NOC-AE-000536, Submits Request for Exemption from Requirements of 10CFR50.34(b)(11),10CFR50,App A,Gdc 2 & 10CFR100,App a, Section VI(a)(3) Re Maint of Seismic Instrumentation.Revised Page to Procedure OERP01-ZV-IN01 Included
| ML20209H199 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 07/13/1999 |
| From: | Sheppard J HOUSTON LIGHTING & POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20209H204 | List: |
| References | |
| NOC-AE-000536, NOC-AE-536, STI:30871968, NUDOCS 9907200160 | |
| Download: ML20209H199 (23) | |
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saaneasa nexttkrocaneratingstri&w ra anzy masawer raas77tsi m July 13,1999 NOC-AE-000536 STI: 30871968 File No.: G20.01 10CFR50.12 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 South Texas Project Units 1 and 2 Docket Nos. STN 50-498, STN 50-499 l Request for j An Exemption From Seismic Instrumentation Reauirements The STP Nuclear Operating Company (STPNOC) submits this request for exemption from the requirements of 10 CFR 50.34(b)(11),10 CFR Part 50, Appendix A, General Design Criterion (GDC) 2, and 10 CFR Part 100, Appendix A, Section VI(a)(3) to the extent that they require the maintenance of seismic instrumentation. This request will not affect the design or ;
qualification of structures, systems or components to withstand the effects of earthquakes. l STPNOC's licensing condition for maintaining seismic instrumentation is specified in the Technical Requirements Manual. STPNOC's seismic instrumentation is described in Section 3.7.4 of the Updated Final Safety Analysis Report. Seismic instrumentation provides the capability to determine the magnitude of a seismic event and to evaluate the response of those l' features important to safety. This capability is required to permit comparison of the measured response to that used in the design basis of the facility to determine whether the plant can continue to be operated safely and to permit such timely action as may be appropriate pursuant to Appendix A of 10C"R100.
STPNOC is located in an area of very low seismioctivity. The STPNOC seismic design margins are documentedin the Updated Final Safety Analysis Report. STPNOC's Probabilistic Risk Assessment estimates that the risk of core damage due to a saismic event at the South Texas Project is not significant (i.e.,7.4 x 10E-8 per year), and the seistric instrumentation does not {
contribute to this low core damage frequency. The Operating Baris Earthquake (OBE) ground .
accelerations for STPNOC is 0.05g. The annual probability of exceedance of this acceleration level at the South Texas Project site is on the order of 5 x 10E4. Therefore, fie probability of an earthquake affecting f ac safe operation of the South Texas Project units is extremely low.
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, 4 NOC-AE-000536 File No.: G20.01 10CFR50.12 Page 2 The seismic instrumentation at the South Texas Project consists of equipment that is c.;
longer being manufactured, and that is becoming increasingly difficult and expensive to )
maintain.- As a result, STPNOC is considering replacement of this equipment. It has been )
determined, however, that the safety benefits of the seismic instrumentation are negligible at the South Texas Project and do not justify the cost of replacing this equipment. Since the probability of an earthquake affecting the safe operation of the South Texas Project units is extremely low, we believe alternative methods can be used to detect a seismic event and obtain information necessary for assessing whether the STPNOC units can continue to be operated safely. The proposed attemative methods result in no increase in risk and meet the principles of risk-informed regulation discussed in NRC Regulatory Guide 1.174, dated July 1,1998, "An Approach to Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific
= Changes to the Current Licensing Basis".
i This request is for an exemption from regulatory requirements regarding the maintenance 1 of seismic instrumentation. This request will not affect the design or qualification of structures, systems or components intended to withstand the effects of earthquakes. As a separate action, the South Texas Project is pursuing an exemption from special treatment regulatory requirements of 10CFR50 for components that are low safety significant or non-risk significant. This separate action proposes to eliminate the need to qualify low safety significant or non-risk significant components for seismic conditions among other equipment qualification conditions. The process proposed to eliminate seismic qualification requirements in this separate action is independent of the request for exemption from maintaining seismic instrumentation in this letter.
In addition and contingent upca approval of this exemption request, pursuant to 10CFR50, Appendix E, Section IV.B, the South Texas Project requests Nuclear Regulatory Commission approval for changes to be made to the Emergency Action 12vels that are used in classification of emergency conditions. These proposed changes in the Emergency Action Levels provide altemative entry requirements for declaration of the emergency. The changes do not decrease the effectiveness of the South Texas Project emergency plan and the plan, as revised, continues to meet the standards of 10CFR50.47(b) and the requirements of 10CFR50, Appendix E. The proposed changes have been presented to state and local authorities and they have provided their approval. The proposed changes are provided in attachment 2 to this letter.
The request for exemption from seismic instrumentation requirements is attached for the Nuclear Regulatory Commission's consideration. The South Texas Project commits to implement the shutdown criteria proposed in Appendix C to Attachment 1 of this letter contingent upon approval of this exemption request.
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NOC-AE-000536 File No.: G20.01 10CFR50.12 Page 3 If you should have any questions concerning this matter, please contact Mr. Ken Taplett at (361) 972-8416 or me at (361) 972-8787. ;
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J. J. Sheppard Vice President, Engineering & Technical Services KJT/
~ Attachments: 1. Request for Exemption from the Seismic Instrumentation Requirements of 10 CFR 50.34(b)(11),10 CFR Part 50, Appendix A, General Design Criterion 2 and 10 CFR Part 100, Appendix A, Section VI(a)(3)
- 2. Procedure OERP01-ZV-IN01," Emergency Classification"(revised pages only)
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NOC-AE-000536 File No.: G20.01 Page 4 Ellis W. Merschoff Jon C. Wood Regional Administrator, Region IV Matthews & Branscomb U. S. Nuclear Regulatory Commission One Alamo Center 611 Ryan Plaza Drive, Suite 400 106 S. St. Mary's Street, Suite 700 Arlington, TX 76011-8064 San Antonio,TX 78205-3692 Thomas W. Alexion Institute of Nuclear Power Project Manager, Mail Code 0-13 D18 Operations - Records Center U. S. Nuclear Regulatory Commission 700 Galleria Parkway Washington, DC 20555-0001 Atlanta, GA 30339-5957 Comelius F. O'Keefe - Richard A.Ratliff Sr. Resident inspector Bureau of Radiation Control c/o U. S. Nuclear Regulatory Commission Texas Department of Health I' P. O. Box 910 1100 West 49th Street Day City, TX 77404-0910 Austin, TX 78756-3189 J. R. Newman, Esquire D. G. Tees /R. L. Balcom Morgan, Lewis & Bockius Houston Lighting & Power Co.
1800 M. Street, N.W. P. O. Box 1700 Washington, DC 20036-5869 Houston,TX 77251 W. C. Gunst/M. T. Hardt Central Power and Light Company City Public Service ATTN: G. E. Vaughn/C. A. Johnson P. O. Box 1771 P. O. Box 289, Mail Code: N5012 ,
San Antonio,TX 78296 Wadsworth,TX 77483 A. Ramirez/C. M. Canady U. S. Nuclear Regulatory Commission City of Austin Attention: Document Control Desk Electric Utility Department Washington, D.C. 20555-0001 721 Barton Springs Road Austin,TX 78704 J
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ATTACHMENT 1 Request for Exemption from the Seismic Instrumentation Requirements of i 10 CFR 50.34(b)(11), l 10 CFR Part 50, Appendix A, General Design Criterion 2 and 10 CFR Part 100, Appendix A, Section VI(a)(3) 0:Wi"NL\NRC-WK\ MISC 99000536 h
Attachment i NOC-AE-000536 Page 1 of 9 Request for Exemption I
from the Seismic Instrumentation Requirements of 10 CFR 50.34(b)(11),10 CFR Part 50, Appendix A, General Design Criterion 2 and 10 CFR Part 100 Appendix A, Section IV(a)(3)
Pursuant to 10 CFR 50.12, STP Nuclear Operating Company (STPNOC) requests an exemption from the requirements of 10 CFR 50.34(b)(11),10 CFR Part 50, Appendix A, General Design Criterion (GDC) 2, and 10 CFR Part 100, Appendix A, Section VI(a)(3) to the extent that they require the maintenance of seismic instrumentation. This request does not affect the design or qualification of structures, systems or components to withstand the effects of eanhquakes.
Thus, except with respect to the seismic instrumentation, the South Texas Project will continue j to meet applicable design criteria and the requirements of 10 CFR 50.34(b)(11), GDC 2 of 10 CFR Pan 50, App. A and 10 CFR Part 100, App. A. ,
A. Background Appendix A to 10 CFR Pan 100 provides Seismic and Geologic Siting Criteria for Nuclear Power Plants (Siting Criteria). These criteria,in addition to addressing site suitability, also include in Section VI provisions on application of seismic and geologic information to engineering design.Section VI(a)(3) describes required seismic instrumentation. In accordance with the provisions of Section VI(a)(3) the South Texas Project has installed seismic instrumentation to measure the response of plant features to an earthquake, and has incorporated into its Technical Requirements Manual requirements for surveillance testing of this l instrumentation.
10 CFR Part 100 does not explicitly require licensees to comply with the Siting Criteria. l Rather, the purpose of Part 100 is to establish approval requirements for proposed sites for stationary power and testing reactors. 10 CFR 100.1, "The Siting Criteria", however, cite GDC 2, and state that the purpose of the Criteria is to set fonh the considerations which guide the Commission in its evaluation of both site suitability and the suitability of the plant design basis.
Thus, the Siting Criteria provide considerations for assessing compliance with GDC 2. In addition,10 CFR 50.34(b)(11) states that the provisions of Appendix A to Part 100 apply to holders of opec. ting licenses for nuclear power plants.
The seismic instmmentation the South Texas Project installed m accordance with 10 CFR Pan 100, App. A,Section VI.(a)(3) consists of equipment that is no longer being manufactured, and it is becoming increasingly difficult and expensive to maintain. As a result, STPNOC is l
considering replacement of this equipment. Appendix A to this attachment provides a basic o WPWL\NRC.WK\ Misc-99 WOO 536
Attachment 1 NOC-AE-000536 Page 2 of 9 description of STPNOC's Seismic Monitoring System. We have determined, however, that the safety benefits of the seismic instrumentation are negligible at the South Texas Project and do not justify the cost of replacing this equipment. The estimated cost of completing the upgrade to the seismic instrumentation at the South Texas Project is $105,000 including engineering, procurement, installation, training and procedure changes. Recent maintenance history indicates the cost of maintaining the current seismic instrumentation at the South Texas Project to be on the order of $25,000 annually. A recent failure of the system cost the station approximately
$30,000. The cost of maintaining the upgraded equipment is expected to be less than the current maintenance costs yet a substantial cost nevertheless since surveillance testing and equipment performance monitoring would still be required as a minimum.
Instead of continuing to maintain the instrumentation, STPNOC proposes to rely on information readily available from the National Earthquake Information Center and correlate it with data obtained by a stand alone instrument maintained on site to assess the continued safe operation of the South Texas Project units. The South Texas Project would follow the Electric Power Research Institute " Guidelines for Nuclear Plant Response to an Earthquake", EPRI NP-6695, December 1989, for inspection and testing of plant equipment upon confirmation of an earthquake. This inspection and testing will assum that appropriate actions are taken in the unlikely event that an earthquake affects the South Texas Project. This approach is acceptable because (1) the South Texas Project is located in an area of very low seismic activity, (2) the plant incorporates adequate seismic design margins, (3) the Probabilistic Risk Assessment for the South Texas Project (STP PRA) estimas that the risk of com damage due to a seismic event at the South Texas Project is not significant (i.e.,7.4 x 10E-8 per year), and (4) the seismic instrumentation does not contribute to this low core damage frequency.
Instead of continuing to maintain the seismic instrumentation, STPNOC requests an exemption from the requirements for such instrumentation. No change or exemption is being proposed by this request regarding the seismic equipment qualification requirements in the South Texas Project's current licensing basis for structures, systems and components. Thus, the South Texas Project will continue to meet applicable design criteria, the mquirements of GDC 2 of 10 I CFR Part 50, and the mquirements in Part 100, including Appendix A, except for the j requirement of seismic instrumentation. J B. Reauest for Exemption 10 CFR 50.12(a) provides that the Commission may, upon application by any interested person or upon its own initiative, grant exemptions from the requirements of the regulations in Part 50, which are authorized by law, will not present an undue risk to the public health and safety, and am consistent 'with the common defense and security. Additionally, Section 50.12(a) states that the Commission will not consider granting an exemption unless special circumstances are present.
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Attachment 1 NOC-AE-000536 Page 3 of 9
- 1. The proposed exemption is authorized by law.
The Atomic Energy Act authorizes the Commission to grant exemptions from the Commission's regulations. No law requires that nuclear power plants have seismic instrumentation installed at the facility. Consequently, the proposed exemption is authorized by law.
- 2. The proposed exemption will not present an undue risk to public health and safety.
The proposed exemption will not present an undue risk to the public health and safety since it involves monitoring equipment only which has no accident prevention or mitigation safe shutdown function. In addition, there am adequate attemative means to determine if a significant earthquake has occurred so that appropriate decisions can be made regarding the continued safe operation of the facility. The bases for these conclusions are discussed further below. Appendix B to this attachment provides information regarding the probability of an earthquake being felt at the South Texas Project site.
- 3. The proposed exemption is consistent with the common defense and security. ,
i The proposed exemption does not pertain to the security or safeguards plans. Therefore it does not have any affect on the common defense and security.
- 4. Special circumstances are present.
Section 50.12 identifies various bases on which the Commission may find that special circumstances are present, including (a) application of the regulation in the particular l circumstances would not serve the underlying purpose of the rule or is not necessary to achieve the underlying purpose of the mie ({50.12(a)(ii)); and (b) there is present any other material circumstance not considered when the regulation was adopted for which it would be in the public interest to grant an exemption (650.12(a) (vi)). If criterion (vi) is relied on exclusively for ;
satisfying the requirement for special circumstances, the exemption may not be granted until the Executive Director for Operations has consulted with the Commission. Both of these circumstances are present in this case, as shown below.
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Attachment 1 NOC-AE-000536 Page 4 of 9 Section 150.12(a)(ii) application of the regulation in the particular circumstances is not necessary to achieve the underivine purpose of the rule.
The underlying purpose of the requirement that nuclear power plants install seismic instrumentation is for use in deciding whether the plant can continue to be operated safely following an eanhquake and to provide information that will permit such timely action as may be appropriate. The exemption is consistent with this purpose. The requested exemption will not change the design functional requirements of plant systems. Information for timely decision-making will remain available. Information regarding the occurrence of an earthquake can be determined using altemative methods. Appendix C to this attachment provides a discussion of the alternative method that STPNOC plans to use in response to an earthquake in lieu of maintaining seismic instrumentation. At the South Texas Project, there is very little risk that an carthquake will affect the facility and the facility design incorporates seismic design margins. As a result, the risk that the South Texas Project will be adversely affected by an canhquake is extremely small. If an earthquake does occur, the purpose of Section VI(a)(3) of Part 100 can be achieved by inspection and testing of plant equipment.
Geotechnical analyses and research shows that the South Texas Project site is in a region that has very low seismic activity such that the occurrence of a Safe Shutdown Earthquake (SSE) is not considered credible. The design basis ground accelerations are based on conservative ,
I extrapolations of seismic activity in regions relatively distant from the South Texas Project that have greater seismic activity than the South Texas Project site. The extrapolation resulted in ground accelerations lower than the 10 CFR Part 100 minimum criterion. Since South Texas Project's design load ground accelerations are based upon the minimal criterion in Part 100 rather than the lower values extrapolated for the site, the South Texas Project has adequate seismic design margins.
The South Texas Project design basis for vibratory ground motion is defm' ed by a SSE having a maximum horizontal acceleration of 0.10 g. Engineering studies conservatively indicate a maximum horizontal acceleration of 0.07 g at the South Texas Project site. The 0.10 g acceleration for a SSE is adopted because this is the minimum ground acceleration in Appendix A of 10 CFR Part 100.
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4 Attachment 1 NOC-AE-000536 Page 5 of 9 The South Texas Project design uses an Operating Basis Earthquake (OBE) with a maximum horizontal acceleration of 0.05g (i.e., % the SSE). However, only three Intensity V Modified Mercalli canhquakes have been reponed within 200 miles of the site in the last 100 years and no earthquakes have been reported within 80 miles. Thus, the maximum earthquake reasonably expected within the site vicinity, based on historical records and geology, is an earthquake of Intensity IV to V modified Mercalli. Acceleration / intensity correlations show the maximum acceleration of an Intensity V modified Mercalli carthquake to be 0.035 g which would represent a reasonable OBE. However, to comply with Appendix A to 10 CFR Part 100, a minimum acceleration of 0.05 g (% of the SSE) was adopted for the OBE. (
Reference:
South Texas Project UFSAR, Section 2.5.1) Two earthquakes ofIntensity VI have been recorded in the South - Central Texas region, one in 1993 and the other in 1997 (see Appendix B). These earthquakes occurred at a distance of greater than 100 miles from the South Texas Project site and their felt area was relatively small and did not include the South Texas Project site.
The seismic design provisions of Appendix A to Part 100 incorporate conservatism to assure that nuclear power plants are designed with ample safety margins. The safety margins for seismic design of the South Texas Project exist because of the difference between the calculated acceleration due to an SSE and the minimum acceleration of 0.10 g required by Appendix A to Part 100. Based on these factors, and detailed analysis of the plant design, the STP PRA estimated that the core damage frequency associated with seismic events at STP is 7.4 x 10E-8 per year, which is an insignificant contributor to risk. Since the seismic instrumentation does not ,
help prevent or mitigate accidents, it is not considered in this estimate of core damage frequency.
In lieu of maintaining seismic instrumentation, Appendix C to this attachment provides criteria for determining the need for plant shutdown. For plant restart, appropriate inspections and surveillances of plant systems, structures and components would be performed. Electric Power Research Institute " Guidelines for Nuclear Plant Response to an Eanhquake", EPRI NP-6695, December 1989 would be used to determine a strategy for the appropriate inspections and testing. This approach is preferable to the requirement for seismic instrumentation because studies of seismic activity in the region of the facility indicate that there is a very low probability of an earthquake that could affect plant operation. In addition, the design criteria for the South Texas Project have resulted in an appropriate margin of safety.
1 Seismic instrumentation is not needed to determine whether an earthquake has occurred.
An canhquake of sufficient magnitude to have a potential to affect plant equipment will be sensed by plant personnel and the general population in the plant vicinity. Information about the o.WP\NL\NRC.WK\ MISC-PNK)0536
Attachment 1 i NOC-AE-000536 !
Page 6 of 9 earthquake magnitude and epicenter will be readily available from the National Eanhquake Resource Center. This information will be assessed against the proposed criteria in Appendix C to determine the need to shutdown the South Texas Project units in response to a seismic event.
A stand-alone instmment would be maintained to measure and record the generated response spectra. The capabilities of the stand-alone instrument are discussed in Appendix C to this attachment.
It is extremely unlikely that the South Texas Project will ever need to respond to a seismic event. The site, as described above,is in an area that, in terms of historical eanhquakes, "is one of the least active areas of the United States." (Ref: Safety Evaluation Report related to the construction of the South Texas Project, Units I and 2, NUREG-75/075, August 1975) Thus, it is highly unlikely that the South Texas Project will ever experience an eanhquake that could potentially impact the plant.
l For these reasons, alternative administrative controls proposed in Appendix C, and controls derived from Electric Power Research Institute " Guidelines for Nuclear Plant Response to an Eanhquake", EPRI NP-6695, December 1989, that require appropriate inspection and testing in the event that an earthquake is felt at the South Texas Project provide a high level of assurance of safety. Consequently,in the circumstances of the South Texas Project, seismic instrumentation is not necessary to achieve the underlying purpose of Section VI.(a)(3) of 10 CFR Part 100, App. A. Therefore, the exemption satisfies the Section 650.12(a)(ii).
Section 650.12(a)(vi) material circumstances, not considered when the regulation was adopted, for which it would be in the public interest to erant an exemption.
Since adoption of the requirement for seismic instrumentation, there have been advances in the state of the art for probabilistic risk assessment. Based on these advances, the seismic characteristics of the South Texas Project site and the design of the facility, the STP PRA estimates the risk of core damage at the South Texas Project due to a seismic event at 7.4 x 10E-8 per year or less than 1% of the total core damage frequency.
This risk level is insignificant. Elimination of seismic instrumentation will not alter this low risk, since seismic instrumentation is not used to prevent or mitigate accidents, and since the PRA does not take into consideration any actions based on the information provided by the seismic instrumentation. This new circumstance of having a quantified risk, provides a sound basis for reassessing the benefit of the seismic instrumentation. This information constitutes a changed circumstance, which justifies exempting the requirement for seismic instrumentation at the South Texas Project. Therefore, the exemption satisfies the Section 50.12(a) (vi).
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T; Attachment 1 NOC-AE-000536 Page 7 of 9
' O. NRC Guidance on Use of Probabilistic Risk Assessment Utilization of this risk insight to assess the need for a continued requirement to maintain seismic instrumentation is consistent with the NRC guidance in Regulatory Guide 1.174 for risk-informed decision making.
- 1. Current regulations .
The proposed change to the current licensing basis is an exemption from the requirement to maintain seismic instrumentation on site. Upon approval the Technical Requirements Manual, the Updated Final Safety Analysis Repon and Emergency Plan would be revised. A stand-alone instrument will be used to determine if the actual response spectra are enveloped by the analytical model at the location of the instrument. The most significant change to the Updated Final Safety Analysis Report will affect Section 3.7.4. The validation of the dynamic model used to design the reactor containment building, as discussed in section 3.7.4.4, would no longer be required upon approval of this exemption. STPNOC would no longer be required to measure seismic msponse at multiple plant locations and to correlate these responses to measured free-field accelerations. The stand-alone instrument will allow comparison of actual response spectra to design response spectra at the location of the instrument. Measurements taken at one location cannot prove that accelerations at all other locations in the plant were less than design values.
Nevertheless, the South Texas Project believes that the calculation techniques used to establish design response spectra wem similar as to methods, assumptions and accuracy for all buildings.
Therefore, establishing that the response at one building location did not exceed design values would provide a strong basis for pmsuming that the seismic responses at other locations in the plant were likewise bounded by design. The South Texas Project would primarily rely on plant inspections and testing to assess the funher capability of systems, structures and components for meeting safety functions. No other changes to the South Texas Project current licensing basis are being proposed. The seismic qualification requirements for structures, systems and components will continue to be as provided in the current licensing basis for the South Texas Project.
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t Attachment 1 NOC-AE-000536 Page 8 of 9
- 2. Defense-in-depth maintained The only components and system affected by this change is the seismic instrumentation.
This change will result in eliminating the technical requirements to maintain or to perform suiveillances on this instrumentation. No physical change or operational practice change is proposed for any stmetures, systems or components required for maintaining the principal safety barriers, for achieving and maintaining safe shutdown, or for mitigating the consequences of accidents. System redundancy, independence and diversity features are maintained. The plant's response to transients or other initiators will not be affected. As described above,if an earthquake does occur, the South Texas Project will use the criteria proposed in Appendix C to determine if operation of the facility should be continued. Thus the defense-in-depth that is pan of South Texas Project's design philosophy described in the South Texas Project Updated Final Safety Analysis Report (UFSAR)is unaffected by this change.
- 3. Sufficient safety margins are maintained This change does not affect any accident parameters discussed in the South Texas Project UFSAR. The seismic equipment qualification requirements described in the current licensing basis for South Texas Project systems, structures and components will continue to be met. ;
Equipment functionality, reliability and availability will be unaffected by this change.
- 4. Proposed changes in risk, both individual and cumulative, are small and do not cause the NRC Safety Goals to be exceeded As discussed above, the seismic instrumentation would only be utilized after an earthquake has occurred. It does not prevent or mitigate any accident, and the STP PRA does not j take credit for the seismic instrumentation. Therefore, its elimination would not cause a change in risk, or cause the NRC Safety Goals to be exceeded.
- 5. Need for Monitoring of Impact of Proposed Change As described above, the South Texas Project is in an area of very low seismic activity. It is unlikdy that an eanhquake will affect the plant site; and as such, a monitoring program is not needed to provide timely feedback and corrective action related to this design change.
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Attachment 1 NOC-AE-000536 Page 9 of 9 D. Conclusion i
The seismic instrumentation requirements of Pan 50 and Appendix A to Part 100 do not serve a significant safety function at the South Texas Project. The plant is in an area that has very low seismic activity and the plant design contains additional safety margins beyond the minimum required by NRC regulations. In the unlikely event that an earthqude potentially affects the South Texas Project, adequate alternative methods exist to determine if the South Texas Project units should be shutdown. The safety of continued operation would be determined on the basis ofinspections and tests of plant structures, systems and components. This exemption request meets the requirements of 10CFR50.12. Therefore, the South Texas Project should be exempted from the seismic instrumentation requirements.
Appendices:
A: Basic Description of STPNOC's Seismic Monitoring System B: Probability of Earthquakes at the South Texas Project j C: Proposed Earthquake Response Plan f
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Appendix A to Attachment 1 NOC-AE-000536 Page 1 of 2 Basic Description of STPNOC's Seismic Monitoring System Types ofInstruments
- Triaxial Time-History Accelerometers (TTHA): These instruments monitor accelen. tion in three directions (North-South axis, East-West axis, and Venical axis) and transmit the acceleration signals to the seismic monitoring panel (CP013) in the Unit 1 Control Room.
There are seven TTHAs in the Seismic Monitoring System, six providing signals to be i recorded at CP013 in Unit 1 Control Room (XT-0001 through XT-0006) and one used solely as a system trigger (XT-002AL e Triaxial Peak Accelerocraphs (TPA): These are local instmments, requiring no power to operate, which record the peak acceleration in three directions. The acceleration is recorded on plates, which must be retrieved and processed with developing solution in order to determine the peak accelerations. There are three TPAs in the Seismic Momtoring System.
- Self Contained Triaxial Accelerocraph (SCTA): The SCTA monitors acceleration in three directions and records the signals on its own recording unit when triggered. The SCTA uses its own trigger, which is set to 0.02g in each direction. The SCTA is independent of the remainder of the Seismic Monitoring System, allowing acceleration data to be obtained in the event of a failure of the Triaxial Time-History Accelerometer trigger and recording system.
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Recording and Analysis Capability
. DCA-300 Master and Slave Units: The DCA-300 consists of six tape recorders to record signals from six of the Triaxial Time-History Accelerometers. The DCA Master is the upper recording unit and consists of three tape recorders. The DCA Slave is the lower unit and l consists of three recorders.
- RSA-50 Response Spectrum Analyzer: Based on the calculations of the response spectrums for the OBE and SSE events, each accelerometer is aesigned a set of limits that are stored in i the internal memory of the RSA-50. The limits connst of OBE and SSE acceleration values J for frequencies between 0 and 32 Hz. Each accelerometer is assigned a unique set oflimits.
The RSA-50 actuates alarms on CP013 if the inner (OBE) or outer (SSE) acceleration limits :
are exceeded at any frequency. The RSA-50 can perform on-line analysis of accelerometer !
data or perform the analysis of data recorded on tape using the SMR-102 playback unit.
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Appendix A to Attachment 1 NOC-AE-000536 Page 2 of 2 e SMR-102 playback unit: Used to plot accelerometer data stored on tape. A tape from one of the DCA-300 Master or Slave tape recorders is played back in the SMR-102, producing output in the form of a four channel plot. One channel on the plot is time and the other channels are the three acceleration signals from the three accelerometer directions (Nonh-South, East-West, and Vertical). The data from playback of a tape on the SMR-102 is also sent to the RSA-50 for analysis.
Automatic System Response The output of TTHA XT-002A is continuously monitored for acceleration greater than 0.02g in any direction. At 0.02g the Seismic Trigger causes the following:
The six tape recorders stan and record the signals from the TTHAs.
e - The RSA-50 starts and performs on-line analysis of two TTHAs (XT-0001 and XT-0006).
- The " SEISMIC SYSTEM TRIGGER" alarm light is illuminated and the audible alarm is actuated on CP013.
- A Seismic Switch (independent of the Sei_smic Trigger) monitors the output of TTHA XT-002A and actuates the "OBE LIMIT SEISMIC SWITCH" alarm light if 0.0f 3 in either horizontal direction or 0.033g in the vertical direction is exceeded, or the "SSE LIMIT SEISMIC SWITCH" alarm light if 0.lg in any horizontal direction or 0.066g in the vertical direction is exceeded.
- The RSA-50 actuates the "OBE LIMIT RSA-50" and/or "SSE LIMIT RSA-50" if the applicable acceleration limits stored in internal memory are exceeded at any frequency during on-line analysis. I e The system continues to operate automatically until the signals from trigger accelerometer XT-002A are less than 0.02g for 5 seconds.
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U' Appendix B to Attachment 1 NOC-AE-000536 Page 1 of 2 Probability of Earthquakes at the South Texas Project The South Texas Project design basis for vibratory ground motion is defined by a SSE having a maximum horizontal acceleration of 0.10 g. The South Texas Project design uses an Operating Basis Earthquake (OBE) with a maximum horizontal acceleration of 0.05g (i.e., % the SSE). However, only three Intensity V Modified Mercalli earthquakes have been reported within 200 miles of the site in the last 100 years and no earthquakes have been reported within 80 miles.
Thus, the maximum earthquake reasonably expected within the site vicinity, based on historical records and geology, is an eanhquake ofIntensity IV to V modified Mercalli.
Acceleration / intensity correlations show the maximum acceleration of an Intensity V modified Mercalli earthquake to be 0.035 g which would represent a reasonable OBE. However, to comply with Appendix A to 10 CFR Part 100, a minimum acceleration of 0.05 g (% of the SSE) was adopted for the OBE. Two Intensity VI Modified Memalli eanhquakes have occurred recently at distance of greater than 160 kilometers. However, the Intensity VI was only felt within a few kilometers of the epicenter.
The following represents the approximate annual probability of exceedance of peak ground acceleration at the South Texas Project site. (Ref: Figure 3.4.4-2 of the South Texas Project Individual Plant Evaluation, Revision 0, August 21,1992)
Peak Ground Acceleration Annual Probability of Exceedance 0.1 g 2 x 10E-5 0.05g 5 x 10E-5 0.01g 6 x 10E-4 The Nuclear Regulatory Commission published NUREG-1488," Revised Livermore Seismic Hazard Estimates for Sixty-Nine Nuclear Power Plant Sites East of the Rocky Mountains",in April 1994. This report is an update of a probabilistic seismic hazard analysis presented in NUREG/CR-5250. Probabilistic evaluations are intended to capture the uncertainties in estimating seismic hazard in the Eastern United States. For the South Texas Project, NUREG-1488 reported that the peak ground acceleration levels of 0.05g and 0.15g had a mean peak ground acceleration hazard estimate of 1.628 x 10E-4 to 3.256 x 10E-5 respectively.
While these probabilities are on the order of half a magnitude higher than the South Texas Project Individual Plant Evaluation, they are still very small.
l O:WP\NL\NRC-WK\ Misc-99000536
f Appendix B to Attachment 1 NOC-AE-000536 Page 2 of 2 On August 31,1998, the University of Texas Institute for Geophysics with support provided by the Federal Emergency Management Agency published a document titled
" Earthquake Hazard Identification and Risk Assessment for Texas; A Preliminary Analysis of Counties at Risk". This repon assessed four regions in Texas where historical earthquake activity (1847 - 1998) indicates there is an canhquake hazard. The closest region to the South Texas Project site assessed is the South - Central Texas region. The closest boundary of this region is approximately 80 to 100 miles from the South Texas Project site. The Regional Hazard Assessment from the report is provided as Tab A to this appendix. The assessment concludes the following regarding the hazard level of this region:
" Earthquakes with epicenters within this region ar. se and small; perhaps 10-20 earthquakes with magnitudes between 3 and 4.5 y a occur each century. A significant fraction of these earthquakes are induced by human activities, notably petroleum production. These events pose little or no risk unless their foci are extremely close to poorly built or very sensitive structures."
l 1
Tab A: " Earthquake Hazard Identification and Risk Assessment for Texas; A Preliminary Analysis of Counties at Risk", by Cliff Frohlich, Scott Davis, and Jay Pulliam, University of Texas Institute for Geophysics,31 August 1998, Renional Hazard Assessment: South-Central Texas Earthauakes (DD 12S-1 through 12S-4).
O:WPWL\NRC-WK\ MISC-9%000536
Tab A to Appendix B NOC-AE-000536 Regionel Hazard Asssssment:
South-Central Texas Earthauakes (Laraest City - San Antonto)
Counties Included (19): Atasoosa, Bastrop, Bexar, Brazos, Budeson, Caldwell, Comat, Gaudelupe, Gr mes, Hayes, Jim Wells, Kames, Lavaca, Lee, Live Oak, Travis, Waller, Washington, Wilson Hazard Level: Earthquakes with epicenters within this region are rare and small; perhaps 10-20 earthquakes with magnitudes between 3 and 4.5 will ooour each century. A significant fraction of these earthquakes are induoed by human activities, notatly petroleum production. These events pose little or no dsk unless their foot arc ex remely close to poody built or very sensitive structures.
Justification: Many small earthquakes, some of natural origin and others induced by man's activities, have oooutred in these counties.
Significant Histodo or Induced Earthauakes Affectina This Region Small earthquakes with epicenters in this region oocasionally do occur-some of natural origin and some apparently induced by petroleum production (see Attachment 128-A). These include:
- A magnitude 3.9 earthquake centered in Travis County south of Austin whloh oooutred on 9 October 1902. This eatthquake is cleady.of natural origin.
~
- A magnitude 4.2 earthquake near Fashing in Atascosa County on 9 April 1993.
This earthquake is one of several in this region whloh may have been induced by petroleum production.
- A magnitude 3.8 earthquake near Allee in Jim Wells County Whloh oooutred on 24 March 1997. This earthquake may have been induced by petroleum production.
Mitigation Strateav
+ Residents of this region should understand that small natural earthquakes oooasionally do ooour in this region. However, the most numerous eatthquakes are small events assoolated with petroleum production in some; but not all fields.
These small earthquakes pose a hazard only in the immediate vloinity of their eploenter; the oooutrence of significantly larger eatthquakes is unlikely.
I 128-1
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Appendix C to Attachment 1 NOC-AE-000536 Page1of1 1 'roposed Earthquake Response Plan This attachment outlines the proposed eanhquake response plan at the South Texas Project in lieu of maintaining seismic instrumentation. An earthquake of sufficient magnitude to have a potential to affect plant equipment (i.e. peak acceleration level greater than 0.035g) will be sensed by plant personnel and the general population in the plant vicinity. Information regarding the earthquake magnitude and epicenter will be readily available from the National Earthquake Resource Center.
Acceleration / intensity correlations show the maximum acceleration of an Intensity V modified Mercalli earthquake to be 0.035 g which would represent a reasonable OBE at the South Texas Project. (
Reference:
South Texas Project UFSAR, Section 2.5.1) Upon sensing ground motion or upon receiving information that a seismic event had occurred within 200 miles of the South Texas Project, the station will contact the National Eanhquake Information Center (NEIC) in Golden, Colorado. For events of a magnitude of 3 or greater, the NEIC has the capability to provide a time of occurrence for the event, a location of epicenter by latitude and longitude, a magnitude of the event and the estimated depth below the surface of the epicenter. The location of the epicenter for earthquakes of a magnitude 3 or greater is considered to be very accurate and for sensed activity less than a magnitude 3 is still within an accuracy of a few kilometers.
A stand-alone instmment will be maintained at the site and will be located at a low elevation in a seismic category I structure. Measured building motion at this location will allow comparison and evaluation of the measured response with the plant's design basis. In the unlikely instance that a seismic evut equivalmt, to the level of an Operating Basis Eanhquake occurs, the instrument will k capable of providing time history acceleration data and of providing response spectra information.
Respense Plan: Upon sensing ground motion or upon receiving information that a seismic event has occurred within 200 miles of the South Texas Project that is collaborated b," the National Earthquake Information Center, acceleration data will be obtained from the stand-alone instrument maintained at the site. This data should be available for processing within approximately 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. Additionally, plant walk-downs will be perfctmed within approximately 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />. Determination of exceedance of the Operating Basis Eanhquake (OBE) for the South Texas Project will consist of a check of the response spectrum and a check on the operability of the instrumentation. If the OBE is exceeded or significant plant damage occurs, both South Texas Project units will be shutdown unless plant walk-downs indicate plant damage precludes achievement of safe shutdown capability without corrective action. In the event safe shutdown is precluded, a plan for safe shutdown will be proposed by the South Texas Project to the Nuclear Regulatory Commission for approval.
o:WMNL\NRC-WK\ Misc-99\000536