ML20245H682

Responds to Requesting Info Re Operation of Facility W/Cracked Bolts in Reactor Vessel Thermal Shield. Thermal Shield Absorbs Gamma Rays Emitted by Reactor to Reduce Heating & Consequent Thermal Stress in Vessel

ML20245H682
Person / Time
Site:	San Onofre
Issue date:	06/19/1989
From:	Zech L NRC COMMISSION (OCM)
To:	Wilson P SENATE
References
NUDOCS 8906300050
Download: ML20245H682 (3)

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o UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 9 June 19, 1989 CHAIRMAN The Honorable Pete Wilson United States Senate Washington, D.C. 20510

Dear Senator Wilson:

I am responding to your letter of May 15,.1989, in which you and Senator Cranston requested information regarding operation of Southern California Edison's San Onofre Unit I facility with cracked bolts in the reactor vessel thermal shield. The Nuclear Regulatory Commission (NRC) staff has been aware of the cracked bolts since January 1989.

The thermal shield (see enclosed diagram) is a 2-1/2 inch thick cylinder.that surrounds the reactor core barrel. Its purpose is to absorb gamma rays emitted by the reactor to reduce heating and consequent thermal stress in the reactor vessel wall. The thermal shield also absorbs high-energy neutrons, reducing irradiation.

damage to the vessel wall. Bolts are used to attach the bottom of the thermal shield to the core barrel, and spring-like devices called flexures are attached at the top. Four lateral displacement limiters are also located at the top.

On January 3, 1989, Southern California Edison conducted a visual inspt tion of the thermal shield with a remote camera; 24 of 30 bolts could be visually inspected. Three bolts out of the'24 inspected were found to be broken. In addition, the locking devices for two bolts and the locking device for one dowel pin had crecks. Five out of six flexures at the top of the thermal shield have been broken since 1978. The flexures were originally added to provide radial and tangential restraint to the top of the thermal shield. When these were discovered to be broken, an ,

evaluation was made which concluded that the flexures were un- '

necessary. In reviewing the results of the January inspection, the licensee found no evidence of damage to, or motion of, the thermal shield. j On January 31, 1989, the NRC sent the licensee a letter requiring that this matter be resolved to our satisfaction before plant 1 startup. The licensee and its consultant, Westinghouse Electric j Corporation, provided an analysis of the thermal shield in its present condition. The analysis concluded that the thermal shield is expected to remain safely in place. However, even under the worst conceivable case of thermal shield movement, flow of cooling water to the reactor core would not be significantly affrcted.

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! Based on the analysis, the licensee proposed to return San Onofre l Unit I to power and monitor the condition of the thermal shield  !

during operation by using neutron noise analysis and acoustical techniques. Although the sixth flexure is no longer necessary, the licensee's monitoring program includes monitoring of this flexure, since failure of the sixth flexure could be an indication of motion of the thermal shield beyond what is predicted. The licensee concluded that the neutron noise analysis would detect a change in vibration should the sixth flexure fail, and if that happened, the licensee would shut down for repairs. The licensee also agreed that a mid-cycle inspection would be conducted not later than June 30, 1990, to visually confirm the expected behavior of the thermal shield. If the inspection proves satis-factory, the licensee will operate the facility until about January 1991, at which time repairs of the thermal shield will L: .

conducted.

Based on the foregoing, the NRC staff issued Amendment No. 127 to the operating license for Unit 1 on May 15, 1989. The amendment authorizes operation of the unit, subject to implementation of the monitoring program and mid-cycle inspection of the reactor vessel thermal shield. These requirements provide reasonable assurance that the health and safety of the public will not be endangered.

The Safety Evaluation attached to the amendment describes the present condition of the thermal shield, the safety implications of this condition for continued operation, and NRC's basis for allowing restart of the unit. On May 16, 1989, the staff concurred in the licensee's evaluation of the remaining technical issues and authorized restart of Unit 1.

For your information, I have enclosed copies of the NRC's May 15 '

1 and 16, 1989 correspondence to the licensee. If you have any further question on this matter, please contact me.

Sincerely,

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I Lando W. Zec Jr

Enclosures:

1. Diagram of the San Onofre Unit 1 Thermal Shield

2. Letter from C. M. Trammell to K. P. Baskin dated May 15, 1989 with enclosures

3. Letter from Dr. T. E. Murley to Dr. L. T. Papay dated May 16, 1989

ENCLOSURE IL 1

CORE BARREL n

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& NO DAMAGE NOTED

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EXPAN!!DN Jt!!NT FLEXL3tC 5 0F 6 BROKEN OR CRACKED SINCE 1978

- FTXTURE NO CHANGE NOTED CTYP G PLACES)

N:. 1 LIMETER KEY G YP 4 PLACES)

THERMAL SHIELD TERMAL SHIELD SW T 3M CTYP G PLACEE) 5 BOLTS PER SUPPORT BLOCK,

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3 BOLTS (TOTAL) BROKEN AFFECTING 2 0F 6 SUPPORTS 4

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l May'15, 1989 Docket No. 50-206 i

Mr. Kenneth P. Baskin Vice President Southern California Edison Company 2244 Walnut Grove Avenue Post Office Box 800 Rosemeno. Ct.11fornia 91770

SUBJECT:

ISSUANCE OF AMENDMENT NO. 127 TO P SAN ONOFRE NUCLEAR GENERATING STATION, UNIT NO.1 (T The Comissior. has issued the enclosed Amendment 127 No.

to Provisional Operating License No. DPE-13 for San Onofre Nuclear Generating Stat No.1. The ansendment consists of changes to the operating license in re to your and May 3application and 8, 1989.dated February 17,1989, as supplemented March 21 and 2 ,

The amenenent provides for a reactor vessel thermal shield monitoring and mid-cycle inspection until the thermal shield fasteners are repaired during the fuel cycle XI refueling and 10-year ASME Inservice inspection .

and plan for the repair of the thermal shield.SCE is requesten to Specific subjects that should of new flexures and modification to the information .fithin 90 days.

limiter keys.be add Please provide this Men the tarmal shield and core barrel are removed, an ultrasonic test of the support block ledge should be performed from the inside of the core barrel. An

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Mr. Kenneth P. Baskin May 15, 1989 ultrasunic the core barrel-to-lowerexamination should support also plate be performed on a representative samp weld.

performed of the entire weld from both the inside and outside surface.A v Copies enclosed.of our related Safety Evaluation and Notice of Issuance are also Sincerely, M #/.' /r Charles Directorate M. Tramell, Y Senior Project Manager Project Division of Reactor Projects III, IV, Y and Special Projects

Enclosures:

1. Amendment flo. 127 to License No. DPR-13

2. Safety Evaluation 3 Notice of Issuance cc w/ enclosures:

See next page i

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4 Mr. Kenneth P. Easkin Southern California Edison Company San Onofre Nuclear Generating Station, Unit No. 1 CC ,

Mr. Kenneth P. Baskin l Vice President Southern California Edison Company 2244 Walnut Grove Avenue Post Office Box 800 Rosemead, California 91770 David R.~Pigott Orrick, Herrington & Sutcliffe 600 Hontgomery Street San Francisco, California 94111 Mr. Robert G. Lacy Nanager, Nuclear San Diego Gas & Electric Company P. D. Box 1831 San Diego, California 92112 Resident Inspector / San Onofre NPS U.S. NRC P. O. Box 4329 San Clemente, California 92672 Mayor City of San Clemente San Clemente, California 92672 Chairman Boaro of Supervisors County of San Diego 1600 Pacific Highway Room 335 San Diego, California 92101 Regional Administrator, Region V U.S. Nuclear Regulatory Commission 1450 Maria Lane, Suite 210 Walnut Creek, California 94596 Mr. Paul Szalinski, Chief Radiological Health Branch State Department of Health Services 714 P Street, Office B1dg. #8 4 Sacramento, California 95B14 i l

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SOUTHERN CALIFORNIA EDIS0lv COMPANY SAN DIEGO GAS AND. ELECTRIC COMPANY DOCKET NO. 50-206 SAN ONOFRE NUCLEAR GD.'ERATING STATION, UNIT NO.1 AMENDMENT TO PROVISIDHAL OPERATING LICENSE Amendment No.127 License No. OpR-13 1.

The Nuclear Regulatory Comission (the Comission) has founo that:

A.

The application for amenoment by Southern California Eoison Company and San Diego Gas and Electric Company (the. licensee) dated February 17, ISP9, as supplemented f! arch 21 and 23 and May 3 aro 8, 1989 complies with the stancards anc requirements of the Atomic Energy Act of 1954, as amenced (tk.a Act), and the Commissiori' s regulations set forth in 10 CFR Chapter .!;

B.

The fccility will operate in confomity with the application, the provisions of the Act, and the regulations of the Comission; C.

There is reasonable assurance (1) that the activities authorized by this anendment can be conducted without endangering the health and safety of the public,'and (ii) that such activities will be conoucted in compliance with the Comission's regulations; D.

The issuance of this amendment will not be inimical to the comon defense and security or to the health and safety of the public; and E.

The issuance of this amendment is in accordance with 10 CFR Part 51 of the Comission's regulations and all applicable requiremstts have been satisfied.

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2. 4 3.M as indicated in the attachment to this license amen 3.

This must belicense amendnent fully implemented is effective as cescribed as of the date of its issuan in the Attachment.

FOR THE NUCLEAR REGULATORY COMMISSION George . Knighto Directbr

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Project Directorate V Division of Reactor Projects III, IV, Y and Special Projects Office of Nuclear Reactor Regulation '.

Attachment:

License Condition 3.M Date of Issuance: May 15, 1989 i l

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3.M cvele X Thermal Shield Monitorine Procr&m The neutron monitor the noise / loose parts detection system shall be used to condition of the reactor vessel throughout Cycle X or until repair. thermal shield Periodic monitoring of both neutren noise and loose-parts vibrations confirms that no long term ,

unacceptable trend of degradation is occurring. The details of this program are described below.

(1) The unit will be shut down no later than June 30, inspect the condition of the thermal shield. 1990 to (2) During the first 7' days of 2 85% power, interim acceptance criteria for neutron noise / loose-parts monitoring will be developed.

final acceptsnceThese interim criteria criteria will be utilized until the is developed.

Final acceptance criteria for neutron moaitering will be established by performing noise / loose-parts baseline evaluations for 45 calendar days at 1 85% power following return to service for Cycle X operation. The base line data vill be established by recording a minimum of 16 segments of l data information, each of 20 minute duration at 1 85% power. {

Adjustments to the acceptance criteria will be made for cycle burnup and boron concentration changes throughout the cycle.  ;

(3) The neutron noise / loose-parts monitoring system shall be I

OPERABLE in MODE 1 with: }

a) At least two horizontal loose parts detecto.'s monitored for at least five (5) minutes 2 times per day; and, b) at least three (3) neutron noise inputs monitored for at least twenty (20) minutes enru a weel:. and be analyzed for cross coherence. power spectral density', including phase and (4) The data provided by the loose-parts / neutron noise monitor shall be analyzed once per week and compared with the i established criteria. If the data exceeds the acceptance l criterint 1

a) Within 1 day the NRC'will be informed of the exceedance, b) Within 14 days the conditions will be evaluated and a report provided to the NRC documenting future plans and actions.

Amendment No. 127

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c) be demonstrated failed.The plant will be shutdown should th (5) demonstrated OPERABLE in MODE 1 by perfo a)

CHANNEL CHECK at least once par 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> b)

CHANNEL TEST at least once per 31 days The surveillance requirements for neutron noisa monitor arefor covered the Power by the Neutron Range Appendix A Technical Specification 411 T1ux. .

(6)

With the neutron inoperabia noise for more than/ loose-parts detection instru 7 days mentation Report to the Commission pursu,antlicensee shall submit a Special Specification 6.9.2 within the nextto Appendix A Tecnnical i 3 days outlining the cause of system to the malfunction operable status. and the plans for restoring the (7)

In the case indicated of asensors, on site seismic avant of 0.25g or greater as initiated. Befera operations a controlled shut down shall be are resumed., it be damage to the seismic avant.de=enstrated that no thermalwill shield ue (8) not applicable to this license condition.The.. provisions are o i

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I Amendment No. 127

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c \; Ci4f SAFETY EVALUATION EY THE OFFICE.0F WUCLEAR REACTOR RE RELATED To. AMENDMENT.UO.127TO PROVISIONAL OPERATIN SOUTHERN CALIFORNIA EDISON. COMPANY' SAW.DIEGO GAS.AND ELECTRIC. COMPANY SAN ONOFRE NUCLEAR. GENERATING STATION, UNIT NO. 1 DOCKET NO. 50-206' 1.0 It'TRODUCTION By letter cated February 17, 1989, as supplemented Marcn 21.and 22, and May 3 and 8, 1989, Southern California Edison Company (SCE or the licensee) requested a change to Provisional Operating License No. DPR-13 for.

operation of San in San Diego Onofre County, Nuclear Generating Station, Unit No.1, located California.

2.0- DISCUSSION In response to an alert from the reactor vendor that reactor vessel .

thermal shield fasteners 6t another facility had been found degradec, SCE inspected the thermal shield for SONGS-1 on January 3-4,'1989. The thermal shield at San Onofre Unit I surrounds the reactor core barrel.

It is 21" thick and about 10 feet in height, and weighs 48,000 lbs. It is supported at the bottom by six support blocks and thirty bolts which attach it to the core barrel. Support at the top is proviceo by six flexures and 4 limiter keys. Five of the six flexures have been known to have been broken since 1978.

The licensee described the inspection results and presented video tape recordings at a January 27, 1989 meeting. During the last refueling outage visual examinations were performed with the internals installed using a high resolution underwater television camera system. Although the core was loaded during the inspection, selected fuel assemblies were shuffled to provide access.

The licensee confirmed that five of six thermal shield flexure fixtures are broken as detected in a previous inspection. Three cut of thirty thermal shield support block bolts are broken.

bolts in support blocks at the 0* and 240' locations.TheseNo areother the 7/8-inch signiti- top cant degradation was observed visually. Ultrasonic testing was not performed.

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, l The licensee has evaluated operation with the thermal shield in the conoition worst observed expected, and considered worst credible, three cases which it characterizes) and worst conceivable.

j The worst expected case involves the degradation of bolts'at the third support block, and the sixth flexure remaining intact. The worst creotble  !

case assumes that all support blocks degrade (all bolts broken) and the last flexure breaks. The worst conceivable case involves the therma )

shield dropping or moving cownward eleven inches to rest on the core  !

barrel radial support keys. 4 In addition to the analyses presented by the licensee, the licensee proposes to inspect the thermal shield during a June 1990 mid-cycle outa {l using tion. the same equipment and rethods used during the January 1989 inspecge i The licensee also proposes to use two monitoring methoes while in operation to detect any further degradation of the thermal shield:- 1 1

neutron noise moratoring and loose-parts monitoring. The licensee i

propuses to shut down if it determines through the monitoring program that the sixth flexure has 1ailad. l 3.0 EVALUATION The video tapes recorded during the visual examination demonstrate that the thermal shield is still in its original position at this time. The tapes do not show any evidence of motion of the thermal shield. The tapes show that three bolts (two in one block; one in another) are protruding sufficiently far beyond allowable tolerances that it is reasonable to assume that they have drifted inward from vibration and are broken.

Because the inspection was only visual it cannot be known if these are the only broken or cracked bolts. Licensee's vibration analysis concludes that the 240' and O' blocks are degraded ar.d that the 300* block would probably degrade during cycle X.

Furthermore, the licensee states and the inspection does demonstrate that the thermal shield is not in the " worst credible" condition or close to it because the last flexure is still intact and no support block wear or ,

thermal shield motion has occurred.

if all of the bolts and dowel pins in a block were failed. No Support evidence block wear w exists to thistocondition.

suggest that any individual support block assembly has progressed The vibration snalysis predicts that a third support block will probably degrade during operation in cycle X, but that no damage will occur to the thermal shield. The analysis performed by the ifcensee used a simplified model consisting of beam elements.and springs to represent linear and rotational stiffnesses of the system. The staff reviewed the pertinent information provided by the licensee and concluded that there are serious flaws in the methodology, modeling and in the evaluation of stresses which would result from the impactive loaos on the support blocks induced by the vibratory motion of the thermal shield. Because the analysis was found to be unacceptable by the staff, the Itcense has been requested to

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perform a mid-cycle inspection and to improve the proposed sonitoring program whereby any further degradation of the shield supporting elements personnel.

operating could be quickly detected and appropriate action taken by At the meeting with the licensee on May 1, 1989, the NRC staff presented its requirements for an inspection of the thermal shield at the mid-cycle outage and changes to the proposed license conditions on thermal shield monitoring. The licensee agreed with the staff position and confirmed this agreement in its letters to NRC dated May 3 and 8, 1989.

In evaluating the safety issues regarding the thermal shield the staff took under consideration the following sequence of events which must take-place prior to the situation which may cause a safety concern. The scenario which would cause a concern is that the shielo tould drop to the bottom coolant of core.

to the the reactor vessel and therefore obstruct the flow of In order that such a situation could exist' the shield must be deprived of its supporting elements and the following stages of further degradation would have to occur:

(1) Failure of the sixth flexure (2) Failure of the all bolts at each support block (3) Shearing off the support blocks which hold the shield in the present position, and (4) Failure of the lower core radial supports The staff criteria require that the licensee provide an edecuate neutron noise monitoring program which will detect any further degradation of any of the above elements and that the plant will be shut down imediately after failure of the remaining flexure, thus precluding any further deterioration of the reactor internals. The staff believes that such an arrangement coupled with the mid-cycle inspection provides adequate assurance of' safety.

The noise signal from the ex-core power range neutron flux detectors will be recorded periodically and analyzed to monitor internal vibrations of j the thermal shield. Four accelerometers mounted on the reactor vessel i flange will monitor acoustical noise in order to detect the possible  ;

l appearance of loose parts in the lower dome of the vessel.

The neutron noise analysis will probably not be effective in detecting gradual degradation of the fasteners, but failure of the last flexure ,

would allow a large beam-mode oscillation at a much lower frequency which '

would be detectable. The occur, as discussed above. plant would be shut down for repairs should this l

i The three bolts which were found to be broken will likely drift out all the way anc become loose parts at some point in cycle X. These parts i will most likely fail to the bottom of the pressure vessel because of their weight and settle in a location of low flow velocity. Detection of s loose parts such as these under these circumstances would not be itkely i i

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due to the reactor arrangement vessel flange. of the accelerometers which are mounted on the In the unlikely event that the loose parts are lifted up against the flow distribution or core support plates, no adverse impact is expected, and these impacts may be detectable since these locations communicate rore directly with the accelero-meters.

The licensee and consultant (Westinghouse) have analyzed the changes in reactor drop 11"coolant flowbarrel to the core to the coresupports.

radial in the event the shield should tilt or The changes in flow and flow distribution would are therefore acceptable. be minor and within the design parameters, and We conclude that operation in cycle X as proposed is acceptable.

4.0 ENVIRONMENTAL CONSIDERATION

4 Pursuant to 10 CFR 51.21, 51.32, and 51.35, an environmental assessment and finding of no significant impact have been prepared and published in the Federal Reaister en May 11 1989 (54 FR 20459). Accordingly, based upon the environmental assessme,nt, the Commission has determined that the issuance of this amendment will not have a significant effect on the quality of the human environment.

5.0 CONCLUSION

We ha've concluded, based on the considerations discussed above, that:

(1) there is reasonable assurance that the health and safety of the public will not be encangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations and (3) the issuance of this amendment will not be inimical to the common defense ano security or to the health and safety of the public.

Principal Contributors: R. Lipinski L. Lois C. Trammell M. Hum Dated: May 15, 1989 l

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7590-01 j UNITED STATES NUCLEAR REGULATORY COMMISSION SOUTHERN CALIFORNIA EDISON COMPANY, ET AL.

DOCKET NO. 50-206 NOTICE OF ISSUANCE.0F AMENDNENT TO PROVISIONAL OPERATING LICENSE The U.S. Nuclear Regulatory Comission (Comission) has issued Amendment No.127to Provisional Operating License No. DPR-13, issued to Southern California Edison Company and San Diego Gas and Electrit, Company (the licensees), for operation of the San Onofre Nuclear Generating Station, Unit No.1 located in San Diego County, California. The amendment was effective as of the date of issuance.

The amendment provides for a reactor vessel thermal shield monitoring pro-gram and mid-cycle inspection until the thermal shield fasteners are repaired during the fuel cycle XI refueling and 10-year ASME Inservice Inspection.

The application for the amendment complies with the standards and requirements of the_ Atomic Energy Act of 1954, as amended (the Act), and the Comission's regulations. The Comission has made appropriate finoings as required by the Act and the Comission's regulations in 10 CFR Chapter 1, which are set forth in the license amendment.

Hotice of Consideration of Issuance of Amendment and Opportunity for i i

i Hearing in connection with this action was published in the FEDERAL REGISTER on l March 2, 1989 (54 FR 8854). No request for a hearing or petitions for leave to intervene were received. Subsequent to issuance of this notice, the licensees provided supplemental information by letters dated March 21 and 23 and May 3 and 8, 1989. These letters provided additional information and revised cum ttments encompassed by the original notice, ww , , ~

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The Commission has prepared an Environmental Assessment related to thisi action and has concluded that an environmental impact statement need not be prepared because operation of the facility in accordance with this amendment will have no significant adverse effect on the quality of the human environment.

For further details with respect to the action see (1) the application for amendment dated February 17, 1989, as supplemented March 21 and 23 an j

May 3 and 8,1989, (2) Amendment No.127to License No. DPR-13, (3) the ^

i Commission's related Safety Evaluation and (4) the Commission's Environmental!

. Assessment.

All of these items are available for public inspection,at the Commission's Public Document Room, 2120 L Street NW., Washington, 20555, DC and at the General Library, University of California, P.O. Box 19557, Irvine, California 92713.

A copy of items (2), (3) and (4) may be obtained upon request j

addressed to the U.S. Nuclear Regulatory Commission, Washington, DC 20555, Attention:

Director, Division of Reactor Projects - III, IV, V and Special P.rojects.

Dated at Rockville, Maryland this 15 day of May,1989.

FOR THE NUCLEAR REGULATORY COMMISSION i

$r lf Charles M. Trammell, Senior Project Manager Project Directorate Y Division of Reactor Projects III, IV, V and Special Projects Office of Nuclear Reactor Regulation

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,. ENCLOSURE 3

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Docket No. 50-206 l l

l Dr. Larry T. Papay, Senior Vice President Southern California Edison Company Post Office Box 800 (

2244 Walnut Grove Avenue Rosemead, California 91770

SUBJECT:

OPERATION OF SAN ONOFRE UNIT 1 This refers to the NRC Confirmatory Action Letter (CAL) dated January 31,-1989 and the CAL followup-letter dated February 8,1989. These letters identified-certain technical. issues to be resolved before Unit I restart and requested your assessment of the aggregate significance of the various single failure and other design problems identified in recent months.

As discussed during our May 1, 1989 meeting and documented in the enclosed

. meeting report, your 7.etters dated March 17 and April 18, 1989 presented the bases for your conclusion that Unit I could safely return to service. We-concur with your characterization of the identified problems and recognize-that you have established programs to identify other potential deficiencies.

be We alsoby identified understand these ongoing that there well may(e.g.other programs design enhanced engineering deficiencies here

/ design activities, design basis upgrade program) a,nd expect that they will be assessed and handled consistent with estabitshed procedures and the requirements of your license. - Accordingly, the NRC hereby concurs with your intention to restart-San Onofre Unit 1.

This conclusion was reached in coordination with the Region V Regional Administrator and is also based on your satisfactory response to NRC concerns,  !

as documented in the meeting summary and your written certification dated May 12, 1989 that all commitments made to the NRC for actions to be completed i

during the Cycle 10 refueling outage have in fact been completed.

Sincerely, 1

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Enclosure:

Meeting Summary -

cc w/ enclosure:

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, Mr. Kenneth P. Baskin San Onofre Nuclear Generating

. Southern California Edison Company Station, Unit No. I cC.

Mr. Kenneth P. Baskin .

Vice President Southern California Edison Company 2244 Walnut Grove Avenue Post Office Box 800 Rosemead, California 91770 David R. Pigott Orrick, Herrington & Sutcliffe 600 Montgomery Street San Francisco, California 94111 Mr. Robert G. Lacy Manager, Nuclear San Diego Gas & Electric Company P. O. Box 1831 San Diego, California 92112 Resident Inspector / San Onofre NPS U.S. NRC P. O. Box 4329 San Clemente, California 92672 Mayor City of San Clemente San Clemente, California 92672 Chairman Board of Supervisors County of San Diego  ;

1600 Pacific Highway Room 335 i San Diego, California 92101  ;

Regional Administrator, Region V ,

U.S. Nuclear Reguistory Commission 1450 Maria Lane, Suite 210 Walnut Creek, Ca?ifornia 94596 Mr. Paul Szalinski, Chief Radiological Health. Branch State Department of Health Services 714 P Street, Office B1dg. f8 Sacramento, California 95814 (7)

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• i May 15, 1989 1

I Mr. Lando W. Zech, Jr. i Chairman, Nuclear Regulatory Commission .i 1717 H Street, N . W. i Washington, D.C. 20555 Dear Chairman Zech )

We are writing with regard to the possible restart of San Onofre's Unit I reactor. It has been brought to our attention that potential safety concerns have arisen in connection with the thermal shield of this unit.

We understand that three broken bolts on two support blocks were discovered and there is concern over the, possibility of an obstruction slip. of the flow of cooling water'if the shield were to We would appreciate an explanation of this situation and would like to be kept informed of the NRC's ultimate decision.

1.ncerely, Alan Cranston, U.S.S.

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Pete Wilson, U.S.S. '

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