United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletins 79-05C & 79-06C: Nuclear Incident at Three Mile Island - Supplement (bl79006c)

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

                                July 26, 1979

                                           IE Bulletin Nos. 79-05C & 79-06C 

NUCLEAR INCIDENT AT THREE MILE ISLAND - SUPPLEMENT 

Description of Circumstances: 

Information has become available to the NRC, subsequent to the issuance of 
IE Bulletins 79-05, 79-05A, 79-05B, 79-06, 79-06A, 79-06A (Revision 1) and 
79-06B, which requires modification to the "Action To Be Taken By Licensees"
portion of IE Bulletins 79-05A, 79-06A and 79-06B, for all pressurized water
reactors (PWRs). 

Item 4.c of Bulletin 79-05A required all holders of operating licenses for 
Babcock & Wilcox designed PWRs to revise their operating procedures to 
specify that, in the event of high pressure injection (HPI) initiation with 
reactor coolant pumps (RCPs) operating, at least one RCP per loop would 
remain operating. Similar requirements, applicable to reactors designed by 
other PWR vendors, were contained in Item 7.c of Bulletin 79-06A (for 
Westinghouse designed plants) and in Item 6.c of Bulletin 79-06B (for 
Combustion Engineering designed plants). 

Prior to the incident at Three Mile Island Unit 2 (TMI 2), Westinghouse and 
its licensees generally adopted the position that the operator should 
promptly trip all operating RCPs in the loss of coolant accident (LOCA) 
situation. This Westinghouse position, has led to a series of meetings 
between the NRC staff and Westinghouse, as well as with other PWR vendors, 
to discuss this issue. In addition, more detailed analyses concerning this 
matter were requested by the NRC. Recent preliminary calculations performed 
by Babcock & Wilcox, Westinghouse and Combustion Engineering indicate that, 
for a certain spectrum of small breaks in the reactor coolant system, 
continued operation of the RCPs can increase the mass lost through the break
and prolong or aggravate the uncovering of the reactor core. 

The damage to the reactor core at TMI 2 followed tripping of the last 
operating RCP, when two phase fluid was being pumped through the reactor 
coolant system. It is our current understanding that all three of the 
nuclear steam system suppliers for PWRs now agree that an acceptable action 
under LOCA symptoms is to trip all operating RCPs immediately, before 
significant voiding in the reactor coolant system occurs. 

Action To Be Taken By Licensees: 

In order to alleviate the concern over delayed tripping of the RCPs after a 
LOCA, all holders of operating licenses for PWR facilities shall take the 
following actions: 
.

IE Bulletin Nos. 79-05C & 79-06C                            July 26, 1979 
                                                            Page 2 of 3 

Short-Term Actions 

1.   In the interim, until the design change required by the long-tem action
     of this Bulletin has been incorporated, institute the following actions
     at your facilities: 

     A.   Upon reactor trip and initiation of HPI caused by low reactor 
          coolant system pressure, immediately trip all operating RCPs. 

     B.   Provide two licensed operators in the control room at all times 
          during operation to accomplish this action and other immediate and
          followup actions required during such an occurrence. For 
          facilities with dual control rooms, a total of three licensed 
          operators in the dual control room at all times meets the 
          requirements of this Bulletin. 

2.   Perform and submit a report of LOCA analyses for your plants for a 
     range of small break sizes and a range of time lapses between reactor 
     trip and pump trip. For each pair of values of the parameters, 
     determine the peak cladding temperature (PCT) which results. The range 
     of values for each parameter must be wide enough to assure that the 
     maximum PCT or, if appropriate, the region containing PCTs greater than 
     2200 degrees F is identified. 

3.   Based on the analyses done under Item 2 above, develop new guidelines 
     for operator action, for both LOCA and non-LOCA transients, that take 
     into account the impact of RCP trip requirements. For Babcock & Wilcox 
     designed reactors, such guidelines should include appropriate 
     requirements to fill the steam generators to a higher level, following 
     RCP trip, to promote natural circulation flow. 

4.   Revise emergency procedures and train all licensed reactor operators 
     and senior reactor operators based on the guidelines developed under 
     Item 3 above. 

5.   Provide analyses and develop guidelines and procedures related to 
     inadequate core cooling (as discussed in Section 2.1.9 of NUREG-0578, 
     "TMI 2 Lessons Learned Task Force Status Report and Short-Term 
     Recommendations") and define the conditions under which a restart of 
     the RCPs should be attempted. 

Long-Term Action 

1.   Propose and submit a design which will assure automatic tripping of the
     operating RCPs under all circumstances in which this action may be 
     needed. 
.

IE Bulletin Nos. 79-05C & 79-06C                            July 26, 1979 
                                                            Page 3 of 3 

Schedule 

The schedule for the short-term actions of this Bulletin is: 

     Item 1:   Effective upon receipt of this Bulletin, 
     Item 2:   Within 30 days of receipt of this Bulletin, 
     Item 3:   Within 30 days of receipt of this Bulletin, 
     Item 4:   Within 45 days of receipt of this Bulletin, 
     Item 5:   October 31, 1979 (as noted in Table B-2 of NUREG-0578, under
               Item 3).

A schedule for the long-term action required by this Bulletin should be 
developed and submitted within 30 days of receipt of this Bulletin. 

Reports should be submitted to the Director of the appropriate NRC Regional 
Office with copies forwarded to the Director, Office of Inspection and 
Enforcement and the Director, Office of Nuclear Reactor Regulation, 
Washington, D. C. 20555. 

Approved by GAO (R0072): clearance expires 7/31/80. Approval was given under
a blanket clearance specifically for generic problems. 
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