View source for NOC-AE-000513, Suppl to Application for Amends to Licenses NPF-76 & NPF-80, Changing Tech Specs to Modify Requirements Associated with CR & Fuel Handling Bldg Ventilation Sys

{{Adams
| number = ML20206A781
| issue date = 04/22/1999
| title = Suppl to Application for Amends to Licenses NPF-76 & NPF-80, Changing Tech Specs to Modify Requirements Associated with CR & Fuel Handling Bldg Ventilation Sys
| author name = Cloninger T
| author affiliation = HOUSTON LIGHTING &amp; POWER CO.
| addressee name = 
| addressee affiliation = NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
| docket = 05000498, 05000499
| license number = 
| contact person = 
| document report number = NOC-AE-000513, NOC-AE-513, STI:30855748, NUDOCS 9904290024
| document type = OPERATING LICENSES-APPLIATION TO AMEND-RENEW EXISTING, TEXT-LICENSE APPLICATIONS &amp; PERMITS
| page count = 19
| project = 
| stage = Request
}}

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April 22,1999       I NOC-AE-000513 File No.: G20.02.01 G21.02.01 10CFR50.90 STI: 30855748 U. S. Nuclear Regulatory Commission                                                                     l Attention: Document Control Desk                                                                        '
Washington,DC 20555 l
South Texas Project                                             l Units 1 and 2 Docket Nos. STN 50-498, STN 50-499 Supplement to Proposed Amendment to                                       i South Texas Project Technical Specifications to Modify Requirements Associated with Control Room and Fuel Handline Buildine Ventilation Systems

==Reference:==
Letter from T. H. Cloninger, South Texas Project to the NRC Document Control Desk dated September 18,1998 (NOC-AE-000305)                                            l l
The referenced letter is a request from the South Texas Project to amend the operatmg licenses for Units 1 and 2 by changing the Technical Specifications to modify requirements         /    l associated with the Control Room and Fuel Handling Building Ventilation Systems. The                  /
amendment proposes an allowed outage time of 12 hours for a condition when all three trains of Control Room or Fuel Handling Building Ventilation Systems are inoperable. Additional risk-             l informed information is provided in this supplement to support the proposed allowed outage
                                                                                                          /j
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time. Revised areas in Attachments 2,3 and 4 are indicated by change bars. No revisions are being proposed to Attachment 5, the Environmental Assessment, or Attachment 6, the annotated Technical Specifications and Bases, from the reference letter. Therefore, Attachments 5 and 6 are not included in this supplemental letter to the original amendment.                                 l South Texas Project has reviewed the proposed amendment pursuant to 10CFR50.92 and determined that it does not involve a significant hazards consideration. In addition, South Texas Project has determined that the proposed amendment satisfies the criteria of 10CFR51.22(c)(9)
;      for categorical exclusion from the requirement for an environmental assessment. The South j      Texas Plant Operations Review Committee and the Nuclear Safety Review Board have reviewed and approved the proposed amendment.
9904290024 990422 ~
PDR      ADOCK 05000498 P                       PDR l
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l l'           The required affidavit, a Description of the Change and Safety Evaluation, a l
Determiriation of No Significant Hazards Consideration, and a Description of Probabilistic l    Safety Analysis Impact and Risk-informed Decision Making Analysis are included as attachments to this letter In accordance with 10CFR50.91(b), South Texas Project is notifying the State of Texas of this supplement to the original request for a license amendment by providing a copy of this letter and its attachments. This proposed amendment is not a high priority change, however, STPNOC requests that it be reviewed and approved by July 31,1999 to allow implementation prior to the fall Unit 2 outage. One of the changes for the Fuel Handling Building HVAC requested by this submittal will conect a condition that resulted in STPNOC requesting enforcement discretion to repair an exhaust fan without entering Technical Specification 3.0.3.
STPNOC requests up to 60 days for implementation.
If there are any questions regarding the proposed amendment, please contact Mr. A. W.
Harrison at (512) 972-7298 or myself at (512) 972-8787.
l l                                                                   /,                       /
T. H. Cl inge Vice P side  ,
j                                                                  Engineerin    dTechni:al Services l
!                                                                                                       I l
l KJT/                                                                                               ,
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l    Attachments-l
: 1. Affidavit
: 2. Description of Change and Safety Evaluation
: 3. Determination of No Significant Hazards
!    4. Description of Probabilistic Safety Analysis Impact and Risk-informed Decision Making L         Analysis L

t                                                                                 j c                                                                                 1 NOC-AE-000513 File No.: G20.02.01
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G21.02.01 Page 3                -
Ellis W. Merschoff -                    Jon C. Wood                           I 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 Cornelius F. O'Keefe                    Richard A. Ratliff Sr. Resident Inspector .                Bureau of Radiation Control c/o U. S. Nuclear Regulatory Commission Texas Department of Health P. O. Box 910                           1100 West 49th Street Bay 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. 205.55-0001
!   721 Barton Springs Road l
Austin,TX 78704 i
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Attachment 1 NOC-AE-000513 Page1 UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION In the Matter                                     )
                                                         )
South Texas Project, et al.,                       )                   Docket Nos. STN 50-498
                                                         )                                 STN 50499 South Texas Project Units 1 and 2                  )
AFFIDAVIT I, T. H. Cloninger, being duly sworn, hemby depose and say that I am Vice President, Engineering and Technical Services of STP Nuclear Operating Company; that I am duly                  i authorized to sign and file with the Nuclear Regulatory Commission the attached supplement to the proposed Technical Specification change to modify requirements associated with control            '
room and fuel handling building ventilation systems; that I am familiar wi          content thereof; and that the matters set forth therein are true and correct to the best of    -
wiedge and belief.
l l
                                                           '. H. Clonin r
                                                                           +          [
Vice Presid it, Engineering a    Technical ervices STATE OF TEXAS                                     )
                                                         )
COUNTY OF                                          )
i M,j Subscribed day of anj     sworn Hee,  / to before      me, a Notary Public in and for the State of Texas, t
                                                    ,1999.
ry P      #9
              ',,,,j        hT[                            Notary Public in and for the State of Texas 7

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O,r Attachment 2 NOC-AE-000513 l*
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ATTACHMENT 2 DESCRIPTION OF CHANGE AND SAFETY EVALUATION                  )
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1 Attachment 2 NOC-AE-000513 Page 2 Description of Change and Safety Evaluation Description of Change:
The proposed changes will modify the requirements applicable when one or more trains of Fuel Handling Building (FHB) Exhaust Air or Control Room (CR) Makeup and Cleanup Filtration are inoperable. The South Texas Project system design for these systems is unique and the proposed changes will account for these design features. In addition, the proposed changes will align the actuating instrumentation and logic system required actions with those that are applicable to the systems. The proposed changes will eliminate the need to enter Technical Specification 3.0.3 when multiple trains of these systems are inoperable, rather specific Actions are proposed to addmss these conditions. Finally, an administrative change is proposed to remove a footnote on page 3/4 7-20 that is no longer applicable to the facility.
Technical Specifications affected by the proposed change am as follows:
3/4.3.2, Table 3.3-3," Engineered Safety Features Actuation System Instrumentation, Control Room Ventilation," and "FHB HVAC," Actions 27,28, and 29 3/4.7.7," Control Room Makeup and Cleanup Filtration System" 3/4.7.8, " Fuel Handling Building (FHB) Exhaust Air System" 3/4.9.12. " Fuel Handling Building Exhaust Air System" The Actions associated with inoperable actuation instrumentation are being modified to align the allowed outage times for less than the minimum channels OPERABLE with those that apply when a similar condition exists on the actuated system. Specifically;
* Action 27 is modified to declare the ventilation train associated with the inoperable channel inoperable and requires the actions for an inoperable ventilation train be carried out per Specification 3.7.7. These changes are consistent with measures described in South Texas Project Unit 2 License Event Report 95-007 dated November 15,1995.
* Action 28 is modified to remove the mode dependent action requirements. This change establishes a standard system alignment, consistent with the actuated position, in response to the inoperability of a radiation monitoring channel and will result in maintaining the control room envelope pressurized while supplying a dilution flow of fresh filtered air regardless of plant mode. The requirement for a filtered recirculation without makeup flow was a holdover from the previously removed toxic gas requirements.
* Action 29 is also being modified to align the allowed outage times for less than the minimum channels OPERABLE with those that apply when a similar condition exists on the actuated

7 4
Attachment 2 NOC-AE-000513 Page 3 system. This change will be worded similarly to Action 27 above. Specifically, Action 29 is modified to declare the ventilation train associated with the inoperable channel inoperable and requires the actions for an inoperable ventilation train be carried out per Specification 3.7.8.
Specification 3/4.7.7 is modified by addition of an Action applicable when operating in MODES 1,2,3, and 4. The proposed new Action is structured similarly to existing Action b. that addresses the condition of two Control Room Makeup and Cleanup Filtration Systems being inoperable. However proposed Action c. provides for up to 12 hours to restoir at least one system to OPERABLE status when all three systems are inoperable, or be in HOT STANDBY within the next 6 hours and in COLD SHUTDOWN within the following 30 hours. The actions applicable in MODES 5 and 6 are proposed to be modified to permit a suspension of all operations involving CORE ALTERATIONS, movement of spent fuel, and crane operations with loads over the spent fuel pool, rather than placing the control room ventilation system in operation while one Control Room Makeup and Cleanup Filtration System is inoperable, j     Actions associated with Specification 3/4.7.8 are proposed to be modified from a single Action l     applicable to degraded system operability, to a series of Actions that more appropriately reflect the design, condition of the system, and the specific function of the inoperable component. A modification to the terminology used in the Specification is proposed, to clarify the required system configuration. The existing Specification lists the requirements for exhaust booster fans, main exhaust fans, and associated dampers separately, while the proposed Specification refers to
!     these components in pairs, as exhaust ventilation trains. The proposed new actions provide for up l      to 12 hours to restore at least one ventilation system and one filter train to OPERABLE status when all three systems are inoperable, or be in HOT STANDBY within the next 6 hours and in COLD SHUTDOWN within the following 30 hours. This change will resolve the conditions that required granting of a notice of enforcement discretion (NOED) to allow repair of an exhaust            l booster fan in May 1998 without entering Technical Specification 3.0.3 when all Fuel Handling Building exhaust air systems components were made inoperable. The proposed Action Statements use a similar terminology.
South Texas Project Unit 1 Licensee Event Reports 98-004, dated June 1,1998 and 98-010, dated November 23,1998, are associated with the NOED. The Fuel Handling Building HVAC ductwork in Unit I has been modified and in Unit 2 is planned for modification during the Fall 1999 refueling outage to facilitate maintenance on the booster fans. This modification will also         i satisfactorily resolve the issues specific to the NOED. However, the modification addresses only those issues that might be associated with the Fuel Handling Building exhaust booster fan. This proposed Technical Specification amendment is more generally applicable and includes the Control Room Envelope HVAC.
      ' An administrative change is proposed to remove the asterisk footnote at the bottom of 3/4 7-20.
This footnote was only applicable during the first six weeks after March 28,1989 and no longer            l serves any purpose in the Technical Specifications. The proposed change also removes the                  I asterisk from the body of the Specification at surveillance requirement 4.7.8.d.(4).

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Attachment 2 NOC-AE-000513 Page 4
      . Finally, Specification 3.9.12 is modified to use the same terminology as used in Specification 3.7.8 for consistency.
The proposed changes are mquired to address the South Texas Project plant design, which incorporates unique, three-train design features. The changes to the Action Statements associated with Table 3.3-3 are required as a result of the need to align the action requirements of the actuation system with those of the system being actuated. The three train design was previously recognized in the system-specific Technical Specifications, however the design is not fully reflected in the actuation instrumentation table. This was a contributing factor to an event in 1995 that resulted in issuance of STP Unit 2 License Event Report 95-007 dated November 15,1995. Additionally, a change is proposed to permit operation in MODES 5 and 6 with the actuation instrumentation inoperable for an extended period without placing the Control Room         3 Ventilation System in operation. As an alternative, the proposed change administratively restricts operations to pmvent conduct of operations that are the assumed precursor activities for the design basis events of the Control Room Ventilation System while in MODES 5 and 6.
The Fuel Handling Building HVAC and Control Room Ventilation Systems each use the three train design to satisfy their design basis requirements. The existing Specifications recognize and partially addmss the design, however they do not fully address operational considerations related to cenain design features. The separate trains of ventilation in the Fuel Handling Building HVAC and Control Room Ventilation Systems typically use common plenums or ductwork that l       must be opened to permit maintenance and required testing. The proposed changes to the actions for each system Specification will permit this maintenance to be conducted without entering Technical Specification 3.0.3 requiring a shutdown of the unit.
l       The administrative change to remove the footnote on page 3/4 7-20 removes extraneous material l       that no longer serves any purpose. It is proposed for removal at this time for convenience because the Specification is being changed for other reasons.
Most of the proposed change would have been addressed in the application for Improved Technical Specifications (ITS), however implementation of the STP ITS has been deferred.              i i
l       To clarify the proposed changes to the Specifications, changes to the Bases are proposed. These l       changes are included and will affect the Bases for Specifications 3/4.7.7,3/4.7.8, and 3/4.0.12.
l Safety Evaluation:
l l       These proposed changes would permit South Texas to utilize the facility in a manner more appropriate for its design. The changes to the required action times associated with Table 3.3-3 align the allowed outage times with those that apply to the associated system. The alignment of allowed outage times does not represent a change in the safety of the facility because the inoperability of an actuated system is no more significant than inoperability of the actuating instrumentation system. The proposed change to Control Room Ventilation configuration with

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!.                                                                                              Attachment 2
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* NCC-AE-000513 Page 5 l       aii inoperable radiation monitoring channel will result in maintaining control room pressurization in all modes of operation and align the system to the actuated condition. This alignment with a filtered makeup supply will result in an increase in protection to the operators.
l
;       The postulated IAss-of-Coolant Accident (LOCA) has been qualitatively determined to be the design basis event resulting in the highest control room operator doses. The annual probability
,       that this~ design basis event would occur during the 12 hour allowed outage time for three trains of inoperable Control Room Ventilation is 5.5E-05. This value includes all IDCA initiating l       events, including a Steam Generator Tube Rupture. Therefore, the change proposed to the actions of Specification 3/4.7.7 does not represent a significant challenge to plant safety because of the low pmbability of a design basis event during the brief allowed outage time. The allowed l       outage time will permit the conduct of requimd maintenance and testing without unnecessarily violating the limits of the Specification by requiring actions be taken in accordance with Technical Specification 3.0.3. The ability to conduct maintenance and testing while in operation will improve overall system reliability and availability. Similarly, the allowance to continue operations in MODES 5 and 6 with an inoperable train while administrative controls prevent l       conduct of operations that could challenge the system does not represent a degradation in overall l       facility safety.
l l       The South Texas Project Probabilistic Risk Analysis (PRA) models loss of Control Room Envelope HVAC as an initiating event.- A loss of Control Room Envelope HVAC is assumed to lead to failure of the electronic components modeled in the reactor protection system, including the actuation relays and instrumentation. This,in turn,is assumed to lead to a plant trip signal with failure of automatic actuation for the systems necessary to respond to the trip. The PRA assumes that these events will not occur within the first 24 hours of failure of the Control Room HVAC system. The proposed 12 hour allowed outage time for all three Control Room HVAC trains inoperable provides adequate time (6 hours) to place the plant in HOT STANDBY and prior to the 24 hours assumed in the PRA before the reactor protection system starts failing.
This request provides up to 12 hours to restore at least one train of CRE HVAC to OPERABLE l       when all three trains are inoperable, or be in HOT STANDBY within the next 6 hours. Since the plant will be required to be in HOT STANDBY before the 24 hours with no HVAC cooling assumed to lead to a plant trip, this submittal will have no impact on the at-power core damage or large early release frequency.
The proposed changes to Specification 3/4.7.8 are primarily directed at improving the definition of the system operability requirements that are applicable to the Fuel Handling Building HVAC system, while more accurately reflecting the system design, and allowing for maintenance on system components. The existing Specification differentiates between the exhaust booster fans, main exhaust fans, and associated dampers, while the proposed Specification will more appropriately refer to exhaust ventilation trains. The Fuel Handling Building HVAC design includes three exhaust booster fans and three main booster fans that can be utilized in multiple combinations to achieve successful design basis accident mitigation by the system. The system design includes a common plenum located at the suction of the sets of fans. This plenum permits L

R Attachment 2 F                                                                                            NOC-AE-000513 Page 6
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fins frorn different trains of equipment to be utilized to compose a flow path that is adequate to
        , perform the required safety functions.
The applicable design basis event for Specification 3/4.7.8 that the FHB HVAC system is designed to mitigate is the Imss-of-Coolant Accident (LOCA). As previously stated, the annual
!         probability that this design basis event would occur during the 12 hour allowed outage time for three trains of inoperable FHB HVAC is 5.5E-05. This value includes all LOCA initiating events, l         including a Steam Generator Tube Rupture. Therefore, the change proposed to the actions of Specification 3/4.7.8 does not represent a significant challenge to plant safety because of the low
;.        probability of a design basis event during the brief allowed outage time. The proposed allowed outage time will permit the conduct of required maintenance and testing without unnecessarily violating the limits of the Specification or requiring actions be taken in accordance with Technical Specification 3.0.3. The ability to conduct maintenance and testing while in operation l         will improve overall system reliability and availability. This change will resolve the condition that required enforcement discretion to correct.
Control Room and Fuel Handling Building HVAC systems are not designed to mitigate core damage or to mitigate the effects of a large early release of radioactive contamination to the L         outside environment. Therefore, the allowed outage times proposed result in no change to Core Damage Frequency or large early Release Frequency.
l         Based on the evaluation above, it is appropriate to make the proposed changes to the l         Specifications. The proposed change will provide a continued assurance that the Fuel Handling l         Building HVAC and Control Room Ventilation Systems am OPERABLE and appropriately
!         tested and maintained. Overall plant safety will not be significantly affected by the proposed L         changes and the proposed changes will not affect any safety limit applicable to the facility.
l l-        An administrative change is proposed to the asterisk footnote at the bottom of page 3/4 7-20, as well as to remove the associated asterisk from the body of the surveillance requirements located i
on the page. This change will have no effect on plant operations, and removes extraneous material from the Specifications. Based on this evaluation,it is appropriate to delete this footnote that is no longer applicable.
The proposed change to Specification 3.9.12 changes the terminology used in the Specification to l         maintain consistency throughout the Specifications and does not change any requirements.
           .% fore, the proposed change will have no safety impact.

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li Attachment 3 l-NOC-AE-000513 L                                                         Page1 i
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ATTACHMENT 3 NO SIGNIFICANT HAZARDS DETERMINATION

o Attachment 3 I
NOC-AE-000513 l                                                                                               Page 2  I No Significant Hazards Determination:
In accordance with the criteria set forth in 10CFR50.92, the South Texas Project has evaluated       j these proposed Technical Specification changes and determined they do not represent a significant hazards consideration. The following is provided in suppon of this conclusion.
1
: 1.      Does the change involve a significant increase in the probability or consequences of an accident previously evaluated?
The proposed changes do not involve an increase in the probability or consequences of an accident previously evaluated. The proposed changes consist of:                              j a) Assuring that the Specifications define consistent allowed outage times when the same safety function is addressed in multiple Specifications, b) Allowing a system to remain inoperable when appropriately restrictive administrative controls are placed on operations that could result in a challenge to the safety function of  .
the system,                                                                                  !
I c) Providing an appropriately short Allowed Outage Time for inoperability needed to permit required maintenance and testing that affects all trains of a system, d) Redefining system operability and associated actions in a manner consistent with the system design and function,                                                                  j 1
e) Aligning a system to the actuated condition on the loss of an actuation channel,           l f) Using consistent terminology throughout the Specifications The proposed changes do not represent significant increases in the probability or            I consequences of an accident because:
a) The alignment of the action times between actuating system and actuated system             l operability requirements do not effect probability or consequences since inoperability of the actuated system has the same effect as inoperability of the actuating system. Since the changes proposed to the actuating system action times will reflect those of the actuated system action times, no change to the allowed outage time applicable to the safety function addressed and fulfilled by both, will occur.
l                                                                                                      j b) Administrative controls to prevent the conduct of operations that could lead to a         {
I challenge to the safety function of the system when the actuation system is inoperable, assures that the design bases functions of the system will not be challenged. Therefore, l

Attachment 3 NOC-AE-000513 l                                                                                                Page 3 the probability or consequences of an event previously identified have not been
!-        significantly changed.
t c) Allowing up to 12 hours to recover from the inoperability of all three trains of Control Room Ventilation or two or more trains of Fuel Handling Building HVAC does not l         represent a significant change to the probability of an accident because the inoperability l         of these ventilation systems are not identified as precursors to a design basis event. The low likelihood of a design basis accident during the limited period of allowed inoperability of these systems does not represent a significant increase in the consequences of an accident. The limited allowed outage time of three inoperable CRE HVAC systems has no detrimental effect on the operation of the Reactor Protection System
!         d) The redefinition of plant operability requirements into functional trains rather than I
individual components does not effect the required system functional operability.
l         Therefore, this change does not represent an increase in the probability or consequences
!         of an accident previouslyidentified.
l                                                                                                       l l         c) The alignment of the Control Room Ventilation System to the same configuration it would be placed in from an actuation of the inoperable radiation monitoring channel places the system in the design condition. This alignment would result in maintaining the control room envelope pressurized and increases the protection afforded to the operators.
f) The change in terminology does not change any requirements or actions in the Specification. Therefore this change does not represent an increase in the probability or consequences of any accident previously evaluated.
Based on the above discussion, the individual changes do not represent an increase in the l         probability or consequences of any accident previously evaluated.
l L         In addition to the changes proposed to controls over Control Room Ventilation, Fuel l         Handling Building HVAC, and associated actuation logic, an administrative change is proposed to remove the footnote at the bottom of page 3/4 7-20. Since the footnote no longer has meaning or relevance to the operation of the facility,its removal does not increase the probability or consequences of any accident previously evaluated.
: 2. Does the change create the possibility of a new or different kind of accident from any accident previously evaluated?
The proposed changes make the existing Specifications internally consistent, manually align a system to the actuated position, provide an alternative measure that assures a safety function which is unavailable is not required to perform, provide an extended period of allowance for all trains of a system to be inoperable, and redefines system e

c
  .4 Attachment 3 NOC-AE-000513 Page 4 operability to reflect its functional design. The proposed changes do not introduce any new equipment into the plant or significantly alter the manner in which existing l           equipment will be operated. The limited allowed outage time of three inoperable CRE HVAC systems has no detrimental effect on the operation of the Reactor Protection System. The systems affected by the proposed changes are not identified as contributing causal factors in design basis accidents, their function is to assist in mitigation of '
l           accidents postulated to occur. Since the proposed changes do not allow activities that am i           significantly different from those presently allowed, no possibility exists for a new or different kind of accident from those previously evaluated.
In addition to the changes proposed to controls over reactivity changes, an administrative change is proposed to remove the footnote at the bottom of page 3/4 7-20. Since the footnote does not perform any function and will never again apply to plant operations, its icmoval cannot c cate the possibility of a new or diffemnt kind of accident from those previously evaluated.
: 3. Does this change involve a significant reduction in a margin of safety?
l           The proposed changes do not involve a significant reduction in a margin of safety because l
the ability of the Fuel Handling Building HVAC and Control Room Ventilation Systems             l will be maintained. The margin of safety is defined by the ability of the syst:,ms to limit the release of radioactive materials and limit exposures to operators respectively following a postulated design basis accident. The only aspect of the proposed change that can be postulated to have any effect on a margin of safety is the proposed allowance for all trains of Control Room Ventilation or Fuel Handling Building HVAC to be inoperable for a limited period. The low probability of a design basis event that would require the system to perform its safety function during the limited period allowed by the proposed action assures that the change does not involve a significant change in a margin l_          of safety. Therefore, the proposed changes do not significantly affect these operating restrictions and the margin of safety which suppost the ability to make and maintain the reactor in a safe shutdown and limit the release of radioactive material is not affected.
Sufficient time is allowed to restore CRE HVAC to the rooms serving the Reactor Protection System before any detrimental effects would occur or to place the plant in MODE 3 if CRE HVAC could not be restored.
In addition to the changes described above, an administrative change is proposed to             j remove the footnote at the bottom of page 3/4 7-20. Since the footnote is no longer applicable to the facility, its removal cannot result in a reduction in a margin of safety.
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Attachment 4
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NOC-AE-000513 Page1 ATTACHMENT 4                          !
DESCRIPTION OF PROBABILISTIC SAFETY ANALYSIS IMPACT AND RISK-INFORMED DECISION MAKING ANALYSIS

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l                                                                                              Attachment 4 l-                                                                                         NOC-AE-000513 l                                                                                                    Page 2 Description of Probabilistic Safety Analysis Impact and Risk-informed Decision Making Analysis Control Room Envelope HVAC The STPNOC Probabilistic Risk Analysis (PRA) models loss of Control Room Envelope HVAC (CRE HVAC) as an initiating event and does not credit the CRE HVAC for post accide it/ transient analysis.
l A an initiating event, failure of the CRE HVAC system is assumed to lead to failure of the electronic components modeled in the reactor protection system, including the actuation relays and instrumentation. This,in turn, leads to a plant trip signal with failure of automatic actuation for the systems necessary to respond to the trip. Loss of CRE HVAC and failure to recover within 24 hours is assumed to result in a plant trip with failure of all actuation signals.
l     This request provides up to 12 hours to restore at least one train of CRE HVAC to OPERABLE when all three trains are inoperable, or be in HOT STANDBY within the next 6 hours. Since the plant will be r, uired to be in HOT STANDBY before the 24 hours with no HVAC cooling assumed to lead to a plant trip, this submittal will have no impact on the at-power core damage or large early release frequency.
The design basis accidents that the CRE HVAC is design to mitigate are:
l
* Fuel Handling Accident in the Fuel Handling Building or the Reactor Containment Building l
* Loss of Coolant Accident l
* Main Steam Line Break                                                                            j
* Steam Generator Tube Rupture The Fuel Handling Accident can be precluded from consideration during the time three trains of        !
CRE HVAC are made inoperable by administratively suspending all operations involving CORE             l l     ALTERATIONS, movement of spent fuel, and crane operation with loads over the spent fuel l     pool.
l     The Licensing Basis for the South Texas Project includes the Irak-Before-Break concept. This methodology has demonstrated that the deterministic Large Break Loss of Coolant Accident is l     not credible. Any large pipe mpture of the reactor coolant system would be preceded by leakage that is detectable by Control Room personnel using installed plant instmmentation. If a CRE HVAC plenum were breached when reactor coolant system leakage was identified, the time                ;
between initiation of the leakage and the actual break would allow adequate time to restore the breach in the ventilation plenum and CRE HVAC operability. There may be other conditions for entering the action other than the need to breach a plenum. Maintenance activities on plant systems are evaluated for compatibility with current plant condition prior to commencement as a pan of the station's work control process. If warranted, appropriate response plans would be l

                                                                                             ' Attachment 4 NOC-AE-000513 Page 3 evaluated for placing the plant in a safe condition for dealing with a potentially escalating situation.
There is no forced intake into the Control Room HVAC system until the system is restored to operable status. Integrity of the Control Room affected by personnel accesses can be established during the initiation of the leakage prior to the break. Section 6.4.2.3 of the South Texas Project Updated Final Safety Analysis Report provides a description of the potential infiltration paths to
;    the Control Room Envelope during the emergency operation mode of the CRE HVAC and l
indicates that infiltration is minimal. Befom restoration of the CRE HVAC, the integrity of these leak paths is unaffected.
l l    The safety analysis demonstrates that approximately 85% of the dose to the Control Room during i    a Loss of Coolant Accident is due to containment leakage. The containment leakage rates assumed in the safety analysis are much higher than the performance of the South Texas Project containment, which is essentially leak-tight. The safety analysis also assumes that the l    containment airborne iodine inventory release to be the flashed portion of the total primary I
coolant iodine inventory based upon a preexisting iodine spike level of 60 Ci/g dose equivalent I-131. The additional probability of this preexisting condition during the limited 12 hour allowed outage time is extremely improbable.
The effects of a Main Steam Line Break or a Steam Generator Tube Rupture on Control Room dose can be mitir,ated by the relatively short time required to restore the ventilation plenum and CRE HVAC oprability. Prior to restoration, the effects are mitigated because there is no forced intake into the Control Room HVAC system until the system is restored to operable status.
For the Steam Generator Tube Rupture event, a potential tube rupture would most likely be preceded by incmased leakage in the steam generator. Activity in the steam and power conversion system is subject to continual surveillance. The South Texas Project Technical Specifications only allows 150 gallons per day of primary-to-secondary leakage through any one steam generator before plant shutdown is required. Maintenance activities on plant systems are evaluated for compatibility with current plant condition prior to commencement as a part of the station's work control process. Since it would be inappropriate to perform maintenance activities that jeopardize the availability of the CRE HVAC when activities are in progress to respond to increased steam generator leakage indicative of a rapidly degrading condition , the potential of a
    - tube rupture during the proposed 12 hours outage time is not credible.
For the Main Steam Line Break event, the radiological concern is a preexisting steam generator tube leak. As stated above, upon an increased trend in primary-to-secondary leakage that is indicative of a rapidly degrading condition, preparations ;te made for plant shutdown. Again, normal processes of evaluating a plant maintenance actNity compatibility with current plant conditions would not allow maintenance on systems critical to such an event, unless the maintenance activity was required to restore system components to service.
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Attachment 4
!'                                                                                     NOC-AE-000513 i                                                                                                 Page 4 Fuel Handline Buildine HVAC The PRA does not credit the Fuel Handling Building Ventilation System for mitigating core damage accidents.
The design basis accidents that the FHB HVAC is designed to mitigate are:
e   Fuel Handling Accident in the Fuel Handling Building
   . Loss of Coolant Accident The effects of a Fuel Handling Accident are precluded by suspending all operations involving movement of fuel within the spent fuel pool or crane operations with loads over the spent fuel pool with no FHB air filter trains OPERABLE required by Specification 3/4.9.12.
During the Imss of Coolant Accident, the concem in the FHB is the leakage of Reactor Containment Building emergency sump water from the Emergency Core Cooling System in the lower regions of the building. Should the FHB HVAC common plenum be breached for maintenance, the leak-Before-Break concept discussed previously provides adequate time to restore the ventilation plenum and FHB HVAC operability. The modification previously described has been installed in Unitl and is scheduled for installation in Unit 2. The modification will facilitate closure of the plenum. In fact, for the anticipated situations involving ,
access to a single booster fan, the modification will preclude the need to apply the proposed         {
Technical Specification action. For other conditions for entering the action other than the need to   l breach a plenum, appropriate response plans would be evaluated for placing the plant in a safe        l condition for dealing with a potentially escalating situation. An evaluation of current plant conditions, prior to commencing maintenance activities, and an evaluation of the need for compensatory measures or action plans, are part of the normal work control process at the             I station.
In addition,it would take a minimum of 16 minutes for the Refueling Water Storage Tank to empty and the Emergency Core Cooling System to go into the recirculation mode by taking               i suction from the containment emergency sump. This also provides additional time to restore the        j ventilation plenum and FHB HVAC operability. Total Emergency Core Cooling System leakage              i is monitored periodically. Three redundant Emergency Core Cooling Systems are available during recirculation.
Another factor minimizing dose to the outside environment and providing time to restore FHB           J HVAC operability is that the lack of airflow with no ventilation would result in an extended          l period of time befom airborne contaminants reached the upper levels of the Fuel Handling              I Building. The safety analysis asaumes that 95.5% of the iodine micased to the Fuel Handling Building is in the elemental form. A large portion of this would plate out in the lower levels of the Fuel Handling Building during leakage from the Emergency Core Cooling System.
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        .Summarv A Fuel Handling Accident is pmvented during maintenance to restore a CRE HVAC or a FHB HVAC fan to OPERABLE status by administrative controls or by South Texas Project's Technical Specifications, which will not allow for operations leading to a potential Fuel Handling Accident during this maintenance condition. The annual probability that a Loss of Coolant Accident would occur during the proposed 12 hour allowed outage time is 5.5E-05. This value includes all LDCA initiating events, including a Steam Generator Tube Rupture. The annual probability that a Main Steam Line Break would occur during the proposed 12 hour allowed outage time is 1.0E-05. This value includes Steam Line Breaks upstream and downstream of the main steam isolation valves. In the extzmely unlikely event that these events l     ' would occur when all three trains of CRE HVAC or FHB HVAC were inoperable, event pmcursors would allow time to mstore system operability. The Steam Generator Tube Ruptum event during the proposed 12 hour allowed outage time is not considered a cmdible event for reasons stated previously.
The FHB main exhaust fan motors and the fan motors in the CRE HVAC system have l       demonstrated a history of reliability. However, the FHB exhaust booster fan motors have developed a history of failure at the South Texas Project. The South Texas Project is taking the
: l.      following actions to mduce the likelihood that the proposed allowed outage time for the FHB i     ' HVAC system due to exhaust booster fan motor failure would be required.
l l-      e    Developed a modification that will allow maintenance and/or replacement of a FHB exhaust booster fan without rendering the other two trains inoperable. This modification has been l            completed in Unit I during the Spring 1999 tefueling outage. This modification is scheduled for completion in Unit 2 during the Fall 1999 mfueling outage e    Systematic replacement and repair of all FHB exhaust booster fan motors.
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* Developed new preventive maintenance activities for insulation resistance testing of the FHB l            exhaust booster fan motors l
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