United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 87-28: Air Systems Problems at U.S. Light Water Reactors

                                                        SSINS No.:  6835 
                                                            IN 87-28

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                      OFFICE OF NUCLEAR REACTOR REGULATION
                             WASHINGTON, D.C.  20555

                                  June 22, 1987


Information Notice No. 87-28:  AIR SYSTEMS PROBLEMS AT U.S. LIGHT 
                                   WATER REACTORS 


Addressees:

All nuclear power reactor facilities holding an operating license or a con-
struction permit.

Purpose:

This information notice is being provided to alert recipients to potentially 
significant problems pertaining to air systems at light water reactors.  The 
NRC expects that recipients will review this notice for applicability to their 
facilities.  The suggestions in this notice do not constitute NRC 
requirements; therefore, no specific action or written response is required.  

Background:

The NRC Office for Analysis and Evaluation of Operational Data (AEOD) has 
recently issued a case study report entitled "Air Systems Problems at U.S. 
Light Water Reactors," AEOD/C701.*  The report discusses degradations of air 
systems and plant responses to air systems losses.  It also highlights more 
than two dozen events in which, contrary to licensing assumptions, a safety-
related system failed as a result of an air system degradation or failure.  
Operating events involving the loss or degradation of air systems were judged 
to be safety significant because they may lead, under different circumstances, 
to potentially serious events and conditions that have not been analyzed. 

Discussion:

The study provides a comprehensive review and evaluation of potential safety 
implications associated with air systems problems.  The report analyzes oper-
ating data, focusing on degraded air systems, and the vulnerability of safety-
related equipment to common mode failures associated with air systems.  The 
report analyzes these data from the perspectives of trends and patterns, risk 
assessments, and cost/benefit studies.  


                        
*A copy of the study report is available in the NRC Public Document Room, 
 1717 H Street NW, Washington, DC  20555, for inspection and copying.


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                                                             IN 87-28
                                                                 June 22, 1987
                                                                 Page 2 of 2


Air systems are not classified as safety-related systems at most operating 
plants.  As a result, plant accident analyses assume that safety-related 
equipment dependent on air systems will either "fail safe" on loss of air or 
perform its intended function with the assistance of safety-related backup air 
accumulators.  This report highlights 29 failures of safety-related systems 
that resulted from degraded or malfunctioning air systems.  These failures 
contradict the assumption that safety-related equipment dependent on air 
systems will always either fail safe on loss of air or perform its intended 
function with the assistance of backup accumulators.  Some of the systems that 
were significantly degraded or failed were decay heat removal, auxiliary 
feedwater, BWR scram, main steam isolation, salt water cooling, emergency 
diesel generator, containment isolation, and the fuel pool seal systems.  For 
example:

1.   Leakage of 140,000 gallons of radioactive water from the spent fuel pool 
     at the Hatch Nuclear Plant on December 3, 1986, was caused by the 
     mispositioning of a single valve in the instrument air system. 

2.   Failure of several main steam isolation valves to close at Brunswick 2 on 
     September 27, 1985, was due to contaminants in the instrument air.   

3.   A loss of the auxiliary feedwater systems at Turkey Point 3 and 4 in July 
     1985 was caused by water and dirt particles in the air system.  

4.   The inability to scram four control rods at Susquehanna 1 on October 6, 
     1984, was caused by oil in the air system.  

5.   A loss of decay heat removal and significant primary system heatup at 
     Palisades in 1978 and 1981 were caused by water in the air system.  

The root causes of most of the failures were traceable to design and/or 
maintenance deficiencies.  The design and operating problems appear to reflect 
a lack of adequate attention to the design, maintenance, operation, and 
administrative control of air systems.  

No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the Regional 
Administrator of the appropriate regional office or this office. 




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

Technical Contacts:  C. Vernon Hodge, NRR
                     (301) 492-8196

                     Hal Ornstein, AEOD
                     (301) 492-4439

Attachment:  List of Recently Issued NRC Information Notices
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