United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 80-12: Decay Heat Removal System Operability

                                                            SSINS No.: 6820 
                                                            Accession No.: 

                                UNITED STATES
                           WASHINGTON, D.C. 20555

                                 May 9, 1980

                                                      IE Bulletin No. 80-12 



The intent of this Bulletin is to improve nuclear power plant safety by 
reducing the likelihood of losing decay heat removal (DHR) capability in 
operating pressurized water reactors (PWRs). PWRs are most susceptible to 
losing DHR capability when their steam generators or other diverse means of 
removing decay heat are not readily available. Such conditions often occur 
when the plants are in a refueling or cold shutdown mode, and during which 
time concurrent maintenance activities are being performed. 

There is a need to assure that all reasonable means have been taken to 
provide redundant or diverse means of DHR during all modes of operation. 
(Note: A redundant means could be provided by having DHR Train A AND Train B 
operable; a diverse means could be provided by having either DHR Train A OR 
Train B operable AND a steam generator available for DHR purposes.) There is 
also need to assure that all reasonable means have been taken to preclude 
the loss of DHR capability due to common mode failures during all modes of 


On several occasions, operating PWRs have experienced losses of DHR 
capability. In each instance, except that of the Davis-Besse Unit 1 incident
of April 19, 1980, DHR capability was restored prior to exceeding the 
specified RCS temperature limit for the specific mode of operation. 
Nonetheless, the risk and frequency associated with such events dictate that
positive actions be taken to preclude their occurrence or at least 
ameliorate their effects. 

The most noteworthy example of total loss of DHR capability occurred at 
Davis-Besse Unit 1 on April 19, 1980. (See IE Information Notice No. 80-20, 
attached hereto as Enclosure 1). Two factors identified as major 
contributors to the Davis-Besse event in the Information Notice are: (1) 
extensive maintenance activities which led to a loss of redundancy in the 
DHR capability, and (2) inadequate procedures and/or administrative controls
which, if corrected, could have precluded the event or at least ameliorated 
its effects. 


1.   Review the circumstances and sequence of events at Davis-Besse as 
     described in Enclosure 1. 

2.   Review your facility(ies) for all DHR degradation events experienced, 
     especially for events similar to the Davis-Besse incident. 

IE Bulletin No. 80-12                                       May 9, 1980 
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3.   Review the hardware capability of your facility(ies) to prevent DHR 
     loss events, including equipment redundancy, diversity, power source 
     reliability, instrumentation and control reliability, and overall 
     reliability during the refueling and cold shutdown modes of operation. 

4.   Analyze your procedures for adequacy of safeguarding against loss of 
     redundancy and diversity of DHR capability. 

5.   Analyze your procedures for adequacy of responding to DHR loss events. 
     Special emphasis should be placed upon responses when maintenance or 
     refueling activities degrade the DHR capability. 

6.   Until further notice or until Technical Specifications are revised to 
     resolve the issues of this Bulletin, you should: 

     a.   Implement as soon as practicable administrative controls to assure
          that redundant or diverse DHR methods are available during all 
          modes of plant operation. (Note: When in a refueling mode with 
          water in the refueling cavity and the head removed, an acceptable 
          means could include one DHR train and a readily accessible source 
          of borated water to replenish any loss of inventory that might 
          occur subsequent to the loss of the available DHR train.) 

     b.   Implement administrative controls as soon as practicable, for 
          those cases where single failures or other actions can result in 
          only one DHR train being available, requiring an alternate means 
          of DHR or expediting the restoration of the lost train or method. 

7.   Report to the NRC within 30 days of the date of this Bulletin the 
     results of the above reviews and analyses, describing: 

     a.   Changes to procedures (e.g., emergency, operational, 
          administrative, maintenance, refueling) made or initiated as a 
          result of your reviews and analyses, including the scheduled or 
          actual dates of accomplishment; (Note: NRC suggests that you 
          consider the following: (1) limiting maintenance activities to 
          assure redundancy or diversity and integrity of DHR capability, 
          and (2) bypassing or disabling, where applicable, automatic 
          actuation of ECCS recirculation in addition to disabling High 
          Pressure Injection and Containment Spray preparatory to the cold 
          shutdown or refueling mode.) 

     b.   The safeguards at your facility(ies) against DHR degradation, 
          including your assessment of their adequacy. 

The above information is requested pursuant to 10 CFR 50.54(f). Accordingly,
written statements addressing the above items shall be signed under oath or 
affirmation and submitted within the time specified above. Reports shall be 

IE Bulletin No. 80-12                                       May 9, 1980 
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to the director of the appropriate NRC regional office, and a copy forwarded
to the Director, Division of Reactor Operations Inspection, NRC Office of 
Inspection and Enforcement, Washington, D. C. 20555. 

Approved by GAO, B180225 (R0072); clearance expires 7-31-80. Approval was 
given under a blanket clearance specifically for identified generic 

IE Information Notice
  No.. 80-20 
Page Last Reviewed/Updated Friday, May 22, 2015