ML13317A279
| ML13317A279 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 08/16/1982 |
| From: | Baskin K Southern California Edison Co |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8208180113 | |
| Download: ML13317A279 (48) | |
Text
Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE
- ROSEMEAD, CALIFORNIA 91770 K. P. BASKIN TELEPHONE MANAGER OF NUCLEAR ENGINEERING, 213) 572 -1401 SAFETY, AND LICENSING August 16, 1982 Director, Office of Nuclear Reactor Regulation Attention:
D. M. Crutchfield, Chief Operating Reactors Branch No. 5 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D.C.
20555 Gentlemen:
Subject:
Docket No. 50-206 Seismic Safety Margins San Onofre Nuclear Generating Station Unit 1 By letter dated April 5, 1982, the NRC indicated that the.67g Housner response spectra being used for seismic reevaluation were generally appropriate except for small exceedances (up to 10%) in specified period ranges.
Specifically, that letter indicated that the staff's best estimates of the 84th percentile response spectra would exceed the horizontal Housner spectra by up to 10% in the period range from 0.7 second to.25 second and the vertical Housner spectra by up to 10% in the period range from.05 second to 0.15 second. The NRC requested that we provide additional information related to the seismic safety margins in structures, systems and components considering these 10 percent exceedances of the Housner spectra.
The enclosure to this letter provides a detailed evaluation of the seismic safety margins in the seismic reevaluation program for San Onofre Unit 1. Based on the information in this report, it is concluded that the margins are adequate and the previous analyses will not be impacted by the exceedances of up to 10% over the specified period ranges.
Based on this conclusion, it is SCE's intention to continue to utilize the 0.67g Housner response spectra for the seismic reevaluation of San Onofre Unit 1.
If you have any questions on any of this information, please let us know.
Very truly yours, Enclosure 7
6208180113 820816 PDR ADOCK 05000206 P
SAN ONOFRE NUCLEAR GENERATING STATION UNIT 1 SEISMIC SAFETY MARGINS WITH RESPECT TO THE 84TH PERCENTILE INSTRUMENTAL SPECTRUM AUGUST, 1982
TABLE OF CONTENTS 1.0 Introduction 2.0 Overall Effect of 10 Percent Exceedances of the Housner Spectrum 3.0 Responses to NRC Request for Additional Information 4.0 Conclusions 5.0 References Appendix
1.0 INTRODUCTION
This report describes the results of an evaluation of seismic safety margins and generic conservatisms in the seismic reevaluation program for San Onofre Unit 1. This evaluation was performed for the purpose of determining the significance of possible increases of up to 10 percent in the.67g Housner response spectrum in the period range of 0.07 to 0.25 second for the horizontal direction and in the period range of 0.05 to 0.15 second in the vertical direction. The report contains specific responses to four items included in a request for additional information which was enclosed in a letter from D. M. Crutchfield to R. Dietch dated April 5, 1982.
Section 2.0 provides a discussion of the overall effects of 10 percent exceedances of the Housner Spectrum. Section 3.0 contains the responses to the four specific items included in the request for additional information. Section 4.0 describes the conclusions of the report.
2.0 OVERALL-EFFECT OF 10 PERCENT EXCEEDANCES OF THE HOUSNER SPECTRUM This section -provides a discussion of the nature of the possible exceedancesof the-Housher design--spectra oyer the specifiedperiod
-.,ranges.: Specifically, the magnitude of the exceedance :as a function of damping and. the shape of the exceedance are discussed.. In addition, overall' margins in.
the seismic reevaluation allowable stresses are addressed.
- a.
Magnitude of the Exceedances In the ree aluation of the San Onofre Unit 1 structures, the damping values used were17 percent 2fdr reinforced concrete structures, 7 percent for bolted and/or riveted steel structures and 4 percent for welded steel.structures.
Newmark and Hall )(Reference 1) recommend 7,to 10-percent damping for reinforced concrete 'structures, 10 to 15 percent damping for bolted and/or riveted steel with-bolted joints, and 6 to 7 percent damping for welded steel structures, at or just below the yield point.
Reference 2 states that the upper levels are-considered to be average or slightly-above average val.ues,.and are acceptable for evaluation of existing structures. -A compar son of-the SONGS'1 damping values with those.recommended in Reference 1 shows the conservatismof the damping values, and thus the response
-parameters, used in.
the reevaluatioh of structures, systems and components
.This factor 'alone would indicate that there is considerable margin in the seismic reevaluation program.
Soil structure'interaction effects tend to increase the equivalent
- composite modal damping vaimues of structures. fActual..
values of up to 50% have been observed.. Therefore, the aforementioned critical damping values should be viewed-as the minimum damping associated with the structures..
References 3 through 5-indicate that the exceedance of the Holusner reanalysis spectrum.dicreases as spectral damping-increases for the 84th percentile instrumental spectrum predictions. -Therefore, based on the above discussions-which indicate high damping for structures at -San Onofre Unit 1, it is concl Uded that the exceedances will -be le s than 10 percent for the-dampi'ng values of concern for-Sn Onofre Unit 1 structures.
In addition, this-implies that any increases-in the structural response parameters ised for-the evaluatioh of systems and &omponents-due td exceedances of, the 84th percentile predictions-will 'also' beh lss than 10. percent.
- b. Shape of the Exceedances Review of References 3"through 5 shows that'the 10 percent exceedances of the, Housher spectra will be similar to a bell 'shape.
These references would imply that the maximum exceedance of the horizontal Housner spectra-should be around 0.12 second tapering to zero towards.,the specified l.imits of 0.07 and 0.25 sec6nd.
This means fhat the magnitude of the exceedances can only approach 10 percent in the previously computed'response parameters, if all the modes of 'importance are clustered around the point of maximum exceedance. This is not the: case for SONGS 1 structures..
Therefore, the actual increase in theresponses will always be less than 10 percent.
The conclusions on the overall effects of magnitude and shape,of the exceedances 'on the previously computed seismic responses are summarized as follows:
a.-
The minimum damping, including soil-structure interaction damping, for structures is 4 percent. Actually:' values up to 50 percent have been observedin certain cases.
Since"exceedances 6f'the Housner spectrum are less for higher dampings it is cohcluded that the actual increases for structures wiIl be less than 10 percent.
be Similarly, the increase, if any, in the sei'smic input to systems and compohents supported by structures will be less than 10 percent.
- c. The fundamental periods of-the struptures at SONGS 1 are higher than 0.12 second.
Therefore, no structure will actually see a 10%
-increase in response.
- d.
The only items which could conceivably be affected by as much as 10%
exceedances-of the.Housner spectrum are items whicfh are supported on the, ground 'with'periods around. 0.12 second, at the peak of the exceedance range.
The increase will' be. less than 10 percent for itemns 'having different periods-.
Therefore, the overall effect of the 10 percent exceedances is minimal in almost all cases.
Furthermore, most allowable stresses have safety margins*of at least 2, and sometimes 3,or more, against failure.
Therefore,. in the-few cases where the calculated stresses 'might approach or exceed the allowable limits as a result of the small -exceedances, it is concluded that the likely result (not taking credit for any other.
conservatisms) would be'to decrease the already large safety factors by a small amount.
3-
It can be concluded, based on just these considerations, that the seismic safety margin in structures, systems and components are adequate, considering up to 10 percent exceedances of the horizontal Housner spectra in the period range from 0.07 second to 0.25 second and.of the vertical Housner spectra in the period range from 0.05 second to 0.15 second. However, in the responses to the specific NRC questions in Section 3.0, the seismic safety margins of structures, systems and components were evaluated on a case by case basis. In spite of the above discussions, these evaluations were based on the following conservative assumptions:
- a. The 10 percent exceedance of the Housner spectra was assumed to apply to all spectral damping values.
- b. The 10 percent exceedance was assumed to be equal over the period range of 0.07 to 0.25 second for the horizontal Housner spectra and over the period range of 0.05 to 0.15 second for the vertical spectra.
- c. Where reviewed, the previously computed responses of structures, systems and components were increased by 10 percent assuming that all modes of importance will fall into the specified period ranges.
- d. The previously calculated design loads other than seismic forces were also increased by 10 percent.
3.0 RESPONSES TO NRC REQUEST FOR ADDITIONAL INFORMATION 3.1 Question 1:
Describe for each structure the effects of this increase in response spectra on the loadings (moments, shears, and bucklings, etc.), stresses and displacements which were calculated using linear elastic analysis and justify their adequacy.
Response 1:
The seismic safety margins of structures were evaluated on a case by case basis as discussed above. Since all conceptual modifications identified in previous reports are being installed during the current outage, this basis is reflected in these evaluations. In addition, the changes in the seismic safety margins of the elements of structures (walls, slabs, beams, etc.) which considered the ductility concept are also addressed herein, rather than in response to question 2.
Fuel Storage Building The results of the evaluation of the fuel storage building were provided in Reference 6.
The seismic input used in the reevaluation of the fuel storage building envelops the 10 percent exceedances of the Housner design spectra.over the specified period ranges. Thus, the margins associated with the seismic response of this structure will not be affected.
The details of the comparisons of the input are presented in response to question 3b, which addresses the masonry walls of the fuel storage building.
Diesel Generator Building and Sphere Enclosure Building The design response spectra which were employed for the design of the diesel generator building and sphere enclosure building were the SONGS 2 and 3 design spectra (Reference 7).
These spectra conservatively envelop the 10 percent exceedances of the Housner design spectra over the specified period ranges. Thus, the margins associated with the responses of these structures will not be affected.
Ventilation Equipment Building The results of the reevaluation, including the safety factors for the structural elements, of the ventilation equipment building were provided in Reference 8.
The safety factors in Reference 8 were reviewed to determine the effect of increasing the previously calculated forces by 10 percent.
The minimum safety factor was computed to be 1.13 at an east-west masonry shear wall.
Thus, the margins associated with the responses of the ventilation equipment building will not be affected by the 10 percent exceedances of the Housner design spectra over the specified period ranges.
Reactor Auxiliary Building, Circulating Water System intake Structure and Seawall The results of the reevaluation of these structures, including the safety factors for the structural elements, were provided in Reference 8.
For the reactor auxiliary building and the circulating water system intake structure the governing loading conditions applied to the external.
below grade peripheral walls and base slabs were due to seismic earth pressures and hydrodynamic pressures computed using the zero period acceleration (ZPA) of the ground design motion in accordance with Reference 9. Therefore, these structural components will not be affected by the 10 percent exceedances of the Housner design spectra over the specified period ranges. The governing loading condition on the below grade interior walls and floor slabs of these structures, as identified in Reference 9, is due to inertial forces and hydraulic pressures.
Since the fundamental frequencies of the internal walls and floor slabs are in the unamplified region of the response spectrum for 7 percent damping, the ZPA of the ground design motion is also applicable for the computation of the inertial forces for these members. Again the margins for these structures will not be affected by the 10 percent exceedances of the Housner design spectra over the specified period ranges.
Furthermore, since the ZPA was the applicable input for the evaluation of the intake structure, those elements which considered the reserve energy method to evaluate inelastic behavior will also not be affected.
For the seawall the governing loading condition was also due to seismic earth pressures and hydrodynamic pressures computed using the ZPA of the ground design motion in accordance with Reference 9. Therefore, the seawall will not be affected by the 10 percent exceedances of the Housner design spectra over the specified period ranges.
Turbine Building, Control and Administration Building The results of the reevaluation, including the safety factors for the structural elements of the turbine building and the control and administration building were provided in References 6 and 10, respectively.
The safety factors in References 6 and 10 were. reviewed to determine the effect.of increasing the previously calculated forces by 10 percent.
Of the over 500. individual stress parameters reviewed,.the onlyistructural elements..that could be affected by these 10 percent increases are shown in Tables 1 and 2.
For-the control and administration building'-the non-critical portions of the-building were not reviewed since it was concluded in Reference '10 that theresponse or" collapse of these structural members Will not impair the integrity orfunction of seismic category A structures, systems and components. In addition,.elements which considered the reserve energy method to evaluate inelastic behavior were included in the review.,
For the turbine building, elements which are being or have been modiffed are not li sted in Table 1 since the final design of the,modificati.ons considered at least a safety-factor of 1.3 on the computed seismic forces. Also not shown 'in Table 1"are west heater platform bolt connection BC1 and east heater platform bolt connections BC3.and BC4, which had a margin of less than 10% in Reference 6. These are not listed because a detailed review.of the calculations indicated that the previously reported safety factors.for: these connections were conservative-and that the actual safety factors will' be within the BOPSSR
-criteria in Reference 11 even when considering a 1U pe centincrease of the Housner spectra.
For.the control and admi-nistration building, structural elements which were evaluated using the instructure,response spectra were not listed in Table 2 since the seismic forces computed based on instructure-response spectra remain valid as discussed inrresponseeto question 4.
Specific elements in.this categ ich are identified in'Reference 10 as having a safety factor of 1.1 or less are reinforced concrete walls WC-c-d, WC-5-a, WC-6 ahd WC-8; reinforced concrete slabs 'SC-1, SC-4, SC-10 and SC-12; and.reinforced concrete beams BC-3, BC-i5 and BC-20.
Several additional elements with.safety factors of 1.1 or less in RefeTence 10 were shown,by further eva1uation to be acceptable.
Specificallywalls WC-C-c,'.WC-C-d, WC-7.5 and WC-D and. slabs SC-8 and SC-2 were found to be acceptable.
The decrease in the safety factors for the structural elements shown in Tables '1 an'd-2 are not cdrnsidered to be significant.
This conclusion is based on the discussion.s presented inSection 2-on the' overall effects of 10 percent exceedances of the Housner spectrum, on the conservative manner in whi-ch-the increase in the forces were calculated as'e'xplained
.in Section 2.0, and on the fact that such a limi-ted subset of the total elements of the structures hav e' even the potential 'for being-affected.
Containment Sphere and Reactor Structure The results of the reevaluation of the containment sphere and reactor structure were provided in Reference 12.
The fundamental modes of the structure are 0.29 second for the vertical direction and 0.27 and 0.28 for the horizontal direction.
These periods are outside the period ranges of the 10 percent exceedances of the Housner spectra and therefore these structures are not affected. In addition, in the analyses of the steel sphere, 4 percent modal damping was used without taking into consideration the possible increases in composite modal damping due to soil-structure interaction affects.
This fact ensures that additional margins exist for this structure.
Table 1 Turbine Buiding Safety Factors Based on Consideration of a 10% Spectra Increase Item Safety Factor
- 1.
North Extension Column B6 0.90
- 2.
North Extension Column D8 0.96
- 3. West Heater Platform Bolt Connection BC1 0.91 Table 2 Control and Administration Building Safety Factors Based on Consideration of a 10% Spectra Increase Item Safety Factor
- 1. Reinforced concrete wall WC-6 0.93 (Shear) above elevation 421-0"
- 2.
Masonry wall WM-A-n 0.91 (Shear) 4.7 (Bending Ductility)
- 3. Masonry wall WM-A-s 0.92 (Shear)
- 4. Masonry wall WM-8-a 0.87 (Shear) 4.9 (Bending Ductility)
- 5. Reinforced concrete beam BC-13 0.93 (Shear)
- 6.
Structural steel column CS-1 0.98 (Combined)
- 7. Connection TS 6 x 3 x 1/4 0.95 (Combined)
- 8. Connection 3/4 - Dia A307 bolts on insert plate 0.90 (Combined) 3.2 Question 2:
Describe for each of the structures, systems (e.g.,
reactor coolant loop), and-components, the effects of this increase in response spectra on the calculated loadings (moments, shears' and bucklings; etc.),
stresses and dis.placem ents when either a nonlinear.:analysis or an inelastic response spectrum analysis- (using ductility concept) was used to account for inelastic-behaviorand justify their adequacy.
Response 2:
The only structure analyzed usihg a nonlinear inelastic analysis was the fuel storage building' The seismic safety margin for this building are addressed in the.response to question 3b which evaluates the masonry walls of the fuel storage building.
The reserve energy method of analysis(with theelastic Housner spectra as input) was used td evaluate the inelastic behavior' of structuralicomponents. Thei sei smic-safety margins of these structural elemertsare'addressed in response to.
question 1.
Nonlinear analysis methods were used for the, evaluation of the reactor coolant loop.
The comparisons of the Housner ground spectra'and the spectra of :the two horizontal and the vertical design time histories used inthe evaluation of the reactor coolant loop are shown in :Figures 1 through 3 forK2-4 and 7 percent critical damping values.
Table 3 shows the average difference of. the spectra of the design time histories and the horizontal.Housner ;spectra in the period range from 0'.07 second to 0.25 second and the vertical Housner spectra in the period range from 0.05 second to 0.15 second.
The average differences over the, specified period ranges.were calculated considering the values at 20 specific periods. for the horizontal-spectra comparisons and at 18 specific periods for the vertical spectra comparisons.
It-is concluded that the spectra of the design time histories satisfactorily envelop the 10% exceedances 6f 'the Housner spectra over the.specified period ranges.
Thus the nonlinear evaluation of the reactor coolant loop will 'not be affected.
Table 3 Average Percent Envelope of Desi gn Time Histories.
Used in Analysis of Reactor Coolant Loop Direction Percent Spectral Average Percent Dampiing Envelope Horizontal 2
24.7 (Trace A) 4 29.9 7
19.3 Horizontal 2
25.9 (Trace B)
.4 25.6 7
13.9 Vertical-2 14.7 4
29.6 7
27.2 3.3 Question 3:
Describe the effects of this increase in response spectra.on the calculated loadings (moments, shears,.and buckling, etc.), stresses and displacementsiof masonry walls Where nonlinear inelastic analyses were used. Justify that the integrity of these walls would not be compromised and equipment supportedby or penetrating through these walls.:,would not be adversely affected by the increase in response spectra.
Response 3:
a)
Turbine Building, Ventilation Equipment Buildinhg and Reactor.,
Auxiliary Building The details of the.nonlinear inelastic analyses of the masonry walls was presented in Reference 13.
References 14 and 15 address the
_criteria and the analysis methodology, respectively.
The Design Basis Earthquake, motion used to evaluate.the masonry walls was the Housner response spectrum-normalized to 0.67g.
Earthquake acceleration records-compatible-with this design spectrum were required-for the nonlinear inelastic analysis.
The-Housner:'
spectra is a-composite smoothed spectraderived from the horizontal.
components of the El Centro.1934, El Centro 1940, Olympia 1949 and Taft 1952 earthquakes.
Therefore, the time histories for analysis.
of the masonry walls were developed using the following steps:
- 1.
Each horizontal component for-the four earthquake events was scaled to have an equal spectrum intensity to the Housner spectrum. This was achieved by computing a scale factor such that the area under the ze'ro damped velocity spectrum curve for the particular component was equal to the equivalent area under the Housner velocity spectrum.
The integration was cafried out over.the range of periods from 0.1 to:2.5 sedonds, where most of the earthquake energy input is-concentrated. The, acceleration time histories used were obtained from the records digitized, filtered and corrected by the Earthquake Engineering Research Laboratory at the California Institute of Technology (EERL).
- 2.
-Asingle peak of the scaled time history was raised to 0.67g to obtain the same zero period acceleration as,the normalized Housner response spectrum..
- 3.
The time histories so.obtained were used to produce 7,percent damped acceleration response spectra.
r.a
- 4.
These 7 percent damped spectra -were then compared with the Housner spectr m for the same damping.
13!-
- 5.
The three earthquake components which collectively enveloped the Housnercurve over the complete frequency range were selected for the inela tic anialyses.
These were:
EARTHQUAKE COMPONENT EERL SCALING DESIGNATION FACTOR El Centro May 18, 1940 S00E AOO1/SOOE 1.57 Taft July 21, 1952 S69E A004/S69E 2.90 Olympia April 13, 19.49 NO4W B029/NO4W 2.51 In Figure 4, the 7 percent.damped Housner spectrum is plotted together with the three.earthquake components listed above. It can be seen that the thY-ee components.clIectively envelop the Housner spectrum'throughout the frequengcy range of interest. It should also be noted that the El Centro May 18, 1940 SOOE.time history by itself almost 'completely enveldops the Housner 7 percent damped response spectrum and that the envelop of the three time-histories exceeds the Housner response spectrum by a substantial margin in the amplified region. of the spectrum (at some periods by nearly 100%).
In Figure 5 the 7 percent spectra of the time histories are plotted together with the Housner spectrum increased by 10 percent'in the period range from 0.07 second to 0.25 second. As shown, thbthree components collectively envelop the modi f ied Hqusner.spectrum
-throughout the.frequency range of fnterest'. Therefore, the calculated out-of-plane responses df the masonry walls will not increase due to the 10 percent exceedance of the horizontal ground design response. spectra..Since.:t-he-out-of-plane responses will not change, the-previously computed seismic input to the equipment supported'or penetrating through these walls remains valid. The..
effects of the combihed Yoadings are reflected in the conclusions of the response to Question. 1.
b)
Fuel Storage Building The details of the nonlinear inelastic analyses of the fuel storage buiilding, including the -masonry walls were presented in Reference 6.
The comoutation of the responses-was achieved, using a suite of scaled'earthquake records as shown in Table 4. The responses Were calculated usin'g a.horizontal' anda verti.cl model.
For the horizontal response analyses the horizontal components of each earthquake were applied simultaneously to the major axes of. the model.
The records were'then rotated 90 degrees relative to the mode. axis and the analyses were repeated for the same two components of the earthquake.
For the vertical response
-computations the vertical model was subjected to the vertical component of each earthquake. Table 5 summarizes the analyses performed.'
14-
In Figure 6 the 7 percent damped Housner spectrum is plotted together with the envelop spectrum of the six horizontal components of the earthquakes listed in Table 4. It can be seen that the six components collectively envelop the Housner spectrum throughout the frequency range of interest. Figure 7 shows the envelop spectrum together with the Housner spectrum increased by 10 percent in the period range from 0.07 second to 0.25 second. As is shown, the modified Housner spectrum is enveloped by the collective spectra of the horizontal components. Figures 8 and 9 show the 7 percent envelop spectrum of the three vertical components together with the corresponding Housner spectrum and the Housner spectrum increased by 10 percent in the period range from 0.05 second to 0.15 second, respectively. As is shown, the collective spectra of the vertical time histories envelop the modified region of the Housner spectrum in this frequency range. Therefore, the calculated out-of-plane responses of the masonry walls will not increase due to the 10 percent exceedance of the horizontal ground design spectra.
Since the responses of the masonry walls will not change, the previously computed seismic input to the equipment supported by or penetrating through these walls remain valid.
Table 4 Time Histories Used in the Fuel Storage Building Analyses EARTHQUAKE SCALING PEAK NO.
NAME COMPONENT FACTOR ACCELERATION 1
El Centro SOOE*
1.57 0.67 2
May 18, 1940 S90W 1.57 0.36 3
V 1.57 0.33 4
Olympia
-N04W*
2.51 0.67 5
April 13, 1949 S86E 2.51 0.70 6
V 2.51 0.23 7
Taft S69E*
2.90 0.67 8
July 21, 1952 N21W 2.90 0.45 9
V 2.90 0.30
- Principal component Table 5 Fuel Storage Building Analyses EARTHQUAKE TIME HISTORY APPLIED*
MODEL DIRECTION ANALYSIS MODEL NUMBER TYPE NS EW V
1 Horizontal 1
2 2
Horizontal 2
1 3
Vertical 3
4 Horizontal 4
5 5
Horizontal 5
4 6
Vertical 6
7 Horizontal 7
8 8
Horizontal 8
7 9
Vertical 9
- See Table 3.1 for earthquake time history designation 3'.4 Question 4:
Describe the effects of. this increase in free field response spectra on the floor response spectra that were used for the qualifications and/or analysis of wa 11s, piping, mechanical and electrical equipmentand justify that the walls, piping, mechanical and electrical equipment are
.adequately' designed.
Response 4:
The methodology used in the development of the instructure response spectra for the reevaluation and design of systems and components was provided in Reference 16.'.The following paragraphs discuss the effects of the 10 percent exceedances of the Housher' design' spectra over the specified period ranges on the instructure response spectra.
Reactor Building, Administration and Control Building, Ventilation Equipment.Building, and Turbine Bui din.g The comparison of the horizontal Housner design,spectra and the spectra of the 'design time-history used in developing instructure response spectra is shown in Figure 10,for..2, -4, 7 and 10 percent critical damping VaTIes. The comparison of the vertical design time history is identical.
since it is taken as 2/3of the horizontal design time history.
Table 6 shows the average difference of the spectra of the design time history and the horizontal Housner spectra in the period range from 0.07 second to 0.25 second and'the vertical. Housner spectra in the period range from 0;05 second to 0.15 second.
The average difference values in the specified period ranges were calculated considering the values at 31 specific'periods for-the horizontal.pectra comparisons and at 25 specific periods for the vertical spectra comparisons.
Table 6 Average Percent Envelope of Design Time History Used to Develop In' Structure Response Spectra Percent Spectral
.'Average Percent Direction Damping Envelope Horizontal 2
15.5 4
17.9 7
9.7 10 8.0 Vertical 2
14.3 4
'11. 1 7
7.0 10 5.7
- As may be.seen, the spectra of the design time history conservatively envelop the Housher spectra. :The margins decrease-for higher damping values, especialy.in.the vertical.direction. However, the overall effects,of exceedances of the.Housner spectrum by up to 10%.are-not considered to bei'significant because the spectra of the design time history-are within a few percent of these exceedances and because of the conservatisms discussed below for: the evaluation of'sys'tems and components.
.Fuel Storage Building The response to question 3b showed that the collective spectra of the time-hi-stories used for the development of' instructure response spectra for this:building conservatively enveloped the10 percent exceedances in the Housher spectra.
Therefore, the finstructure response_:spectra for this structure will not be affected.
Reactor Auxiliary Building,.Circulating Water Intake Structure,
.Nonstructural Slabs and Equipment oundations, at.Grade.
The instructure response spectra -for these structures were the Housner ground design spectra as described in Reference 16.
The 10 percent exceedances in the.Housner ground spectra Will exceed-the instructure spectra ;bythe same percentage.
The overall effects of exceedances of the Housner spectrum by up to 10 percent on the evaluation of systems and components are notconsidered to be significant..,This was discussed in detail in section 2.
The following specific considerations are also applicable.
.a) In the evaluation of electrical raceways and electrical equipment anchorages an. equivalent static load-method of analysis,'was used.
For a large number of these items,the peak spectral value increased by 1.5 was selected as the seismic coefficient for the analysis.
For rigid equipment the ZPA of the ground.design spectrum 'was used.
Therefore, these items, which represent the majority of items at ground level, will not be affected by 10 percent exceedances of the, Housner spectrum.
b) Where modifications for piping supports are required, the final design of the supports considers a factor of 1.15 on all the loads computed. Therefore,,. the margin is sufficient to allow for 10' percent exceedances of the. Ho.usner Spectrum.
c)
Damping values used at San Orfofre Unit 1 for the.;evaiuatidn of piping and equipment are conservative as discussedin the Appendix.
For example, the majority of the piping 'at San Onofre Unit 1 is less than 12" and 2.percerit critical damping was used in the evaluation.
References 1 and 2 suggest that a damping value of 3'percent is more appropriate, although an even higher value could be considered as discussed in the Appendix. Assuming that the amplification due to damping of ground design.motion is proportional to the square root of the damping, one obtains a margiJn-of 1.2 when using. 2 percent critical damping.
This ould be sufficient to'allow for 10 percent exceedances of the Housner spectrum.
d) The majority of fundamental structural frequencies-are notin the period i.ntervals where the maximum exceedances are expected to occur.
20-
4.0 CONCLUSION
S Based on the previous discussions the following specific conclusions can be made about the seismic, safety margins<of str ctures, systems and components with respect to 10 percent e-ceedances.of the Housner design spectra over the specified period ranges:
- 1.
Almost all structural analyses are unaffected by the increase over the Housner spectrum. In only alimited number of.cases Were items identified which even have the potential to be affected by increasing the previously calculated forces by 10 percent. Since
.most allowable stresses have safety margins of at least 2, and sometimes.3 'or more,-against failure, it is concluded that this would only decrease the already large safety factors by a [small amount in those few cases where the calculated stresses could exceed
-the allowable limits.
- 2.
The seismic input to the majority of systems and components are the instructu e response spectra which are developed using synthetic time histories which cbnservativelyienvelop the Housner spectra.
The majority of.fundamental structural frequencies are not in the period intervals where maximum exceedances-are identified. For items using ground spectra as input, the, analyses of the majority of the items.incorporate conservatisms which wouldaccommodate the exceedances.
It is concluded that the.seismic safety margins in structures, systems and components are adequate, considering up to 10 percent exceedances of the horizontal Housner spectrja in the period range from 0.07 second to 0.25 second and, of the vertical Housner spectra in the period range from 0.05 second to 0.15 second.
5.0 REFERENCES
- 1.
N. M. Newmark an'd W. J. Hall "Development of Cr teria for Seismic Review of Selected Nuclear-Power Plants",, U.S.
Nuclear Regulatory Commission, NUREG/CR-0098.(1978).
- 2. "Recommended Revisions'to Nuclear Regulatory Commission Seismic Dedign Criteria", Lawrence Livermore Laboratory, University. of California, NUREG/CR-1161, May 1980.
- 3.
"Development of Instrumental ResponselSpectra, for the'SanOnofre Site", Woodward-Clyde Consultants, June 1982..
Forwarded by letter from K. P. Baskin to D. M., Crutchfield.dated June 29, 1982.
- 4.
"Estimation of Selected. Spectral Values at the San Onofre Nuclear.
Generating Station", Tera Corporation, June 1982.
Forwarded by letter from K. P. Baskin to D. M.. Crutchfield dated June 29, 1982.
- 5. Letter from K. P. Baskin to D. M. Crutchfield dated August, 9, 1982.
- 6. Enclosure to letter from K. P. Baskin (SCE) to D. M. Crutchfield (NRC) dated April 30, 1982.
- 7.
Final Safety Analysis Report, San Onofre Nuclear Generating Station, Units 2 and 3.".
- 8.
Enclosure to letter-from K. P. Baskin (SCE) to 0. M. Crutchfield (NRC) dated December 8, 1981.
.9. "Balance of Plant (BOP) SONGS Unit 1 Soil Structure Interactiion Methodology Report" Rev.
1, July 20, 1978, Woodward-Clyde Consultants, Orange, Cal ifornia.
- 10. Enclosure to letter from R.. W. Kri eger (SCE) to D. M. Crutchfield (NRC) dated February 9, 1982.
- 11.
"Balance of Plant Structures Seismic Reevaluation Criteria" San Onofre Nuclear Generating Station, Unit 1, February 17, 1981.
- 12.
"San Onofre Nuclear Generat.ing Station, Unit 1, NRC Docket 50-206, Seismic Reevaluation and Modification", April 29, 1977.
- 13.
Computech Engineering Serv ices, Inc., San Onofre Nuclear Generating.;
Station Unit 1, Seismic Evaluation of Reinforced Concrete Masonry Walls, Volume 3:
Masonry Wall Evaluatioi", forwarded by 1etter from K. P.. Baskin to D. M. Crutchfield dated January 11, 1982.
22-
-14. Computech Engineering.Services, Inc., 'San Onofre Nuclear Generating Station Unit 1, Seismic-Evaluation of Reinforced Concrete Mahonry Wa ls, Volume. 1: ',Criteria", forwarded by letter from K. P. Baskin.
to D. M. Crutchfi 0d dated January 15, 1982.
- 15. Computech Engineering Services, Inc., "San Onofre Nuclear Generating Station Unit 1, Seismic Evaluation of Reinforced Concrete Masonry Walls, Volume 2:
Analysis Methodology", forwarded by letter from K.
P. Baskinito D. M. Crutchfield dated January 11, 1982.
- 16.
"Balance of Plant Structures Seismic Reevaluatioh Instructure Response Spect'ra:
San-Onofre Nuclear Generating Station Unit 1" July 1982. Forwarded by letter from K. P. Baskin (SCE) to 0. M.
Crutchfield dated July 9, 1982.
a nsberry: 5163 a i 23-
PERCENT OF/
CR!TICAL DAMPING
~
~
-l 4 1:
F I I
GROUND-MOTION
- SPECTRA, HORIZONTAL TRACE A (MAXI LLY ACCELERATION 0.67g)
200 20 PERCENT OF CRITCAL DAMPING PE DD (scs F2GURE I
Y C
(
AL I
4 4V X
2 6B 0 OE2 A
E 6 1
2 4
6 610 2
PERIOD (secs)
FIGURE "2
GROUND-MOTION SPECTRA, HORIZONTAL TRACE B (MA.XIl~7M ACCELERATION 0. 67g)
40^
400 200 0
so PE C NT OF 0
0:CRITICAL AMPING 80 0
0
\\
2 8
02 PERIOD (secs)
FIGURE
3 GROUNDl-MOTION SPECTRA, VERTICAL (KAXIM'M ACCELERATION 0.44gX
LEGENO HOUSNER ELC40-SOO-
.5-------
LY49-NO4W 1.25
- - - - TFT52-S69E 76~ ~
itoo 75
.5 0
.25
.00 IT 0.1 1.0 10 100 FREoi/ENCY (Hz)
F 19UI 4
COuPAAI1 2^1 F^TIfUAKF* WITH HOUSNER
LEGEND 4.-
MODIFIED HOUSNER
. j.
ELC4O-SOOE 0Y49-N04W 1.2 5 I.00 75 r-
.25 EL4-S00E..
II OY49-NO4W
'0
~
TF5-S69E-I 0.1.
_0 C
FREQUENACY (Hz)
FN--a-t-cra.narner..
LFGEND I I SEISMIC ENVELOPE HOUSNER.87G 2.50 2.00 1.50 1.00
.50 0.1 1.0 10 100 FIGURE!6 HORIZONTAL COMPONENT 7% ENVELOPE SPECTRUM FOR FUIEL STORAGE BUILDING
SISMIC ENVELOPE MODIFIED HOUSNER 150 2.00
.50
.0 0 I_
0.1
.o 100 FIGURE HORIZONTAL. COMPONENT 7%. ENVELOPE SPECTRUM FOR FUEL STORAGE BUILD)ING
DRIIf HNd I'M II II J
I 1.11~~~~--
-~
~~
4-- 1 FIGURE \\8 VERTICAL COMPONENT 7% ENVELOPE SPECTRUM FOR FUEL STORAGE BUILDING
)m
.ri-08N I I AI1 IWe OR 11"A
- f.
K1W,1 111 I t JI ( l r I FIGURE 9-1VERTICAL COMPONENT 7% ENVELOPE SPECTRUM FOR FUEL STORAGE BUILDING
'oc 4c 0g S3
)
4 6
.8 1 2
4 6
8 10 2
PE RK POOam)
FIGURE
.10 DESIGN TIME HISTORY RESPONE SPECTRUM
APPENDIX RATIONALE FOR THE SPECIFICATION OF STRUCTURAL DAMPING FOR SONGS 1 SEISMIC REEVALUATION
RATIONALE FOR THE SPECIFICATION OF STRUCTURAL DAMPING FOR SONGS I SEISMIC REEVALUATION I.
INTRODUCTION Nonlinearities below the threshold of overall elastic structural response have been found to dissipate significant energy.
Energy absorption below elastic limits is represented through structural damping. For convenience, structural damping is typically approximated assuming It is viscous/velocity dependent and is expressed as a percentage of critical damping.
Structural damping represents a complex physical process that depends upon the properties of the material, the magnitude of internal and applied stress, the stress history and stress frequency.
The geometric configuration, boundary conditions, joint slippage, gaps, and friction play an important role.
The appropriate specification of structural damping in the seismic evaluation of nuclear power plant structures, systems, and components is an important consideration because it is a determining factor in how well linear elastic dynamic analysis can approximate experimental results and observations. His torically, structural damping has been specified with conservatism.
This has been in part due to a lack of data and also an attempt to deal with the dispersion data.
Current regulatory guidance embodied in Regulatory Guide 1.61 present damping values which should be considered conservative lower.bounds.
These damping values are suitable for use in the design of new facilities in the absence of real data. Over the years, more data has become available both experimentally and through observations during actual earthquakes. Accordingly, many earthquake engineers have recommended the use of higher structural damping values to more accurately represent the response behavior of structues.
The following discussion focuses on a summary of existing structural damping data for nuclear facilities and components, an evaluation of the data, recommen TERA CORPORATION
dations by experts, a rationale for the specification of damping values for seismic reevaluation for SONGS 1, and an estimate of margins associated with a conservative specification of structural damping values.
II.
SUMMARY
AND DISCUSSION OF AVAILABLE DATA The initial vibration tests of nuclear facility structures, systems, and compo nents were conducted in the mid-1960s.
These tests, along with limited data taken during actual earthquakes, have provided valuable insight into parameters such as structural damping which cannot be directly calculated. The vast portion of available data has been measured at relatively low response levels
(
0.1 x Yield for Components and Piping, 0.25 x Yield For Concrete Struc tures). In view of the fact that structural damping mechanisms tend to increase in magnitude with increasing stress levels, damping anticipated at stress levels corresponding to that of the design earthquake are generally unknown because structural elements have not been stressed to this degree. Several investigators have suggested means of extrapolating the low level data to higher levels. While these estimates are largely unconfirmed, they are supported by observations of structural response during actual earthquakes. It follows that direct utilization of available data is generally conservative for the seismic response modeling of nuclear power facilities.
A search of available nuclear facility experimental and observed data was performed.
This data was collected at the facilities listed in Table I.
A summary comparison of this data with current regulatory requirements and various recommendations by the technical community is presented in Table 2.
From these data, it is evident that recent recommendations made by Newmark and Hall in NUREG/CR-0098 and experts providing input to the NRC's Task Action Plan A-40 in NUREG/CR-1161 are conservatively based. Notwithstand ing the fact that these experimentally measured data are taken at low response leveli, a significant portion meets or exceeds the expert's recommendations. Of particular interest are measured data that have been normalized to a 0.9 yield stress level which corresponds to that expected during a design earthquake 2
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(Item 4, Table 2).
This. estimate is believed to be more realistic for higher response levels and would more accurately reflect the true seismic response during the design earthquake.
The NUREG/CR-0098 and NUREG/CR-1161 recommendations tabulated under Item 2, Table 2, are considered to be conservative median damping values.
NUREG/CR-1706,. Subsystem Response Review, characterizes the associated logarithmic standard deviation to be 0.4. This corresponds to a 16% and 84%
exceedance range of 1.49 and 0.67 times the median, respectively. Accordingly, the one standard deviation ranges expressed in terms of percent critical damping would be:
piping 2-4.5%
mechanical components 4.7-10%
concrete structures 6.7-15%
The higher end of the above ranges more closely agrees with the estimates presented in Item 4, Table 2, with the exception of piping. It is expected that in addition to loading magnitude and history, piping damping estimates would be extremely sensitive to parameters such as geometry, support configuration, flooding, and insulation. Therefore, while the 12.7% estimate of Item 4, Table 2, may be valid for the sample, in the absence of site specific information its use may be slightly unconservative.
Item 14 in Table 2 is worth noting, in that it reflects data for SONGS I recorded from both historical earthquakes (San Fernando and Lytle Creek) and tests, typically at very low response levels.
For the higher levels of response associated with the design earthquake, these values are expected to increase to levels consistent with those suggested in the following section.
Vibration tests of large bore piping at the Heissdampfreaktor (HDR) suggest that a damping of 7% for piping is required to obtain agreement between analytical predictions and experimental data.
Data collected at Kernkraftwerk/Phillippsberg I and Fugen further support piping damping in the range of 6 to 9% for both large and small bore piping.
3 TERA CORPORATION
Ill.
BASES FOR THE SPECIFICATION OF STRUCTURAL DAMPING VALUES FOR REEVALUATION OF SONGS I The philosophy of the Systematic Evaluation Program is based upon application of a median centered, yet conservative methodology for the evaluation of many design basis events (The seismic event is considered a DBE).
The intent is to conduct a more realistic evaluation to represent and explain response behavior without stacking up conservatisms at each stage in the process. The approach recognizes the conservatism associated with current licensing criteria and practical considerations for evaluating and possibly backfitting older facilities.
Decisions relative to required levels of conservatism are made during an integrated assessment of all DBEs at the end of the review. Accordingly, the NRC's SEP seismic review process has attempted to more realistically quantify unclaimed factors such as structural damping which contribute to seismic resistance capability. Clearly, the mode has been to consider median centered parameters in the review process rather than bounding values which are common in the review of new plants.
The NRC has adopted NUREG/CR-0098 criteria for the SEP seismic evaluation.
The damping criteria of this NUREG is supported by recommendations of NRC consultants participating in TAP A-40 (NUREG/CR-II61).
Conservative, median damping values have been considered in the ongoing SEP reviews corresponding to the values tabulated in Item 2, Table 2. Notwithstanding this, the SONGS I seismic reevaluation program has considered damping values which correspond to the even more conservative values specified in Regulatory Guide 1.61 (Item 1, Table 1).
It follows that significant margin exists between the NUREG/CR-0098 and Regulatory Guide 1.61 values. Even further margin can be justified in consideration of the data presented in Section 11.
During a large seismic event, the stress in structural elements will vary throughout the plant. Higher stressed elements will dissipate relatively more energy.
On the average, this energy will approach a level that can best be represented by a "median" damping value. In view of the higher seismic setting at the SONGS site, it can reasonably be assumed that a larger portion of structural elements will see higher stress levels.
Accordingly, it may be 4
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expected that damping would approach levels considered higher than a median level, approaching and possibly exceeding the values presented in Item 4, Table 2.
It is believed that the NUREG/CR-0098 damping values (Item 2, Table 2) are conservative median values and that the one standard deviation values may more closely approximate a "true" median. Accordingly, in consideration of the above points and the previously discussed piping data, it is suggested that the following damping values used in conjunction with an appropriate analysis may more accurately represent and predict the seismic response of SONGS I during a major earthquake:
piping 7%
mechanical components 10%
concrete structures 15%
IV.
SUMMARY
A review of existing structural damping data for nuclear facilities and components indicates that significant margins exist between the damping values used in the SONGS I reevaluation and those which would be expected to appropriately represent the seismic response of SONGS I during a major earthquake. While the exact margins attributable to damping conservatisms are a function of the specific structures, systems, and components of interest, the general use of Regulatory Guide 1.61 damping values for the seismic reevaluation of SONGS I represents a significant structural margin. According ly, any increases of loading could be offset by this factor as well as many others that have not been discussed, such as ductility and modeling considerations.
5 TERA CORPORATION
TABLE I NUCLEAR FACILITIES FOR WHICH STRUCTURAL DAMPING DATA HAVE BEEN COLLECTED Enrico Fermi Indian Point I and 2 Madras Atomic Power Project San Onofre Unit I Oak Ridge Experimental Gas-Cooled Reactor CaroIinas-Virginia Tube Reactor Rajasthan Power Project Diablo Canyon I Tsuruga Nuclear Power Plant Heissdampfreaktor (HDR)
Kernkraftwerk Fukashima I Shimane Fugen Hamaoka Humboldt Bay Enel IV Tokai UCLA Reactor Kuosheng 6
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TABLE 2 COMPARISON OF AVAILABLE NUCLEAR FACILITY EXPERIMENTALLY MEASURED DAMPING WITH REGULATORY REQUIREMENTS AND RECOMMENDATIONS Best Estimate or Median Damping Values
(% Critical)
Data, Requirement, Mechanical Concrete or Recommendation
> 12"0
<12"0 Components Structures R.G. 1.611 for stress levels at:
- a. ~ 0.5 yield (OBE) 2 I
2 4
- b. ~ 0.9 yield (SSE) 3 2
4 7
- 2.
NUREGS/CR-0098 2, CR-I 1613 for stress levels at:
- a. ~ 0.5 yield 2
2 3
5
- b. at or just below yield 3
3 7
10
- 3.
Average of measured data for 3.4 6.2 3.8 5.2 stress levels at or less than (n=4)
(n=2)
(n=35)
(n=31) 0.1 x yield for components and piping and 0.25 x yield for concrete4 (n = sample size)
- 4.
Measured data from (3) 12.7 7.7 I8.7 normalized to 0.9 yield stress4
- 5.
Heissdampfreaktor (HDR)
- a. measured5,6,I I,12 5.5
<52.0
- 57.1 (0.06g)
- b. inferred by analysis7 7
(Reactor Vessel)
- 6.
Laboratory tests of small bore piping for stress levels at:
- a. ~ 0.5 yield (2"OD)
I-2(2"OD)
- b.
- 0.9 yield 12('"OD) 2-36(2"OD)
- 7.
Diablo Canyon4 3-15 h-15
- 8.
Indian Point 1&24,10 1-5 2
1-5 (Stress -
0.2 yield)
.7 TERA CORPORATION
TABLE 2 (continued)
Best Estimate or Median Damping Values
(% Critical)
Data, Requirement, Piping Mechanical Concrete or Recommendation
> 12"0
< I2"O Components Structures
- 9.
Kernkraftwer69 Phillipsberg I 6-9
- 10. Fukushima 5-8(10 g)
- 11.
Fugen 15 6-8
< 4.5 (0.1g)
(0.02g)
- 12.
Hamaoka 16 20(10-3)
(Str.-Str. Int.)
- 13.
Tokai 219 15-20
(.0 I g)
(Soil-Str. Int.)
- 14.
SONGS 117,18,20,21 1.5-4.0 3-9*
6-20 (10- 2-10-1g)
(Soil-Str. Int.)
1-2.5 (IO-4-10-3g)
- 15.
Kuoshena Nuclear Power 1.5-9 Station22
- Based on data recorded from actual earthquakes.
8 TERA CORPORATION
REFERENCES
- 1.
U.S. NRC Regulatory Guide 1.61, "Damping Values for Seismic Design of Nuclear Power Plants," October 1973
- 2.
NUREG/CR-0098, "Development of Criteria for Seismic Review of Selected Nuclear Power Plants," N. M. Newmark and W. J. Hall for the U.S. NRC, May 1978
- 3.
NUREG/CR-1161, "Recommended Revisions to Nuclear Regulatory Commission Seismic Design Criteria," Lawrence Livermore Laboratory, May 1980
- 4.
J. D. Stevenson, "Structural Damping Values as a Function of Dynamic Response Stress and Deformation Levels," paper K I I/I, 5th International Conference on Structural Mechanics in Reactor Technology (August 1979)
- 5.
HDR Test Program "Quick Look" Data Report; Containment Testing Performed in November 1979, prepared for the U.S. NRC, ANCO Engi neers, March 1980
- 6.
Memorandum from ANCO Engineers to U.S. NRC, "HDR Summary Report for NRC," ANCO Engineers, February 8, 1980
- 7.
NUREG/CR-1913, HDR Response-Experimental and Analytical, prepared for U.S. NRC, EG&G Idaho, Inc., February 1981
- 8.
WCAP-7921-AR, Damping Values of Nuclear Power Plant Components, Westinghouse Electric Corporation, May 1974
- 9.
ANCO Report I122-48, Vols. 1-9, "Vibration Tests of Equipment at the Diablo Canyon Nuclear Power Plant" (Prop.) 1978 TERA CORPORATION
- 10.
WCAP 7920, "Indian Point No. 2 Primary Loop Vibration Test Programs,"
B. E. Olsen, et. al., Westinghouse Electric Corporation, September 1972 I1.
Jehlicka, P., et. al., "Low-Level Earthquake Testing of HDR - Comparisons of Calculations and Measurements of Reactor Building," 5th SMIRT Conference, Paper K 13/2, August 1978
- 12.
Jehlicka, P., "Low-Level Earthquake Testing of HDR, Comparisons of Calculations and Measurements for Mechanical Equipment," 5th SMIRT Conference, Paper K 13/3, August 1978 I 3.
ANCO Report 1098-2 (Prop.), 1976
- 14.
Paper K 5/3, 2nd SMIRT Conference, 1973 IS.
Paper K 13/8, 5th SMIRT Conference, 1978
- 16.
Mizuno, N., "Experimental and Analytical Studies for a BWR Nuclear Reactor Building; Evaluation of Soil-Structure Interaction Behavior," 3rd SMIRT Conference, Paper K 3/2, 1975
- 17.
"Vibration Testing and Seismic Analysis of Nuclear Power Plants," A special issue of Nuclear Engineering and Design, Vol. 25, No. 1, 1973
- 18.
NUREG/CR-1423, Vol. II, "Structural Building Response Review," prepared for U.S. NRC by Lawrence Livermore Laboratory, May 1980
- 19.
Proceedings of the 5th Japan Earthquake Engineering Symposium, Tokyo, 1978
- 20.
Ibanez, P., et. al., "San Onofre Nuclear Generating Station Vibration Tests," UCLA-ENG - 7037, August 1970
- 21.
Matthiesen, R.G., et. al., "San Onofre Nuclear Generating Station Supple mentary Vibration Test," UCLA-ENG - 7095, December 1970 TERA CORPORATION
- 22.
"Test Results, Mechanical Impedance Tests on Selected Components, Kuosheng Nuclear Power Station," prepared for EG&G Idaho, Transitek, Inc., April 1981 TERA COPPORATION