ML19269C913
| ML19269C913 | |
| Person / Time | |
|---|---|
| Issue date: | 01/26/1979 |
| From: | Mattson R Office of Nuclear Reactor Regulation |
| To: | Julie Ward ATOMIC INDUSTRIAL FORUM |
| Shared Package | |
| ML19269C914 | List: |
| References | |
| NUDOCS 7902210130 | |
| Download: ML19269C913 (1) | |
Text
.
m
[p %,*g' NUCLEAR REGULATORY CCMMISSION 4
UNITED STATES g
g
- .. 2i WASHINGTON. O. C. 20553
%. %d.L s' l
%, cay JAh 2 3 079 Mr. John E. Ward, Chairman Committee on Reactor Licensing and Safety Atomic Industrial Forum, Inc.
7101 Wisconsin Avenue Washington, D. C.
20014 De'r Mr. Ward:
Your letter of December 18, 1978 to Mr. Denton, addressing load combinations, has been received. The questions you have asked will require substantial effort to provide you with information representative of the Nuclear Regulatory Comission staff po.
ion.
We anticipate providing you with a response by April 1,1979.
Sincerely, Roger ad. son,Dkector Division of Systems safety Office of Nuclear Reactor Regulation 7902210130
Ate mic Industrial Forum,Inc.
71f 1 Wisconsin Avenue Washington. O C. 20014 Teiephone 001)654-9260 Cabie: Atomfonam Washingtondc F-~
December 18, 1978 Mr. Harold Dent.on, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C. 20555
Dear Harold:
The AIF Committee on Reactor Licensing and Safety has recently formed an Ad Hoc Committee on Load Combinations, under the chairmanship of Dr. S. A. Bernsen, Bechtel Power Corporation.
This committee met with members of the NRC Staff on October 20, 1978, to discuss objectives and issues.
The purposes of this letter are to describe the concerns this committee will be addressing, and to request your assistance in focusing and resolving these concerns.
This committee will be looking at generic, long-range load combinations related issues, and will not get involved in the discussion of specific issues involved in specific licensing actions.
There are three basic issues before this committee, and they are as follows:
1.
Whether or not certain low probability loads should be combined.
For example, it is our belief that a solid technical basis exists, and can be synthesired, to demonstrate convincingly that postulated pipe break and SSE loads need not be combined if the piping system is designed for SSE.
In order t, accomplish this, o f course,
an adequate and consistent safety margin must be demonstrated.
One of our objectives is to assist in synthesizing the technical basis needed t'o der.onstrate the necessary safety margin while showing that the loads need not be combined.
Furthermore, it is our judgement that General Design Criterion 2 does not require these extreme loads o
be combined.
The current practice of combining loads results in inconsistent safety margins in various systems and from plant to plant.
We are interested in your views on GDC 2 and its interpretation._
2.
If it turns out that the interim or final position of NRC is that loads must be combined, how should this be done?
Mr. Harold Denton December 18, 1978 The industry and the NRC have already spent onsiderable time discussing appropriate methods for combining loads.
This committee will keep abreast of, and provide a central industry focus for, new developments in this area.
3.
What acceptance criteria are appropriate, e.g.
for stress levels in structures, equipment, piping and components, for the events that must be considered?
It is our judgement that some of the acceptance criteria used in these analyses are overly conservative, and that more appropriate criteria, e.g.
emergency condition stress levels for OBE loads, can be identified and technically justified.
Another objective of this committee is to promote the demonstration of a rational technical basis for the specification of acceptance criteria such that adequate safety margins are assured with some measure of consistency.
The intent of this AIF Ad Hoc Committee is to perform a sorting and focusing function, to provide synthesis of the issues and some guidance to relieve some of the inconsistencies, fragmentation and frustrations now associated with the load combinations issue.
We do not intend at this time to perform or sponsor detailed technical studies or analyses, but will not completely rule this out if conditions change.
We are aware of, and intend to follow closely, the concerns expressed by the ACRS on this subject.
By copy of this letter, we are also informing the ACRS of the existence of this new AIF Committee so that they will be aware of the availability of industry expertise on this subject.
In order to better focus industry resources, and to foster cooperation among all concerned parties in resolving these issues, we would like to request responses to the following questions from the NRC Staff-1.
Does NRC leel that with adequate technical justification they can allow decoupling of dynamic loads such as SSE and postulated pipe break?
What considerations
,. ~'
are necessary to allow decoupling of loads?
What NRC and consultant activities are going on to investigate decoupling?
2.
What does NRC require for use of probability of occurrence to define conditions that must be designed for and the applicable acceptance criteria?
(e.g.
OBE of 10-2 probability against ASME emergency condition
Mr. Harold Denton December 18, 1978 stress levels.)
/- "1ternative way of stating this question is does t.e NRC have a collective judgement concerning what probability ranges are appropriate for stress level acceptance criteria in the upset, emergency, and faulted conditions?
3.
What activities does NRC have underway now to extend the application of NUREG-0484, " Methodology for Combining Dynamic Responses", generically to other load combinations?
Considered and timely NRC responses to these questions will enable us, working with other segments of the industry, to better focus our resources to resolve this difficult and important issue We thank you for your assistance and co-operation in this matter.
Very truly yours.
John E. Ward, Chairman Committee on Reactor Licensing and Safety JEW /skh cc:
Dr. Stephan Lawroski, Chairman ACRS
.