ATWS (Generic Letter 79-53)
NUCLEAR REGULATORY COMMISSION
WASHINGTON, D.C. 20555
This past March, the NRC transmitted to you a copy of Volume 3 of
NUREG-0460, "Anticipated Transients Without Scram for Light Water Reactors"
(ATWS) and a copy of an NRC letter that was sent this past February to each
of the four nuclear reactor vendors. The letters to the vendors contained
requests for information needed to perform generic analyses related to ATWS.
As we pointed out in our March letters, the generic analyses we requested
were intended to confirm that the modifications proposed by the NRC staff
for various classes of LWR designs would in fact accomplish the degree of
ATWS prevention and mitigation described by the staff in its report. We also
pointed out that we had chosen to work directly with the vendors in
obtaining this information in an effort to conserve both NRC and industry
resources. We requested that utilities cooperate with the vendors in
performing the requested analysts.
Shortly after sending the letters to the vendors, the NRC Staff met with
representatives of each of the NSSS vendors and many Utility representa-
tives in Bethesda on March 1. 1979. The meeting was called to discuss the
"early verification" approach in which we planned to use generic analyses as
the basis for rulemaking. We hoped thereby to avoid costly and unnecessary
repetitive analysis for individual plants. At the meeting, a tentative
schedule was agreed to for generic analyses for each class of plants to be
provided in three separate packages to be submitted May 1, September 1, and
December 1, 1979.
Immediately following the March 1 meeting, the NRC staff met separately with
each of the NSSS vendors and agreements were made as to the minimum
information to be supplied in the May 1 package. Also, as noted above,
copies of the ATWS staff report and the generic analyses questions were
transmitted to the utilities.
On March 28, 1979 the Three Mile Island accident occurred. Because of the
heavy expenditure of NRC resources required for Three Mile Island related
activities, essentially no staff effort was applied to the ATWS issue for
three months or so following the accident. There was also a substantial
reduction in effort on the part of the PWR industry during that period, and
some reduction for BWRs.
In June, 1979. the NRC Office of Nuclear Reactor Regulation was temporarily
reorganized. Within this interim organization a group was assigned under
the direction of S. Hanauer to work on the 19 Unresolved Safety Issues as
designated by the Commission and reported to Congress this past January in
NUREG-0510. ATWS is one of these 19 issues.
A preliminary NRR Staff review suggested that, for PWRs, the Three Mile
Island accident raised new questions with regard to the appropriateness and
adequacy of the resolution of ATWS as proposed by the Staff in Volume 3 of
NUREG-0460. For BWRs, the staff has concluded that the technical impact of
Three Mile Island was minimal and that the completion and review of the
generic analyses for BWRs as specified in March should proceed as
expeditiously as possible.
A meeting was held in Bethesda on July 251 1979 to discuss, with representa-
tives of PWR utilities and designers, considerations arising from the Three
Mile Island accident that might be relevant to ATWS. For your information, a
copy of the staff minutes of that meeting is attached as Enclosure 1. As can
be seen from the minutest at the meeting the staff:
a) Reiterated that ATWS is still believed by the staff to be a serious
safety concern and that future protection should be provided. We stated
that we art unwilling to wait another year to make progress on ATWS.
b) Expressed some general and specific technical concerns raised by
the Three Mile Island accident with regard to the ATWS resolution
proposed in Volume 3 of NUREG-0460.
c) Asked the industry to provide in writing, within 30 days of the meeting
date, its preliminary assessment of the Three Mile Island impact on
ATWS, the scope of effort now foreseen to resolve TMI issues, and a
realistic schedule for providing the needed ATWS information. This
would include both the March request and the TMI-related analyses.
Subsequent to the July 25 meeting, we have met with representatives of the
four NSSS vendors and of soft Utility/Owners. We have met with GE to discuss
the scope of the remaining generic analysis information to be supplied for
BWR 4/5/6's. We have also met with representatives of the GE BWR/3 Owners,
B&W, BSW ATWS Owners Group, W, W ATWS Owners Group, and CE. At all these
meetings, we considered further required inforation and the schedule for its
We have now received letters (See the list in Enclosure 2, attached) from
the various groups describing the information to be furnished and projected
schedules, On the basis of our review of these letters and meetings with the
industry representatives, we perceive that the projected responses in
several casts would not address several questions in our February 15 letter.
In particular, several items art lacking that we will need to justify
acceptance of the hardware approaches of NUREG 0460 Vol 3 rather than using
the design basis accident approach.
I am determined to submit a proposed ATWS rule to the Commission for both
PWRs and BWRs early In 1980. The type and content of the rule we will
propose will depend critically upon the types and content of the information
available to the staff. This will, of course, include whatever responses are
actually provided by the industry in response to the questions attached to
the February 15 staff letter, the March meetings, and the Three Mile Island
related concerns as discussed in the July 25 and subsequent meetings.
I still believe that it is possible for the early verification generic
analysis program to provide an acceptable resolution of the ATWS issue and
that this is the way to achieve resolution with the least possible
expenditure of NRC and industry resources. However, I want to reiterate that
the success of this approach depends on whether or not all of the
information necessary for the suff to confirm that its proposed ATWS
modifications provide an acceptable level of protection, for all plants, is
provided by the industry.
I strongly encourage you to join or form Utility/Owners Groups, if you have
not already done so, and provide the resources necessary to supply the
needed technical information pertaining to your plants, either operating or
under construction. It would further reduce the impact on the industry as
well as the staff resources if the ATWS effort coordination and the review
role is performed by one industry group.
If you have additional questions on the generic analysis early verification
program discussed in this letter, please contact Mr. Ashok Thadani,
H. R. Denton, Director
Office of Nuclear Reactor Regulation
1. NRC-Industry ATWS Meeting
Summary dtd 7/25/79
2. List of letters from Industry
on Content of Report
Page Last Reviewed/Updated Thursday, March 25, 2021