Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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:
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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.
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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.
