ML20029D037

LER 94-004-00:on 940324,found Five Slow Rods While Scram Time Testing Was Being Performed.Caused by Contamination of Internal Scram Solenoid Pilot Valve Head Assemblies. Corrective Action:Install New Head assemblies.W/940426 Ltr

ML20029D037
Person / Time
Site:	Grand Gulf
Issue date:	04/26/1994
From:	Holifield C, Hutchinson C ENTERGY OPERATIONS, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GNRO-94-00069, GNRO-94-69, LER-94-004-02, LER-94-4-2, NUDOCS 9405030317
Download: ML20029D037 (6)

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• R;tt Gbrn M5 39150 ki 601437 2KO C. R. Hutchinson a v w>ca April 26, 1994 oa n cmmu n a w, l

U.S. Nuclear Regulatory Commission  ;

Mail Station P1-137 l Washington, D.C. 20555 i

Attention: Document Control Desk

SUBJECT:

Grand Gulf Nuclear Station Unit 1 Docket No. 50-416 License No. NPF-29 Multiple Control Rods Failing Technical Specification Scram Time Requirements LER 94-004-00 GNRO-94/00069 Gentlemen:

I Attached is Licensee Event Report (LER)94-004 which is a final report.

Yours truly, Q4/ ~

CRH/CDH attachment cc: Mr. R. H. Bernhard(w/a)

Mr. H. W. Keiser(w/a)

Mr. R. B. McGehee (w/a)

L Mr. N. S. Reynolds_(w/a) l Mr. H. L. Thomas (w/o)

Mr. Stewart D. Ebneter (w/a)

Regional Administrator U.S. Nuclear Regulatory Commission Region II 101 Marietta St., N.W., Suite 2900 Atlanta, Georgia 30323 Mr. P. W. O'Connor Office or Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Mail Stop 13H3 Washington, D.C. 20555 I

9405030317 940426

(( DR ADOCK05000gg6

April-26, 1994 GNRO-94/00069 Page 2 of 2 i bec: Mr. P. W. Alberstadt (w/a) l Mr. C. A. Bottemiller (w/a)

Mr. R. W. Byrd (w'a)

Mr. L. F. Dalt s/o)

Mr. L. F. Daus it *ry (w/a) l Mr. J. G. Dewt se (w/a)

Mr. M. A. Diet .ch (w/a)

Mr. C. M. Dugg( s- (w/a)

Mr. J. L. Ensley (ESI) (w/a)

Mr. C. C. Hayes (w/a)

Mr. C. D. Holifield (w/2)

Mr. M. G. Hurley (w/a)

Mr. R. J. King (ANO) (w/a) l Mr. L. W. Laughlin (W3) (w/a) l Mr. R. M. Liddell (w/a)

Mr. M. J. Meisner (w/o)

Mr. R. V. Moomaw (w/a)

Mr. D. L. Pace (w/a)

Mr. R. L. Patterson (w/a)

Mr. T. E. Reaves (w/a) l Mr. G. D. Swords (w/a)

Required Reading Coordinator (w/a)

SRC Secretary (w/a)

File (LCTS) (w/2)

File (RPTS) (w/a)

File (NS&RA) (w/a)

File (Central) (w/a) (6)

INPO Records Center (w/a) 700 Galleria Parkway Atlanta, Georgia 30339-5957 Mr. W. T. Donovan (w/a)

Illinois Power Company Clinton Power Station Mail Stop V-920 P.O. Box 678 Clinton, Illinois 61727 Mr. J. J. Fisicaro (w/a)

River Bend Nuclear Station Mail Stop MA-3 Gulf States Utilities P.O. Box 220 St. Francisville, LA 70775

Attachment to GNRO-94/00069 NRC. FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB No. 31504104 (5M) EXPIRES 5/31/95 IN O TION C E RE S 50 HR WR LICENSEE EVENT REPORT (LER) COMMENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AND RECORDS MANAGEMENT BRANCH (MNB8 D TO PAPERWOR R OJECT (3150 4104). OFFICE OF MANAGEMENT AND BUDGET.

W ASHINGTON. DC 20503 FActuTV NAML (i) DOCKET NUMBER (2) PAGE (3)

Grsnd Gulf Nuclear Station, Unit 1 05000-416 01 of 04 TITLE (4)

Multiple Control Rods Falling Technical Specification Scram Time Requirements EVENT DATE (5) LER NUMBER (6) REPORT DATE (7) oTHER FACILITIES INVOLVED (8)

MCMTH DAY YEAR YEAR SEQUENTIAL REVISION MONTH DAY YEAR F ACILITY NAME DOCKET NUMBER NUMBER NUMBER N/A 05000 F ACluTY NAME DOCKET NUMBER 03 26 94 94 004 00 04 26 94 N/A 05000 OPERATING THIS REPORT IS SUBMITTED PURSUANT To THE REQUIREMENTS oF 10 CFR l (check one or more)(11)

MODE (9) 1 20.402(b) 20.405(c) 50.73(a)(2)(iv) 73.71(b)

POWER 20.405(a)(1)(i) 50.36(c)(1) 50.73(a)(2)(v) 73.71(c)

LEVEL (10) 073 20.405(a)(1)(ii) 50.36(c)(2) X 50.73(a)(2)(vii) OTHER 20.405(a)(1)(iii) 50.73(a)(2)(i) 50.73(a)(2)(viii)(A) DC FN7'" '"

M -

20.405(a)(1)(iv) 50.73(a)(2)(ii) 50.73(a)(2)(viii)(B) 20.405(a)(1)(v) 50.73(a)(2)(iii) 50.73(a)(2)(x)

LICENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER (inclue. Ar Cod.)

Charles Holifield / Licensing Engineer 601-437-6439 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE SYSTEM COMPONENT MANUFACTURER R TABLE CAUSE SYSTEM COMPONENT MANUFACTURER RE A E B AA V A610 Y EXPECTED M NTH DAY YEAR SUPPLEMENTAL REPORT EXPECTED (14)

YES X NO SUBMISSION (if y . com#e. EXPECTED SUBMIS$10N DATE)

DATE (15)

ABSTRACT (umn 14co c..l . . .ppn= mat.e v is mv c.d typ.wmt.a i,a msi On March 26,1994, scram time testing was being performed which found five slow rods. Although these failures did not constitute a violation, the plant was ordered shutdown in consideration of Technical Specification 3.1.3.2 Action c.1. An additional 163 control rods were analyzed at 0001 on March 27, 1994, when the reactor was manually scrammed and scram times recorded. Of these rods,44 additional rods were slow moving but all were satisfactory for insertion to position 13.

Tha cause of the slow moving control rods was determined to be contamination of the internal surfaces of tha scram solenoid pilot valve head assemblies. A thread sealant used during maintenance on the valves caused the seats in the top head assembly to adhere slightly to adjacent surfaces resulting in a delay in the initial opening of air exhaust ports. In its uncured state, the sealant attacked the viton seats and may have caused metallic moving parts to stick.

Immediate remedial actions included installing the pilot valve top head assemblies using a thread sealant tapa rather than the sealant previously used and using an approved detergent to clean 193 new assemblies.

Long term corrective actions are: evaluate training maintenance personnel on proper use of various thread sealants, write generic procedure on proper use of various thread sealants and evaluate, in other applications, the use of sealants and other similar generic materials.

A r: view of operating data determined that all safety systems behaved as expected. This incident did not degrade the ability of other plant systems or equipment to perform their intended function. The safety and health of the general public were not compromised by this event.

i Attachment to GNRO-94/00069 NRC. FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 31604104 j Sn) EXPlRES 54126 5"#A**ca"en"h"0TM 'mRT EM LICENSEE EVENT REPORT (LER) g g REgARo smgN EgAg g TEXT CONTINUATION g AR E TMY OF MANAGEMENT AND BUDGET, 1 04) OFF f ACILRY NAME (1) DOCKET NUMtsER (2) LER NUME6ER (6) PAGE (3)

Grand Gulf Nuclear Station, u.ilt 1 05000-416 94-004-00 2 of 04 A. Reportable Occurrence

On March 26,1994, scram time testing was being performed on 20 randomly selected control rods in

addition to post-maintenance testing of 6 other control rods with recently rebuilt Hydrualic Control Units. The testing resulted in failure of 4 rods from the sample group in addition to failure of one rod from the post-maintenance test group. Being only one control rod failure away from the 10 percent Tcchnical Specification limit, the plant was ordered shutdown in consideration of Technical Specification 3.1.3.2 Action c.1. This event could have eventually resulted in a condition that alone might have prevented the fulfillment of the Control Rod Drive System [AA) safety function. This

condition is reportable per 10 CFR 50.73(a)(2)(vii).

i I

B. Initial Condition 4

The reactor was in OPERATIONAL CONDITION 1 with reactor water level, temperature and power at 36 inches,530 degrees F and 73 percent respectively. Scram time testing was being performed.

l C. Description of Occurrence

! On March 26,1994, scram time testing was being performed on 20 randomly selected control rods in

! addition to 6 other control rods with recently rebuilt Hydraulic Control Units. Twelve rods had been

tested resulting in eight fast and four slow times obtained for insertion from position 48 to position

! 43. Testing the next rod scram time resulted in the fifth slow rod. Since all slow rods were not a part of the 10 percent sample group, this failure did not constitute a violation of Technical Specifications.

The plant was ordered shutdown in consideration of Technical Specification 3.1.3.2 Action c.1. An 1 additional 163 control rods were analyzed at 0001 on March 27,1994, when the reactor was manually scrammed and scram times recorded. Of these 163 rods,44 additional rods were slow l moving to position 43. However, all rods were satisfactory for insertion to position 13, i I A nonconformance report was issued to identify the slow scram times for the 49 control rods.

Disposition of the nonconformance report required that Electrical Maintenance remove and replace all scram pilot valve head assemblies. Removed assemblies were retained for testing and l

inspection to aid in a root cause determination.

l

Attachmnnt to GNRO-94/00069 NRC. FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3160 0104 rA2) EXPIRES 6/31/95 OR T ON COLLE RE hT 50 HR ORW R o

LICENSEE EVENT REPORT (LER) gyg R,eg4R gNyA TEXT CONTINUATION u R4egTgyg g g g

@ 540 OFF OF MANAGEMENT AND BUDGET, F ACUTY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) )

Gr:nd Gulf Nuclear Station, Unit 1 05000-416 94-004-00 3 of 04  ;

D. Apparent Cause Th3 cause of the slow control rods was determined to be contamination of the internal surfaces of the scram solenoid pilot valve (SSPV) head assemblies. A thread sealant used during maintenance work on the SSPVs caused the elastomeric (Viton) seats to adhere slightly to the adjacent seating surfaces, resulting in a delay in the initial opening of air exhaust ports. In its uncured state, the thread sealant attacked the Viton seats, and may also have caused metallic moving parts to stick upon curing.

Further investigation revealed that the root cause was the lack of readily available vendor and industry experience information related to the incompatibility of thread sealant materials with Viton seating materials. Vendor supplied SSPV installation instructions indicate that a pipe compound should be used. However, a list of vendor approved compounds is not provided. Numerous thread l sealant materials have been used on SSPV connections throughout the industry, with varying d::grees of success. Thread sealants have been identified as contributing to SSPV malfunctions in cases where excess sealant was introduced into the valve internals. Industry experience identified that SSPVs with urethane seat materials could be adversely affected by use of sealants with ester base. However, use of urethane seats was discontinued by the vendor in favor of Viton seats.

SIL 509 was reviewed by GGNS in 1990 and it was determined that all urethane rebuild kits at GGNS had been discarded. No further action was considered necessary in response to SIL 509.

The potential for ester based thread sealants to contribute to malfunctions in SSPVs with Viton seats was identified by GE in 1991 after SSr>V malfunctions at Perry. However, this information was not widely disseminated throughout the industry. SSPV malfunctions at Brunswick 2 in October,1993 were also later attributed to use of a thread sealant similar to that used at GGNS. Information regarding the root cause of the malfunctions was not made available until March,1994. The lack of detailed information related to the potential effects of thread sealant compounds on Viton resulted in this failure mechanism not being identified by GGNS. Therefore, the potential effects of changes in tho SSPV rebuild process during RF06 were not fully considered.

During RF06, the SSPVs were rebuilt in the field using the valve manufacturer's pre-assembled rcplacement top-head assembly. Rather than removing and replacing the entire valve as a unit, only tha top-head assembly kit and diaphragm kit were replaced. Neolube 100, a Methacrylate Ester based thread sealant, was used on tubing fittings at the air intet port as done in the past. In some cases, the valves were pressurized soon after installation and the Hydraulic Control Unit (HCU) returned to service during the shift following the SSPV rebuild. When returning a HCU to service, tha SSPV is tested in place which results in a couple of air blasts through the valve. This apparently caused the uncured Neolube 100 to migrate within the valve internals.

Attachment to GNRO-94/00069 NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3160-0104 fu2) EXPIRES 5/31/96 MYMATON CE"E RE 5 50 HR W LICENSEE EVENT REPORT (LER) gg RgARy BURgN A TO TEXT CONTINUATION E R RE uta ss4Nya MANAGEMENT AND BUDGET, oi g g OFF g OF F ACLITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

Grand Gulf Nuclear Station, Unit 1 05000-416 94-004-00 4 of 04 D. Apparent Cause (cont'd)

Prior to RFO6, the SSPVs were rebuilt in the shop by insta!Mg replacement parts kits. During this rebuild process, Neolube 100 was used as a thread sealant. After rebuilding, the valves would be sat aside for days awaiting reinstallation. Since Neolube 100 requires only 24 to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> in the presence of metal ions and the absence of oxygen to cure properly, this pre-RFO6 rework process adequately allowed for this cure time and did not result in SSPV malfunction.

Saveral contributing causes of the SSPV malfunctions were identifed during the investigation. The work instructions for rebuilding the SSPV had a precaution regarding introduction of Neolube 100 into the air system, but did not specify the proper method for applying the thread sealant. Also, parforming the rebuild work in the field rather than in the shep, as had been done in the past, made it more difficult to keep the valve internals completely free of thread sealant. A final contributing cause was that evaluations of two previous similar events at GGNS were not successful in identifying the root cause of suspected SSPV malfunctions.

E. Corrective Actions immediate remedial actions included:

- Using an approved detergent, disassemble and clean 193 new SSPV top head assemblies.

- Install new top head assemblies using Teflon tape as a thread sealant.

- NPE evaluated similar industry events to provide possible generic implications.

Long term corrective actions are:

- Evaluata training maintenance personnel on proper use of various thread sealants.

- Write generic procedure on proper use of various thread sealants.

- Evaluate use of sealants and other similar generic une rnatorials in other applications.

F. Safety Assessment Tha plant was manually scrammed from 73 percent power. Based on a review of operating data, it was determined that all safety systems behaved as expected. l his incidFnt resulted in slow control rod operation but scram function was still maintained. Additionally, it did not degrade the ability of oth:r plant systems or equipment to perform their intended function. The safety and health of the general public were not compromised by this event.

G. Additionalinformation Energy Industry identification System (Ells) codes are identified in the text within brackets [ ).

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