Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.:
IN 84-17
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
March 5, 1984
Information Notice No. 84-17: PROBLEMS WITH LIQUID NITROGEN COOLING
COMPONENTS BELOW THE NIL DUCTILITY
TEMPERATURE
Addressees:
All holders of nuclear power reactor operating licenses (OLs) or
construction permits (CPs).
Purpose:
This information notice is provided to advise licensees and applicants of
potentially significant problems associated with the use of liquid nitrogen
that may cool components below the nil ductility temperature (NDT) of
associated materials susceptible to brittle fracture. It is expected that
the recipients of this notice will review the information for applicability
to their facilities. No specific action or response is required.
Description of Circumstances:
On February 3, 1984, Georgia Power Company notified the NRC of a throughwall
crack almost completely encircling the vent header within the containment
torus of Hatch Unit 2. Later that day IE Bulletin 84-01, "Cracks in Boiling
Water Reactor Mark I Containment Vent Headers," was issued for action to the
licensees of BWR facilities with Mark I containments that were in cold
shutdown. The bulletin requested that these licensees perform inspections
for similar cracks. The inspections revealed no cracks.
Georgia Power Company is continuing its detailed investigation of the Hatch
Unit 2 crack. The preliminary investigation has revealed that the vent
header crack is located in the vicinity of the purge line outlet to the
torus. The purge line is approximately 20 inches in diameter with the outlet
about 7 feet directly above the vent header crack. A nitrogen line
approximately 6 inches in diameter is connected to the purge line outside
the torus for use in inerting the primary containment. The nitrogen thus
enters the torus through the purge line. The preliminary indications are
that the crack is a brittlefracture type of failure resulting from cooling
of the vent header below the NDT by impingement of cold gaseous or liquid
nitrogen. The thermal stresses generated by this cooling may have
contributed to crack initiation and propagation. The vent header material
for Hatch Unit 2 is SA 516 Grade 70 carbon steel with the nil ductility
temperature in the range of -20F to 0F.
8402090011
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IN 84-17
March 5, 1984
Page 2 of 2
The nitrogen is used to create an inert atmosphere inside the primary
containment when the plant is in operation. The nitrogen supply system is
designed to evaporate liquid nitrogen and warm the nitrogen gas before it is
discharged. Heater controls are used to maintain the temperature of the
nitrogen leaving the system at about 100F. The discharge valve of the
system is controlled by a temperature switch and is designed to isolate the
system if discharge temperatures drop to 0F. However, at Hatch Unit 2,
the licensee has indicated that there have been problems with control of the
nitrogen evaporators and heaters and with the low-temperature isolation
provisions. Under worst-case conditions of equipment failure, the discharge
temperature could approach -200F. It appears that the vent header
temperature dropped below the nil ductility temperature when the evaporator
and heater were not operating properly.
Although there is no indication of other cracks at Hatch Unit 2, there are
other components in the vicinity of or associated with the nitrogen piping
and purge line that may have experienced large temperature drops and that
may be susceptible to brittle fracture. These components include the
nitrogen piping, the purge line, containment penetrations and associated
valves, and the high pressure coolant injection (HPCI) steam exhaust piping.
The general concern is that liquid or cold gaseous nitrogen can potentially
cool vital components of the plant below the nil ductility temperatures of
susceptible associated materials. This may lead to failures such as the one
at Hatch Unit 2. Licensees who have used liquid nitrogen (or other
potentially very cold fluids) in applications where the fluid could come in
contact with safety-related components subject to brittle fracture should
consider inspecting these components for possible indication of cracks.
If you have any questions regarding this matter, please contact the Regional
Administrator of the appropriate NRC Regional Office, or this office.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: R. Singh, IE
(301) 492-8068
Attachment:
List of Recently Issued IE Information Notices