Information Notice 2003-19, 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 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
______________________________________________________________________________________
OL = Operating License
CP = Construction Permit
Attachment 1 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________________
Information
Date of
Notice No.
Subject
Issuance
Issued to
_____________________________________________________________________________________
2003-18
General Electric Type SBM
Control Switches With
Defective Cam Followers
09/26/2003
All holders of operating licenses
for nuclear power reactors, 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
Automatic Switch Company
(ASCO) Solenoid Valves With
Buna-N Material
09/29/2003
All holders of operating licenses
for nuclear power reactors.
2003-16
Icing Conditions Between
Bottom of Dry Storage System
and Storage Pad
Pending
All 10 CFR Part 72 licensees and
certificate holders.
2003-15
Importance of Followup
Activities in Resolving
Maintenance Issues
09/05/2003
All holders of operating licenses
for nuclear power reactors except
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
Computer Network to Worm
Infection
08/29/2003
All holders of operating licenses
for nuclear power reactors, except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor vessel.
Note:
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