Information Notice 2003-19, Unanalyzed Condition of Reactor Coolant Pump Seal Leakoff Line During Postulated Fire Scenarios or Station Blackout

Unanalyzed Condition of Reactor Coolant Pump Seal Leakoff Line During Postulated Fire Scenarios or Station Blackout

ML032760027
Person / Time
Site:	Millstone
Issue date:	10/06/2003
From:	Beckner W NRC/NRR/DIPM
To:
Lyon W, SRXB/DSSA, 415-2887
References
TAC MB7782 IN-03-019
Download: ML032760027 (7)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, DC 20555-0001 October 6, 2003 NRC INFORMATION NOTICE 2003-19: UNANALYZED CONDITION OF REACTOR

COOLANT PUMP SEAL LEAKOFF LINE DURING

POSTULATED FIRE SCENARIOS OR STATION

BLACKOUT

Addressees

All holders of operating licenses or construction permits for pressurized water reactors (PWRs).

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to alert

addressees to the recent identification of an unanalyzed condition involving the design of the

reactor coolant pump (RCP) seal leakoff line. The NRC anticipates that recipients will review

the information for applicability to their facilities and consider taking appropriate actions.

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 13, 2003 the Millstone Unit 3 licensee identified that an over-pressurization of RCP

seal leakoff lines could result from an extended loss of seal cooling following station blackout

(SBO) scenarios or postulated fires in specific plant areas coincident with a loss of offsite

power. Specifically, the licensee relies on operators to isolate the low pressure portion of the

seal leakoff to prevent the line from over-pressurizing. The licensee determined this

expectation may not be achievable because the valve used to isolate the low pressure portion

of the seal leakoff line is an air-operated valve. This valve is designed to fail open upon loss of

electrical power or instrument air, either of which could occur during a SBO or a loss of offsite

power coincident with a postulated fire event.

The seal return line for RCPs is designed to recover leakoff volume, at low pressure and

temperature, and return it to the volume control tank or charging pump suction. In the event of

a fire in the cable spreading area, main control room, or instrument rack rooms, coincident with

a loss of offsite power, a loss of RCP seal cooling could result. This situation can lead to a

significant increase in RCP seal leakage which would increase the pressure and fluid

temperature in the seal return line. This over pressurization could result in a pressure boundary

failure of the seal return line, further increasing the RCP seal leakage beyond that assumed in

the safe shutdown analysis.

The resulting rupture would divert more of the credited boric acid storage tank (BAST) volume

than was assumed in the development of the licensees fire safe-shutdown strategies.

Therefore, the strategies may not be adequate to achieve safe-shutdown.

Discussion

The licensee identified this issue while reviewing a Westinghouse (W) document on RCP seal

performance during loss of RCP seal cooling events, OG-00-009, "Transmittal of RCP

Operation During Loss of Seal Cooling (MUHP-1063)," dated February 11, 2000. The W

document states that up to 21 gallons per minute (gpm) leakoff from each RCP could occur for

loss of seal cooling events following postulated fire or Station Blackout (SBO) events, which

exceeds the 3 gpm assumed in the Millstone Unit 3 fire safe shutdown analysis. Therefore, the

licensee concluded that the fire safe shutdown analysis was invalid, but the SBO analysis, which assumes 25 gpm leakoff, was valid.

Upon further investigation, the licensee determined that a loss of seal cooling event could not

be mitigated successfully because the seal leakoff line could not be isolated by the air-operated

valves (AOVs) located in the RCP seal return piping. These AOVs cannot be credited to close

because they are not fed by a safety-related air system, and they are designed to fail open. As

a result of the loss of seal cooling and fire scenarios described above, pressures in the seal

leakoff line would reach approximately 800 to 2000 psig. Since the piping segment

downstream of each AOV and upstream of the flow restriction orifice is designed 150 psig, this

portion of the leakoff line could rupture, inducing leakoff flow rates in excess of the 21 gpm

identified in the W document. These flow rates severely challenge the credited contents of the

BAST and the requirements for achieving and maintaining safe shutdown in accordance with

the applicable licensing basis.

The licensee had been aware of the potential for over pressurization of the seal leakoff line

from a 1992 Westinghouse Technical Bulletin, NSD-TB-91-07-R1, "Over pressurization of RCP

1. 1 Seal Leakoff Line." However, while the licensee had implemented specific

recommendations contained in the bulletin, the licensee had not considered the potential for the

AOVs in the seal leakoff line to be open. Therefore, the licensee did not consider a potential

pressure boundary failure in the leakoff line that would divert the BAST contents credited for

achieving and maintaining safe shutdown.

To mitigate and resolve the events described in this IN the licensee has: (1) instituted

compensatory measures for the degraded condition, including continuous fire watches, placement of additional fire extinguishers in the three affected plant areas, and administratively

controlling transient combustibles; (2) initiated plant design changes involving the RCP seal

leak-off lines to preclude the possibility of rupture during loss-of-all-seal cooling events, i.e.,

replacement of susceptible valves and flanges; (3) performed engineering analyses regarding

the event's impact on charging pumps and pressurizer level during the event; and (4) revised

fire shutdown strategies to effectively mitigate the event. 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.

/RA/

William D. Beckner, Chief

Reactor Operations Branch

Division of Inspection Program Management

Office of Nuclear Reactor Regulation

Technical Contacts: Paul Cataldo, Region I Warren Lyon, NRR

(860) 701-3470 (301) 415-2897 E-mail: pcc1@nrc.gov E-mail: wcl@nrc.gov

Phil Qualls, NRR

(301) 415-1849 E-mail: pmq@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

ML032760027 DOCUMENT NAME:C:\ORPCheckout\FileNET\ML032760027.wpd

See previous concurrence*

OFFICE OES:RORP:DRIP Tech Editor RGN:I SPLB:DSSA

NAME CPetrone* Pkleene* PCCataldo (per email) JHannon*

DATE 06 /19 /2003 02 /24 /2003 07/14 /2003 09/30 /2003 OFFICE SRXB:DSSA SRXB:DSSA EMEB/DE SC:OES:DRIP PD:RORP:DRIP

NAME JUhle* JRWermiel* EImbro* TReis* ejb for WDBeckner

DATE 09/02/2003 09/05 /2003 06/20 /2003 10/02/2003 10/06/2003

Attachment 1 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

_____________________________________________________________________________________

Information Date of

Notice No. Subject Issuance Issued to

_____________________________________________________________________________________

2003-18 General Electric Type SBM 09/26/2003 All holders of operating licenses

Control Switches With for nuclear power reactors, Defective Cam Followers except those who have

permanently ceased operations

and have certified that fuel has

been permanently removed from

the reactor vessel.

2003-17 Reduced Service Life of 09/29/2003 All holders of operating licenses

Automatic Switch Company for nuclear power reactors.

(ASCO) Solenoid Valves With

Buna-N Material

2003-16 Icing Conditions Between Pending All 10 CFR Part 72 licensees and

Bottom of Dry Storage System certificate holders.

and Storage Pad

2003-15 Importance of Followup 09/05/2003 All holders of operating licenses

Activities in Resolving for nuclear power reactors except

Maintenance Issues those who have permanently

ceased operation and have

certified that fuel has been

permanently removed from the

reactor vessel.

2003-14 Potential Vulnerability of Plant 08/29/2003 All holders of operating licenses

Computer Network to Worm for nuclear power reactors, Infection except those who have

permanently ceased operations

and have certified that fuel has

been permanently removed from

the reactor vessel.

Note: NRC generic communications may be received in electronic format shortly after they are

issued by subscribing to the NRC listserver as follows:

To subscribe send an e-mail to <listproc@nrc.gov >, no subject, and the following

command in the message portion:

subscribe gc-nrr firstname lastname

______________________________________________________________________________________

OL = Operating License

CP = Construction Permit