United States Nuclear Regulatory Commission - Protecting People and the Environment

Required Actions Based on Generic Implications of Salem ATWS Events (Supplement 1 to Generic Letter No. 83-28)

                                  October 7, 1992




The U.S. Nuclear Regulatory Commission (NRC) is issuing this generic letter
supplement to inform licensees that the actions of items 4.2.3 (life testing)
and 4.2.4 (periodic replacement of breakers or components) as originally
described in the enclosure to Generic Letter (GL) 83-28, "Required Actions
Based on Generic Implications of Salem ATWS Events" are no longer needed.


On February 22 and 25, 1983, the Salem Nuclear Generating Station experienced
anticipated transient without scram (ATWS) events.  These events prompted the
NRC to issue IE Bulletin 83-01, "Failure of Reactor Trip Breakers
(Westinghouse DB-50) to Open on Automatic Trip Signal," to address the short-
term corrective actions.  The NRC also formed a task force to assess the
generic implications of these events.  Upon reviewing the findings of the task
force, the NRC issued GL 83-28.

In GL 83-28, the staff requested the licensees to implement long-term
corrective actions in response to the Salem events.  GL 83-28 included two
major actions to improve the reliability of the reactor trip system:
(1) install a plant modification that provided for the automatic actuation of
the shunt trip attachment of the reactor trip breaker (RTB) following any
automatic reactor trip signal, and (2) establish a comprehensive program of
preventive maintenance and surveillance testing to ensure reliable
RTB operation.  In addition, items 4.2.3 and 4.2.4 of GL 83-28 requested
licensees to perform life testing of RTBs and periodically to replace the
breakers or components in accordance with their demonstrated life. 


The modifications to automatically actuate the shunt trip attachments of RTBs
following any automatic reactor trip signal and the program of preventive
maintenance and surveillance testing requested by GL 83-28 have been
implemented by licensees.  However, the life testing and program for periodic
replacement of breakers or components requested by items 4.2.3 and 4.2.4 of
GL 83-28 have not been fully implemented.  In response to these items, many


Generic Letter 83-28, Supp. 1         -2-             October 7, 1992

licensees have referenced WCAP-10852(1) for DB-50 RTBs, WCAP-10835(2) for 
DS-416 RTBs, and a joint Combustion Engineering and Babcock and Wilcox
trending program for General Electric (GE) AK-2 RTBs.  The staff has not found
these responses to be acceptable primarily because no life testing was
conducted for the GE RTBs and only limited testing was conducted for the
Westinghouse RTBs.  The licensees contend that further life testing of the
RTBs is not necessary because of their extensive quality assurance, preventive
maintenance, and surveillance testing programs.  In the process of determining
if additional guidance on items 4.2.3 and 4.2.4 was needed, the staff reviewed
operating experience for the period 1986 through early 1991 based upon
information in the Nuclear Plant Reliability Data System and in Licensee Event
Reports.  The review revealed that the vast majority of reported failures have
been failures to close, rather than failures to open, or degraded conditions
detected during planned maintenance, testing, and inspection.  Three cases of
slow opening were identified, as well as several cases where either the shunt
trip or the undervoltage trip attachment, but not both, failed to perform
satisfactorily.  However, the review identified only one failure of a RTB to
open, in which both the undervoltage and the shunt trip attachments failed to
cause the breaker to open.  Since the staff conducted this review in
December 1991, there has been an additional instance in which a RTB failed to
fully open on demand during a routine surveillance test.  In light of this RTB
operating experience, the staff has concluded that the actions already
completed pursuant to GL 83-28 have been effective in improving RTB
reliability to open and that further actions to address the end-of-life
degradation in breaker reliability are not justified.  Furthermore, since
issuing GL 83-28, the NRC has promulgated the requirements for reducing the
risk from ATWS events in 10 CFR 50.62.  The modifications associated with this
regulation further reduce the risk resulting from the failure of RTBs. 
Therefore, the staff concludes that licensee actions in response to items
4.2.3 and 4.2.4 of GL 83-28 are not necessary.

To the extent that licensees may have made commitments to programs for
periodically replacing RTBs or components in responses to GL 83-28, they may
review and modify these programs taking into account their plant-specific
operating experience, maintenance programs, and root cause determination
programs for RTBs.

     (1) WCAP-10852, "Report of the DB-50 Reactor Trip Breaker, Shunt and
Undervoltage Trip Attachments, Life Cycle Tests," James P. Chizmar, et al,
May 1985

     (2) WCAP-10835, "Report of the DS-416 Reactor Trip Breaker Undervoltage
and Shunt Trip Attachments, Life Cycle Tests," James P. Chizmar, et al,
May 1985

Generic Letter 83-28, Supp. 1         -3-              October 7, 1992


In issuing this generic letter supplement, the staff is relaxing the original
positions taken in items 4.2.3 and 4.2.4 of GL 83-28, and hence this generic
letter supplement is not considered a backfit.  The staff prepared an
evaluation of the positions in this generic letter supplement in accordance
with the charter of the Committee to Review Generic Requirements (CRGR) and
concluded that the public health and safety and common defense and security
will be adequately protected, and the proposed changes will not affect the
public health and safety.  This evaluation is available in the public document
room with the minutes of the 220th meeting of the CRGR.  

This generic letter supplement does not seek to collect any information, and
hence, the Paperwork Reduction Act does not apply.

No response is required to this letter.  If you have any questions regarding
this matter, please contact the technical contact or the lead project manager
listed below.


                                      ORIGINAL SIGNED BY

                                   James G. Partlow
                                   Associate Director for Projects
                                   Office of Nuclear Reactor Regulation

List of Recently Issued Generic Letters

Technical Contact:  Peter C. Wen, NRR
                    (301) 504-2832

Lead Project Manager:  Leonard N. Olshan, NRR
                       (301) 504-3018
Page Last Reviewed/Updated Wednesday, June 19, 2013