United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 79-05: Nuclear Incident at Three Mile Island

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                           WASHINGTON, D.C. 20555 

                                April 1, 1979

                                                      IE Bulletin No. 79-05 

NUCLEAR INCIDENT AT THREE MILE ISLAND 

Description of Circumstances: 

On March 28, 1979 the Three Mile Island Nuclear Power Plant, Unit 2 
experienced core damage which resulted from a series of events which were 
initiated by a loss of feedwater transient. Several aspects of the incident 
may have general applicability in addition to apparent generic applicability
at operating Babcock and Wilcox reactors. This bulletin is provided to 
inform you of the nuclear incident and to request certain actions. 

Actions To Be Taken By Licensees 

(Although the specific causes have not been determined for individual 
sequences in the Three Mile Island event, some of the following may have 
contributed.) 

For all Babcock and Wilcox pressurized water reactor facilities with an 
operating: 

1.   Review the description (Enclosure 1) of the initiating events and 
     subsequent course of the incident. Also review the evaluation by the 
     NRC staff of a postulated severe feedwater transient related to Babcock 
     and Wilcox PWRs as described in Enclosure 2. 

     These reviews should be directed at assessing the adequacy of your 
     reactor systems to safely sustain cooldown transients such as these. 

2.   Review any transients of a similar nature which have occurred at your 
     facility and determine whether any significant deviations from expected
     performance occurred. If any significant deviations are found, provide 
     the details and an analysis of the significance and any corrective 
     actions taken. This material may be identified by reference if 
     previously submitted to the NRC. 

3.   Review the actions required by your operating procedures for coping 
     with transients. The items that should be addressed include: 
.

IE Bulletin No. 79-05                                       April 1, 1979 
                                                            Page 2 of 3 

     a.   Recognition of the possibility of forming voids in the primary 
          coolant system large enough to compromise the core cooling 
          capability. 

     b.   Operator action required to prevent the formation of such voids. 

     c.   Operator action required to ensure continued core cooling in the 
          event that such voids are formed. 

4.   Review the actions requested by the operating procedures and the 
     training instruction to assure that operators do not override automatic
     actions of engineered safety feature without sufficient cause for doing
     so. 

5.   Review all safety related valve positions and positioning requirements 
     to assure that engineered safety feature and related equipment such as 
     the auxiliary feedwater system, can perform their intended functions. 
     Also review related procedures, such as those for maintenance and 
     testing, to assure that such valves ar e returned to their correct 
     positions following necessary manipulations. 

6.   Review your operating modes and procedures for all systems designed to 
     transfer potentially radioactive gases and liquid out of the 
     containment to assure that undesired pumping of radioactive liquids and 
     gases will not occur inadvertently. 

     In particular assure that such an occurrence would not be caused by the
     resetting of engineered safety features instrumentation. List all such 
     systems and indicate: 

     a.   Whether interlocks exist to prevent transfer when high radiation 
          indication exists and, 

     b.   Whether such systems are isolated by the containment isolation 
          signal. 

7.   Review your prompt reporting procedures for NRC notification to assure 
     very early notification of serious events. 

The detailed results of these reviews shall be submitted within ten (10) 
days of the receipt of this Bulletin. 
.

IE Bulletin No. 79-05                                       April 1, 1979 
                                                            Page 3 of 3 

Reports should be submitted to the Director of the appropriate NRC Regional 
Office and a copy should be forwarded to the NRC Office of Inspection and 
ENforcement, Division of Reactor Construction Inspection, Washington, D.C. 
20555. 

For all other operating reactor or reactor under construction, this Bulletin
is for information purposes and no report is requested. 

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

Enclosures:
1. Preliminary Notifications
     Three Mile Island -
     PNO-67 and 67A, B, C, D,
     E, F, G
2. Evaluation of Feedwater
     Transients w/attachment
3. List of IE Bulletins issued 
     in last 12 months
Page Last Reviewed/Updated Tuesday, July 23, 2013