ML20002B091
| ML20002B091 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 12/05/1980 |
| From: | Tribble J YANKEE ATOMIC ELECTRIC CO. |
| To: | Eisenhut D Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20002B092 | List: |
| References | |
| WYR-80-127, NUDOCS 8012090423 | |
| Download: ML20002B091 (9) | |
Text
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Telephone 617 366-90ll
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TWX 710-390-0739 YANKEE ATOMIC ELECTRIC COMPANY B.a.2.1
[
WYR 80-127 ff 4 20 Tarnoike Road Westborough, Massachusetts 01581
- W December 5, 1980 U.S. Nuclear Regulatory Commission 9
U I
Washington, DC 20555 Q
Attention:
Mr. Darrell G. Eisenhut, Director
'O '
~'3 Division of Licensing Office of Nuclear Reactor Regulation
[3
,d
References:
(a) License No. DPR-3 (Docket 50-29)
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(b) YAEC Letter to USNRC dated October 15, 1980, WYR;80-114" 1
(c) Geology and Seismology, Yankee Rowe Nuclear PoweY j
IE Plant - Weston Gaophysical Corporation, January 29, 1979 (d) Site Dependent Response Spectra, Yankee Rowe -
Weston Geophysical Corporation, February 1980
Enclosures:
(A) Preliminary Probabilistic Risk Assessment for Yankee Nuclear Power Station (B)
Interim Seismic Design Basis for Yankee Nuclear Power Station (C) Preliminary Structural Evaluation for Yankee Nuclear Power Station Gentlemen:
This letter and its enclosures are provided to summarize the position of Yankee Atomic Electric Company with respect to continued operation of the Yankee plant while detailed seismic analyses are being performed and further structural modifications, if necessary, are made. This position is based on:
(1) A preliminary probabilistic risk assessment of the relative safety of the Yankee plant, compared to other operating plants (see Enclosure (A)].
(2) A detailed seismic evaluation of the Rowe site, based on real data recorded at sites with similar geological characteristics [see References (c) and (d)].
(3) A probabilistic analysis of the seismic hazard at Rowe [see Enclosure (B)].
(4) A structural evaluation of key systems and structures using an Interim Seismic Design Spectrum with median exceedance probability of 10-3 [see Enclosures (B) and (C)].
sole 9901N
/
U.S. Nuclctr R:gulatcry Commiscion P gs 2 Attention:
Mr. D;rroll G. EicGnhut, Dir:ctor Dsetmber 5, 1980 A brief' summary of this material is given below.
PROBABILISTIC RISK ASSESSMENT Recognizing that (1) the low power level, (2) conservative system design, (3) extremely low population density near the Rowe site give Yankee major and advantages over most other operating plants from the standpoint of public safety, we have undertaken a detailed Probabilistic Risk Assessment (PRA) for the Yankee plant. This program is expected to be completed in 1981.
In addition, to get an early indication of the relative safety of Yankee we have conducted a preliminary PRA using two different approaches:
(1) WASH-1400 methodology was used on the Yankee systems to calculate the probability of plant specific accident sequences leading to fission product release for comparison with WASH-1400.
(2) The second approach used was to assume WASH-1400 failure rates and release categories for all plants and compare only the reactor power level and the demographic characteristics of various sites from the standpoint of risk to the public.
The results of these studies are shown on the attached Figures L-1 and L-2.
Clearly, the risk associated with operati of the Yankee plant is orders of magnitude less than exists at many other operating plants across the country.
In addition, a conservative r.nalysis [ Enclosure (A), page 17] indicates that the additional risk for two years of generation amounts to about 20% of the remaining lifetime risk of ear.ee operation to 1997 If the 2 years additional operation are comparec.co the total lifetime risk of a new large plant as analyzed in WASH-1400, the additional risk of 2 years of Yankee operation is about 10% of the total new plant risk. This is well below the doubling of risk suggested as acceptable for a 3-year interim period by R. Mattson in his memo to D. Eisenhut on August 8, 1980.
SEISMIC EVALUATION While Yankee is located in an area that is characterized by very infrequent earthquakes of low intensity (see Figure L-3), we are presently conducting a comprehensive seismic analysis of all key systems and structures in the plant, to be completed by December 31, 1981. This analysis will be performed for two different response spectra, in order to evaluate the sensitivity of systems and structures to the design basis chosen. One of these spectra can be the LLL/ TERA spectrum (if NRC wishes), but we weuld not recommend that spectrum.
While this comprehensive seismic analysis is being done, an Interim Seismic Design Basis Spectrum was chosen for use in a preliminary seismic evaluation of key structures and systems (see Figures L-4 and L-5).
This interim spectrum is consistent with Appendix A of 10CFR100, and is more conservative than site specific spectra that were developed for Rowe from real seismic data on sites with similar geological claracteristics.
'U.S. Nuclear R3gulatory Commission Page 3
, Attsntion: Mr. D rrell G..Eistnhut, Director Deccmber 5, 1980 SEISMIC PROBABILITY ANALYSIS A Seismic Probability Analysis has been performed for the Rowe site using the methods developed by Cornell and McGuire (See Enclosure (B)]. Having determined the probabilities associnted with various peak ground accelerations by this method, the uniform hazard spectra shown on Figure L-4 were developed using NUREG/CR-0098.
This analysis shows that the Interim Design Basis Spectrum has a median e'tceedance probability of 10-3 This is consistent with probabilities generally accepted for new nuclear plants.with an expected life of 40 years.
For an interim period of only the next two years (while seismic analysis and upgrade are underway) we could tolerate a probability 20 times higher, or once in 50 years, with no greater risk of the seismic event occurring,;.this is an additional factor in any interim evaluation, which should not be overlooked.
STRUCTURAL EVALUATION Using this Interim Design Basis Spectrum, a structural evaluation has been performed on the following key systems and structures:
Main coolant system Main coolant by-pass piping Pressurizer surge line Pressurizer safety valve inlet piping Safety injection piping inside vapor container Shutdown cooling piping inside vapor container Main steam piping inside vapor container Feedwater piping inside vapor container Main steam piping cutside vapor container Feedwater piping outside vapor container Vapor container Concrete reactor support structure Primary auxiliary building and pipe chase Turbine building Turbine pedestal All these systems will withstand the interim design basis seismic event without failure.
In this analysis, credit was taken for two major structural modifications:
(1) Laterial supports installed on all four steam generators (this modification was completed in October).
(2) Collars and anchor bolts installed at the base of six containment support columns (this modification is underway and is expected to be completed before April 1981.)
The fact that only a few modifications are necensary is not surprising and bears out the statements made by H. Denton to E. Weiss, in a letter dated January 10, 1980, that power plant systems and structures possess inherent resistance to seismic events. This inherent resistance is often ignored.
U.S. Nucl:Cr R:gul0 tory Commicsion P g2 4 Att:ntion: Mr. D rrell G. Eicinhut, Director D:c:mb;r 5, 1980 CONCLUSION Based on these studies, it is our position that the Yankee plant can continue to be operated safely and efficiently (as it has for the last 20 years) at least until detailed seismic analyses are completed and any needed modifications made. Inceed, our preliminary probabilistic studies indicate that the o
low power level, o
conservative design o
stable geology, and o
low population density make oper: tion of Yankee less of a risk to the public than many other operating nuclear plants across the country.
Very truly yours, YANKEE ATOMIC ELECTRIC COMPANY
(
J. E. Tribble President c--
Enclosures
. FIGURE L-1 PRELIMINARY PROBABILISTIC RISK ASSESSMENT FOR EARLY FATALITIES (PLANT SPECIFIC FAILURE RATES USED FOR YANKEE) 5 0
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FIGURE L-2 PRELIMINARY PROBABILISTIC RISK ASSESSMENI SITE COMPARISON FOR EARLY FATALITIES (b' ASH-1400 Failure Rates Used For All Plants - Site Specific Power, Population, k'ind Rost 5
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