ML19309H503
| ML19309H503 | |
| Person / Time | |
|---|---|
| Site: | Vallecitos File:GEH Hitachi icon.png |
| Issue date: | 05/08/1980 |
| From: | Darmitzel R GENERAL ELECTRIC CO. |
| To: | Eisenhut D Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19309H504 | List: |
| References | |
| NUDOCS 8005130416 | |
| Download: ML19309H503 (20) | |
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ENGINEERING GENERAL ELECTRIC COMPANY, P.O. box 460, PLEAsANTON, CALIFORNIA 94566 DIVISION May 8,1980 Mr. Darrell G. Eisenhut, Director Division of Project Management Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C.
20555
Subject:
Response to NRC Questions - Structural Issues - Part II, Recent Investigations - License TR Docket 50-70
Reference:
Summary of Meeting with General Electric Regarding the General Electric Test Reactor (GETR) Seismic Review, March 21, 1980
Dear Mr. Eisenhut:
Enclosed are General Electric Company's responses to the remaining five of the original eleven structural questions raised by the NRC at a meeting on i
January 31, 1980 concerning the General Electric Test Reactor (GETR) reactor building. The eleven questions and responses were arranged in two parts.
The first part included six questions which refer only to information sub-mitted previously to the NRC.
Responses to these six questions were sub-mitted with our letter of April 23, 1980.
The second part includes responses to the remaining five questions which refer to previously submitted reports as well as recently completed investi-gations which are reported in reference documents as follows:
Reference 1.
Review of Seismic Design Criteria for the GETR i
Site (EDAC Report 117-254.03)
Reference 2.
Probability Analysis for Combined Surface Rupture Offset and Vibratory Ground Motion (JBA Report 11-014-01)
Reference 3.
Additional Investigations to Determine the Effects
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of Combined Vibratory Motions and Surface Rupture Offset Due to an Earthquake on the Postualted Verona Fault (EDAC Report 117-253.01) l Reference 4.
Additional Investigations to Determine Effects of Vibratory Motions Due to an Earthquake on the Calaveras Fault (EDAC Report 117-253.02)
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GENER AL $ ELECTRIC Mr. Darrell G. Eisenhut May 8,1980 Reference 5.
Additional factors to be considered in the evalu-ation of the adequacy of the GETR Reactor Building to resist postulated seismic effects (EDAC Report 117-254.02)
Reference 6.
A Seismological Assessment of the Probable Expec-tation of Strong Ground Motion at the GETR Site (R. L. Kovach, April 28, 1980)
References 2 and 6 were submitted with our letter of April. 23, 1980.
Refer-ences 1, 3, 4 and 5 are included herein.
The previous investigations of the GETR Reactor Building showed that the facility is adequate to resist seismic events which produce ground accel-erations of 0.8 g at the site.
In response to inquiries from the NRC Staff, additional investigations were undertaken to examine the effects of near field phenomena on the peak ground motions postulated for the GETR site.
The results of these investigations are reported in Reference 1.
In brief, it was concluded that the GETR reactor building should be evaluated for the peak ground motions induced at the site due to seismic events on the Calaveras and postulated Verona faults as follows:
Calaveras Fault:
Horizontal Acceleration 0.6 g
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Vertical Acceleration 0.4 g
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Postulated Verona Fault: Horizontal Acceleration 0.40 g
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Vertical Acceleration
= 0.27 g Surface rupture offset at the GETR site is an event with a probability of occurrence so low that it should not be included as an evaluation basis event. However, in the interest of responding to NRC requests, the integrity of the reactor building has been evaluated for the hypothetical combined loading case of vibratory motions and surface rupture offset due to a postu-lated seismic event on the Verona fault using the results of Reference 2.
These investigations are described in Reference 3.
In this report combin-ations of fault displacement and ground motion were selected. The investi-gation shows that the concrete core structure of the GETR reactor building is adequate to withstand the combined load case of vibratory ground motion and surface rupture offset due to postulated seismic events on the hypothetical Verona fault.
The previous analyses for the Calaveras ennt were reviewed as described in Reference 4, and it was concluded that these evaluations demonstrated that the GETR reactor building is adequate to withstand motions induced by postu-lated seismic events on the Calaveras Fault.
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7 G E N ER A L (2) E LE CTRIC Mr. Darrell G. Eisenhut May 8,1980 It is well known and accepted in the field of earthquake engineering that conventional analysis and evaluation procedures include many conservative assumptions which contribute to the overall safety margins used to deter-mine the ability of structures to withstand seismic motions. Reference 5 presents a discussion of the safety margins in the procedures used to eval-uate the adequacy of the GETR reactor building to resist postulated seismic events on both the Calaveras and Verona faults. These individual safety margins are cumulative.
If they were quantified, it would produce a total margin of safety which is substantially above (a minimum of two times) that determined by the evaluation of the GETR.
i In conclusion, it is our opinion that the investigation of the GETR reactor building described in documents previously submitted to the NRC, as well as i
those documents submitted with this letter, conclusively demonstrate that the GETR reactor building is adequate (with a significant safety margin) to withstand the seismic motions induced by earthquakes on the Calaveras and postulated Verona faults.
i This completes the information planned to be submitted in relation to the GETR structural matters.
It should now be possible to complete the struc-tural portion of the Safety Evaluation Report.
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AFFIRMATION The General Electric Company hereby submits the attached responses to NRC Questions - Structural Issues - General Electric Test Reactor - Part II and four r:. ports titled:
(1) Review of Seismic Design Criteria for the
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GETR Site (EDAC Report 117-254.03); (2) Additional Investigations to Determine the Effects of Combined Vibratory Motions and Surface Rupture Offset Due to an Earthquake on the Postulated Verona Fault (EDAC Report 117-253.01);
(3) Additional Investigations to Determine Effects of Vibratory Motions Due to an Earthquake on the Calaveras Fault (EDAC Report 117-253.02);
(4) Additional Factors to be Considered in the Evaluation of the Adequacy of the GETR Reactor Building to Resist Postulated Seismic Effects (EDAC Report 117-254.02).
To the best of my knowledge and belief, the information contained therein is accurate.
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RESPONSES TO NRC REQUESTS
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Contents Page Request No. 2 1
Request No. 4
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Request No. 2 Discuss in detail the final orientation, support conditions and locations, and status of all structural portions of,the reactor building and core structure resulting from the most severe surface offset conditions.
Response to Request No. 2 A conservative maximum surface rupture offset case was analyzed and is reported in References 1 and 2 (Phase 1 and Phase 2 reports, respectively).
In addition, a second case for a 17-foot unsupported cantilever length and a 0.3 g effective ground acceleration was also analyzed (Ref. 3).
Both cases are highly improbable from both a probabilistic viewpoint (Refs. 4 and 5) and from physical considerations (Ref. 3).
The second case represents a severe combined load-ing case.
The final orientation support conditions, and locations and status of all structural components of the reactor building for both cases are discussed below.
Maximum Surface Rupture Offset Case Figure 1 shows the orientation and support conditions of the i
reactor building for the maximum surface rupture offset case i
as analyzed and reported in Reference 2.
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rupture offset / reactor building configuration.
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In this analysis case, the building is supported by the assumed soil bearing area shown in Figure 1.
In the actual physical situation, any vibratory ground motion which occurs will cause the building to tilt and be supported near the far left wall.
This latter configuration produces lower stresses in the building than for the case analyzed.
In this configuration, the estimated angle of tilt of the reactor building would be approximately five degrees.
The locations and status of all major structural components are as follows:
The concrete core structure as outlined in Figure 1 will not be cracked and the floor slabs on the south-west side will be supported by the uncracked portion of the basement wall; thus, safety-related components.will be adequately protected.
There may be some cracking in the floor slabs and basement walls as shown in Reference 1 (see Figures 3-8a and 3-8b) and in Reference 2 (see Figure 3-13).
However, this distress will not effect the capacity of the concrete core structure or the sa bty related piping, equip-ment, and components, which is contained within the core structure.
Combined Surface Rupture Offset and
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Vibratory Ground Motion Case Reference 3 describes the additional investigations performed to demonstrate that the reactor building concrete core l
structure is capable of withstanding the effects of combined l
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vibratory motions and surface rupture offset due to an earthquake on the postulated Verona fault.
As explained in Reference 3 (pages 2-3), stress analyses vere performed for the case of an unsupported cantilever length of 17 feet and ground motion of 0.3 g.
This case was selected because it provides a very conservative evaluation of the stresses in the concrete core structure, based on probabilistic and physical considerations.
Analyses of the soil pressures for this case showed that the concrete core structure will actually settle down and be essentially continuously supported, which is a condition which can be easily tolerated (see further discussion, page 3, Ref. 3).
In this case, the tilt of the reactor building concrete core structure will be approximately 5 degrees as described above.
The stress analyses for the 17 ft/0.3 g case were based on the severe and conservative assumptions that the structure does not settle down.
Stresses in the concrete core structure for this con-servative case were shown to be within allowable limits.
Also, the core structure remains vertical,'is supported as shown in Figure 4 of Reference 3, and is undamaged.
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References 1.
Engineering Decision Analysis Company, Inc., " Seismic Analysis of Reactor Building, General Electric Test Reactor, Phase 1," EDAC-ll7-217.02, prepared for General Electric Company, 3 February 1978.
2.
Engineering Decision Analysis Company, Inc., " Seismic Analysis of Reactor Building, General Electric Test
' Reactor, Phase 2," EDAC-117-217.03, prepared for General Electric Company, 1 June 1978.
- 3. Engineering Decision Analysis Company, Inc., " Additional Investigations to Determine the Effects of Combined Vibratory Motions and Surface Rupture Offset Due to an Earthquake on the Postulated Verona Fault," EDAC-117-253.01, Rev. 1, prepared for General Electric Company, 8 May 1980.
4.
Engineering Decision Analysis Co.,
" Probability Analysis of Surface Rupture Offset Beneath Reactor Building -
General Electric Test Reactor," report to General Electric Company, San Jose, California, April 12, 1979.
5.
Jack R.
Benjamin and Associates, Inc., " Additional Probability Analyses of Surface Rupture Offset Beneath Reactor Building - General Electric Test Reactor," report to General Electric Company, San Jose, California, March 12, 1980.
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Request No. 4 If, due to a surface rupture under the plant, the mat cantilevers off the edge of the soil, describe the load path through which all loads are transmitted from the reactor building to its support.
Quantify any increase in stresses which result from the absence of support originally provided direct.;r by the mat and soil.
Response to Request No. 4 Two configurations of surface rupture offset were analyzed.
i The first case is described in the Phase 1 and Phase 2 reports (Refs. 1 and 2) wherein the reactor building core area is assumed to cantilever 20 feet over the foundation.
A second case was als.o analyzed based on a l'7-foot cantilever configuration combined with a 0.3 g effective ground accel-eration (Ref. 5).
Both cases are highly improbable from both a probabilistic viewpoint (Refs. 3 and 4) and from physical considerations (Ref. 5).
tie load path and increase in stresses for the two cases are given below.
Maximum Surface Rupture Offset Case Figure 1 shows the support conditions and generalized load path for the maximum surface rupture offset case.
(See response to Request No. 2 for discussion of support conditions.)
The loads in the concrete core structure will primarily be supported by the soil in the area directly beneath the core as shown in Figure 1.
The flow of forces is reflected in the stresses that were computed and reported in the Phase 2
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report (see discussion below).
The area outside the core will be supported by the foundation area to the right side of the core (see Figure 1).
Stresses outside the core area do not affect the safety-related components.
All stresses in the core area are less than the capacity (defined as the threshold of cracking) and are given in Tables 3-2a, 3-2b, and 3-2c in the Phase 2 report (Ref. 2).
Discussions of the stresses are given on pages 3-12 through 3-14 of Reference 2.
The stresses given in the Phase 2 report (Ref. 2) are generally higher than the fully supported building configuration (i.e.,
before an offset).
However, all stresses in the concrete core structure are less than the capacity.
Thus, the supports for all safety-related piping, equipment, and components are not affectud by surface rupture offset.
Combined Surface Rupture Offset and Vibratory Ground Motion Case Reference 5 describes the additional investigations performed to demonstrate that the reactor building concrete core struc-ture is capable of withstanding the effects of combined vibratory motions and surface rupture offset due to an earth-quake on the postulated Verona fault.
As explained in Refer-ence 5 (pages 2-3), stress analyses were performed for the l((
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This case was selected because it provides a conservative evaluation of the stresses in the concrete core structure,' based on probabilistic and physical considerations.
The analytical model and its boundary conditions represent the load path for the surface rupture offset load case.
Figure 4 of Reference 5 shows the region of support of the analytical model.
The generalized load path is similar to that shown in Figure 1.
Stresses for this analysis case are described on pages 4 through 6, and summarized in Table 1 and Figures 6 through 10 of Reference 5.
The investigations described in Reference 5 thus incorporate the appropriate support conditions and load path in the stress analysis model, compare calculated stresses with acceptance criteria, and demonstrate that the capacity of the reactor building con-crete core structure is adequate.
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References 1.
Engineering Decision Analysis Company, Inc., " Seismic Analysis of Reactor Building, General Electric Test Reactor, Phase 1," EDAC-ll7-217.02, prepared for General Electric Company, 3 February 1978.
2.
Engineering Decision Analysis Company, Inc., " Seismic Analysis of Reactor Building, General Electric Test i
' Reactor, Phase 2," EDAC-ll7-217.03, prepared for General Electric Company, 1 June 19 78.
3.
Engineering Decision Analysis Co.,
" Probability Analysis of Surface Rupture Offset Beneath Reactor Building -
General Electric Test Reactor," report to General Electric Company, San Jose, California, April 12, 1979.
4.
Jack R.
Benjamin and Associates, Inc., " Additional Probability Analyses of Surfdce Rupture Offset Beneath Reactor Building - General Electric Test Reactor," report to General Electric Company, San Jose, California, March 12, 1980.
5.
Engineering Decision Analysis Company, Inc., " Additional Investigations to Determine the Effects of Combined Vibratory Motions and Surface Rupture Offset Due to an Earthquake on the Postulated Verona Fault," EDAC-ll7-253.01, Rev.
1, prepared for General Electric Company, 8 May 1980.
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RESPONSES TO NRC REQUESTS Con tents Page REQUEST NO.
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1 REQUEST NO. 10....................
2 REQUEST NO. 13....................
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1 Request No. 6 Discuss how a dip of 60 degrees in the surface offset, rather than the 15 degrees assumed in your analysis, will affect the analysis procedures and results.
Include a discussion of the support conditions, and provide a diagram indicating forces acting on the core structure.
Response to Request No. 6 L
The investigations described in Reference 1 demonstrate that the concrete core structure can adequately resist one-meter surface rupture offsets with a range of dips of 60 degrees to 15 degrees. The analytical models used in these investigations which are conservative representations of the phenomenon are not sensitive to dip angles in this range and thus the integrity of the concrete core structure is not significantly influenced by the dip angle.
It is also important to recall that the only item of seismic safety related equipment that has potential for being affected by a tilt of the reactor building produced by an offset beneath it would be the fuel element storage tank. Even with an offset dip of 60 degrees (and corresponding larger vertical displacement), the proper operation of the fuel element storage tank would be unaffected.
Reference 1.
Engineering Decision Analyd-Company, Inc., " Additional Investigations to Determh.c tne tifiects of Combined Vibratory Motions and Surface Rupture Offset Due to an Earthquake on the Postulated Verona Fault," EDAC-117-253.01, Prepared for General Electric Company, 30 April 1980.
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2 Request No. 10 Address the issue of the reactor building impacting the mat during the surface rupture and simultaneous vibratory motion.
Response to Request No.10 It is assumed that the primary concern of this question is possible impact between the reactor building and supporting soil. As stated in i
Reference 1, certain hypothetical scenarios envision a series of maximum l
" unsupported lengths" of the Reactor Building.
For lengths shorter than these values, there would be no " impact" of the reactor building with the supporting soil, since the soil can adequately support the reactor building. As also explained, offsets located nearer to the building center than the above unsupported lengths would result 'in local yielding of the soil at the edge of the offset and thus a settling down of the structure. The contact of the " unsupported length" with the undisplaced portion of the soil would not be of an impact nature because the soil is a flexible medium and would cushion the contact. Further, the surrounding soil embedment would restrain the structure from moving abruptly. Thus, the phenomenon would be gradual and not be of an impact nature.
Reference 1.
Engineering Decision Analysis Company, Inc., " Additional Investigations to Determine the Effects of Combined Vibratory Mations and Surface Rupture Offset Due to an Earthquake on the Postulated Verona Fault," EDAC-ll7-253.01, Prepared for General Electric Company, 30 April 1980.
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- 3 Request No. 13 Provide a detailed discussion verifying that a seismic design basis of 0.8 EPGA combined with some small amount of surface offset has been considered, and will not be as severe as the design bases used in your surface offset or post-offset analyses.
Include a discussion verifying that any structural degradation resulting from surface offset effects has been considered and accounted for in your post-offset analysis.
1 Response to Request No. 13
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A specific calculation for a design basis of 0.8g EPGA and a small offset (interpreted here to mean " unsupported length" as defined in Reference 1) has not been performed. However, the following should be noted:
The evaluations described in Reference 1, performed in response to NRC requests, show that the Reactor Building core structure is clearly adequate to withstand postulated combined surface rupture offset and vibratory motion scenarios without damage or degradation.
(See Figure 6 and related text on page 6 of Reference 1).
Since there is no degredation to the Reactor Building concrete core structure, the previously performed Phase 2 (Ref. 2) post-offset models and analyses are applicable and the results still valid. These results permitted the conclusion that the core structure is adequate to withstand substantial aftershocks, at least of a severity which can reasonably be envisoned for the Verona f ault.
As stated previously, it is the opinion of GE and its consultants that the probability of occurence of a surface rupture offset at the GETR site is so low that the event should not even be included in the design bases.
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Engineering Decision Analysis Company, Inc., " Additional Investigations to Determine the Effects of Combined Vibratory Motions and Surf ace Rupture Offset Due to an Earthquake on the Postulated Verona Fault," EDAC-ll7-253.01, Prepared for General Electric Company, 30 April 1980.
2.
Engineering Decision Analysis Company, Inc., "Saismic Analysis of Reactor Building, General Electric Test Reacto., Phase 2,"
l EDAC-ll7-217.03, Prepared for General Electric Company,1 June 1978.
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