Information Notice 1986-56, Reliability of Main Steam Safety Valves

Reliability of Main Steam Safety Valves

ML031220712
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Skagit, Marble Hill
Issue date:	07/10/1986
From:	Jordan E NRC/IE
To:
References
IN-86-056, NUDOCS 8607030267
Download: ML031220712 (3)

SSINS No.: 6835 IN 86-56 UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF INSPECTION AND ENFORCEMENT

WASHINGTON, D.C. 20555 July 10, 1986 IE INFORMATION NOTICE NO. 86-56: RELIABILITY OF MAIN STEAM SAFETY VALVES

Addressees

All pressurized-water reactor facilities holding an operating license or

construction permit.

Purpose

This information notice (IN)is provided as additional notification of NRC's

concern for the reliability of spring-actuated main steam safety valves follow- ing reports of multiple failures during testing and problems during power

operations and scram recovery. IN 86-05, "Main Steam Safety Valve Test Fail- ures and Ring Setting Adjustments," previously addressed the problem of inade- quate flow capacity of these valves.

It is expected that recipients will review the information for applicability to

their facilities and consider actions, if appropriate, to preclude similar

problems from occurring at their facilities. However, suggestions contained in

this notice do not constitute NRC requirements; therefore, no specific action

or written response is required.

Description of Circumstances

While researching IN 86-05, the following problems with main steam safety

valves (MSSVs) that had occurred during testing, power operations, or scram

recovery were tabulated from the licensee event report files.

MAIN STEAM SAFETY VALVE PROBLEMS (01/01/81-03/01/86)

---

PROBLEM NUMBER NUMBER TESTING POWER POST-SCRAM

VALVES PLANTS (EVENTS) (EVENTS) (EVENTS)

---

FAILURE TO OPEN 13 6 5 0 1 FAILURE TO RECLOSE 15 9 2 1 8 SPURIOUS OPENING 6 4 2 3 1 LEAKING 7 4 1 3 0

SET POINT DRIFT

HIGH 44 10 11 0 1 LOW 97 14 18 3 3 UNSPECIFIED 75 11 14 0 0

8607030267

1; , IN 86-56 July 10, 1986 A number of reports have been received concerning events involving MSSVs. Four

of the more significant reports are summarized in this and the following para- graphs. At North Anna 2, 8 of 15 valves would not lift at the maximum pressure

available to the testing device at the site (1147 to 1161 psig). All 15 valves

were subsequently sent to Wyle Laboratories for further testing. The as-found

setpoints varied from 1105 to 1223 psig compared with the specified 1085 +/- 11 to 1135 +/- 11 psig setpoints. All valves were refurbished and setpoints were

adjusted to be within technical specification limits (LER 50/339-86/001).

Salem 2 reported one valve leaking during heatup following a refueling outage.

After the spindle nut was backed away from the forked lever, the valve reseated, but later it lifted and did not immediately reseat. It was gagged shut.

Subsequently two other valves prematurely lifted. They too were gagged shut.

Later, when a fourth valve lifted, it was declared inoperable. All 20 MSSVs

were then tested and reset to the appropriate setpoints. The licensee was unable

to determine the cause for the setpoint drift (LER 50/311-85-007).

Oconee 2 reported that 2 MSSVs had failed to reseat promptly. They reseated at

900 psig instead of 1010 psig following a transient that included a reactor

scram (LER 50/270-85/006).

On October 19, 1985, the 16 MSSVs of Calvert Cliffs Unit 2 were tested to check

and, if required, to adjust the relief pressure setpoints. Unit 2 contains 2 steam generators, each with 8 MSSVs on a steam header. Eleven of the 16 valves

were determined to be out of specification, with the as-found setpoints between

22 to 69 psi higher than their nominal setpoints, compared with the technical

specification requirement of +/- 10 psi. The Licensee Event Report is included

in this notice as Attachment 1 to give an example of the problems found during

testing, and because it is an especially thorough treatment of corrective actions

that may be of value to other facilities.

Discussion:

The safety significance of failure of the MSSVs to open on a PWR is a potential

for over-pressurizing the secondary system with a possibility of a loss of its

pressure boundary integrity. Failure to reclose has led to overcooling tran- sients and lower-than-normal water levels in the steam generator. Spurious

opening, usually at power, has led to reactor scrams. Leaking valves tend to

have more problems than properly functioning valves. Setpoint drift-low may

cause spurious opening of the valves and may interact synergistically with a

steam generator tube rupture to cause relief through the faulted steam genera- tor in the case where the MSSVs on the faulted steam generator have

lower-than-required setpoints. Setpoint drift-high can cause secondary pres- sure to rise above the American Society of Mechanical Engineers (ASME) Boiler

and Pressure Vessel Code-specified system pressure limit.

IN 86-56 July 10, 1986 No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact the Regional

Administrator of the appropriate regional office or this office.

4wardL. rdan, Di r

Division 01 Emergency Preparedness

and Engheering Response

Office of Inspection and Enforcement

Mary S. Wegner, IE

(301)492-4511 Attachments:

1. LER 50/312-85/011

2. Recently Issued IE Information Notices