and modifications implemented) are generally acceptable, except for specific items for which either additional information is needed or the issues are still being reviewed by the staff.

The following evaluation describes the status of the staff's overall review of the seismic capability of San Onofre Unit 1 under SEP Topic III-6,

" Seismic Design Considerations," and, more specifically, the staff's review and conclusions regarding the licensee's implementation of the RTS plan for plant restart.

In general, the staff believes that the seismic capability for safety-related structures and electrical equipment, including electrical cable trays and conduits, has been adequately established for the design-basis earthouake (0.679 ); however, the documentation is incomplete, and therefore, so is the staff's confirmatory review. Exceptions are noted in the body of the evaluation.

The major open issues at this point in the review concern the seismic capability of the safety-related piping and equipment and their supports.

Consequently, the scope of the RTS plan is directed at this type of equipment.

)

~

5.1 Structures The staff's review of safety-related structures is discussed in the November 16, 1981 Safety Evaluation Report (Reference ). As discussed in Section 4.1, the modifications to the south extension of the turbine building have not been completed. The earthquake-induced collapse of this structure could affect the remote shutdown panel, ECCS loop C electrical power, one loop of ECCS recirculation, the condensate storage tank as a source of cooling water. However, these failures would not prevent decay heat removal following a design-basis earthquake as discussed later.

Other issues raised in the staff's review of the safety-related structures are as follows:

Masonry Walls - In response to NRC IE Bulletin 80-11 and the SEP seismic review, the licensee and their consultant have developed a non-linear masonry wall analysis technique and have conducted a series of full scale reinforced masonry wall tests to validate the applicability of the proposed non-linear analysis method. This analysis method was then used to evaluate the adequacy of all safety-related masonry walls in the plant. The evaluation report, including the test results, is currently being reviewed by the staff. For the purpose of the plant restart, a review meeting and a site visit were conducted by the staff on September 5 and 6, 1984. As stated in the meeting summary (Ref. ), the staff

believes that the masonry walls will withstand the seismic loading induced by the postulated ground motion based, in part, on the licensee's October 27, 1984 (Reference ) confirmation that the rebar arrangement in the existing masonry walls conform with that of the test samples. The staff is continuing to review the licensee's testing program and the coorelation between the tests and analyses to ensure that there is sufficient margin to offset the uncertainties in this approach.

Ventilation Stack - The staff's concern about this structure was that the failure of the ventilation stack could impact such items as the auxiliary feedwater system piping, component cooling water system, ventilation systems, and safety-related electrical cable trays and conduits. As a result of the staff's review of the evaluation reports submitted by the licensee (References and ) and the field inspection and review meeting held during the September 6, 1984 site visit, the staff does not believe that the stack poses a serious threat to the equipment identified above from the postulated earthquake. However, the licensee provide additional information in a letter dated October 27, 1984 (Reference )

so that the staff can complete the review of this structure.

l

Soil Conditions - The original staff's concerns relating to this issue were: (a) the appropriateness of the soil parameters at different depths of soil deposit used for the soil-structure interaction antlysis; (b) the compactness of backfill materials adjacent to and/or underneath (partially or entirely) the safety-related equipment and structures (i.e., potential liquefaction of the soil), and (c) the potential static and dynamic settlements and differential settlements between structures and equipment items. The staff is currently reviewing the licensee's responses to items (a) and (c). Based on a preliminary review and the meeting held on September 6, 1984, the staff believes that these two items are not sigt.ificant with respect to plant restart and can be confimed in the continuing seismic review. With regard to item (b), new reinforced concrete grade beams, which are founded on undisturbed soil, have been installed in the foundation of the auxiliary feedwater pumps and the 480-volt switchgear room. It is the staff's judgment that this corrective action is sufficient to preclude settlement of these two foundations. However, the detailed design information for these modifications has not yet been submitted to the staff for review. This issue will similarly be confirmed in the ongoing seismic review.

Intake Structure - The criteria, analysis methods and results of the intake structure seismic reevaluation to 0.679 , originally presented by the licensee, are acceptable. However, during recent maintenance activities, the licensee discovered delamination of the intake structure facial concrete and significant corrosion of the underlying rebar. The licensee subsequently analyzed the extent of structural degradation and installed reinforcing plates and associated cathodic protection to restore the seismic integrity of the intake structure. The licensee's report of the repair design and procedures (Reference ) is currently being reviewed by the staff. The licensee's repair of the intake structure may be adequate; however, since the seismic capability of the saltwater cooling system has not been completely upgraded to 0.67g nor is it relied on for hot standby capability, the staff does not believe that resolution of this issue is necesary before plant restart.

Sea Wall - The staff's original concern about this structure was that the failure of the seawall due to postulated earthquake loading or tsunami loading may cause severe flooding on the plant site because of tsunami waves. In response to the staff's concern, the licensee upgraded the seawall foundation by building a new " Beach Walkway" on the ocean side and raising the ground surface up to elevation 14'-0. As a result of the site meeting held on February 8-9, 1984 (References ) and the review of the licensee's submittal on this issue dated May 17, 1984 (Reference ),

the staff concludes that the seawall will withstand the postulated seismic

loading or tsunami loading and retain its integrity and thus prevent site flooding (Reference ). Because of the degradation in the intake structure discussed above, the staff suspects that corrosion may have i similarly occured at the lower portion of the seawall sheet (piles).

However, the staff realizes that the condition of these two structures are different; i.e., the intake structure is directly submerged in the salt water and the lower portion of the seawall is exposed to ground water. ,

Also, the presence of the stainless steel pumps and the carbon steel rebar in the intake structure sets up a galvanic reaction which accelerates the corrosion process; this situation does not exist at the seawall. It is the staff's judgment that the possible corrosion of the sheet piles should not be as severe as was found for the intake structure rebar. Therefore, the staff does not believe that this issue is a concern for plant restart.

For the long term operation of the plant, the licensee should conduct a field inspection to identify any degradation of the seawall due to sheet pile corrosion and should evaluate the significance of such degradation.

5.2 - Electrical Equipment and Cable Trays In response to the NRC letters dated January 1 and July 28, 1980, the licensee initiated a program for the evaluation of the safety related electrical equipment anchorage (References ), and upgraded them as necessary to ensure that the equipment anchorage will withstand the postulated 0.67g seismic loading. According to the licensee (Reference

), all the required anchorage modifications are complete. As a result of the field inspection of the sampled equipment items performed during the site visit on July 31 and August 1 of 1984, the staff found that the electrical equipment and componencs are properly anchored. Therefore, 4

c

the staff concludes that the program conducted by the licensee has met the requirements for the short-term operation of the plant. However, the detailed review of the anchorage evaluation criteria, analysis methods, design of modifications, and the overall structural integrity is still being continued under the SEP seismic review.

Based on the past earthquake experience and laboratory test results, a piece of electrical equipment, when properly anchored, will possess enough inherent seismic ruggedness and capability to withstand substantial seismic loading without structural damage.

On October 2, 1984, the licensee submitted its " Electrical Raceway Support Implementation Plan for Return to Service of SONGS-1" (Reference ) as 1

part of its return to service efforts at San Onofre Unit 1. This report provided a detailed description of the electrical raceway (cable trays and conduits) support reevaluation and upgrade plan. This report is currently being reviewed by the staff. During the July 31 and September 6, 1984 site visits, the staff observed that modifications of raceway supports (support, tie-down, replacement of masonry wall expansion anchors, etc.) were properly installed. Based nn the test data, and the past earthquake experience which shows that the raceway systems possess inherent margins to resist significant earthquake loadings if the systems l are properly supported, it is the staff's judgment that the raceway systems in the plant will similarly remain functional after the i

- postulated earthquake

..-..e

- ,-- - ,e - .- ., ., - ---n- . - - - . . - - - , , -. -,

5.3 Return to Service Scope As part of the RTS plan, the licensee committed to upgrade, as necessary, all structures, systems and components necessary to ensure a capability to achieve and maintain a " hot standby" condition following a design-basis earthquake. Specifically, these systems and components are:

a. Reactor Coolant Pressure Boundary - Main reactor coolant loop and branch piping up to and including two supports beyond the isolation valve.
b. Main Steam and Main Feedwater Piping - The main pipe lines and major branch piping (two inches in diameter and above) up to and including two supports beyond the isolation boundary.
c. Auxiliary Feedwater System - This system includes the new auxiliary feedwater storage tank, the auxiliary feedwater pumps, the new suction oipe from the tank to the pumps, the new discharge piping between the pumps and the main feedwater line, and the steam supply system for the turbine-driven auxiliary feedwater pump,
d. Reactor Conlant System Make-Up Lines - The charging pumps, the ECCS recirculation lines to the cold legs and to the reactor coolant pump seals and the new piping connectino to the spent fuel pool are included in this system. Other lines which are directly connected to the above components whose. failure could prevent system function by diverting cooling flow have also been upgraded.
e. The atmospheric dump valves and their motive force (nitrogen) have been upgraded.

1

f. The anchorage of electrical distribution equipment needed to support operation of the above systems has been upgraded.
g. The diesel generators and their support systems were designed and installed in 1976-1977 to withstand the 0.679 earthquake.

In addition to the systems shown above, all structures, structural

, elements and components whose failure would prevent the function of these systems are also included in the scope of this review as discussed in Reference .

The objective of the RTS program is to ensure the ability to prevent loss-of-coolant (LOCA) accidents and to achieve and maintain a hot stendby condition should a severe seismic event, up to the design-basis earthouake, occur before the seismic reevaluation program be completely resolved.

With the reactor coolant pressure boundary and portions of the main steam and main feedwater systems necessary for system integrity upgraded to 0.679 , the likelihood of a seismically-induced LOCA occurring as a result of a severe seismic event and requiring the use of accident-mitigating systems is very small.

I i

In this concept, following a severe seismic event, the reactor would be cooled through the steam generators with steam being exhausted to atmosphere through the steam dump valves and feedwater provided by the auxiliary feedwater system. There is sufficient water in the auxiliary feedwater storage tank for at least 32 hours3.703704e-4 days <br />0.00889 hours <br />5.291005e-5 weeks <br />1.2176e-5 months <br /> of decay heat removal before any other water sources would have to be aligned. The service water reservoir (3 million gallon capacity) is available to provide auxiliary feedwater as v'll as other tanks on the site. However, these water sources do not have seismically-qualified piping systems to the auxiliary feedwater system. Therefore, contingency pumping arrangements would have to be established, after.a seismic event disabling all of the unquali#ied water sources, to transfer cooling water to the auxiliary feedwater storage tank.

To provide makeup to the primary system to compensate for shrinkage and reactivity control, the charging pumps would be aligned to draw suction from the spent fuel pool. The discharge of the charging pumps would be through the reactor coolant pump seal iniection lines to maintain seal i

integrity. The fuel pon1 water contains sufficient boron for reactivity i

control as the conidown continues.

Spent fuel pool cooling would not be in operation and sone water will be taken from the spent fuel pool for RCS makeup. Due to the low decay heat levels of the fuel in the pool, there is sufficient time to either 9

24 reestablish cooling or to add borated water to the pool. The integrity of the fuel pool has been demonstrated capable of withstanding the 0.679 earthquake. In addition, the fuel storage building including the masonry walls on the upper level have been upgraded to withstand the 0.679 earthquake, thus, there will not be collapse of the upper structures into the pool.

Prior to startup, emergency operating procedures will be established which describe the reoufred operator actions for responding to such a seismic event, including alignment of the spent fuel pool suction and alternative sources of auxiliary feedwater.

As previously stated, the significant outstanding issues for the San Onofre Unit I seismic review concern the methods and criteria for piping system analyses. Therefore, the staff's review of the implementation of the RTS plan concentrated on the analyses conducted by SCE to establish the seismic integrity of the piping systems and related mechanical equipment and supports which would be relied on to achieve and maintain a hot standby condition. These RTS systems are: reactor conlant pressure boundary, main steam and main feedwater piping, auxiliary feedwater system, and reactnr coolant system make-up lines. The staff's review of the seismic analyses for the RTS systems relied on an audit of representative portions of the piping systems and associated supports of these systems. The sample calculations selected were based on: (a) )

observation of vulnerable piping configurations during the previous l

l l

1

walkdown of the facility, (b) review of the analyses conducted for SEP Topic III-6, and (c) a range of pipe sizes. As a result of the audit review of piping analyses and the field inspection nf support modifications held on July 27 through August 1 of 1984 and the review of licensee's submittals dated December 23, 1983 and June 8, 1984 (References ),the staff's conclusions are as follows:

1) In general, the methods applied for the large bore piping (21 inches in diameter and larger) and the results obtained appear reasonable and the seismic upgrading program meets the requirements of the RTS plan.
2) For the reevaluation of small bore piping and tubing (2 inches in diameter and smaller), the accepted walkdown approach, which includes methodology, criteria and procedures, has generally been implemented in an acceptable manner. If the same approach is applied for the long term (i.e., under the SEP review), the licensee should provide additional guidance in the walkdown criteria and procedures to ensure that sufficient horizontal and uplift supports are established as required. In addition, sample analyses (verification of the adequacy of pipe supports, valve eccentricity effects, anchor movement effects, span criteria for the elbows and bends, etc.) should be performed to confirm the adequacy of the walkdown evaluation.
3) The methods being used by the licensee for pipe support asymmetrical bending calculations (e.g., angles, channels, etc.) were found to be incorrect during the staff audit reviews in 1983. According to the licensee, this issue has already been corrected for those piping problems which were either reanalyzed or are being analyzed for return to service. The licensee committed to perform a review of the remaining piping problems and to identify any additional corrections that need be made as part of the ongoing seismic review. The staff did not identify any cases of any incorrect asymetrical bending calculations in the audit of the RTS analyses.
4) The licensee has acceptably implemented the RTS plan, .uch that the systems relied on to achieve and maintain a hot stan:1by condition should be capable of withstanding the postulated 0.679 earthquake with sufficient margin to offset the uncertainties in the analysis methods used.

In addition, Region V has conducted periodic inspections of the installation of seismic modifications, management controls, cuality assurance practices, and the licensee's contractors work. These inspections also generally concluded that the seismic upgrades wera acceptably implemented (References to ).

In a letter dated November 3,1984 (Reference ), the licensee certified that the return to service plan is complete and concluded that the related seismic analyses have all of the necessary quality control approvals.

i.

In that letter, the licensee presented the results of a systems interaction review which concluded that the systems for which seismic upgrading is not complete would not fail in such a way as to impair the function of the

" hot standby" systems. The staff has reviewed that report and concludes that the methods applied are reasonable and appear sufficiently thorough  :

to support the stated conclusion.

5.4 Seismic Capability of Other Safety-Related Systems and Components

! One of the principal factors which led the licensee to commit to a major seismic upgrade program in June 1982 and led the staff to confirm that commitment by Order in August 1982, was the concern that the plant design may not have conformed to the original seismic design basis. In addition, the RTS plan relies principally on an established seismic capability only for the " hot standby" systems. This approach does not ensure defense l in depth against unforeseen complicating circumstances of a design-basis seismic event or explicit margins for seismic events beyond the design-basis.

i

Consequently, at the staff's suggestion, the licensee undertook sampling analyses to judge the seismic capability of the systems outside the scope of the RTS plan (cold-shutdown and mitigation systems), as they are currently ennfigured, against the original design-basis of 0.5g.

In a meeting held on October 16, 1984 and in a submittal dated November 3, 1984, the licensee presented the results of quantitative sampling analyses for the systems which were not within the RTS scope. These analyses were evaluated using RTS criteria for a 0.5g Housner spectra earthquake. The as-built condition of the plant was established for these analyses, including any modifications implemented during this outage.

The sample analyses were selected using the following considerations:

1) select problems from those than exhibit the highest stresses in the April 30, 1982 BOPMEP report;
2) consider cases of special interest, such as cast-iron piping;
3) represent all major piping systems not in RTS scope;
4) represent the range of pipe sizes; and
5) include piping cases that run between buildings and thus may have significant seismic anchor movement effects.

The scope of the analyses included the following:

1) pumps (including. RHR pumps, CCW pumps, SWC pumps, B refueling water pumps, and safety injection pumps);
2) heat exchangers (recirculation, CCW and 2 RHR);

- 29 -

31 CCW surge tank;

4) refueling water storage tank;
5) thirteen large bore piping problems;
6) twenty-one small bore piping calculations; and
7) supports for these cases.

The large bore piping problems examined included 33% of the remaining cases of safety-related large-bore piping and supports. The small-bore piping problems assessed were those which exhibited overstresses in the April 30, 1982 B0PMEP report which were not already evaluated in the return to service scope.

In order to readily establish a 0.5g forcing function, floor response spectra had to be generated from the 0.67g analyses. Two effects of the lower earthquake level were considered: spectral amplitude and soil behavior. Scaling factors were developed to adjust the response spectra to a zerio period acceleration at 0.5g. The first made peak for each spectrum, was broadened toward the high frequency end by 6% to account for the higher soil stiffness for the lower earthquake level.

The licensee notes that the resulting spectra have 20% margin based on the difference between the synthetic time history used to develop the floor response spectra and the actual smooth Housner spectra. The staff concurs that the scaling approach for the 0.5g forcing function is conservative; for the pipe support problems, the licensee takes credit for some or all of this 20% margin to demonstrate seismic capability.

~.

Equipment for which overstresses were reported in 80PMEP were reevaluated using the scaled 0.5g spectra. In general, the RTS criteria were used; however, specific criteria were applied in special cases. For example, for the refueling water storage tank (RWST) shell, a reduced factor of safety was used for the compressive stress allowables based on the effects of the internal pressure and axial versus bending load effects.

For the pumps, a factor of safety of 2.0 was used for expansion anchor bolt allowable stresses. This criteria is consistent with approach under IE Bulletin 79-02 for short-term functionality assessment.

For evaluation of tank nozzles, a Bijlaard analysis technique was used.

This technique has geometry limitations to preclude localized stress concentrations; e.g., ratio of the tank to pipe diameters. The staff i assumes that the licensee has conformed to these limitations.

)

i A total of 13 large-bore piping analyses were analyzed, including 8 analyses from the BOPMEP report. One analysis was the buried cast-iron 4

pipe that is part of the salt water cooling system. Linear elastic piping analysis codes were used. Typical pipe support flexibilities as a function l

of pipe diameter based on previous more detailed seismic analyses, were used. When piping ran between substructures such that the ends could i

experience relative displacement, seismic anchor motion was included in the analysis in accordance with the RTS criteria. j

--,e - - -

, l The licensee concluded that the acceptance criteria for 0.5g were satisifed. However, in a few cases, the 20% margin in the spectra was s

credited and the support loads due to seismic anchor movement and to seismic inertia were combined by square root of the sum (SRSS) of the square combination rather than " absolute sum." The staff does not believe that SRSS could be completely justified in this case because of the relationship between seismic inertia and anchor movement; however, the staff does believe that this combination is at least realistic.

l

The cast-iron piping case was evaluated under two different conditions, both during and after the earthquake. This is because part of the line is buried in backfill soil which may liquefy during the earthquake and thus result in significant settlement of the supporting soil. The l licensee used an allowable stress for the cast-iron piping based on j minimum ultimate tensile strength for the pipe material (A21.6), 18 ksi.

All of the pipe stresses met this criteria. There are no generally ,

accepted acceptance criteria for cast-iron piping particularly in the

nuclear industry. Cast-iron is generally too brittle for nuclear i applications, but has been used in older nuclear power plants. The staff has not been able to confim the minimum strength for an A21.6 material; however, the staff has not found a minimum strength reported for general cast-iron materials less than about 18 ksi. In addition, it appears that
the licensee has conservatively ignored any support the loose backfill might provide such that the ongoing review of the magnitude of settlement due to liquefaction does not bear on the calculated stresses. This i

analysis applies to the only cast-iron piping in the plant and the calculated stress was reported to be 14 ksi. On this basis, the staff concludes the cast-iron piping should withstand a 0.5g event.

For all of the large-bore piping analyses, the licensee neglected the effects of pipe support structural elements (e.g., beams), because, in their judgment, the local amplification effects would be small. The staff believes that the amplification effects mr.y cause large local displacements in some cases; however, the staff also believes that, if such large local displacements were to occur, the overall system would remain functional.

The small bore piping analyses included all small bore piping that had calculated stresses reported in B0PMEP in excess of the 80PMEP reevalua-tion criteria, and which had not already been reevaluated as part of the return to service effort. The RTS walkdown criteria were used to assess the adequacy of the piping systems. For a few cases where the span exceeded the allowable lengths, stress calculations were performed. The stresses were less than the RTS allowable for a functional capability of 2 Sy.

In general, the staff concludes that the sampling analyses performed for the systems outside the scope of the RTS plan appear reasonable with respect to the capability to function following a 0.59 seismic event.

Based on the information presented and the staff's frmiliarity with the systems involved, the staff concludes that these systems would probably continue to function following a 0.5g event, although there may be some local damage.

33 -

In addition to the studies performed specifically to San Onofre Unit 1, there are generic studies of seismic capabilities that are germane to staff's judgments concerning the existing seismic capability of San Onofre Unit 1. These are relative seismic risk and experience from actual seismic events.

4 In terms of seismic risk, there are considerable uncertainties in the definition of the design-basis ground motion and the associated return period. The licensee believes that 0.67g modified-Housner response spectra has been conservatively defined. However, the staff does not believe that it is appropriate to judge the conservatism of the initiating event because of the uncertainties involved. On the other hand, seismic risk studies have generally found that plants with similar 2

design standards have particular failure modes which tend to dominate the overall contribution of seismic risk. During the course of this review, the staff has not found any of those vulnerabilities identified in the seismic risk studies or has found that the vulnerability has been corrected; e.g., pipes traversing buildings and the control room ceiling, respectively.

I 6

1 i

1

~

As part of Unresolved Safety Issue A-46, " Seismic Oualification of Equipment," the Seismic Qualification Utilities Group has amassed a significant amount of experience from commercial plants which have been subjected to severe seismic events. That information has been correlated and reviewed by a Senior Seismic Review Advisory Panel with respect to seismic functionality of existing equipment in nuclear power plants.

This experience demonstrates that similarly designed facilities with a lesser standard for seismic capability have survived severe seismic l events with little or no significant damage. This experience further suggests that there are inherent margins in large commercial plants beyond those that can be quantitatively established by analysis.

5.5 Seismic Capability Summary Based on the review of the licensee's RTS program descriptions, the ,

audits of the RTS analyses, and all of the related inspection activities, the staff concludes that the licensee has reasonably established the seismic capability of the systems which would provide the capability to achieve and maintai,n a hot standby capability for a 0.67g modified-Housner response spectra. Moreover, the staff believes that the scope of systems for plant restart (i.e., hot standby capability) is sufficient to ensure the public health and safety until the overall seismic reevaluation can be completed because (1) the seismic integrity of the primary system and its isolation boundaries has been established such that a severe seismic

event would not be expected to cause an accident recuiring systems that have not been completely upgraded, and (2) there is sufficient time available to manually set up cooling water supplies to achieve and maintain cold shutdown.

For the systems outside the return to service scope, and for specific issues related to the soil conditions, structural design, and electrical system design, additional information and staff review are necesary to complete the overall seismic evaluation for San Onofre Unit 1. Neverthe-less, the staff believes that there is a reasonable amount of information current available, as described in this evaluation, which suggests that the plant would likely survive a 0.5g seismic event, and may even survive larger seismic events, without substantial damage. However, additional plant modifications will probably be required in order to clearly and competely demonstrate the plant's capability to withstand a 0.679 4

design-basis earthquake.

6. OTHER SIGNIFICANT SAFETY ISSUES Inasmuch as San Onnfre Unit I has been shutdown for approximately 32 months, it is apprcpriate to consider other significant safety issues that have been raised during that time with respect to the plant's readiness to restart. The mnre significant of these issues are (1) design deficiencies for the Transamerica Delaval diesel generators, (2) reactor trip breaker design and maintenance, (3) equipment qualifica-tion, (4) fire protection, and (5) operator qualification and training.

The licensee has addressed such issues and taken corrective action as necessary. The staff's reviews of these issues are addressed in separate

correspondence to the licensee. In no case has an outstanding issue been identified which should preclude restart. However, some of these reviews are continuing, as they are for other operating plants, and may require further corrective actions.
7. CONCLUSIONS The licensee has completed a program of seismic upgrading to support plant return to service. Based on the considerations discussed above, the staff concludes that the scope, analysis criteria and methods, and implementation of the plant modifications, as required, are acceptable and provide reasonable assurance that operation of San Onofre Unit 1, until completion of the SEP seismic reevaluation program, will pose no undue risk to

, public health and safety. For long-term operation, evaluation of the remaining scope of structures, systems and components will be completed and the other issues discussed in this evaluation will be resolved. It is anticipated that this review will be completed by the next refueling outage.

i

I..<

8. REFERENCES l
Retrieved from "https://kanterella.com/w/index.php?title=ML20126H078&oldid=3468271"