Category:NRC Information Notice[Table view]The following query condition could not be considered due to this wiki's restrictions on query size or depth: <code> [[:Beaver Valley]] OR [[:Millstone]] OR [[:Hatch]] OR [[:Monticello]] OR [[:Calvert Cliffs]] OR [[:Dresden]] OR [[:Davis Besse]] OR [[:Peach Bottom]] OR [[:Browns Ferry]] OR [[:Salem]] OR [[:Oconee]] OR [[:Mcguire]] OR [[:Nine Mile Point]] OR [[:Palisades]] OR [[:Palo Verde]] OR [[:Perry]] OR [[:Indian Point]] OR [[:Fermi]] OR [[:Kewaunee]] OR [[:Catawba]] OR [[:Harris]] OR [[:Wolf Creek]] OR [[:Saint Lucie]] OR [[:Point Beach]] OR [[:Oyster Creek]] OR [[:Watts Bar]] OR [[:Hope Creek]] OR [[:Grand Gulf]] OR [[:Cooper]] OR [[:Sequoyah]] OR [[:Byron]] OR [[:Pilgrim]] OR [[:Arkansas Nuclear]] OR [[:Braidwood]] OR [[:Susquehanna]] OR [[:Summer]] OR [[:Prairie Island]] OR [[:Columbia]] OR [[:Seabrook]] OR [[:Brunswick]] OR [[:Surry]] OR [[:Limerick]] OR [[:North Anna]] OR [[:Turkey Point]] OR [[:River Bend]] OR [[:Vermont Yankee]] OR [[:Crystal River]] OR [[:Haddam Neck]] OR [[:Ginna]] OR [[:Diablo Canyon]] OR [[:Callaway]] OR [[:Vogtle]] OR [[:Waterford]] OR [[:Duane Arnold]] OR [[:Farley]] OR [[:Robinson]] OR [[:Clinton]] OR [[:South Texas]] OR [[:San Onofre]] OR [[:Cook]] OR [[:Comanche Peak]] OR [[:Yankee Rowe]] OR [[:Maine Yankee]] OR [[:Quad Cities]] OR [[:Humboldt Bay]] OR [[:La Crosse]] OR [[:Big Rock Point]] OR [[:Rancho Seco]] OR [[:Zion]] OR [[:Midland]] OR [[:Bellefonte]] OR [[:Fort Calhoun]] OR [[:FitzPatrick]] OR [[:McGuire]] OR [[:LaSalle]] OR [[:Fort Saint Vrain]] OR [[:Shoreham]] OR [[:Satsop]] OR [[:Trojan]] OR [[:Atlantic Nuclear Power Plant]] OR [[:Crane]] </code>.
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
This information notice is intended to alert addressees to the potential
consequences associated with failure of freeze seals used to perform mainte- nance in piping systems. Of particular concern would be a failure when used
could lead to core uncovery. 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 contained in-this
information notice do not constitute NRC requirements; therefore, no specific
action or written response is required.
Description of Circumstances
On April 19, 1989, at the River Bend Station, a freeze seal failed on a 6-inch
service water line. The freeze seal was used to allow inspection and repair of
manual isolation valves to a safety-related auxiliary building cooler. The
bonnet of one manually operated valve was off the valve and the service water
system was in operation at the time'-of the event. The failure of the freeze
seal resulted in the flooding of portions of the auxiliary building. Approxi- mately 15,000 gallons of service water were discharged through the disassembled
isolation valve, covering portions of the floor at the 141-foot level of the
auxiliary building. A portion of the water flowed through holes in the floor
under safety-related 480-Vac motor control centers onto nonsafety-related
cabinets on the 114-foot level containing disconnect links and a
13.8-kV/480-Vac transformer. As the cabinets were not designed to shed water, they allowed the water to enter, shorting circuits and causing a fire that
damaged one cabinet and its components. A 13.8-kY supply breaker opened and
deenergized the cabinet and two others, causing the loss of the operating
June 27, 1991 While the Oconee Nuclear Station, Unit 1, was shut down for a refueling outage
in 1987, the licensee used a freeze seal to enable plant personnel to replace a
3-inch-diameter section of low-pressure injection piping because no valves were
available to isolate the affected piping. The freeze seal was in a line
connected to the borated water storage tank, which supplies borated water for
the low-pressure injection system.
The freeze seal failed, and approximately
30,000 gallons of slightly radioactively contaminated water leaked into various
areas of the auxiliary building. A portion of the water from the borated water
storage tank drained through the station yard drainage system and flowed past
the site boundary before the leak was brought under control 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> after the
freeze seal failed. Further information may be found in NRC Inspection Report
No. 50-269/87-51.
Discussion:
Freeze seals are used to isolate components (such as inboard isolation valves)
for maintenance in locations that cannot otherwise be isolated. The seal is
created and maintained by applying a cooling agent such as liquid nitrogen to
the exterior of the pipe.
The cooling agent freezes the water within the pipe
The staff has estimated that the reactor core could be uncovered in less than
1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> if the freeze seal failed completely in the RWCU system.
Freeze seal failures in secondary systems can also be significant because of
the potential for consequential failures, such as the loss of decay heat
removal in the River Bend event. The licensee for the River Bend Station
attributed the causes of the event to procedural inadequacies that resulted in
a failure to install and monitor a temperature detection device, and to a lack
of personnel training in the use of freeze seals.
Some licensees have used piping mockups to thoroughly evaluate freeze seal
applications prior to their use on reactor system piping.
Important considera- tions include examining training, procedures, and contingency plans associated
with the use of freeze seals, and evaluating the need for and availability of
additional water makeup systems and their associated support systems.
-IN
91-41 June 27, 1991 This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact the
technical contact listed below or the appropriate NRR project manager.
