Information Notice 1992-04, Potter and Brumfield Model Mdr Rotary Relay Failures

Potter and Brumfield Model Mdr Rotary Relay Failures

ML031200770
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:	01/06/1992
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-92-004, NUDOCS 9112300138
Download: ML031200770 (10)

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UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 January 6, 1992 NRC INFORMATION NOTICE 92-04: POTTER & BRUMFIELD MODEL MDR ROTARY RELAY

FAILURES

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 of failures experienced with MDR series Potter

& Brumfield (P&B) rotary relays installed in safety-related systems at certain

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

On January 14, 1986, September 17, 1987, and December 8, 1987, an emergency

diesel generator (EDG) failed an operability surveillance test at the LaSalle

County Station, Units 1 and 2. In each case, while the Commonwealth Edison

Company (CECO) attempted to synchronize the EDG to its bus, the EDG output

breaker would not close. CECO replaced all P&B MDR relays in the output

breaker closing circuits with General Electric HFA relays. The NRC staff has

received no reports of relay failures at LaSalle affecting EDGs since these

were replaced.

On October 10, 1988, the Arizona Public Service Company (APSC), the licensee

for the Palo Verde Nuclear Generating Station, submitted a report in accordance

with Title 10 of the Code of Federal Regulations, Part 21 (10 CFR Part 21).

This report documented 18 instances over a 2-year period in which P&B MDR

relays failed to change position.

APSC detected these failures during either routine surveillance testing or

actuation of the engineered safety features (ESF) actuation system or the

reactor trip switchgear. After replacing all P&B MDR series relays, APSC

experienced only two failures; improperly sized coils or contamination in the

insulating material of the switch caused these two failures.

9112300138 PDK SV(E to<tr 1a

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IN 92-04 January 6, 1992 On July 19, 1991, during a monthly surveillance test, the River Bend Station

experienced ESF actuation of containment isolation valves, control room filter

trains, the standby gas treatment system, and the fuel building filter trains

because of an MDR relay failure.

On July 23, 1991, during a monthly surveillance test at the River Bend Station, the failure of an MDR-5111-1 relay caused an ESF isolation of a reactor water

sample valve. The Gulf States Utilities Company (GSU), the licensee, committed

to replace all P&B MDR relays.

Discussion

P&B MDR relays are used in various safety-related applications in commer- cial nuclear power plants with reactors manufactured by the Babcock and Wilcox

Company; Combustion Engineering, Incorporated; the General Electric Company;

and the Westinghouse Electric Corporation. Industry records identify over

60 instances of P&B MDR rotary relays failing to operate properly since 1984.

An MDR relay failure may cause the loss of a train-of the ESF actuation system, the emergency core cooling system', or the reactor protection system. A common- mode failure may result in the loss of one or more of these systems. GSU

performed a probabilistic risk assessment (PMA) of the reactor protection

system at River Bend, based on plant-specific, P&B MDR relay failure rates that

were greater than the generic failure rates by a factor of 5.1. This PRA

showed that the reactor protection system failure rate increased by a factor of

25 to 3.3E-4.

The principal failure mechanism of P&B MDR rotary relays'appears to be mechani- cal binding of the rotor'caused by deposits from coil varnish outgassing and

chlorine corrosion products. , A secondary failure mechanism appears to be the

intermittent continuity of electrical' contacts. A number of variables contribute

to these failure mechanisms and cause the relays to fail at random mostly

within 2 to 5 years of the in-service date. 'Failures may occur regardless of.

current or wattage, the use of ac or dc power, or whether normally energized or

de-energized. It is also important to note that a relay rotor can bind immedi- ately 'after a surveillance test.

Attachment 1 provides a detailed description of the failure mechanisms, con- tributing causes, and failure investigations. Attachment 1 also discusses

modifications made to P&B MDR series relays by the manufacturer to reduce

susceptibility to the failure mechanisms discussed above.

,a e . .

IN 92-04 January 6, 1992 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 E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical contacts: K. R. Naidu, NRR

(301) 504-2980

R. A. Spence, AEOD

(301) 492-8609 Attachments:

1. Potter & Brumfield Model MDR Rotary Relays

2. Figure 1, Potter-Brumfield Model MDR Rotary Relay

3. Figure 2, MDR Non-Latching Relay

4. List of Recently Issued NRC Information Notices

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Attachment 1 IN 92-04 January 6, 1992 Potter & Brumfield Model MDR Rotary Relays

Description of the MDR Rotary Relay

Potter & Brumfield (P&B) manufactures two types of MDR rotary relays: latching

and non-latching. Various series of these relays are provided for service at

28 and 125 volts (V) dc and 115 and 440 Vac, with from 4 to 24 pole double

throw (PDT) contacts. While each series has a different number of contact

stacks and has a different coil, power, and current capacity, each of the

series is similarly constructed and exhibits similar failure mechanisms.

Non-Latching Relays

The non-latching MDR relay has two coils connected in series inside the relay

which, when energized, rotate the relay rotor shaft, which operates the con- tacts through a shaft extension. The stator faces and stop ring limit the

rotor movement to a 30-degree arc. Two springs return the rotor to the stop

ring and the contacts to their normal positions when the coils are

de-energized. The non-latching MDR relays have two positions: 'energized" and

"de-energized." (See figures 1 and 2).

Latching Relays

Each relay in the MDR latching series has two sets of series coils, which

provide a latching two-position operation. When one set of coils is energized, the rotor shaft rotates through a 30-degree arc, changing the state of the

contacts. The other set of coils must be energized to return the relay to its

original position.

Failure Investigations

The Commonwealth Edison Company (CECO) determined that the three events at the

LaSalle County Station resulted from the failure of P&B MDR-137-8 or MDR-138-8,

125 Vdc normally energized relay contacts to close. CECO performed diagnostic

testing after the earlier events but could not repeat the failure. This lack

of repeatability is typical of MDR intermittent failures.

The Arizona Public Service Company (APSC) found that three of the P&B MDR relay

rotors at Palo Verde Nuclear Generating Station (PVNGS) would not move more

than 12 degrees of the complete 30-degree arc. The failed relays, located

in cabinets without forced ventilation were in an ambient temperature of

95 to 104OF (the design limit is 1490F5 and had an external surface temperature

of 157 0F.

Attachment 1 IN 92-04 January 6, 1992 APSC detected no relay failures ii cabinets with forced ventilation which

provided an ambient temperature of 81'F or less. Such relays had a temperature

of 112'F on their external surfaces. APSC determined that it had applied up to

39.8 Vdc to the 28 Vdc coils. APSC tested 7 of the 18 failed relays on an

18-month frequency and 10 on a 62-day frequency. APSC had the relay failures

analyzed and determined that varnish on the relay coils outgassed, condensed, and accumulated between the rotor shaft and the end-bell bearings, binding the

rotor and the bearings together. The outgassing was due to excessive coil

temperatures that occurred when the coils were continuously energized at

voltages above their nominal ratings. The heat also may have caused the

release of chlorine from (1) the PVC coating on the fiberglass tubing covering

the solder joint between the magnet wire and the Teflon coated lead wire, and

(2) the Neoprene rubber grommet through which the coil lead wires penetrate the

base of the relay. The chlorine corroded brass parts inside the relay. P&B and

APSC concluded that long intervals between de-energizing of the relays may have

also contributed to the failures.

In May 1989, APSC installed replacement P&B relays at PVNGS that were manufac- tured with coils'coated with epoxy instead of varnish. APSC conducted tests and

found that 5 of the 42 relays tested would not rotate to their de-energized

position and that 5 other relays operated slowly. Two independent laboratories

observed that; (1) the relays' epoxy was not properly cured, (2) uncured epoxy

contaminated the rotor and (3) P&B did not de-aerate the epoxy prior to use, contrary to the manufacturer's recommendations. This caused the rotor and

stator surfaces to bond together, preventing the rotor from rotating freely.

P&B informed the NRC that APSC returned the 42 relays and that P&B rebuilt

them.-

On September 10, 1990, the General Electric Nuclear Energy Division (GENE)

issued Rapid Information Communication Services Information Letter 053 to

address P&B MDR relay failures reported at two GE boiling water reactors. P&B

believed that chlorine released from rubber grommets and polyvinyl chloride

sleeves caused corrosion and that varnish on the-coils outgassed while the

relays were continuously energized.' Both chlorine-corrosion products and

varnish accumulated in the bottom end-bell bearing and caused the rotor shaft

to bond to the bearing. P&B suspected that the failed relays were exposed to

high ambient temperatures and could have been exposed to high coil voltages or

could have been rarely cycled.

On November 2, 1990, GENE-issued Potentially Reportable Condition 90-11 in

which it stated that both 24 Vdc and 120 Vdc'coils had lower coil powers than

the 125 Vdc relays and were therefore not vulnerable to this failure mode.

GENE concluded that no substantial safety hazard existed. However, upon

investigating the failed MDR relays at River Bend as discussed below, the NRC

obtained results that may contradict these conclusions.

On July 19, 1991, a high resistance on one set of contacts on a P&B 24 Vdc, MDR-5111-1 rotary relay, which should have been closed, caused a voltage drop

to the downstream relays which opened their contacts and resulted in an ESF

Attachment 1 IN 92-04 January 6, 1992 actuation at the River Bend Station. The Gulf States Utilities Company (GSU),

the licensee, later performed bench testing of this failed relay and verified

that the relay actuated properly and all contacts changed state properly, and

exhibited proper continuity. The coil was meggered and found to be acceptable.

The contacts all appeared to be clean and shiny, with no evidence of pitting or

residue. GSU found no foreign material in the relay or on the rotor shaft and

found nothing that may have contributed to the high resistance across the

contacts.

On July 23, 1991, GSU investigated another MDR relay failure at River Bend and

found two MDR-5111-1 relay contacts open that should have been closed when the

coil was energized. GSU also found that the contacts operated intermittently

with some contacts closing several minutes after the coil was energized or

sometimes not at all.

Both River Bend failed relays had been in service within tightly-regulated

design voltage and temperature conditions and were mounted inside stainless

steel isolation cans for divisional separation. GSU measured the temperature

inside the isolation can at 1130 F, while the ambient cabinet temperature was

920F. In each case, the failed relay had been recently cycled because of a

short loss of power to the coil that had occurred a few days before the relay

failure was discovered, and it appears that not all contacts engaged properly

when power was restored.

Failure Mechanisms

The primary failure mechanism of the P&B model MDR rotary relay appears to be

a mechanical binding of the rotor caused by organic outgassing and deposition

of contaminants and corrosion particles on the relay rotor shaft. The contamin- ants are deposited in the end bell bearings and sleeves and cause the rotor

shaft to bond or stick to the bearing, preventing the rotor shaft from fully

rotating when the relay coils are energized or de-energized. The principal

contaminant is outgassed material emitted from the brown enamel varnish used to

coat the relay coils. This contamination may not be apparent to the naked eye.

The corrosion results from chlorine released from the rubber grommets and the

polyvinyl chloride sleeves. Gulf States and P&B disassembled six operable and

two failed relays that had been in service since December 1984. The thickness

and color of the deposits on the rotor, sleeve, and end-bell bearings of the

relays varied widely among the eight relays, indicating varnish outgassing.

A secondary failure mechanism appears to be intermittent continuity of the elec- trical contacts. High resistance and intermittent continuity may result from

chemical reactions on the fixed and movable silver contacts. P&B tested a

MDR-5112-1, 125 Vdc relay that had been in service at River Bend and found

intermittent continuity on a set of clean, unused contacts.

A number of variables contribute to these failure mechanisms and reduce the

length of the operating life of the complex P&B MDR rotary relays. These

variables include coil wattage, applied ac or dc voltage, normally energized or

de-energized coil, manufacturing tolerances, ambient and coil temperatures, varnish thickness, mounting configurations and enclosures, cabinet ventilation,

e

Attachment 1 IN 92-04 January 6, 1992 relay breathing, testing frequency, operational cycling, the number of contact

decks, and the amperage and voltage of the contact load. These contributory

factors cause an apparent random failure history. While each of the MDR

relays failed between 1 month to 13 years after it was placed in service, most

failed within 2 to 5 years.

Modifications to MDR Relays

P&B has made the following design changes to MDR series relays:

Changed the movable contacts from silver to silver-cadmium-oxide in

October 1985. However, P&B recommends against using MDR relays with

either silver or silver-cadmium-oxide in low current circuits.

Changed the coil coating from varnish to Dolphon CC-1090 epoxy resin in

February 1986. This reduced the coil outgassing rate. However, P&B does

not de-aerate Dolphon CC-1090 prior to use, contrary to Dolphon's recommen- dations. P&B informed the NRC that the epoxy manufacturer plans to cease

production of this currently used and tested epoxy. The NRC is unaware of

when P&B will change to a new epoxy. Licensees may wish to determine if

PAB has examined the replacement epoxy for susceptibility to outgassing

after aging. Licensees may also wish to determine if P&B applies the

epoxy in accordance with the manufacturer's recommendations.

Replaced the brass switch studs in medium size MDR relays with stainless

steel studs in November 1986.

Began lubricating end-bell bearings in July 1988.

Changed chloride-containing materials to chloride-free materials in

June 1989.

Changed the rotor spacers from brass to stainless steel in May 1990.

Changed the brass spring retainer in small size MDR relays from brass to

stainless steel in May 1990.

Changed shims from brass to phosphor bronze in May 1990.

P&B had implemented all these modifications to its MDR rotary relay design by

May 1990.

When APSC reported having problems with MDR relays at Palo Verde in 1988, P&B

believed that only relays normally energized with excessive voltage and operat- ed infrequently were susceptible to the corrosion and outgassing failure mode.

PAB did not notify other licensees about these problems since this condition

appeared to occur only at plants with reactors manufactured by Combustion

Engineering, Incorporated. P&B informed the NRC that since 1988 it has only

supplied MDR relays as commercial grade components without accepting the

reporting requirements of 10 CFR Part 21.

Attachment 3 IN 92-04 January 6, 1992 MDR NON-LATCHING RELAY

SPACER

Figure 2

POTTER-DRUMWIELD MODEL 14DR ROTARY RELAY

ROTOR IN ROTOR IN

DEENERGIZED

POSITION ENERGIZED

POSITION (

0A

F-A

5. 75'

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COIL

HOUSING ROTOR ROTOR t QX

STOPS ASSIIBLY F t

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Attachment 4 IN 92-04 January 6, 1992 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

92-03 Remote Trip Function 01/06/92 All holders of OLs or CPs

Failures in General Electric for nuclear power reactors.

F-Frame Molded-Case Circuit

Breakers

92-02 Relap5/Mod3 Computer Code 01/03/92 All holders of OLs or CPs

Error Associated with the for nuclear power reactors.

Conservation of Energy

Equation

92-01 Cable Damage Caused by 01/03/92 All holders of OLs or CPs

Inadequate Cable Installa- for nuclear power reactors.

tion Procedures and Controls

91-87 Hydrogen Embrittlement of 12/27/91 All holders of OLs or CPs

Raychem Cryofit Couplings for nuclear power reactors.

91-86 New Reporting Requirements 12/27/91 All licensees authorized

for Contamination Events at to use byproduct materials

Medical Facilities for human use.

(10 CFR 30.50)

91-85 Potential Failures of 12/26/91 All holders of OLs or CPs

Thermostatic Control Valves for nuclear power reactors.

for Diesel Generator Jacket

Cooling Water

91-84 Problems with Criticality 12/26/91 All Nuclear Regulatory

Alarm Components/Systems Commission (NRC) fuel

cycle licensees, interim

spent fuel storage licens- ees, and critical mass

licensees.

91-83 Solenoid-Operated Valve 12/20/91 All holders of OLs or CPs

Failures Resulted in for nuclear power reactors.

Turbine Overspeed

OL = Operating License

CP = Construction Permit