ML20042D315
| ML20042D315 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 12/29/1989 |
| From: | Taylor J NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | Cox C HOUSE OF REP. |
| Shared Package | |
| ML20042D316 | List: |
| References | |
| CCS, NUDOCS 9001080264 | |
| Download: ML20042D315 (5) | |
Text
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NUCLEAR REGULATORY COMMISSION g
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December 29,1989 The Honorable Christopher Cox
.Ur.ited States House of Representatives
}ashington, D.C.
20515 Gear Congressman Cox:
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I.am responding to your letter of December 12, 1989, regarding your constituent, Mrs. Elise Ranauro, who expressed concern about operation of Southern California Edison's San Onofre tinit 1 facility with cracked bolts in the reactor vessel thermal shield. The U.S. Nuclear Regulatory Comission (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 i
irradiation damage to the vessel wall. Bolts are used to attach the bottom of l
the thermal shield to the core barrel, and spring-like devices called flexures L
are attached at the top.
Four lateral displacement limiters are also located at the top.
L On Januarv 3,l shield with a remote camera; 24 of 30 bolts could bc visually 1989 of the therma E
inspected. Three bolts out of the 24 inspected were found to be broken.
In I
addition, the locking devices for two bolts and the locking device for one dowel pin had cracks.
Five out of six flexures at the top of the thermal shield have been broken since 1978. The flexures were originally added to I
provide radial and tangential restraint to the top of the thermal shield.
When these flexures were discovered to be broken, an evaluation was made which concluded that the flexures were unnecessary.
In reviewing the results of the January inspection, the licensee found no evidence of damage to, or motion of, the thermal shield.
On January 31, 1989, the NRC sent the licensee a letter requiring that this matter be resolved to our satisfaction before plant startup. The licensee and its consultant, Westinghouse Electric 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 worstconceivablecaseofthermalshieldmovement,flowofcoolingwaterto the reactor core would not be significantly affected.
Based on the analysis, the licensee >roposed to return San Onofre Unit I to power and monitor the condition of t1e thermal shield during operation by l-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 as failure of the sixth flexure could be an t
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' 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 inspec-tion would be conducted not later than June 30, 1990, to visually confirm the expected behavior of the thermal shield.
Based on'the foregoing, the NRC staff issued an amendment 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. On May 16, 1989, the staff concurred in.the licensee's evaluation of the remaining technical issues and authorized restart of Unit 1.
In a letter' dated October 2, 1989, Southern California Edison advised us that it will proceed with repairs to the thermal shield in the outage commencing June 30, 1990, rather than conduct an inspection.
I trust this information is responsive to your request.
If you have any further questions on this matter, please contact me.
Sincerely, Original Signed By:
James M. Taylor James M. Taylor Executive Director for Operations
Enclosure:
Thermal Shield Diagram DISTRIBU110N N.(50-206)%
GPA/PA l
NRC' PDR w/cy of" incoming J. Taylor Local PDR w/cy of incoming G. Holabn l
LD0 #4996 J. Zwolinski ED0 Reading' J. l.ee l
T. Murley/J. Sniezek PD5 Green Ticket File l
J. Partlow PD5 Reading w/cy of incoming a
G..Holahan M. Krebs OGC C. Trammell w/cy of incoming
'J. Martin, Region V F. Miraglia F. Gillespie D. Crutchfield DMossburg, PMAS (ED0#4996) w/cy of incoming
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EDO Principal Correspondence C see,*
-FROM DUE: 01/02/90.
EDO CONTROL: 0004996 7
-DOC'DTr. 12/12/89 FINAL REPLY:
oREP.= CHRISTOPHER COX
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GRN CRC NO: 89-1338
' EXECUTIVE: DIRECTOR l
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'l CONSTITUENT; MRS,-lELISE RANAURO, CONCERNS ADOUT JMARTIN. RV
>THE CAFRTY OF.THE RESTART OF SAN ONOFRE UNIT 1
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NRRRECEIVEDi DEC: 18, 1989 iV ACTION:.
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OFFICE OF THE SECRETARY CORRESPONDENCE CONTROL TICKET
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-PAPER NUMBER:
CRC-89-1338 LOGGING DATE: Dec 17 89
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<; ACTION OFFICE:
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' AUTHOR:~
Christopher'Cox l
AFFILIATION:
U.S.. ROUSE OF REPRESENTATIVES E
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' LETTER DATE:
Dec 12 89 FILE CODE:.~ID&R-5 San Onofre i
-Safety of the San Onofre gen sta--rpts of broken l
O SUBJECT.
bolts on the thermal shield i
ACTION::
Direct Reply DISTRIBUTION:
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LSPECIAL HANDLING: None-t I~
NOTES:
j DATE DUE:
Jan: '2 90 f
SIGNATURE:
DATE SIGNED:
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AFFILIATION:
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Rec'd O!!. ED0 Date
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