Information Notice 2005-11, Internal Flooding/Spray-Down of Safety-Related Equipment Due to Unsealed Equipment Hatch Floor Plugs And/Or Blocked Floor Drains
| ML050870351 | |
| Person / Time | |
|---|---|
| Issue date: | 05/06/2005 |
| From: | Hiland P NRC/NRR/DIPM |
| To: | |
| Telson, R - NRR/DIPM/IROB - 415-2256 | |
| References | |
| IN-05-011 | |
| Download: ML050870351 (5) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001 May 6, 2005 NRC INFORMATION NOTICE 2005-11: INTERNAL FLOODING/SPRAY-DOWN OF
SAFETY-RELATED EQUIPMENT DUE TO
UNSEALED EQUIPMENT HATCH FLOOR PLUGS
AND/OR BLOCKED FLOOR DRAINS
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 the possibility of flooding safety-related equipment as a result of (1) equipment
hatch floor plugs that are not water tight and (2) blockage of the equipment floor drain systems
that are credited to mitigate the effects of flooding in the final safety analysis report (FSAR) and
plant design basis calculations.
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 in this IN are
not NRC requirements; therefore, no specific action or written response is required.
DESCRIPTION OF CIRCUMSTANCES
On August 18, 2004, during an extended backwash evolution on the reactor water cleanup
demineralizer at Susquehanna Unit 1, approximately 1,500 gallons of contaminated water from
the backwash-receiving tank overflowed into the reactor building equipment floor drain system.
The drain header became blocked by the resin from the receiving tank and rust displaced from
inside the drain pipes. The water flowed up and out of the blocked drains on a lower elevation, across the floor, and down into the Division II core spray and the high-pressure coolant injection
system compartments. The water entered these compartments by flowing though unsealed
spaces between the equipment hatch floor plugs and the floor. The equipment floor drains in
the emergency core cooling system (ECCS) compartments were isolated, as per design, and
the water accumulated on the floor. Approximately 2 inches of water accumulated on the floor
of the Division II core spray and high-pressure injection system compartments.
The licensee disabled the automatic start feature of the Division II core spray pumps and
declared the pumps inoperable but functional for approximately 2hours until an assessment was
completed to verify operability. The licensees immediate actions were to perform system
walkdowns and determine the effect of the flooding on the Division II core spray and high- pressure coolant injection systems. The walkdowns determined that the water leakage into the
room did not significantly impact the systems and that the systems remained operable. The
walkdowns also confirmed that the other ECCS compartments were not affected.
DISCUSSION
The licensees FSAR flooding analysis stated that the ECCS compartments were water tight.
However, the equipment hatch floor plugs were not sealed and therefore did not constitute a
water-tight barrier. The plant-specific design calculations did not address leakage around these
plugs. Water leaked through the ceiling into the Division II core spray and high-pressure
coolant injection compartments through gaps between the equipment hatch floor plug and the
floor. The licensee did not scope the equipment floor drain system function (mitigating internal
flooding) into the Maintenance Rule. The FSAR and flooding design calculations credited the
equipment floor drain system to assist in removal of water from internally flooded areas. Part of
the licensees corrective actions were to place the floor and equipment drain functions within the
scope of the Maintenance Rule and to revise the plant calculations to reconcile the plant design
analysis and the FSAR. The licensee has also developed and installed a modification to seal
the equipment hatch floor plugs above the ECCS compartments.
CONCLUSION
The event described above illustrates the potential for degradation of multiple trains of ECCS as
a consequence of potential flooding of safety-related equipment outside containment. All
holders of reactor operating licenses should be aware of the effect of unsealed equipment hatch
floor plugs and malfunctioning drains on their plant-specific FSARs and plant design analyses
for flooding. Unsealed reactor building equipment hatch floor plugs and less than optimal
maintenance monitoring of the equipment floor drain systems can result in additional internal
flooding vulnerabilities. Licensees should consider several actions to mitigate these
vulnerabilities:
(1) Verify that the actual plant configuration and design of the equipment hatch floor plugs
meet the FSAR description and design basis calculations for water-tight compartments.
Consider appropriate actions to achieve floor plug water tightness, such as the use of
gaskets and sealers. Additionally, if the analysis allows for leakage through the
equipment hatch floor plugs, the qualification of equipment below these plugs should
consider water spray as well as submergence.
(2) In addition, if the drain system is required for water removal, periodically verify that the
floor drain system performs as intended and perform maintenance to assure that the
system can perform the water removal function assumed in the FSAR and design
calculations. GENERIC IMPLICATIONS
Flooding due to internal causes has been shown to be a significant contributor to risk at some
facilities. Flooding also has the potential to make multiple trains of equipment and support
equipment inoperable, significantly increasing plant risk. Flooding also has the significant
consequence of preventing or limiting operator mitigation and recovery actions. As a result, semiannually, NRC inspectors select one or two plant areas and inspect internal flood
protection features for risk-significant structures, systems, and components in accordance with
Inspection Procedure Attachment 71111.06 Flood Protection Measures.
Multiple previous NRC generic communications have addressed flood protection issues:
1. Circular POTENTIAL COMMON MODE FLOODING OF ECCS EQUIPMENT ROOMS
CR 78-06 AT BWR FACILITIES
2. IN 83-44 POTENTIAL DAMAGE TO REDUNDANT SAFETY EQUIPMENT AS A
RESULT OF BACKFLOW THROUGH THE EQUIPMENT AND FLOOR DRAIN
SYSTEM
3. IN 83-44 S1 POTENTIAL DAMAGE TO REDUNDANT SAFETY EQUIPMENT AS A
RESULT OF BACKFLOW THROUGH THE EQUIPMENT AND FLOOR DRAIN
SYSTEM
4. IN 87-49 DEFICIENCIES IN OUTSIDE CONTAINMENT FLOODING PROTECTION
5. IN 92-69 WATER LEAKAGE FROM YARD AREA THROUGH CONDUITS INTO
BUILDINGS
6. IN 94-27 FACILITY OPERATING CONCERNS RESULTING FROM LOCAL AREA
FLOODING
7. IN 98-31 FIRE PROTECTION SYSTEM DESIGN DEFICIENCIES AND COMMON-
MODE FLOODING OF EMERGENCY CORE COOLING SYSTEM ROOMS AT
WASHINGTON NUCLEAR PROJECT UNIT 2
CONTACT
S
This IN requires no specific action or written response. Please direct any questions about this
matter to the technical contact(s) listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
/Original Signed by Eric J. Benner/
Patrick L. Hiland, Chief
Reactor Operations Branch
Division of Inspection Program Management
Office of Nuclear Reactor Regulation
Technical Contacts: Alan Blamey, R-I/DRP Ross Telson, NRR
570-542-2134 301-415-2256 E-mail: ajb3@nrc.gov E-mail: rdt@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.
ML050870351 DOCUMENT NAME: C:\MyFiles\Copies\IN-FLOOD-rev3.wpd
OFFICE OES:IROB:DIPM TECH EDITOR RGN-I/DRP RGN-1:DRP RGN-1:DRP
NAME RTelson PKleene ABlamey/MS for/ Mshanbacky/MS for/ ARBlough/
DATE 3/3/2005 / /2005 03/22/2005 03/22/2005 03/28/2005 OFFICE SPLB:DSSA SPLB:DSSA IPSB:DIPM A:SC:OES:IROB:DIPM C:IROB:DIPM
NAME JGuo SJones DThatcher EJBenner PLHiland
(EJBenner for)
DATE 03/18/2005 03/18/2005 03/27/2005 05/06/2005 05/06/2005