Information Notice 1988-31, Steam Generator Tube Rupture Analysis Deficiency

Steam Generator Tube Rupture Analysis Deficiency

ML031150151
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, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	05/25/1988
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-88-031, NUDOCS 8805200086
Download: ML031150151 (8)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D. C. 20555 May 25, 1988 NRC INFORMATION NOTICE NO. 88-31: STEAM GENERATOR TUBE RUPTURE ANALYSIS

DEFICIENCY

Addressees

All holders of operating licenses or construction permits for Westinghouse

(W)- and Combustion Engineering (CE)-designed nuclear power reactors.

Purpose

This information notice Is being provided to alert addressees to potential

problems resulting from a non-conservatism in the safety analysis for rupture

of a steam generator tube which may increase offsite dose consequences. 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 do not constitute NRC

requirements; therefore, no specific action or written response is required.

Description of Circumstances

Following the steam generator tube rupture at North Anna Unit 1 on July 15, 1987, the Virginia Electric and Power Company (VEPCO) modified the flow resistance of

the steam generator downcomers at North Anna by the addition of flow baffle

plates. This modification necessitated the reanalysis of certain design basis

events including rupture of a steam generator tube. The new analysis utilized

a revised Westinghouse method for calculating steam generator water mass and

indicated that during the event, the water level on the secondary side could

fall below the top of the steam generator tubes for a 10-minute period at the

beginning of the event.

Steam generator tube uncovery is significant because, If the break location

becomes uncovered, a direct path might exist for fission products contained

in the primary coolant to be released to the atmosphere without partition

with the secondary coolant. VEPCO and Westinghouse reanalyzed the design

basis steam generator tube rupture accident for Surry using the revised

methods and determined that the steam generator tubes at Surry could also

become uncovered even though the Surry plants were not modified by the ad- dition of flow baffle plates.

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IN 88-31 May 25, 1988 The licensee further concluded that the offslte dose consequences exceeded

those calculated in the Surry Updated Final Safety Analysis Report (UFSAR)

because tube uncovery could produce a direct path for fission product release.

Based on the Surry results, the analysis of steam generator Inventory during

a steam generator tube rupture at other plants may show that the steam generator

tubes may uncover. Thus, for those plants where the steam generator tubes were

thought to remain covered following tube rupture, the previously calculated

safety analysis offsite doses might be exceeded and since the primary coolant

activity limit in Technical Specifications is based upon the occurrence of this

accident, the allowable technical specification limit may be too high.

Discussion

A postulated steam generator tube rupture Is one of the design basis accidents

analyzed in plant Safety Analysis Reports (SARs). Using conservative assump- tions of single failure and loss of offsite power, it must be shown that the

offsite dose consequences will be limited to the guideline doses of 10 CFR 100

or a fraction of the guideline doses depending on the assumptions made for

iodine spiking. The iodine in the reactor coolant may be previously dissolved

from allowable operational fuel failure or may result from an Iodine spike which

is the sudden increase In coolant iodine concentration produced by the transient

conditions during the accident. Mechanisms for transport of the iodine that

exits the reactor system to the atmosphere are discussed in Standard Review Plan

(NUREG-0800) Section 15.6.3. In determining the amount of iodine that is trans- ported to the atmosphere, credit may be given for "scrubbing" of iodine-contalned

in the steam phase- andL4n-the atomized-primary -coola t-droplits suspended in the

steam phase for release points which are below the steam generator water level.

The Surry UFSAR assumed that the break is always covered with water so that 99%

of the iodine would remain within the steam generator coolant and only 1% would

be released through the atmospheric relief valves. The break location is as- sumed to be always covered in the UFSAR calculations because an Initial steam

generator water mass that may be non-conservatively large was assumed in order

to conservatively account for the possibility of overfill and because steam

generator tube failures were thought only to occur close to the tube sheet.

The North Anna tube rupture demonstrated that steam generator tube failures

can occur near the top of the tube bundle. The revised steam generator water

mass calculations by Westinghouse with the assumption that the break occurs at

the top of the tube bundle led to the conclusion that the break could be un- covered for a significant period of time. Tube uncovery occurs because of the

level shrink that accompanies reactor trip/turbine trip during the tube rupture

event. The tubes would be recovered by the flow of auxiliary feedwater into

the ruptured steam generator and by the reactor coolant which would be added

due to the ruptured tube; however, the amount of iodine released from the

ruptured steam generator could be larger than that previously calculated.

IN 88-31 May 25, 1988 The NRC staff is evaluating the impact that these non-conservative assumptions

may have on calculated offsite doses and the need for further generic action.

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact the technical con-;

tact listed below or the Regional Administrator of the appropriate regional

office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Walton L. Jensen

(301) 492-21190

Attachment: List of Recently Issued NRC Information Notices

VI

Attachnent

IN 88-31 May 25. 1988 Page 1 of I

LIST OF RECENTLY ISSUED

NRCINFORMATI0N NOTICES

Information Date of

Notice No. SubJect Issuance Issued to

88-30 Target Rock Two-Stage 5/25/88 All holders of OLs

SRV Setpoint Drift or CPs for nuclear

Update power reactors.

88-29 Deficiencies In Primary 5/24/88 All holders of OLs

Containment Low-Voltage or CPs for nuclear

Electrical Penetration power reactors.

Assemblies

88-28 Potential for Loss of 5/19/88 All holders of OLs

Post-LOCA Recirculation or CPs for nuclear

Capability Due to power reactors.

Insulation Debris Blockage

88-27 Deficient Electrical 5/18/88 All holders of OLs

Terminations Identified or CPs for nuclear

In Safety-Related power reactors.

Components

85-35, Failure of Air Check 5/17/88 All holders-of OLs

Supplement I Valves to Seat or CPs for nuclear

power reactors.

88-26 Falsified Pre-Employment 5/16/88 All holders of OLs

Screening Records or CPs for nuclear

power reactors and

all major fuel

facility licensees.

88-25 Minimum Edge Distance for 5/16/88 All holders of OLs

Expansion Anchor Bolts or CPs for nuclear

power reactors.

88-24 Failures of Air-Operated 5/13/88 All holders of OLs

Valves Affecting Safety- or CPs for nuclear

--- t lted System- - power- reactors.- -

OL

• Operating License

CP* Construction Permit

UNITED STATES FIRST CLASS MAIL

POSTAGE & FEES PAID

NUCLEAR REGULATORY COMMISSION USNRC

WASHINGTON, D.C. 20555 PERMIT No. 0-7 OFFICIAL BUSINESS

PENALTY FOR PRIVATE USE. $300

IN 88-31 May 25, 1988 The NRC staff Is evaluating the impact that these non-conservative assumptions

may have on calculated offsite doses and the need for further generic action.

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact the technical con- tact listed below or the Regional Administrator of the appropriate regional

office

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Walton L. Jensen

(301) 492-21190

Attachment: List of Recently Issued NRC Information Notices

• see previous concurrence

EAB:NRR EAB:NRR CRPRB:NRR C:EAB:NRR

WJensen:db* RLobel* LCunningham* WLanning*

4/7/88 4/7/88 5/5/8 RSB:NRR TECH:ED C:G B: R D R.4 WHodges* * CHBerlinger CERossi

5/17/88 / /88 .f/p'e/88 .i70'/88

IN 88- May , 1988 The NRC staff is evaluating the impact that these non-conservative assumptions

may have on calculated offsite doses and the need for further generic action.

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact the technical con- tact listed below or the Regional Administrator of the appropriate regional

office

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Walton L. Jensen

(301) 492-21190

Attachment: List of Recently Issued NRC

Information Notices

• see previous concurrence

EAB:NRR EAB:NRR CRPRB:NRR

WJensen:db* RLobel* LCunningham* WLa~ ing

/ /88 / /88 / /88 SJ /7'88 RSB:NRR TECH:ED C:GCB:NRR D: OEA:NRR

WHodges* * CHBerlinger CERossi

/ /88 / /88 / /88 / /88

4 IN 88- May , 1988 The NRC staff is evaluating the impact that these non-conservative assumptions

may have on calculated offsite doses.

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact the technical con- tact listed below or the Regional Administrator of the appropriate regional

office

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Walton L. Jensen

(301) 492-21190

Attachment: List of Recently Issued NRC

Information Notices

• see previous concurrence

EAB:NRR EAB:NRR CRPRB:NRR C: X RR

WJensen:db* RLobel* LCunningham*

/ /88 / /88 / /88 , //'9 88 RSB:NRR TECH:ED C:GCB:NRR D:DOEA:NRR

WHodges* * CHBerlinger CERossi

/ /88 / /88 / /88 / /88

4 IN 88- April , 1988 The NRC staff is evaluating the impact that these non-conservative assumptions

may have on calculated offsite doses.

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.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Walton L. Jensen

(301) 492-21190

Attachment: List of Recently Issued NRC

Information Notices

LL

EAB: NR EAB:NRR C:EAB:NRR C:GCB:NRR TECH: ED

WJensen:db RLobel LCunningham WLanning CHBerl inger AThomas

4 /1 /88 A /.i/88 S /g/88 / / 88 / /88 / /88 RSB RRq D:DOEA:NRR

WHodges CERossi

5 /(I /88 / /88