ML20210S788
| ML20210S788 | |
| Person / Time | |
|---|---|
| Site: | Satsop |
| Issue date: | 05/07/1976 |
| From: | Maccary R Office of Nuclear Reactor Regulation |
| To: | Deyoung R Office of Nuclear Reactor Regulation |
| References | |
| CON-WNP-1636 NUDOCS 8605290403 | |
| Download: ML20210S788 (5) | |
Text
9 DISTRIBUTION:
Docket File STN 50-503
. _ _ _. _ - ~
Docket Nos. th cn_cna j 50-509 MS 27-13 STN 50-509 NRR - Rdg MS 27-13 SEB - Rdg R. C. DeYoung Assistant Director for Light Water Reactors Division of Project Management WPPSS NUCLEAR PROJECT NO. 3 (W?PSS UNITS 3 & 5)
SUPPLEftENT TO SAFETY EVALUATION REPORT Flant Name: WPPSS Nuclear Project NO. 3 Licensing Stage: PSAR-SER SUPPLEMENT Project Numbers: STN 50-500/509 Responsible Branch an Project Manager: LWR 1-3, A. Bournia Requested Completion Date: May 7, 1976 Applicant's Response Date Necessary for Completion of Next Action Planned on Project: As Scheduled Description of Response: N/A Rev12w Status: Complete In response to the concerns expressed by ACRS members in April 16, 1976 ACRS report to Chairman Rowdon on WPPSS Projects No. 3 and 5, the Structural Engineering Branch has reviewed and evaluated the concerns.
Our sections of supplenent to SER to cover these concerns are enclosed.
l R. R. Maccary, Assistant Director for Engineering Division of Systems Safety
Enclosure:
Structural Evaluation Report Supplement cc w/o enc 1:
ccw/ enc 1:
R. Boyd, PM R. Heineman W. Mcdonald, MIPC F. Schroeder.
B. Vassallo A. Bournia 1
- 1. Sinweil K. Kapur C. Tan 8603290403 760507 PDR ADOCK 05000508 E
PDR D55:5EB
_x27807//l DSS:SEg DSS;. SIB.y.,._
o
.a
- C._ Tan._ pf
...KKapur -
.IS1hwe.il cary oo-.==*
05//,/76 05/f /76 05/7/76 05/7 /76 Foran AEC 513 (Rev. 9 53) AECM 0240 Tr u. s. eovsequeant pan = vias oe scan i.74.sas.nes
g g,
gay 0 7 1973
'I The following is cur response.to the first paragraph cf p. 4 of i
i the MPPSS Prejects llo. 3 and !!o. 5 ACRS letter, dated April 16, 1975:
m
- The !!RC staff has in the past identified as a desirable safety ebjective for a large population of reactors that the probability of an a:cident
'with consequences that would significantly exceed the Part 100
-7 guidaiines from cne accident source should be 10 per reactor-year or less. This objective wt.s primarily set for application in postulated accidents where the staff has beer, able to quantify or bound the probabilities (e.g., in the AT!!S cese and in considering aircraft crashes), but was not intended for use in seisnic design.
In the case of-seismic design, the staff believes'that a quantitative definition of various probabilistic parameters is still beyond the e
reach of the current state of the art. Therefore, the use of a detcrrainistic and conservative approach to ensure seismic design adequacy of: safety related structures and systems is niore appropriate.
- The seismic design criteria of UPPSS Units 3 and 5 were reviewed and accepted en the basis of deterministic considercticr.s. The staff c
concluded that the i!PPSS seismic design will comply with applicable
. staff positions as set forth in Section 3.7 of the Standard Revieu Plan.-
The measures noted are nevertheless considered significant and should be. implemented if we were to further improve the reliability and conservatism of seismic design of safety related structures and systems.
The fiRC staff is currently studying the advisability of implementing the reco m. ended reasures, specifically, the implementation of an in-dependent partial design review of plants at various stages of licensing.
The staff believes that the acceleration for seismic design which was accepted for the UPPSS tio. 3 & 5 site is near an upper bound value based on the geology and seismicity of the Puget Sound Region.
9 L
4 g.
T r
r
--,4-
~r 4,,
O 1,*AY C 7 270 Though the probability of this event being exceeded has not been I
determined, the staff believes that it is extremely low.
-Ilith respect to the comment on the probability of not achieving safe shutdo:n given an SSE of about 1003 years recurrence period, the design criteria are such that such a probability is indeed very small but cannot be realistically quantified at this time.
The staff is of the opinion that tnere is no further need to implement other neasures such as independer.t desigr review, low amplitude shaking and detection of possible inservice degradation, in so f ar as licensing of L'PPSS Units 3 and 5 is concerned.
.m -
mv- 0 7 1975 The following is our response to the second paragraph of p. 4 of the WPPSE Project flos. 3 and flo. 5 ACRS letter, dned April 16, 1976:
The staff considered the concerns expressed by Ityer Bender of The ACRS on the appropriate degree of censervatism to' be included in the seismic design criteria for nuclear power plants, and with his vieupoint that the needs of public safety would be best served if inelastic design principles instead of the elastic design approaches currently used were applied in the design and ar.alysis of structures for the severe seismic conditions.
g Research efforts in recent years have demonstrated that earthquake effects, including lack of damage as well as damage, usually cannot be reconciled with elastic unit stresses and current design procedures to total satisfaction.
The staff recognizes some of the anomalies of elastic design. However, the current clastic design approach to seismic design has been estab-lished after extensive 1research and development and is difficult to change. Even though various inelastic design methods have been pro-posed by various investigators, certain empirical relationships and approximations are employed in order to reduce the complex problea of inelasticity and energy to nore general application, and there is-a lack of more rigorous approach and the absence of complcte scientific
' justification. For instance, if the response spectrum approach, which is rigorously applicable to structures only in the elastic range, is-used, inelastic response spectra have to be established.~ Since r.nnlinear systems have no true vibrational modes, such inelastic response spectra are generally obtained by modifying the elastic response spectra, which is, at best an approximation and reouires experience and judgment.
There are other questions such as the damping values and ductility ratios to be used, to name a few. Basically, the state-of-the-art of the non-linear design approach has not yet reached the point for more general and immediate application.
l.'.AY 0 719?C a
Realizing the limitations of the elastic design approach, the staff has allowed the use of ultimate strength design for concrete structures and plastic design for steel structures in the design of member sections. The staff is also ccnsidering the use of the inelastic epproach for reevaluation of already built nuclear plants.
Furthermore, the staff is considering the retention of experienced consultants to investigate and establish nonlinear design approaches.
In addition, the inelastic approach is being considered for non-Category I structures, systems and compcnents.