ML20154M164

Part 21 Rept Re Design Defect in Automatic Switch Co Tripoint SB12BMR/TL10A22 Pressure Switches.Surveillance Cycle Increased from Monthly to Semimonthly & Mfg to Assist in Determining Cause of Failure

ML20154M164
Person / Time
Site:	Yankee Rowe
Issue date:	04/26/1988
From:	Devincentis J YANKEE ATOMIC ELECTRIC CO.
To:	Russell W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
REF-PT21-88, REF-PT21-88-037-000 FYR-88-56, PT21-88-037-000, PT21-88-37, NUDOCS 8806010197
Download: ML20154M164 (3)

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• i Telephone (617) 872-8100 TWX 710-380 7619 YANKEE ATOMIC ELECTRIC COMPANY e

1671 Worcester Road, Framingham, Massachusetts 01701 April 26, 1988 FYR 88-56 United States Nuclear Regulatory Commission Office of Inspection and Enforcement Region I 475 Allendale Road King of Prussia, PA 19406 Attention: Mr. William T. Russel.1 Regional Administrator

Reference:

(a) License No. DPR-3 (Docket No. 50-29)

Subject:

Notification of Potential Existence of a Design Defect in Accordance with 10CFR21.21

Dear Sir:

In accordance with the provisions of 10CFR21, Section 21, we are hereby notifying you that we have obtained information indicating that a design defect may exist with respect to Automatic Switch Company Tripoint SB12BMR/TL10A22 pressure switches.

Enclosure I to this letter documents the details of this evaluation.

Should you have any questions regarding this matter, please contact me.

Very truly yours, YANKEE ATOMIC ELECTRIC COMPANY lq}

ohn DeVincentis Vice President JDV/25.560 Enclosure

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• ENCLOSURE I Page 1 of 2 Company Informing the Commission: Yankee Atomic Electric Company 1671 Worcester Road Framingham, Massachusetts -07101 Facility: Yankee Nuclear Power Station Star Route Rowe, Massachusetts 01367 Component: ASCO Tripoint SB12BMR/TL10A22 Pressure Switch Firm Supplying Components: Automatic Switch Company (ASCO)

Florham Park, New Jersey Nature of Defect on December 3, 1987, with the plant in Mode 1 at 100% power, five of the twelve main steam line isolation valve pressure switches were found during monthly surveillance to be out of Technical Specification tolerance (Technical Specification Table 3.3-2, Item 3.a). Of five pressure switches that failed the surveillance, three were adjusted back to the required trip setpoint. The remaining two (MS-PS-13 and MS-PS-31) were replaced in kind because of their failure to operate properly.

On April 5, 1988, the two failed switches (MS-PS-13 and MS-PS-31) as well as two other switches (MS-PS-24 and MS-PS-34 which had been replaced for deadband widening and setpoint drift on March 10, 1988 and March 25, 1988 respectively) were disassembled and inspected by ASCO in the presence of Yankee Atomic Electric Company (YAEC) personnel. This inspection revealed the polyurethane disc, which acts as a buffer to protect the process sensing viton diaphragm from adverse action of the piston had, in each of four switches, "extruded" into the area between the piston and the cylinder walls. The degree of extrusion varied from switch to switch witn at least one failed switch showing material over the top of the piston. Although no final report has, to date, been received from ASCO, this extrusion of material is currently considered as the cause of switch failure.

On April 6, 1988 inspection of two additional switches (MS-PS-32 and MS-PS-33 which were removed and replaced for deadband widening on March 26, 1988) noted the same extrusion mechanism as those pressure switches inspected at ASCO on April 5, 1988.

Date of Incident The pressure switch failure of MS-PS-13 and MS-PS-31 occurred on December 3, 1987. Licensee Event Report 50-29/87-15 was submitted on December 31, 1987. The potential Part 21 Report Evaluation was initiated on April 11, 1988.

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ENCLOSURE I Page 2 of 2 (Continued) r Number of Components

'YAEC has twelve safety-related ASCO Tripoint SB12BMR/TL10A22 pressure switches in service in the Main Steam Isolation System.

Corrective Action After the initial discovery of the failed pressure switches the routine surveillance cycle was increased from monthly to semimonthly and the manufacturer (ASCO) was contacted to assist in determining the cause of the pressure switch failures. Testing and inspection of failed pressure switches indicates the pressure switch failures and deadband widening are due to the generic failure / extrusion of the polyurethane disc. This type of occurrence has never been observed by ASCO.

YAEC has taken the following actions to ensure the pressure switch failure mode does not create a substantial safety hazard:

1. Replace in kind the remaining six pressure switches (MS-PS-11, 12, 14, 21, 22, and 23) as soon as practicable.

2. Perform the survelliance cycle biweekly until further evaluations indicate the switches are experiencing proper actuation.

3. Cycle each pressure switch three times during each surveillance.

Related Advice Our evaluation has determined that a significant safety hazard does not exist at Yankee Nuclear Power Station since we have taken appropriate corrective actions on all the ASCO Tripoint SB12BMR/TL10A22 pressure switches. However, ASCO appears not to have given notification to other utilities of the possible pressure switch failure mechanism. Therefore, this Part 21 is being submitted to forewarn other utilities of this potential problem.

It is recommended that utilities review this information for applicability to their locations.

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