Information Notice 1994-53, Hydrogen Gas Burn Inside Pressurizer During Welding

Hydrogen Gas Burn Inside Pressurizer During Welding

ML031060575
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:	07/18/1994
From:	Grimes B Office of Nuclear Reactor Regulation
To:
References
IN-94-053, NUDOCS 9407080212
Download: ML031060575 (22)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 July 18, 1994 NRC INFORMATION NOTICE 94-53: HYDROGEN GAS BURN INSIDE PRESSURIZER DURING

WELDING

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

ui

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

notice to alert addressees to the potential for the ignition of hydrogen gas

mixtures during welding operations while the reactor coolant system is

depressurized. It is expected that recipients will review the information for

applicability to their facilities and consider actions, as appropriate, 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 February 3, 1994, a control room operator at Surry Power Station, Unit 1, observed pressure spikes on the pressurizer level instruments. At the same

time, a loud rumbling sound was heard in the containment. The containment

vent radiation alarm was received, and as a precaution, the containment was

evacuated.

At the time of the event, the pressurizer was drained and vented to both the

pressurizer relief tank and the containment atmosphere through a filtered

covering over the piping where the safety valves had been removed. The

reactor vessel head had just been detensioned. There was fuel in the reactor

vessel. A modification to eliminate the pressurizer loop seals was in

progress.

The pressure fluctuations inside the pressurizer caused the expulsion of

radioactive gases from the pressurizer into the containment causing alarms on

both the containment radiation monitor and the ventilation radiation monitor

where the ongoing filtered containment purge was directed. Licensee personnel

calculated the release rate through the monitored ventilation purge path to be

approximately 30 percent of the technical specification limits. One worker

received an estimated internal exposure of 70 pSv [7 mrems] and a total dose

of 160 pSv [16 mrems].

The licensee investigation showed that the screens for excluding foreign

material that were taped over the pressurizer side of the piping where the

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fit

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IN 94-53 July 18, 1994 three safety valves were removed were discolored and appeared burned. The

licensee concluded that a hydrogen gas burn had occurred inside the

pressurizer. Welding activities associated with the pressurizer loop seal

modification had ignited the hydrogen gas that had come out of solution and

accumulated inside the pressurizer and associated piping. There were no

personnel inquiries.

Additional details pertaining to this event can be found in Licensee Event

Report 50-280/94-001 dated March 4, 1994, and NRC Inspection Report

50-280/94-002 dated March 7, 1994.

Discussion

During refueling operations, the reactor coolant system was depressurized and

the pressurizer level was drained while a nitrogen blanket was provided via

the pressurizer relief tank. Before the coolant system was depressurized, the

system was degassed and the hydrogen concentration was reduced to less than

5 cc/kg in accordance with recommendations from Westinghouse, the nuclear

steam system supplier.

The source of the hydrogen gas inside the pressurizer was investigated by the

licensee's root cause team. The team concluded that pockets of trapped gas

either in the reactor coolant system or in the pressurizer relief tank had

moved as a result of the effects of changing containment pressure on the

pressurizer. The pressure changes had acted through the removed safety valve

openings. Because the licensee had maintained the containment at a slight

negative pressure during most of the refueling shutdown, opening and closing

of the equipment hatch caused changes in the containment pressure.

The licensee investigation showed that a similar event had occurred at the

Wolf Creek Nuclear Plant in October 1987.

The licensee imposed additional controls for welding on the primary system.

These require that samples be taken and analyzed before initiating an arc to

determine if explosive gasses are present. The licensee also evaluated

pressurizer stresses associated with the rapid hydrogen burn and completed a

piping support inspection and internal inspection of the pressurizer. The

evaluation showed that no unacceptable stresses had resulted, and no damage

was noted during the inspections.

Related Generic Communications

In Information Notice 82-28, 'Hydrogen Explosion While Grinding in the

Vicinity of Drained and Open Reactor Coolant System," the NRC described a

hydrogen gas explosion that took place when maintenance personnel at Arkansas

Nuclear One, Unit 1, were grinding a recently cut high-pressure injection

pipe. The cut was approximately 46 centimeters [18 inches] from the nozzle

connecting the injection pipe to the reactor coolant system piping.

. I

KY IN 94-53 July 18, 1994 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 manaIger. /7 rian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: Morris Branch, RII

(804) 357-2101 Mark A. Caruso, NRR

(301) 504-3235 Attachment:

List of Recently Issued NRC Information Notices

r

4J c (6Sc'Aht ri6z1 r,&. J4,

. I I

A'Attachment

IN 94-53 July 18, 1994 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

94-52 Inadvertent Containment 07/15/94 All holders of OLs or CPs

Spray and Reactor Vessel for nuclear power reactors.

Draindown at Millstone

Unit 1

94-51 Inappropriate Greasing 07/15/94 All holders of OLs or CPs

of Double Shielded Motor for nuclear power reactors.

Bearings

94-50 Failure of General 07/14/94 All holders of OLs or CPs

Electric Contactors for nuclear power reactors.

to Pull in at the

Required Voltage

94-49 Failure of Torque 07/06/94 All holders of OLs or CPs

Switch Roll Pins for nuclear power reactors.

94-48 Snubber Lubricant 06/30/94 All holders of OLs or CPs

Degradation in High- for nuclear power reactors.

Temperature Environments

94-13, Unanticipated and Unin- 06/28/94 All holders of OLs or CPs

Supp. 1 tended Movement of Fuel for nuclear power reactors.

Assemblies and other

Components due to Improper

Operation of Refueling

Equipment

94-47 Accuracy of Information 06/21/94 All U.S. Nuclear Regulatory

Provided to NRC during Commission Material

the Licensing Process Licensees.

94-46 NonConservative Reactor 06/20/94 All holders of OLs or CPs

Coolant System Leakage for nuclear power reactors.

Calculation

94-45 Potential Common-Mode 06/17/94 All holders of OLs or CPs

Failure Mechanism for for nuclear power reactors.

Large Vertical Pumps

OL = Operating License

CP = Construction Permit

IN 94-53 July 18, 1994 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.

Odfgtnl gned by

Sdan K. Grimes

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: Morris Branch, RII

(804) 357-2101 Mark A. Caruso, NRR

(301) 504-3235 Attachment:

List of Recently Issued NRC Information Notices

• see JRJohnson memorandum to BKGrimes dated April 4, 1994 and Drevious concurrence sheets

OFFICE *RPB2/REG-II *C:RPB2/REG-I1 *DRP/REG-II *D:DRS/REG-II

NAME GABelisle MVSinkule JPJaudon AFGibson

DATE 3/21/94 3/22/94 3 _2994_3/3 1/94 OFFICE *D:DRP/REG-II *OGCB/NRR *Tech Editor *SRXB/NRR

NAME JRJohnson RJKiessel MMejac MACaruso

DATE 4/ 4/94 5/5/94 5/9/94 5/16/94 OFFICE *C:SRXB/NRR *D:DSSA/NRR *AC:OGCB\NRR D l

NAME TECollins MJVirgilio RLDennig Gr es l

DATE 5/18/94 6/11/94 6/15/94 7/e /94 Document Name: 94-53.IN

IN 94-xx

June xx, 1994 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.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: Morris Branch, Region II

(804) 357-2101 Mark A. Caruso, NRR

(301) 504-3235 Attachment:

List of Recently Issued NRC Information Notices

• see JRJohnson memorandum to BKGrimes dated April 4, 1994 and previous concurrence sheets

OFFICE *RPB2/REG-II *C:RPB2/REG-II *DRP/REG-II *D:DRS/REG-41 NAME GABelisle MYSinkule JPJaudon AFGibson

DATE 3/21/94 3/22/94 3/29/94 3/31/94 OFFICE *D:DRP/REG-II *OGCB/NRR *Tech Editor *SRXB/NRR

NAME JRJohnson RJKiessel MMeJac MACaruso

DATE 4/ 4/94 5/5/94 5/9/94 5/16/9M

OFFICE *C:SRXB/NRR *D:DSSA/NRR *AC:OGCB\NRR D:DORS/NRR

NAME TECollins MJVirgilio RLDennig BKGrimes

DATE 5/18/94 6/11/94 6/15/94 6/ /84 Document Name: NRCIN.451

IN 94-xx

May xx, 1994 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.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: Morris Branch, Region II

(804) 357-2101 Mark A. Caruso, NRR

(301) 504-3235 Attachment:

List of Recently Issued NRC Information Notices

• see JRJohnson memorandum to BKGrimes dated April 4, 1994

-

and Previous concurrence sheets

OFFICE *RPB2/REG-II *C:RPB2/REG-II *DRP/REG-II *D:DRS/REG-I1 NAME GABelisle MVSinkule JPJaudon AFGibson

DATE 3/21/94 3/22/94 3/29/94 3/31/94 OFFICE *D:DRP/REG-II *OGCB/NRR *Tech Editor SRXB/NRR

NAME JRJohnson RJKiessel MMejac MACaruso J

DATE 4/ 4/94 5/5/ 9/94 5//b/94 OFFICE C:SRXB/NRR D:DSSA/NR P B/NRR C. ,RPB/NR <

NAME TECollin~4lr

RiJVirgilio JDB n LCu am

DATE 5/g/941 (X14/ a L9u /9Jh

OFFICE 'bsPRSS/NRR,--' D:DORS/NRR 11 NAME FJC[y 6X/e Y

BKGrimes 7 DATE XI /94 \"N &4 1fl/94 5/ /84 I.)

Document Name: NRCIN.451

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Attachments:

1. List of Recently Issued NRC Information Notices

• see JRJohnson memorandum to BKGrimes dated April 4, 1994 and previous concurrence sheets

OFFICE *RPB2/REG-II *C:RPB2/REG-II *DRP/REG-II *D:DRS/REG-II

NAME GABelisle MVSinkule JPJaudon AFGibson

DATE 3/21/94 3/22/93 3/29/94 3/31/94 OFFICE *D:DRP/REG-II OGCB/NRR Tech Editor SRXB/NRR

NAME JRJohnson RJKiessel& 2 !e;_ MACaruso

DATE 4/ 4/94 5/ "/94 5/q /94 5/ /94 OFFICE C:SRXB/NRR D:DSSA/NRR PRPB/NRR C:PRPB/NRR

NAME TECollins MJVirgilio JDBuchanan LCunningham

DATE 5/ /94 5/ /94 5/ /94 5/ /94 OFFICE D:DRSS/NRR C:OGCB\NRR D:DORS/NRR

NAME FJCongel AJKugler BKGrimes

DATE 5/ /94 5/ /94 5/ /84 Document Name: G:\RJK\NRCINS\NRCIN.451

r . 05-.OZE-1994 14:27 841 S510 US NRC RG II P.03 K>

Brian K. Grimes 21 APR - 4 1994 cc w/encl cont'd:

M. Branch, RI

G. Lainas, NRR

H. Berkow, NRR

B. Buckley, NRR

R. Benedict, NRR

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RI 4RP RI JDV

GB Isle MSinkul e JJaud n AG s on

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