ML13308B443
| ML13308B443 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 10/14/1977 |
| From: | Head J SOUTHERN CALIFORNIA EDISON CO. |
| To: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| References | |
| NUDOCS 8103050906 | |
| Download: ML13308B443 (3) | |
Text
Southern California Ed/so yC mDany P. 0. sox 800 2244 WALNUT GROVE AVENUE J.T.
HEAD, JR.
ROSEMEAD, CALIFORNIA 91770 TELEPHONE VICE PRESIDENT 213-572-1472 8
October 14, 1977 4
U. S. Nuclear Regulatory Commission (4
R Region V
/Ast Office of Inspection and Enforcement Walnut Creek Plaza, Suite 202 1990 North California Boulevard Walnut Creek, California 94596 011 ATTENTION: Mr. R. H. Engelken, Director Docket No. 50-206 San Onofre Unit 1
Dear Sir:
Reference:
Letter from SCE (Mr. J. M. Curran) to USNRC, Region V dated October 3, 1977 The referenced letter provided prompt notification to the Regional Office of an unplanned reactivity insertion due to Boron dilution during the past maintenance outage. This letter constitutes the follow-up report submitted in accordance with the provisions of Section 6.9.2.a of Appendix A to the Pro visional Operating License No. DPR-13.
The U-Bend sections of three tubes were removed from "B" Steam Generator for metallurgical analysis on September 23, 1977. This activity was conducted to determine the condition of tubes following the antivibration bar modifica tion performed during the past refueling outage. The tube U-Bend regions were cut into four pieces using a tungsten inert gas (TIG) torch and removed through an opening cut into the steam generator swirl vane riser. Cuts were made at six inches above the fourth support plate and in three other locations spaced around the U-Bend.
Following tube removal operations, an eddy current inspection was performed on tubes adjacent to those removed to determine if any damage had been caused by the tube cutting operation. One of the adjacent tubes (Row 42, Column 76) was noted as being restricted at the fourth support plate and therefore not tested around the U-Bend where damage was most likely to occur. The significance of this restriction was not identified when the data was first reviewed. Our procedures required that tubes listed as restricted be retested with smaller diameter probes until the restriction is transversed or an attempt to pass the smallest probe available is unsuccessful. Tubes that were restricted to
U. S. Nuclear Regulatory Commission October 14, 1977 Page 2 the extent that an eddy current inspection could not be conducted from either the cold leg or the hot leg side were to be explosively plugged.
Tube R42-C76 was inadvertently not retested with a smaller diameter probe or explosively plugged.
On October 1, 1977, at the completion of eddy current testing, thirteen (13) tubes were explosively plugged in "B" steam generator. The water level in the secondary side was subsequently raised to 210 inches. This was done to provide personnel shielding while welding on that section of the swirl vane riser previously removed for access to the tube bundle. Approximately one-half hour later the control room operator noted that the water level had decreased to 185 inches and the boron analyzer reading had decreased about 80 ppm. Investigation revealed that secondary to primary side leakage was occurring through a defect in Tube R42-C76. The water level was then lowered to a point below the tube defect and the reactor coolant system borated to compensate for the dilution.
During steam generator maintenance, the reactor coolant system is drained to mid-loop. This corresponds to a water volume of about 13,200 gallons. At the time of the dilution, Boron concentration was 1609 ppm.
This provided a shutdown margin of greater than 6% Ak/k (1410 ppm Boron provided 6% Ak/k shutdown under conditions existing at the time).
Follow ing the dilution, a boration of 50 gallons of 12% boric acid was made to return the boron concentration to its initial value.
The calculated change in concentration that occurred during the dilution was 75 ppm. This agrees closely with the boron analyzer trace readings and corresponds to a positive reactivity insertion of $1.16. The reactor, there fore, remained shutdown by greater than 6% Ak/k during the entire transient.
It should also be noted that containment integrity as defined by our technical specifications was intact throughout the transient.
In order to prevent a recurrence of this incident following future tube removal operations, the tube sheets will be visually inspected for leakage during filling of the steam generator secondary sides. This precaution will be in addition to our continued use of eddy current testing to identify tube defects.
Sincerely
Attachment:
LER 77-014/01T-0 cc: Director, Office of Inspection and Enforcement (40)
Director, Office of Management Information & Program Control (3)
LER 77-014/01T-0 NRC FORM 366 U. S. NUCLEAR REOULATORY COMMISSION
(-7-77)
LICENSEE EVENT REPORT CONTROL BLOCK:
(PLEASE PRINT OR TYPE ALL REQUIRED INFORMATION) 6 EE1 Cl1A IS10lS 111 010 10-10 10101 01-0 1) 1()
4
_11 1L 1Ij05 7
8 9
LICENSEE CODE 14 LICENSE NuM8ER 25 26 LICENSE TYPE J0 57 CT CON'T o011 SORE D
U6L-G15 10 1 010'1 210 16 7 11 1 01 Oil l 717
) 11 10 10 19 I j7 J1 7
a
&V f1 oOCKET NUNSER 68
. 69 EVENT DATE 74 75 REPORT DATE HU EVENT DESCRIPTION AND PROBABLE CONSEQUENCES 10 1o2 jAn inadvertent dilution of the eactor coolant system occurred when t
o3 I the secondary side of "B" steam generator was filled following tube
[oT I plugging operations. The dilution was caused by primary to secondary OF5 I leakage through a tube removal related defect in an adjacent tube.
[O6 Boron dilution of approximately 75 ppm resulted in a positive reactivity 0 ~
addition insertion of $1.16(T.S. 6.9.2.a (4). Shutdown margin remained 8 l>6%,containment integrity was intact.
7 89 SYSTEM CAUSE CAUSE COMP.
VALVE CODE CODE SUSCODE COMPONENTCOUE SUBCODE SUBCODE 0
C1LI L
a L
U 1
8-9 10 11 12 13 18 19 20 SEOLENTIAL OCCURRENCE REPORT REVISION LER'RO EVENT YEAR REPORT No.
CODE TYPE NO.
REPORT ZIJ U
ll 41 1J 111 L
d L
1 7 17 1-1
[ 0 11 1 4 Lt-1
- L2 22 22426 27 28 29 33 31 32 AATO AUTUOE OEFFEC SHUTDOW N HOR 2
ASBI D
FO B
E ATIN TUU; EFET SUDWTAHEN T
NPRD-4 PRIME CO,-.1P.
COMPONENT TKN ACTION ON PLANT METHOD HOURS ~?
UMTED FOR-M SUB.
SUPPLIER MANUFACTURER B S*j(9 LZ(
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10101 Li~ I N 1 1 W11 1210 l, 3
34 35 337 40 41 42 43 44 47 CAUSE DESCRIPTION AND CORREC OVE ACTIONS E ~I Eddy current testing indicated the defective tube was restricted I
at the fourth support plate. This restriction was not identified as being related to tube damage when the data was first reviewed
[T I by staff enqineers,'In the future tube sheets will be visually in I spected for leakage during filling of the secondary side.
FACItLTY METHOD OF STATUS
%POWER OTHER STATUS &
OISCOVEHY DISCOVERY DESCRIPTIO1Q EE [1J (
1010 10 C-NA I
[LJl l Operator observation 7
8 10 12 13 44 ACTIVITY CONTENT RELEASED OF RELEASE AMOUNT OF ACTIVITY 35 E
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7 8
9 10 11 44 PERSONNEL EXPOSuRES s
NU.ER TYPE.
DESCRIPTION
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10 1 0 @ ZN A
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flPE CEIONOO so METHO OF A
0';SC)FD-DAVLEOOFSCOVERY4 ISSUED SD DP0.
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80 L
O NAME OF PRE0AER J. M. CURRAN
'(714) 492-7700 o6