ML19296A682
| ML19296A682 | |
| Person / Time | |
|---|---|
| Site: | Vallecitos File:GEH Hitachi icon.png |
| Issue date: | 10/12/1979 |
| From: | Page B STANFORD UNIV., STANFORD, CA |
| To: | Kerr W Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-CT-1178, NUDOCS 8002150131 | |
| Download: ML19296A682 (2) | |
Text
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STANFORD UNIVERSITY (7-#98 STANFORD CALIFORNIA 943o3 i
Of PARTMENT of CEoLGOY k""E*""k*""
12 October 1979 Dr. William Kerr
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Ch a ir man, Subcommittee on GITR a5 '
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Department of Nuclear Engineering University of Michigan OCT191979 Ann Arbor, MI 48109 au/gtut@
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Dear Dr. Kerr:
This letter concerns the geologic / seismic conditions at the General Electric Test Reactor (GETR) a t Vallecitos, California. I will be in South America at the time of the November 14 meeting on this subject, so will state my opinions herewith.
The GETR area is near my home base, so I have visited the exploratory trenches two or three times and have participated in meetings at the site.
I have listened to the views of GE's consul tants, USGS representatives, and.VRC technical e xp er t s.
very good one because of the controversial implications The site is not a of geological features in the vicinity. However, the plant exists, so these implica tions must be resolved one way or another. A good deal of progress has been made. largely thanks to an elaborate trenching program.
As you know, an overriding question is whether certain geological and topographic anomalies denote the presence of (1) young faults or (2) large l a n ds l i des. Or. this matter. I am confident that the fault hypothesis is correct. Prior to the trenching program I was sympathetic toward the land-slide interpretation. but the trenches exposed little that supports the landslide idea. Instead, all the conspicuous dislocations seen in the trenches (e.g., A, B-1, B-2, B-3) are readily explained by f aulting. Morecver, the absence of " pull-away" features in trenches of the E Series and G Series in the supposed headwall area's of postulated landslides effectively disproves the existence of the envisioned major slides. To be sure. some minor slides are discernible.
Since faults are almost certainly present, their behavior and the time of last movement become important problems. The faults cut the Livermore Gravels, which are probably a bout 4.5 - 0.5 million years old. The Gravels are displaced a significant amount, - tens or perhaps hundreds of meters.
Unlike some USGS geologists, I do not see offsets in the youngest s, oil, which R. J. Shlemon (a recognized expert) thinks is at least 8,000 years old. The f aults do displace a horizon which Shlemon thinks is 10. 000s17,000 years old.
Therefore probably some f aulting occurred intermittently until a f ew thousands of years before the present, and it may recur in the future. I think any single future event would entail a f aul t slippage of less than 1 meter, judging from the total displacement ( 1 m ) of the "stoneline" horizon which is believed to be at least 10,000 years old, and judging from displacements of comparable horizons in several trenches.
With regard to possible disruption of the reactor by surf ace faulting, I The surface trace of the th ink this is properly a matter of great concern.
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. thrust fault exposed in trenches 3-1 and B-3 (at the foot of the main hillside) passes within about 100-110 m of the GETR containmant structure; the f ault dips away from the plant. The surface trace of the
- however, thrust fault exposed in Trench B-2 is about 300 m from, and on the opposite side of, the containment structure, but because of this f ault's gentle in-at a clination (ca. 30 ) to the northeast, it must pass beneath the plant This markedly detracts from the margin of saf ety.
15 0-2 00 m.
depth of only despite these unwelcome circumstances, exposures in Trench Nev er th el es s,
B-1 indicate that it is most unlikely that the plant itself is sitting on the trace of a fault. The possibility of a new fault forming directly under GETo is so remote that it does not worry me. All things considered, I believe the plant is not in danger of being " cut in two" by surface faulting.
future earthquakes, I consider the Calaveras f ault to be more As for the f aults exposed in the exploratory trenches. The generation i=portant than of strong earthquakes requires a certain range of confining pressure, which is largely a function of depth. In the case of a thrust fault such as those exposed at the plant site, the earthquake source (if any) would be well least 5 km, and more down dip. Presumably the depth of focus would be at lik el y 10-20 km. If the thrust faults at the GETR site dip 30. any signif-least 8 km earthquakes generated on these f aults would be centered at icant and nore probably over 15 km. On the other hand,- the Calaveras f ault, away, is apparently a nearly vertical strike-slip f ault and is a known which source of earthquakes, passes within approximately 3.5 km of the plant.
a subsurface Co nc ei va bl y, it might produce an earthquake originating at within 6 km of GETR. The Calaveras f ault is currently very seismic point in Sunol Valley south of GETR, bet Aeen the town of Hollister and a point the present-day seismicity shif ts to the Hayward but if it is any comf ort, fault near Fremont. I do not think we should assume that this is a permanent pattern, however.
I an int erested in the situat' ion at GETR and regret that I cannot at t end the f or thcoming meeting on November 14. I expect to return about December 12.
Sincerely, y)
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last-Senjamin M.
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