Information Notice 1992-64, Nozzle Ring Settings on Low Pressure Water-Relief Valves

Nozzle Ring Settings on Low Pressure Water-Relief Valves

ML031200030
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, 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, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	08/28/1992
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-92-064, NUDOCS 9208240139
Download: ML031200030 (6)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555

-August 28, 1992 NRC INFORMATION NOTICE 92-64: NOZZLE RING SETTINGS ON LOW PRESSURE

WATER-RELIEF VALVES

Addressees

-

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing-this information

notice to alert addressees to problems that could result-from the inadequate

control of maintenance of low pressure water-relief valves in operating

nuclear power plants. It is expected that recipients will review the informa- tion for applicability to their facilities and consider actions, as appropri- ate, to avoid similar problems. However, suggestions contained in this

information notice are not-NRC requirements; therefore, no specific action or

written response is required.

Description of Circumstances

Shearon Harris - -

On August 8, 1991, at the Shearon Harris Nuclear Power Plant,'an operator

started a second component cooling water (CCW) pump to support diagnosing a

problem with a flow indicator. The operator immediately noted a decreasing'

level in the CCW surge tank and began manually filling the system. Additional

operators were dispatched to the area, and they reported that various CCW

relief valves were lifting. Even though the control board operator initiated

actions to reduce the system pressure from 140 psig to 120 psig (the reseat

pressure for these valves was 135 psig in the vendor test reports), the '

leakage continued until the second CCW pump was secured and the system

pressure dropped below 105 psig. These valves-were manufactured by the Crosby

Valve and Gage Company.

In its review,-the licensee found that the nozzle rings on various CCW valves

had incorrect settings which resulted-in a reseat pressure lower than the

system design specified. The licensee reviewed the maintenance history and

found that these valves had been disassembled and rebuilt before the initial

startup in 1986. 'During these activities, the nozzle rings had been

improperly set. Procedural guidance on 'the setting of the'nozzle-rings'was

lacking and the manufacturer's design data and technical manual were difficult

to interpret.

9208240139 'f ' ' A2 -+/--6-- 'a

%O$

c K3I

IN 92-64 August 28, 1992 Subsequent to the event, the licensee identified 34 low pressure relief valves

on various safety related systems that required verification of the nozzle

ring settings. These valves were chosen because they had previously been

subjected to maintenance which may have disturbed-the nozzle ring settings.

The 16 valves checked as of May 1992-all had incorrect settings varying from a

few notches to over 170 notches (method used to set nozzle rings). The

licensee intends to check the remaining valves during forthcoming plant/system

outages.

Trojan

On July 23, 1991, at the Trojan Nuclear Plant, a CCW relief valve lifted

during a system pressure surge and did not reseat until it was manually

isolated. The licensee investigated the incident and found the nozzle ring

settings in the relief valves in both CCW trains substantially different from

the required setting. While conducting preliminary tests, the licensee found

the reseat pressure to be from about-60 to 80 psig, while the expected value

was 135 psig. This event was cited by NRC as part of a severity level III

violation of 10 CFR Part 50, Appendix B, Criterion XVI.

The licensee found that the incorrect ring settings were the result of lack of

procedural controls to set and maintain the nozzle ring settings on certain

plant relief valves. In 1989, the licensee had established controls to return

the nozzle rings to their "as-found" position after maintenance was performed.

However, this was not sufficient to assure that ring settings were in

accordance with vendor test data. Subsequent to this event, the licensee

checked the nozzle ring settings on 54 low pressure relief valves in various

safety related,systems that previously had maintenance. Thirty valves had

incorrect settings; twelve of these settings were significantly outside the, tolerance band.

Braidwood

In December 1989, during operations to start up Unit 1 at the Braidwood

Station, a suction relief valve in one of the RHR trains suddenly opened as

the operators were drawing a bubble in the pressurizer. In the first

18 minutes after the valve opened, the pressure in the primary system dropped

to about 270 psig, which was well below the expected reseat pressure for the

suction relief valve. Approximately 67,000 gallons of reactor coolant system

water were released to the radwaste holdup tanks before the operators isolated

the RHR train having the open relief valve about 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, later.

About 18 months before the event, the licensee had performed maintenance on

the affected RHR relief valve prior to its being installed in the plant. At

that time, the licensee discovered four RHR suction relief valves at the site

that had nozzle ring settings considerably different from those specified in

the vendors's valve test package. A temporary set of instructions was

developed to return the ring settings to the vendor's specified value using a

different reference point and notch count instead of the "as found" setting

and reference pointlas directed in theiexistingjmaintenance procedure. Both- sets of instructions were contained in 'the sime'work'package used to perform

IN 92-64 August 28, 1992 the corrective maintenance for the valve that subsequently stayed open for an

,extended time. The mechanic apparently confused the two sets of instructions, adjusting the nozzle ring about 220 notches from its proper position.

Haddam-Neck

In 1986, one of the RHR suction relief valves opened following a pressure

spike to 380 psig and failed to reseat until the pressure decreased to

260 psig (expected reseat pressure was 342 psig) about 10 minutes later when

the affected-RHR train was isolated. Upon'disassembling the valve, the

licensee noted that the nozzle-ring was unmovable. The nozzle ring was jammed

in a locked position about 225-notches from its proper position.

Foreign Pressurized Water Reactor

In May 1985, about 25,000 gallons of reactor coolant were released to the

containment sump through an RHR, suction relief valve. The primary system

pressure stopped decreasing about 30 minutes into the event when the RHR

system was isolated. The event was attributed to an improperly set nozzle

ring. The utility also found a broken disc insert pin when the valve was

inspected.

Discussion -

All of the valves involved in the referenced events were Crosby relief valves

which are used in a number of nuclear plants in the U.S. The expected reseat

pressure for these particular valves was about 90% of the valve lift set

pressure. Other style relief valves, whether Crosby or another manufacturer, may have different reseat pressures relative to the lift set pressure.

Those relief valves that do have nozzle rings (or guide rings as the case may

be) generally are set by counting notches on the ring from some specified

reference point as it is rotated about the nozzle. The nozzle ring is

initially~set by the manufacturer during full-flow tests and locked into

position by a set screw that engages a notch in the ring.

An incorrect nozzle ring setting on a relief valve adversely affects the

valve's characteristics and can result in uncontrolled leakage or discharge

from the valve. A low setting (high reseat pressure) may cause the valve to

open and close intermittently, leading to valve failure and uncontrolled

leakage. A very high nozzle ring setting (low reseat pressure) may delay the

valve reseating until lower than expected pressures are reached as occurred in

the events noted above. -

Some of the potential problems observed in setting the nozzle rings are:

(1) If the relief valves were worked on during plant construction or other

earlier operating period without adequate control of nozzle ring

settings, there is high likelihood that they are misadjusted. Shearon

Harris, Trojan, and Braidwood all found multiple, low pressure, relief

valves with incorrect ring settings on various safety related systems.

.1.

IN 92-64 August 28, 1992 (2) The misadjusted nozzle rings are not self-revealing until the valves are

challenged by a plant transient as illustrated in all the events cited

above.

(3) Procedures which require that ring settings be returned to their "as- found" positions may be inadequate. At Shearon Harris, Trojan, and

Braidwood the "as-found" ring settings were incorrect as a result of-some

previous incorrect maintenance or test activity. The licensees found it

necessary to go back to the manufacturer's specified nozzle setting after

maintenance or testing is performed. 10 CFR Part 50 Appendix B,

Section III, addresses configuration control which-includes the nozzle

ring setting on these valves. The ASME test code (PTC 25.3) for relief

valves directs that the rings be set to their original test data. Trojan

specifically flagged this problem.

(4) There may be confusion introduced by the use of two different reference

points (location from which to start notch count) in the vendor's

documentation for setting the nozzle rings. The reference points in some

cases may also be difficult to establish in the field.

(5) Specific directions for adjusting nozzle ring settings may cause

confusion. Including two different instructions for setting the nozzle

ring in the same work package may contribute to the confusion. Terms

such as counter-clockwise and up and down may not be adequate directions

when looking edgewise at a slowly moving ring. These problems are

discussed in the NRC staff's report AEOD/E90-02, "Crosby Low Pressure

Relief Valve Ring Problems," February 1990.

The licensees, noted above, have generally modified/improved their procedures

and instituted personnel training to address nozzle ring setting. To

eliminate errors, the valve manufacturer suggested training maintenance

personnel on the specific valve before they attempt to adjust it.

The Trojan plant found that procedures, even with the manufacturer's nozzle

ring setting stamped on the valve body, were not sufficient to preclude errors

in maintaining their steam safety valves. A mechanical location indicator or

similar device might preclude the gross errors observed in the ring settings

and also provide a means of independently verifying the ring position without

dislocating it.

At Braidwood, a picture, taken through the valve discharge port while it was

on the bench, was used in conjunction with the valve drawing to determine that

the nozzle ring was set too high. However, Trojan and Shearon Harris checked

most of their ring settings with the relief valves in place so only the small

ring adjustment hole was available for observing the ring position.

Fiberoptic technology could be useful where the only opening to observe the

nozzle ring is small.

IN 92-64 August 28, 1992 Related Generic Communications

Information Notice 90-18, "Potential Problem with Crosby Safety Relief Valves

Used on Diesel Generator Air Start Receiver Tanks"

Information Notice 90-05, "Inter-System Discharge of Reactor Coolant"

A more detailed account of problems with nozzle ring settings is contained in

the NRC staff's report AEOD/E90-02, "Crosby Low Pressure Relief Valve Ring

Problems," February 1990.

This information notice requires no specific action or written response.

If you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

Charles F. ~-Rossi, ~'Directo7 Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical contacts: Sanford Israel, AEOD Francis Jape, RII

(301) 492-4437 (404) 331-4182 Mary S. Wegner, AEOD Melvin C. Shannon, RII

(301) 492-7818 (919) 362-0601 Attachment: List of Recently Issued NRC Information Notices

6-, fr-, T o-c-n

" I K

Attachment

IN 92-64 August 28, 1992 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

92-63 Cracked Insulators in 08/26/92 All holders of OLs or CPs

ASL Dry Type Transformers for nuclear power reactors.

Manufactured by Westing- house Electric Corporation

92-62 Emergency Response 08/24/92 All U.S. Nuclear Regulatory

Information Require- Commission licensees.

ments for Radioactive

Material Shipments

92-61 Loss of High Head 08/20/92 All holders of OLs or CPs

Safety Injection for nuclear power reactors.

92-60 Valve Stem Failure 08/20/92 All holders of OLs or CPs

Caused by Embrittlement for pressurized water

reactors (PWRs).

7- J9

- 59 Horizontally-Installed 08/18/92 All holders of OLs or CPs

Motor-Operated Gate for nuclear power reactors.

Valves

92-58 Uranium Hexafluoride 08/12/92 All Fuel Cycle Licensees.

Cylinders - Deviations

in Coupling Welds

92-57 Radial Cracking of 08/11/92 All holders of OLs or CPs

Shroud Support Access for boiling water reactors

Hole Cover Welds (BWRs).

92-56 Counterfeit Valves in 08/06/92 All holders of OLs or CPs

the Commercial Grade for nuclear power reactors.

Supply System

92-55 Current Fire Endurance 07/27/92 All holders of OLs or CPs

Test Results for for nuclear power reactors.

Thermo-Lag Fire Barrier

Material

92-54 Level Instrumentation 07/24/92 All holders of OLs or CPs

Inaccuracies Caused by for nuclear power reactors.

Rapid Depressurization

OL = Operating License

CP = Construction Permit