Information Notice No. 90-53: Potential Failures of Auxiliary Steam Piping and the Possible Effects on the Operability of Vital Equipment

                                UNITED STATES
                           WASHINGTON, D.C.  20555

                               August 16, 1990

                                   PIPING AND THE POSSIBLE EFFECTS ON THE 
                                   OPERABILITY OF VITAL EQUIPMENT


All holders of operating licenses or construction permits for nuclear power 


This information notice is intended to alert addressees to potential 
problems resulting from unanalyzed failures of auxiliary steam lines.  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:

During the winter of 1989 at the Millstone Nuclear Power Station, personnel 
of the Northeast Nuclear Energy Company (the licensee) encountered 
difficulty in maintaining room temperatures at various locations in the 
plant.  To correct this problem, the licensee initiated a plant design 
change to install new heating coils.  The safety analysis performed for the 
design change included analyzing the effects of a failure of the house 
heating steam line.  Upon completing this analysis, the licensee decided to 
examine other piping used for house heating steam.  During this 
investigation, the licensee discovered that a failure of the house heating 
steam system could degrade equipment located in areas classified as "mild 
environments."  The licensee identified that the areas that were vulnerable 
to a house heating steam line break included the Unit 1 switchgear room, 
lower and upper HVAC rooms, and the control room.  Further investigation 
revealed five general areas within Millstone 2 that had not been analyzed 
for an auxiliary steam system steam line break.  These areas included 
control room air conditioning, A & B emergency diesel generator (EDG) rooms, 
EDG tank room, and Auxiliary Building 1406.  A break in Building 1406 could 
affect the fans that cool vital switchgear and the room adjacent to the 
spent fuel pool.  On May 25, 1990, the licensee identified two more areas in 
the Unit 2 auxiliary building that had not been analyzed for an auxiliary 
steam line break.

In response to these findings at Millstone, personnel at the Haddam Neck 
Generating Station investigated their piping configuration to determine if a 
similar concern existed.  They determined that a break of a heating steam 
line could affect the operation of safety-related 480-volt switchgear.


                                                            IN 90-53 
                                                            August 16, 1990 
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The house heating steam system is classified as a high-energy line break 
(HELB) system at Millstone.  Because this system is not seismic and house 
heating steam lines are present in many areas of the plant, a seismic event 
could result in the degradation of safety related equipment classified for 
mild environments.  The licensee determined that this condition could 
potentially affect safety related structures and systems needed to (a) 
shutdown the reactor and maintain it in a safe condition and (b) remove 
residual heat.  The licensee identified the cause of the oversight to be an 
incorrect conclusion drawn from the HELB study performed in 1973.  This 
report addressed an auxiliary steam system line break and its non-relevance 
on safety-related equipment, stating that the environmental conditions 
following any break would be of no consequence to any shutdown methods.  

House heating steam systems (or other auxiliary steam line systems) are not 
considered typical high-energy line systems.  As such, they may have been 
overlooked or improperly analyzed when failure modes and effects and single 
failure analyses were performed as part of the HELB safety assessment.  
Millstone Units 1 and 2, and Haddam Neck have three different nuclear steam 
supply systems and three different architect/engineer firms.  Therefore, the 
oversight which occurred at these plants may have also occurred at other 

This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
one of the technical contacts listed below or the appropriate NRR project 

                               Charles E. Rossi, Director
                               Division of Operational Events Assessment
                               Office of Nuclear Reactor Regulation

Technical Contacts:  P. Baranowsky, NRR
                     (301) 492-1156

                     A. Mattson, NRR
                     (301) 492-1174

                     R. Architzel, NRR
                     (301) 492-0804 

Attachment:  List of Recently Issued NRC Information Notices

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