ML20137D601
Text
'
(
ATTACHMENT 3 2
September 13, 1977 Hr. Edson G. Case, Acting Of rector Serial No. 398 Of fice of fluclear Reactor Regulation PSESC/H'.!SJ r/CMRJ r:beb Attention:
Mr. J. F. Stolz, Chief Docket Hos: 50-338 x
Light \\later Reactors Branch flo.1 50-339 T
Division of Project flanagercent 50-404 U. S. Ilucicar Regulatory Commission 50-405
\\lashington, D. C.
20555 Ocar Mr. Case:
The enclosed forty (40) copics of the report titled "A SEISitlC !!OHi-TORll!G PROGRAM AT THE liORTH AHilA SITE lH CENTRAL VIRGilll A - JANUARY 21,~1974, THROUG!! AUGUST 1,1977" were prepared by Dames 5 Moore and are fontarded to you as required by Supple:nent 2 to the flerth Anna Units 1 and 2 Safety Evalua-tion Report (SER) Docket !!os. 50-338 and 50-339 Also included are forty (40) copics of a letter f rom Dr. G. A. Bollinger to Mr. H.11. Bohannon, Jr. dated June 10, 1977 in which the significance of the microsolsmicity at the North Anna site is discussed. A like number of copics of the enclosure to Dr.
Pollinger's letter titled "SIGNIFICA! ICE OF THE filCROSEISMICITY AT THE HORTH ANNA PO'.lER PLANT SITE" are also forwarded.
This information presents a very comprchenstvc cvaluation of the data obtained by the progran during its more than three and one half (3i) year life.
The scismic monitoring program at North Anna was originally required by the U. S. Nuclear Regulatory Commission to determine:
1.
If there was any Indication of scismic activity occurring along known faulting at the site, and; 2.
If there was any indication that Lake Anna was reactivating known faulting at the site..
In addition, Supplement 2 to the North Anna Units 1 and 2 Safety Evaluation Re-port required additional monitoring at least until August 1,1977.
This add!-
tional monitoring was required to determine if the occurrence of microcarth-quakes continued to be bounded by a hypothetical extension of the faults in the vicinity of the plant site.
As you will see fron revicuing these reports, there has been no Indi-cation of scismicity occurring along known faulting at the site, there is no Indication of reactivation of known faulting at the site due to Lake Anna and there is no marked change in the location of scismic activity since llay 1,1976.
For these reasons we concur with the opinion of our consultants that the present 8508220521 850722 PDR FOIA DELL 85-363 PDR
(
,Mr.,Edson G. Case 2
microselsmic monitoring network at florth Anna has fulfilled Its Intended func-tion. As the seismic raonitoring program at llorth Anna has met all the require-ments specified, and as there have been no indications that microselsmic activity in any way constitutes even a remote threat to the health and safety of the public, we plan to terminato operation of the network on October 1,1977 Scismic monitoring of the central Virginia Piedmont area will continue, however. Uc Intend to fully cooperate with responsibic parties to assimilate one or several stations from the llorth Anna network into one of the networks currently planned by others for central Virginia.
Various Vepco equipment and station locations are available for incorporation into these networks commensurate with equipr1cnt compatability requirements.
Uc plan no further reports on,the operation of the North Anna micro-scismic network as wa feel the enclosed reports constitute an exhaustive analysis of the llorth Anna data.
If you have any questions, please contact us.
, Very truly yours, ow si, e,g S. C.13R()n,gi,, g Sam C. Drc.m, J r.
Vice President Power Station Engineering and Construction Enclosures s
~
ATTACHMENT 4 I,
G{. Bo r.r.rwo r n M 8d "
- L^NE B LACKsnUno, VA. 24000 June 10, 1977 r
t Mr. Harold W. Bohannon., Jr.
Vepco P. O. Box 26666 Richmond, Virginia 23261
Dear Mr. Bohannon:
Attached are my responses to The Atomic Safety and Licensing for interpretation of the significance of the micro-Board's request June 6, 1977).
earthquake activity at North Anna site (your memo dated I act as a private In the preparation and submittal of this report Virginia citizen on civil 1 cave from his employ, i.e., I do not represent I have acted and Polytechnic Institute and State University or Vepco.
i and continue to act as Vepco's consultant with respect to_ the collect on but there will analysis of the seismic data from the North Anna network
- Also, be no invoice from me for the preparation of the enclosed report.
I have had excellent cooperation from the I wish to state formally that k pro-Dames and Moore staff associated with the operation of the networ I have seen all the seismograms and Mr. Niles Severy of Dame gram.
Moore has complied with all my requests for data reductions and an
~
To summarize my response to the questions posed by your memo:
It is the significance of the microscismicity at North Anna?
What 1) is part of the ambient low-level' seismicity characteristic of the for more char. a century although Lake Anna may be a minor pertur I see no evidence of strain release on the faults mapped influence.
i 4
i b
{
page 4 The rationale at the plant site or for their reactivation by Lake Anna.
for this interpretation is:
' a)
There is no significant lineation of epicenters parallel to the northeast trend of the plant site faults, Neuschel's lineament and the tectonic fabric of the region.
Rather, a scattered paitern of epicenters has been observed; The average rate of microearthquake occurrence near the plant b) site is less than that predicted for central Virginia from histori' cal felt earthquakes; The proportion of small to large shocks (b-value) monitored c) about the plant site is virtually the same as that determined for the region from historical felt earthquakes; and
[
Lake Anna and'the cluster d)
The pattern of microcarthquakes about The facts near the dam are not unexpected at new reservoirs.
I the focal that the b-value is not anomalously high, that mechanisms favor reverse fault motions and that no felt earth--
quakes have occurred in the 5 1/2 years since filling all the reservoir is not inducing a significant indicate that change in scismicity.
A detailed discussion of the above points is presented in the attached report.
flow could information obtained from further operation of the l
2) the plants are microscismic network be used to provide assurance that safe to operate?
Because of the above mentioned factors I see no need to continue the intense survelliance of the plant site that the existing network
(
9 page 3 provides. However, one station near the plant (o(20 km) would be appro-priate to simply monitor the numbers and energy levels of events occur-ring nearby as a precaution against unexpected future changes in the local seismic regime.'
What kind of inforenation in the seismic data would cause me to be 3) concerned for the safety of the site?
f The converse of the factors noted in (1) above, i.e.,
a)
Significant lineations in the epicenters; Hi h rates of earthquake occurrence and energy-release levels; b)
E and c)
Significant changes in the b-value.
I As. example of that type of data base note the attached pages 1957 and 5
1958 from a paper by Stander et al (Bull _. Seism. Soc. M., 1976, pp.
t In their monitoring of the New Madrid seismic zone they 1953-1964).
found pronounced lineations of epicenters and rates of i shock per day Additionally, in the with magnitudes between magnitudes 0.5 and 5.0.
less than 2 year monitoring period they have recorded events with magnitudes of 4.3, 4.5 and 5.0.
Very truly yours, V
i G. A. Bollinger GAB:brs e
ATTACHMENT 5 1
SUl@iARY OF MONITORING PROGRAM 4
I i
f ACCOMPLISILMENTS -
Essentially continuous scismic monitoring of the plant site i
1.)
j area for 1285 days (3.5 years) complete to a magnitude i:
threshold of M3 > 0.0-for A i 10 km and M3 > 0.5 for 10 km.
L I
I
< A < 45 km.
Nineteen microcarthquakes meeting the U.S. Nuclear Regula-2.)
tory Commission (NRC) minimum magnitude criteria [ magnitude l
> 1.0, (S-P) $ 5 sec.] were recorded (1 event every 68
~
l days).
Considering all locatable events (-1. 0 $ Mg i 2.1) 152 microcarthquakes were recorded for A 3 45 km. (1 event 1
overy 8 days).
Five CFMS were obtained for activity recorded in the Lake i
l 3.)
Anna region.
t A duration-magnitude relationship was established.
4.)
i A regional recurrence relationship was determined.
5.)
CONCLUSIONS It should be emphasized that no microcarthquakes, recorded 1.)
by the Phase I or Phase II networks, have occurred within the mapped extent or the projected spatial extent of the I
plant site f ault zone and that the impoundment of Lake i
l Anna has not reactivated this fault zone.
The seismicity within the Lake Anna area and the surround-12. )
l
~
This activity f
ing region is expectable and not anomalous.
i 1
is considered to have the same relationship to the safe l
operation of the North Anna Power Station as the occurrence t
i j
5-I E3 A%M 01ti 83 MOctlet f
i
~.
o
(
of any other expectable seismic activity within central Virginia.
3.)
No macroseismic (M > 3) activity was recorded within the (A 1 45 km) during the monitoring program.
The two area largest events were at magnitude 2.1 and 2.0.
4.)
The rate of microearthquake activity is low (1 event every 8 days for A 1 45 km).
5.)
There is.no apparent steady increase of number of events, average magnitude, or energy level within the monitoring area (A I 45 km).
i 6.)
There is no conclusive evidence that the activity within A _< 10 km is reservoir-induced.
7.)
There is no definitive indication of any activity being re-lated to the Spotsylvania'Lincament, the Stafford Fault Zonc, or their hypothetical extensions.
8.)
Depth sections and CFMS indicate the absence of any sing 1c, continuous geologic feature which would explain the activ-ity within the Lake Anna area.
9.)
The majority of the CFMS constructed for events in the Lake Anna region suggest a northerly strike for the nodal plancs j
with widely varying dips.
Most motions suggest a persist-ont reverse component.
CFMS and FMS for scismic events in the castern United States are dominated by high-angic re-verse motions, suggesting that the CFMS and FMS for the s
North Anna area are entirely compatibic with regional anal-yses.
e, A
?
6-I
,,,,g,,, y o o,,,,
J
r 7,
(
10.) Both historical macroseismicity and recent u.icrocarthquake monitoring indicate the absence of activity west to north-west of the North Anna Site (A < 50 km).
This ascismicity is not viewed as anomalous.
11.) b-values for the North Anna monitoring area compare favor-ably with historically-derived values for the central
~
The use of b-values from microscismicity Virginia rcgion.
studies in the prediction of macroscismicity must be ten-pered.
12.) More frequent and generally higher levels of strain release arc observed outside the plant site area in the surrounding region (45 km < 6 < 100 km).
A trend or cluster of epicenters is observed near the Fall 13.)
Line from Fredericksburg south to Richmond which, if repre-the activity recorded stithin the network, sentative of would most likely be related to low 1cyc1 activity in a minor scismic area.
RECOMMENDATIONS The Phase II monitoring program be discontinued.
1.)
Limited monitoring be conducted in conjunction with the 2.)
central Virginia network, presently being installed.
1 A
k l
7-I smmr.n n moosers
.,