ML20141H108

From kanterella
Jump to navigation Jump to search
Forwards Responses to 850610 Questions Re Diablo Canyon OL Proceeding.Responses Delayed Due to Press of Other Business
ML20141H108
Person / Time
Site: Diablo Canyon, 05000000
Issue date: 07/09/1985
From: Asselstine J
NRC COMMISSION (OCM)
To: Markey E
HOUSE OF REP., ENERGY & COMMERCE
Shared Package
ML20140C992 List:
References
FOIA-85-653 NUDOCS 8601130420
Download: ML20141H108 (12)
v • d • e


Text

________________

/ o

~,, UNITE ~J STATES E ' ,(; n NUCLEAR REGULATORY COMMISSION

,E

{ ,

CASHIN1 TON, C.C. 20555

%**,<*/ l S-r f

OFFICE OF THE CoMMIS3IONER July 9, 1985 The Honorable Edward Markey, Chairman Subccmittee on Energy Conservation and Power Comittee on Energy and Commerce United States House of Representatives Washington, D.C. 20510

Dear Mr. Chairman:

I did not provide answers to your June 10, 1985 questions en the Diablo Canyon operating license proceeding when the Commission did in its letter of June 27, 1985. The press of other business prevented me frcm providing detailed responses at that time. Since your questions were in part based upon my concerns about the Diablo Canyon proceeding, I did not think it was necessary to elaborate on those concerns beyond what I have said on previous occasions. Upon further reflection, I have decided that brief responses to sone of the questions might be useful. Therefore, my responses to your questions are enclosed.

Sincerely, ,

_ _ d.-

'/James K. Asselstine cc: Rep. Carlos Moorhead 8601130420 851125 PTR FOIA DELL 85-653 PDR

QUESTION 1. THE COMMISSION MAJORITY'S FEBRUARY 25, 1985 LETTER STATES:

"THERE IS RECORD SUPPORT FOR THE COMMISSION MAJORITY'S FINDING THAT THE DIAsLO CANYON SITE IS

'AT MOST, ONE OF MODERATE SE!$MICITY.' CLI-84-12 AT 8, J.A.S. AT 258. AS THE APPEAL BOARD NOTED

'THE REGION IS AT MOST ONE OF LOW TO MODERATE SEISMICITY.' ALAB-664 (SICl, 13 NRC 903, 994 (1981)."

(A) WHAT IS THE ON THE RECORD SUPPORT FOR THE CONCLUSION OF THE COMMIS$10N AND ITS LICENSING BOARDS THAT THE DIABLO CANYON $1TE IS OF LOW TO MODERATE SEISMICITY? PLEASE PROVIDE ANY CITATIONS TO THAT ASPECT OF THE HEARING RECORD WHICH SUPPORTS THE CONCLUSION OF THE COMMISSION AND LICENSING BOARDS.

ANSWER.

THE APPEAL BOARD'S CONCLUSION THAT THE AREA IN WHICH DIABLO CANYON IS LOCATED IS ONE OF " LOW TO MODERATE SEISMICITY" IS BASED ON A PLOT (APPEAL BOARD EXH, 2), FIG. 2) DEVELOPED BY DRS. ANDERSON AND TRIFUNAC FOR THE YEARS 1950 THROUGH 1974 0F THE KNOWN EP! CENTERS IN THE PEGION, CENTERED AROUND DIABLO CANYON, AND THE CALCULATED MARKEY/0GC 6/26

o .

QUESTION 1 (A) (CONTINUED ,

LOW RECURRENCE RATE OF AN OBE AS WELL AS THE TESTIMONY OF PG4E WITNESS STEWART W. SMITH, FOL. TR. 5490 AT P. 14. ALAB-644, 13 NRC 903, 993, 994 (1981). ON THE BASIS OF THl3 RECORD EVIDENCE, THE APPEAL BOARD REJECTED THE CLA!M THAT THE AREA WAS e ONE OF HIGH SE!SMICITY, FINDING INSTEAD THAT: "[T]HE RECORD, l HOWEVER, DOES NOT BEAR 00T THE CLAIM THAT THE DIABLO CANYON SITE  ;

IS ONE OF 'HIGH SEISMICITY.'" 3 THE PLOT DEVELOPED BY DRS. ANDERSON AND TRIFUNAC IS CONTAINED IN A REPORT ENTITLED " UNIFORM RISK ABSOLUTE ACCELERAT!0N SPECTRA FOR THE DIAsto CANYON SITE, CALIFORNIA," DATED DECEMBER 30, 1976.

DR. STEWART W. SMITH TEST!FIED THAT

"(T]HE SOUTHERN COAST RANGE PROVINCE IN WHICH DIABLO CANYON IS LOCATED !$ AN AREA 0F LOW TO MODERATE SEISMICITY." SMITH, FOL. TR. 5490 AT P. 14. f i

T l

i i

I MARKEY/0GC 6/26  ;

QUESTION 1. (a) COMPARED TO OTHER REACTOR SITES, IS THE DIABLO CANYON SITE OF LOW TO MODERATE SEISMICITY?

ANSWER.

THE CHARACTERIZATION OF THE SEISMICITY AT THE DIABLO CANYON SITE AS " LOW TO MODERATE" WAS NOT BASED ON A COMPARISON WITH SE!SMICITY AT OTHER REACTOR SITES. RATHER, THE APPEAL BOARD IN ITS SE!$MIC DESIGN DECISION (ALAB-644), BASED ON ITS ANALYSIS OF THE EVIDENCE IN THE DIABLO CANYON RECORD, FOUND THAT THE DIABLO CANYON $1TE D!D NOT MEET THE PART 100, APPENDIX A DEFINITION OF "HIGH SE!SMICITY".

O e

a MARKEY/0GC 6/26

Cuestion 1 (8)

- Comissioner Asselstine's coments:

The Comission's answer to this question is certainly interesting, but it does not answer the question asked by the Comittee. The answer to the question is that compared to other reactor sites the Diablo Canyon site has a higher level of seismicity than any other site except perhaps San Onofre.

The clearest evidence for this is a comparison of the seismic design requirements for Diablo Canyon with the seismic design requirements for other plants in the country. For example, the SSE and OBE for Diablo f

Canyon are .75g and .20g respectively. The only other site with comesrable requirements is San Onofre .679 and .34g. The typical SSE for other  ;

plants is .25g or less and the typical OBE is .11 .12g or less. Clearly, by requiring the plant to be designed to withstand an earthquake with ground motions almost twice those of other plants in the country, the Comission explicitly trade the technical judgment that the earthqake risk for the Diablo Canyon area is not comparable to other areas of the country, and is, in fact, much higher.

The Comission argues, however, that frequency, not magnitude of the earthquakes is the operative statistic. The Comission says in effect that earthquakes are so infrequent that the seismic risk is not an important part of risk for the plant. I would point out that the Operatirg Basis Earthquake for Diablo Canyon is higher than for any plant other than San Onofre. The Operating Basis Earthquake is defined as "that earthquake

, -P-i 1

which ...could reasonably be expected to affect the plant site during tne operating life of the plant." Further, publicly available information compiled by tha.U.S. Geological Survey (USGS) would seert to indicate 'thet t earthquakes of sufficient magnitude to cause possible damage, obstruction or disruption to roads, buildings, bridges and connunication networks occu:-

throughout many parts of California, including the San Luis Obispo aree, with some regularity. " Earthquake History of the United States ,

Publicatica 41-1, 1982 Reprint with Supplement. According to this infonnation, four earthquakes have occurred in the innediate San' Luis Obispo area since 1830, and at least one of these earthquakes has been of magnitude 7-8 on the Modified Mercalli scale. jd..,pp.138,140,141,156, 162,164 In addition, two other earthquakes, c' magnitudes 6.5 and 7.5, have occurred within 50 miles of the Diablo Canyon site since 1922. .

" Earthquake Epicenter Map of California,1900 thrcugh 1974 $ tate of California, the Pesources Agency, Department of Conservation 1978.

W 0

i L. .A-

e I

QUESTION 1. (C) COMPARED TO OTHER REACTORS, IS DIABLO CANYON BUILT TO MORE OR LESS STRINGENT SEISh!C STANDARDS?

~~5PECIFICALLY WHAT, IF ANY, REACTORS HAVE MORE

. STRINGENT SEISMIC CESIGN REQUIREMF.NTS?

ANSWER.

ALTHOUGH THFY ARE NOT EXACTLY THE SAME, THE DIABLO CANYON AND SAN ONOFRE UNIT 2 AND 3 FACILITIES HAVE BEEN DESIGNED AND CONSTRUCTED TO ACCOMMODATE THE MOST STRINGENT SEISMIC STANDARDS (GR0VND MOTION) 0F ALL U.S. REACTOR FACILITIES. ,

4 4

k e

I MARKEY/0GC 6/26

. . . - ._ .-. - . _=

. ,- t  ;

QUESTION 1. (D) WHAT !$ THE COMMIS$10N MAJORITY'S RESPONSE t ,

TO COMMIS$10NER ASSELSTINE'S CHARGE! !N HIS s ,I

~

r' MARCH 19, 1985 LETTER THAT: "!N BASING A  ;

DECISION ON A FINDING THAT THE DIABLO CANYON AREA IS ONE OF LOW TO MODERATE SEISMICITY, THE COMMIS$!0N MISUNDERSTOOD WHAT THE LICENSING BOARD AND NRC STAFF EXPERTS MEANT- i BY'THAT PHRASE."  !

M. . ,

THE COMMISSION'S UNDERSTANDING OF THE PPRASE " LOW TO MODERATE" SEISMICITY WAS BASED ON THE, APPEAL BOARDS'S DECISION IN I ALAB-644, 13 NRC AT 992-94.- THE APPEAL BOARD BASED ITS DECIS!0N ON THE PLOT OF EARTHQUAKE ACTIVITY IN LICENSING 50ARD EXHIBIT l

2J, FIG. 2 AND T,HE CALCULATED LOW OCCURRENCE RATE OF AN EARTHQUAKE OF THE MAGNITUDE ASSIGNED TO THE 0BE (THE LOWEST AVERAGE RETURN PERIOD COMPUTED WAS 275 YEARS). THE APPEAL BOARD ALSO FOUND THAT ITSDECISIONWASSUPPORTEDBfTHESMITHTESTIMONYFOLLOWINGTR.

5490 AT P.14. THE PLOT IN EXHIBIT 2J SH0WS THAT FEW EARTHQUAKES ,

OCCURRED IN THE VICINI,TY OF DIAsLO CANYON DURING THE PERIOD i CONSIDERED. THE RECORD SHOWED THAT THE MINIMUM RECURRENCE TIME  !

FOR THE OBE WAS.275 YEARS, WHICH WAS FOUND TO BE "WELL BEYOND"  !

THE EXPECTED 0PERATING LIFE OF THE PLANT. AND THE SMITH TESTIMONY STATES THAT "THE SOUTHERN COAST RANGE PROVINCE IN WHICH .

l DIABLO CANYON IS LOCATED IS AN AREA 0F LOW TO MODERATE SEISMICITY."

g MARKEY/0GC 6/26

O QUESTION 1 (D) (CONTINUED) THE COMMISSION MAJORITY PROVIDED A NUMBER OF ARGUMENTS TO SUPPORT ITs DIABLO CANYON DECISION ON SEISMIC CONSIDERATIONS IN EMERGENCY PLANMiNG (CL-84-12) . THE COMMISSION MAJORITY BELIEVES THAT THOSE CONSIDERATIONS WERE RELEVANT TO THAT DECISION.

HOWEVER, BY INITIATING RULEMAKING, THE COMMISSION RECOGNIZES THAT THIS IS A GENERIC ISSUE ON WHICH PUBLIC COMMENT SHOULD BE SOUGHT IN REACHING A FINAL COMMISSION POLICY POSITION.

MARKEY/0GC 6/26

Question 1 (D)

Comissioner Asselstine's coments:

The Comission argues that on an absolute scale the Diablo Canyon area is one of low to moderate seismicity. Merely saying that does not end the inquiry. The question is whether earthquakes are a significant part of the risk for the Diablo Canyon site. If they are, some effort should be made to reflect that in planning for emergencies for the plant.

Obviously, earthquakes are a significant part of the risk for the Diablo Canyon site or the plant would not have been built to such stringent requirements. The Diablo Canyon site has the most stringent seismic requirements of any plant in the ccuntry, with the possible exception of San Onofre. The Comission notes, however, that the return rate or frequency of earthquakes at the OBE level has been calculated to be once every 275 years. The Comission tries to argue that this is tantamount to the seismic risk being so low that we need not consider it for emergency planning purposes. The Comission's reasoning ignores some very important points.

First, establishing the probability of the occurrence of an earthquake is far from a precise science. There are major uncertainties associated with doing so. These uncertainties are one reason the ACRS suggested and the Comission imposed a license condition for Diablo Caryen requiring a new seisnic evaluation five years after grant of the operating license.

(See Attached letter, p. 5). Even granting for the sake of argument the accuracy of the probability number, it is still more probable than other occurrences we-do consider for emergency planning which are in the neighborhood of 10-4 or 10-5 per year, (See Staff memo of July 5,1985).

Once in every 275 years is roughly 4 x 10-3 per year, which is more likely to occur than something with a probability of 10'4 or 10-5. Indeed, as the staff's July 5 memorandum points out, even earthquakes exceeding the SSE have a probability within the range of occurrences now routinely considered for emergency planning purposes.

A second source of uncertainty is that associated with whether the plant will indeed function as intended and withstand an earthquake less than an SSE. There is always some risk associated with any plant even if it meets our regulations. The Comission tries to argue that since Diablo Canyon has been the subject of such intensive seismic reviews this uncertainty is not large. However, the reason this plant has been the subject of such review is because of errors found which raise questions about the adecuacy of the seismic design. First was the discovery of the Hosgri fault after construction began. Rather than make major design changes to the plant to provide typical margins of safety, most of the effort was aimed at recalculations to justify the design that was based on a lesser earthouake than that which was attributable to the Hosgri fault.

As the ACRS said in a letter to the Comission, the result was that less conservative values were used than would have been used in an original design. (Seeattached) Thus, the safety margins accepted were smaller than the staff usually accepts. In addition, when the mirror image problem

..Q

was discovered the major effort was another recalculation with some plant modifications, not on a redesign of the plant. This adds yet another level of uncertainty:-

These types of uncertainties are exactly why we have emergency planning. We prepare for the unlikely, but not improbable, occurrence in order to have defense in depth. The Commission's argument simply ignores these uncertainties and this fundamental precept of emergency planning.

Further, both staff experts and the ACRS think that the seismic risk is significant enough that it ought to be considered. The NRC has in fact required the emergency plan to incorporate consideration of earthquakes at less than the SSE.

e 5

h _, - , - - - - , -

,y

Retrieved from "https://kanterella.com/w/index.php?title=ML20141H108&oldid=2856114"