Information Notice No. 84-17: Problems with Liquid Nitrogen Cooling Components Below the NIL Ductility Temperature

                                                                SSINS No.: 
                                                                IN 84-17   

                               UNITED STATES 
                           WASHINGTON, D.C. 20555 

                               March 5, 1984 

                                   COMPONENTS BELOW THE NIL DUCTILITY 


All holders of nuclear power reactor operating licenses (OLs) or 
construction permits (CPs). 


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. 


                                                             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 

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