Information Notice 2007-01, Recent Operating Experience Concerning Hydrostatic Barriers
| ML063540449 | |
| Person / Time | |
|---|---|
| Issue date: | 01/31/2007 |
| From: | Michael Case NRC/NRR/ADRA/DPR |
| To: | |
| Laura Rich, NRR/DIPM/IROB, 301-415-1837 | |
| References | |
| IN-07-001 | |
| Download: ML063540449 (5) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001
January 31, 2007
NRC INFORMATION NOTICE 2007-01:
RECENT OPERATING EXPERIENCE
CONCERNING HYDROSTATIC BARRIERS
ADDRESSEES
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.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
addressees of operating experience during 2006 concerning water leaking into buildings or
between rooms due to deficient hydrostatic (watertight) barriers. NRC expects 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 IN are not NRC
requirements; therefore, no specific action or written response is required.
DESCRIPTION OF CIRCUMSTANCES
During 2006, there were at least three events involving water leaking into areas containing
safety-related equipment due to deficient hydrostatic barriers. These barriers were either
degraded, missing, or composed of non-watertight materials such as fire stop (e.g., silicone
foam). These events occurred at the Catawba, Seabrook, and Surry Power Stations.
Seabrook Power Station
On February 5, 2006, at the Seabrook Power Station, the licensee inadvertently actuated one of
five deluge subsystems during a scheduled surveillance test of the water deluge system in the
cable spreading room (CSR). Approximately 1,000 gallons of water discharged into the CSR.
Shortly after the event, the licensee discovered several small puddles of water on the floor of
the safety-related A train essential switchgear room, located directly below the CSR. The
licensee determined that most of the water had entered through degraded foam penetration
seals in the CSR floor, and some water may have passed through floor construction joints.
Upon review of the design bases documents, the licensee determined that the CSR floor was
designed as a watertight hydrostatic barrier. Also, the licensee determined that they had failed
to incorporate design basis flood protection requirements into the original penetration seal
specifications and the CSR floor slab design. The CSR floor and associated seals were not
originally specified, designed, or installed as watertight hydrostatic barriers. The licensee
submitted a voluntary licensee event report (LER) to describe the event
(LER 50-443/2006-003-00, Agencywide Documents Access and Management System
(ADAMS) Accession No. ML0615203450).
The licensee at the Seabrook Power Station attributed the deficient hydrostatic barriers to
degraded foam penetration seals, foam seals made of a non-watertight material never intended
for hydrostatic applications, and unsealed floor construction joints. All of the penetration seals
in the CSR floor are supposed to function as both fire and flood barriers. The licensee routinely
inspected seals under a fire protection PM program but had never inspected seals from a flood
protection standpoint. The criteria in the PM program allowed for small gaps and cracks of a
limited size. The foam seals should expand and close up the cracks when exposed to high
temperatures such as those experienced in a fire. However, following the CSR deluge event, the plant staff recognized that the acceptance criteria for a penetration seal to function as a fire
barrier are not sufficient enough to ensure function as a watertight hydrostatic barrier.
Catawba Power Station
On May 22, 2006, at the Catawba Power Station, the licensee identified water leaking through
cable conduits into the 1A emergency diesel generator (EDG) room. The licensee attributed
the water to one of Catawbas mechanical draft cooling towers, which had overflowed when
excessive silting clogged the cooling tower screens. The overflow entered cable trenches and
migrated downhill, from the cooling tower to the diesel generator room. The water entered the
1A EDG room through unsealed, underground, 4-inch conduits. The flow rate was greater than
the capacity of the EDG room sump pumps. As a result, the licensee declared the 1A EDG
inoperable. The licensee installed portable sump pumps to mitigate the flooding conditions.
Subsequently, the licensee determined that the 4-inch conduits had been unsealed since initial
plant construction. During an extent-of-condition review, the licensee identified unsealed or
improperly sealed conduits leading into all four EDG rooms, load sequencer corridors, or areas
of the auxiliary building containing safety-related equipment. Some of the improperly sealed
conduits contained only fire stop, and others had fire stop topped with a water-tight sealant, which had loosened or degraded over time. Of the degraded seals, most were installed at initial
plant construction and were never inspected to ensure continued watertight construction. NRC
inspectors identified several deficiencies in how the licensee maintained and tested their
hydrostatic seals (NRC Inspection Report 50-413; 414/2006-009, ADAMS Accession No.
The licensees corrective actions included developing a preventative maintenance (PM)
program to periodically inspect and repair hydrostatic seals. Before this PM program could be
completely implemented, a similar event occurred in which water entered the turbine building
through a nonsafety-related flood wall intended to protect the 6.9-kV transformers. Surry Power Station
On October 7, 2006, at the Surry Power Station, heavy rainfall resulted in water leaking into the
Unit 1 turbine building basement (TBB) and the Unit 2 emergency switchgear room (ESGR). In
the Unit 1 TBB at the D ductbank, the estimated flow rate was 200 gpm - 250 gpm; in the
Unit 1 TBB in the lube oil storage room the estimated flow rate was 1 gpm - 3 gpm and in the
Unit 2 ESGR, the estimated flow rate was 5 gpm - 10 gpm. The water entered through a
manhole in the switchyard at a rate exceeding the capacity of the two installed sump pumps.
As a result, water from this manhole overflowed into a second manhole where the water
exceeded the capacity of a 6-inch gravity drain. An increasing water level in the second
manhole caused a pressure increase forcing the water through six unsealed 5-inch conduits
into the D ductbank, thereby entering the Unit 1 TBB and the Unit 2 ESGR.
The TBB conduits were unsealed. In the ESGR, the licensee found that inadequate installation
of the fire stop (i.e., General Electric RTV silicone fire foam) in the ESGR allowed water
pressure to push the seal out of the conduit penetration.
During initial construction at Surry, the licensee used fire resistant silicone foam to seal
electrical conduits. In 1991, the licensee upgraded its conduit seal standards. The new
requirements stipulated that conduits which penetrate any building, such that one end is in an
electrical enclosure and the other end is inside the building, shall be sealed at the end with the
highest elevation. However, the licensee applied the new standard to new conduit seal
activities only and, thus, did not prevent this event.
BACKGROUND
Relevant Generic Communications
NRC Information Notice 92-69, Water Leakage from Yard Area Through Conduits Into
Buildings
NRC IN 92-69 describes two events when large quantities of water entered areas of buildings
that contained safety-related equipment. The safety analysis did not consider the leak paths
specifically through manholes and connecting conduits. The licensee neither inspected nor
tested the conduit seals to detect the absence or deterioration of the seals.
NRC Information Notice 88-60, Inadequate Design and Installation of Watertight Penetration
Seals
NRC IN 88-60 describes an event at Vogtle Unit 1 from June 3, 1988, when an inadvertent
pressurization of the fire protection system in the B train CSR caused water to accumulate
around cable penetrations in the floor. As water seeped through the floor into the control room, it entered various process panel cabinets and triggered the opening of a pressurizer
power-operated relief valve at power.
DISCUSSION
These events illustrate the importance of installing and maintaining watertight hydrostatic
barriers in accordance with plant design controls to avoid any adverse effect on safety-related
equipment from water intrusion. In particular, when a penetration seal functions as both a fire
barrier and a flood barrier, it is important for licensees to consider both functions in the design, installation, inspection, and maintenance. This includes accounting for static head pressure to
ensure watertight seals do not dislodge.
CONTACT
This information notice requires no specific action or written response. Please direct any
questions about this matter to the technical contacts listed below.
/RA by TQuay for/
Michael J. Case, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contacts: Nicole Sieller, NRC/RI
Richard Laura, NRR/DIRS
610-337-5380
301-415-1837 E-mail: nss@nrc.gov
E-mail: ral1@nrc.gov
Jerry Purciarello, NRR/SBPB
Eugene Guthrie, NRC/R2
301-415-1105
301-415-4662 E-mail: gjp@nrc.gov
E-mail: gxg@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections
DISCUSSION
These events illustrate the importance of installing and maintaining watertight hydrostatic
barriers in accordance with plant design controls to avoid any adverse effect on safety-related
equipment from water intrusion. In particular, when a penetration seal functions as both a fire
barrier and a flood barrier, it is important for licensees to consider both functions in the design, installation, inspection, and maintenance. This includes accounting for static head pressure to
ensure watertight seals do not dislodge.
CONTACT
This information notice requires no specific action or written response. Please direct any
questions about this matter to the technical contacts listed below.
/RA by TQuay for/
Michael J. Case, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contacts: Nicole Sieller, NRC/RI
Richard Laura, NRR/DIRS
610-337-5380
301-415-1837 E-mail: nss@nrc.gov
E-mail: ral1@nrc.gov
Jerry Purciarello, NRR/SBPB
Eugene Guthrie, NRC/R2
301-415-1105
301-415-4662 E-mail: gjp@nrc.gov
E-mail: gxg@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections
DISTRIBUTION:
IN FILE
ADAMS Accession Number: ML063540449 OFFICE
IOEB:DIRS
SBPB:DSS
R11:DRP
R1:DRP
NAME
RLaura
JPurciarello
EGuthrie
NSieller
DATE
01/05/2007
01/08/2007
01/10/2007
01/08/2007 OFFICE
PGCB:DPR
PGCB:DPR
TL:DIRS:IOEB
BC:PGCB:DPR
D:DPR
NAME
CHawes
DBeaulieu
JThorp
CJackson
TQuay for MCase
DATE
01/10/2007
01/24/2007
01/10/2007
01/ /2007
01/31/2007 OFFICIAL RECORD COPY