Information Notice 2003-07, Water in the Vent Header/Vent Line Spherical Junctions
| ML031750146 | |
| Person / Time | |
|---|---|
| Issue date: | 06/24/2003 |
| From: | Beckner W NRC/NRR/DRIP/RORP |
| To: | |
| Dozier J, NRR/RORP 301-415-1014 | |
| References | |
| IN-03-007 | |
| Download: ML031750146 (6) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
June 24, 2003 NRC INFORMATION NOTICE 2003-07:
WATER IN THE VENT HEADER/VENT LINE
SPHERICAL JUNCTIONS
Addressees
All holders of operating licenses for boiling water reactors (BWRs) with a Mark I containment.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
addressees of recent issues involving the pressure suppression containment system in BWRs
with a Mark I containment. During a recent refueling outage at Nine Mile Point Unit 1 (NMP1),
unanticipated standing water was found inside the vent header/vent line (VH/VL) spherical
junctions (vent system low point or bowl). The weight of this standing water inside the VH/VL
spherical junctions was not included in the generic Mark I containment accident analysis
because the spherical junctions are assumed to remain dry. This standing water inside the
VH/VL spherical junction increases the thrust loads on the vent system. The primary concern is
that this standing water will increase vent system thrust loads during reactor blowdown after a
loss-of-coolant accident inside containment beyond design limits.
The licensees for other plants with Mark I containment designs have also noted standing water
in the VH/VL spherical junctions (Pilgrim, Hope Creek, and Fermi). It is expected that recipients
will review the information in this notice 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.
Background
The pressure suppression containment system of a Mark I BWR consists of a drywell, a torus- shaped pressure suppression chamber, which is approximately half filled with water, a
connecting vent system between the drywell and the pressure suppression chamber, isolation
valves, a vacuum relief system, a containment cooling system and other service equipment. An
illustration of portions of this system is provided in Figure 1.
The vent pipe descending from the drywell joins the ring header at a VH/VL spherical junction.
There are 8 to 10 vent pipes and spherical junctions in most Mark I containments. The ring
header is arranged within the suppression chamber shell, with downcomer pipes from the
header extending below the water surface in the suppression chamber. Submergence of the
downcomer pipes is operationally maintained by a minimum required suppression chamber
water level in Technical Specifications.
The limiting event for containment pressurization and vent system flow rates is the design basis
loss-of-coolant accident (DBA-LOCA). The DBA-LOCA results in the maximum pressurization
rate, maximum pressure, and highest vent system flow rates; therefore, it produces the highest
vent system thrust loads. The vent system thrust load is a function of the vent system pressure
relative to the suppression chamber air space and the mass flow and velocity through vent
piping. The Mark I Containment Program for NMP1 has previously defined vent system thrust
loads for the DBA-LOCA based on these parameters.
Description of Circumstances
During a refueling outage, NMP1 personnel discovered that the VH/VL spherical junctions
contained approximately 3 feet of standing water or 1100 gallons per sphere (11,000 gallons
total) where it should be dry. Because of the system geometry, the volume of water in
the spherical junction was at its maximum. Addition of more water would result in
spilling into the ring header and downcomers. The source of the water is believed to be
condensation in the relatively cool vent header lines. The original plant design of some Mark I
containments had drain lines from the spherical junctions to the torus. Some of the plants
having these drain lines removed them in the early 1980s to eliminate a potential torus bypass
path. These drain lines were not part of the original design at NMP1 and were not installed.
The licensees analysis of the standing water in the spheres concluded that the mass could
become entrained in the initial blowdown and would increase the thrust loads during a LOCA. A
subsequent analysis demonstrated that the majority of the system components met American
Society of Mechanical Engineers (ASME) Code allowable stress values with the exception of
the VH/VL spherical junction at the connection to the ring header. The calculated stress level
for the VH/VL junction exceeded the original design acceptance criteria (ASME Service Level
A/B), but remained below ASME Service Level C and the higher acceptance stress level limits
for operability (ASME Service Level D). The guidance provided in NRC Generic Letter 91-18 was used to demonstrate that the VH/VL spherical junction stress levels remained operable. At the time of this information notice, analysis was continuing to determine if additional actions
were needed to restore compliance with the original design criteria.
This information notice requires no specific action or written response. If you have any
questions regarding the information notice, please contact the technical contacts listed below or
the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
/RA/
William D. Beckner, Program Director
Operating Reactor Improvements Program
Division of Regulatory Improvement Programs
Office of Nuclear Reactor Regulation
Technical contact:
Gordon K. Hunegs, RI
(315) 342-4041 E-mail: gkh@nrc.gov
Jerry Dozier, NRR
(301) 415-1014 E-mail: jxd@nrc.gov
Attachment: List of Recently Issued NRC Information Notices At the time of this information notice, analysis was continuing to determine if additional actions
were needed to restore compliance with the original design criteria.
This information notice requires no specific action or written response. If you have any
questions regarding the information notice, please contact the technical contacts listed below or
the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
/RA/
William D. Beckner, Program Director
Operating Reactor Improvements Program
Division of Regulatory Improvement Programs
Office of Nuclear Reactor Regulation
Technical contact:
Gordon K. Hunegs, RI
(315) 342-4041 E-mail: gkh@nrc.gov
Jerry Dozier, NRR
(301) 415-1014 E-mail: jxd@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
DISTRIBUTION:
IN File
DOCUMENT NAME: G:\\RORP\\OES\\Staff Folders\\Dozier\\Information Notice Water in Torus Ventsrevised.wpd
Adams Accession No.:
- See previous concurrence
OFFICE
OES:RORP:DRIP
Tech Editor
RI
BC:RI
NAME
JXDozier
GKHunegs
JMTrapp
DATE
06 /09/2003
06 /10/2003
06 /12/2003
06 /12/2003 OFFICE
OES:RORP:DRIP
SC:RORP:DRIP
PD:RORP:DRIP
NAME
CDPetrone
TReis
WDBeckner
DATE
06/08/2003
06/24/2003
06/24/2003
/ /2003
OFFICIAL RECORD COPY
______________________________________________________________________________________
OL = Operating License
CP = Construction Permit
Attachment 1 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________________
Information
Date of
Notice No.
Subject
Issuance
Issued to
_____________________________________________________________________________________
2003-06 Failure of Safety-related
Linestarter Relays at San
Onofre Nuclear Generating
Station
06/19/2003
All holders of operating licenses
or construction permits for
nuclear power reactors, except
those that have permanently
ceased operations and have
certified that fuel has been
permanently removed from the
reactor.
2003-05
Failure to Detect Freespan
Cracks in PWR Steam
Generator Tubes
06/05/2003
All holders of operating licenses
or construction permits for
pressurized-water reactors
(PWRs).
2002-15, Sup 1
Potential Hydrogen
Combustion Events in BWR
Piping
05/06/2003
All holders of operating licenses
for light water reactors, except
those who have permanently
ceased operations and have
certified that fuel has been
permanently removed from the
reactor.
2002-21, Sup 1 Axial Outside-diameter
Cracking Affecting Thermally
Treated Alloy 600 Steam
Generator Tubing
04/01/2003
All holders of operating licensees
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:
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