ML20248C530
| ML20248C530 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 05/29/1998 |
| From: | Graesser K COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20248C535 | List: |
| References | |
| BYRON-98-0166, BYRON-98-166, NUDOCS 9806020180 | |
| Download: ML20248C530 (12) | |
Text
_ _ _ _ _ _ _ .
Comrnonwealth IMimn Gimpany o o 11yron Generating Station 4 30 North German Church Road llyron, IL 6)O109-'9 i
, TelMIS2314641 May 29,1998 LTR: BYRON 98-0166 FILE: 2.01.0301 U. S. Nuclear Regulatory Commission Washington,DC 20555 ATTN: Document Control Desk
SUBJECT:
Application for Amendment to Facility Operating Licenses Byron Station Units 1 and 2 Facility Operating Licenses NPF-37 and NPF-66 NRC Docket Nos. 50-454 and 50-455 Braidwood Station Units 1 and 2 Facility Operating Licenses NPF-72 and NPF-77 NRC Docket Nos. 50-456 and 50-457 l 1
Change to Credit Automatic PORY Operation for Mitigation ofInadvertent Safety Injection at Power Accident i
REFERENCE:
" Comed Plan to Resolve Spurious Safety Injection at Power,"
J. Hosmer (Comed) to NRC Document Control Desk, dated December 19,1997.
Pursuant to 10 CFR 50.90, Commonwealth Edison (Comed) proposes to amend Facility Operating Licenses NPF-37, NPF-66, NPF-72, and NPF-77. As initially discussed in the referenced letter, Comed proposes to revise Technical Specification (TS) Bases Section 3/4.4.4, " Relief Valves," to specifically credit the automatic function of the pressurizer power operated relief valves (PORVs) to provide mitigation for the Inadvertent Operation of ECCS (Spurious SI) at Power Accident.
l Additionally, Comed proposes to revise the applicable leniting Condition for Operation (LCO) in TS Section 3/4.4.4 to include two actions to specifically address PORV inoperability due to the automatic actuation circuitry. Finally, Corned proposes to revise Surveillance Requirement 4.4.4.2 to reflect the changes made to the LCO.
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NRC Document Control Desk May 29,1998
' Page 2 The Spurious SI at Power accident is discussed in the Byron /Braidwood Updated Final Safety Analysis (UFSAR), Section 15.5.1. Currently, a discrepancy exists between the description of the UFSAR Section 15.5.1 analysis and the B/B TS Bases Section 3/4.4.4 related to credit for PORV operation. The current B/B TS Bases indicates that no credit for PORV operation is taken in the FSAR analyses for Mode 1,2, and 3 transients. A revised UFSAR safety analysis for the Spurious SI at Power transient credits making a PORV available to mitigate the maximum pressurizer overfill case in the analysis. During preparation of the UFSAR change to resolve the discrepancy between the safety analysis and the TS Bases,it was determined that a TS LCO change would also be needed to take credit for the automatic function of the PORVs. Approval of this amendment request will allow a B/B UFSAR revision to cre. lit the automatic function of tne PORVs to mitigate the Spurious SI at Power transient, only.
This proposed amendment request is subdivided as follows:
- 1. Attachment A gives a description and safety analysis of the proposed changes in this amendment.
- 2. Attachment B includes the marked up Technical Specification LCOs and Bases pages for the current Byron and Braidwood Technical Specifications.
- 3. Attachment C describes Comed's evaluation performed in accordance with 10 CFR 50.92(c),
which confirms that no significant hazards consideration is involved.
- 4. Attachment D provides the Environmental Assessment.
- This proposed amendment has been reviewed and approved by Comed Onsite and Offsite Review in accordance with Comed procedures. Comed is notifying the State ofIllinois of this application for amendment by transmitting a copy of this letter and its attachments to the designated state
- official.
I l-i
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(p:\98byttrs\980166. doc)
l 1
( l NRC Document Control Desk j May 29,1998
- Page 3 i
To the best of my knowledge, the statements contained in this document are true and correct.
L Please direct any questions you may have concerning this submittal to this office.
l 1 Sincerely,
~t K. L Graesser Site Vice President l Byron Nudcar Power Station KLG/L2/mn +^"-^: : ^= ^ =- ^ :- ^:' .
- OFFICIAL SEAL" '
Patncie Havenge I' Subscribed and swom to before me, a Notary Public q m Mhc state onihnois q My Commission Empires March 27,2000 ;
in and for the State ofIlh.nois, tlu.s 09 day m_=ccc_cc_cz,, -,_ j -
of % b- .1998 Notary Public h kh '& Y Attachments cc: Regional Administrator - RIII Byron Project Manager NRR Braidwood Project Manager - NRR Senior Resident Inspector - Byron Senior Resident inspector - Braidwood Office of Nuclear Facility Safety - IDNS (p:\98byltn\980166. doc) i
ATTACHMENT A DESCRIPTION AND SAFETY ANALYSIS FOR THE PROPOSED CHANGES A.
SUMMARY
OF PROPOSED CHANGES Pursuant to 10 CFR 50.90, Commonwealth Edison (Comed) proposes to amend Facility Operating Licenses NPF-37, NPF-66, NPF-72, and NPF-77. The proposed change revises Byron and Braidwood (B/B) Technical Specification (TS) Section 3/4.4.4, " Relief Valves," and the corresponding TS Bases. The proposed revision to Byron and Braidwood Limiting Condition for Operation (LCO) 3.4.4 includes two new actions to address pressurizer power operated relief valve (PORV) inoperability due to automatic circuitry failures. A change is
- also proposed to Surveillance Requirement 4.4.4.2 to reflect the changes made to the LCO.
Comed also proposes to revise TS Bases Section 3/4.4.4, " Relief Valves," to indicate that the automatic control function of the pressurizer PORVs is credited on a limited basis to mitigate the Inadvertent Operation of Emergency Core Cooling System (Spurious SI) at Power transient only. In addition, the proposed revision to the Bases states that both manual and automatic operation capabilities are required for the PORVs to be considered operable. The TS Bases further state that if the automatic actuation circuitry of a PORV is inoperable, that PORV is considered inoperable.
In conjunction with NRC approval of the above changes, the corresponding description of the Spurious SI transient in Section 15.5.1 of the Byron and Braidwood (B/B) Updated Final Safety' Analysis Report (UFSAR) will be revised to reflect that automatic action of the
- pressurizer PORVs is credited to mitigate the potential consequences of a Spurious SI at Power transient.
The proposed TS LCO and Bases change is described in detail in Section E of this attachment. .
I Marked up pages are provided in Attachments B-1 and B-2 for Byron and Braidwood, respectively.
B. DESCRIPTION OF THE CURRENT REQUIREMENTS The LCO for TS Section 3/4.4.4 requires that the pressurizer PORVs (1/2RY455A and 1/2RY456) and their associated block valves (1/2RY8000A/B) be OPERABLE in Modes 1,2, and 3. The LCO action statements allow for the closure of one or both PORV block valves, with power maintained, in the event either PORV is INOPERABLE due to excessive seat leakage only. However, if one PORV is INOPERABLE due to any other reason besides excessive seat leakage, action statement b. allows for closure of its associated block valve, with power removed, for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> if operability of the PORV cannot be reestablished within i hour. If both PORVs are considered INOPERABLE due to any other reason than excessive !
' seat leakage, action statement c. requires restoration of a PORV within a 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> timeframe or - l l
1 Attachment A. Safety Analysis
~
l the plant must be in HOT STANDBY within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and HOT SHUTDOWN within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
C. BASES FOR THE CURRENT REQUIREMENTS The current Bases for TS 3/4.4.4 state that no credit for PORV operation is taken for Modes 1,2, and 3 transients. This statement establishes the criteria that the pressurizer PORVs are considered OPERABLE in either the manual or automatic mode, although the automatic mode is preferred since this mode minimizes required operator action.
As discussed in the B/B UFSAR Section 15.5.1, the Spurious SI at Power transient is considered an ANS Condition II event. In the current licensing basis for B/B, the analysis establishes the acceptance criteria for the Spurious SI at Power transient as follows:
- 1. Pressure in the reactor coolant and main steam systems should be maintained below 110% of the design values,
- 2. Fuel cladding integrity shall be maintained by ensuring that the minimum departure from nucleate boiling ratio (DNBR) remains above the DNBR limit, derived at a 95%
confidence level and 95% probability, and
- 3. An incident of moderate frequency should not generate a more serious plant condition without other faults occurring independently.
The Spurious SI at Power transient analyses are documented in Section 15.5.1 of the B/B UFSAR. There are two cases that are analyzed for this transient to determine compliance with the acceptance criteria documented above. The first analysis is the minimum DNBR case which verifies acceptance criteria 1 and 2 are met. The second analysis is the pressurizer overfill case which ensures that acceptance criteria 3 is met. B/B UFSAR Section 15.5.1, currently states that if the pressurizer becomes water solid during this transient when Reactor Coolant System (RCS) pressure is at or above the pressurizer safety relief valve (PSRV) setpoint, it is difficult to demonstrate that the Condition II Spurious SI transieat does not lead to a more serious plant condition. This statement in the UFSAR is based on the fact that the PSRVs have not been qualified to reseat after passing subcooled liquid. Therefore, the analysis establishes conservative acceptance criteria that a PORV becomes available for pressure relief prior to the pressurizer becoming water solid. Therefore, the capability of the PSRVs to reseat after passing subcooled liquid is never challenged as long as the acceptance criteria for pressurizer overfill is met. Since the current TS allow for the potential condition of the plant operating with both PORVs blocked, action must be taken by plant operators to terminate the ECCS injection flow or ensure that at least one PORV is unblocked and available for water relief prior to reaching a water solid condition in the pressurizer.
2 Attachment A. safety Analysis
D. NEED FOR REVISION OF THE REQUIREMENT
. Currently, a discrepancy exists between the description of the UFSAR Section 15.5.1 analysis and the B/B TS Bases Section 3/4.4.4 related to credit for PORV operation. The current B/B TS Bases indicates that no credit for PORV operation is taken in the FSAR analyses for Mode 1,2, and 3 transients. A revised UFSAR safety analysis for the Spurious SI at Power transient credits making a PORV available to mitigate the maximum pressurizer overfill case in the analysis. During preparation of the UFSAR change to resolve the discrepancy between the safety analysis and the TS Bases, it was determined that a TS LCO change would also be needed to take credit for the automatic function of the PORVs.
This revision to the TS Bases is needed to support the proposed change to B/B UFSAR Section 15.5.1 allowing for the automatic function of the pressurizer PORVs to be credited to mitigate the consequences of the Spurious SI at Power transient. The ability of plant operators to manually control RCS pressure via the PORVs is questionable with the RCS in a water solid condition. Therefore, this proposed revision will allow Byron and Braidwood Stations to specifically credit the automatic function of the PORVs to provide mitigation for the Spurious SI at Power transient only.
Approval of the TS and Bases changes described below will allow for the appropriate UFSAR text to be updated and will bring both plants in compliance with their licensing basis.
E. DESCRIPTION OF THE PROPOSED CHANGES -
TS LCO 3.4.4 is revised by adding two new actions as items b. and c. The uisting action items b., c., d., and e are relabeled as d., e., f., and g., respectively. New LCO action b.
addresses the condition ofinoperability of one PORV as a result of automatic actuation
[ circuitry malfunctions. This action requires closing the associated block valve, with power
(' maintained, if the PORV is not restored to operability within one hour. The new action i allows a period of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to restore the inoperable PORV to OPERABLE status or the plant must be in at least HOT STANDBY within the next six hours and in HOT SHUTDOWN within the following six hours. New LCO action c. addresses the inoperability of two PORVs as a result of automatic actuation circuitry malfunctions. If at least one PORV is not restored to OPERABLE status within one hour, this action requires closing the associated block valves, with power maintained, and the plant is required to be in at least HOT STANDBY within the next six hours and in HOT SHUTDOWN within the following six hours. Finally, changes are made to the current actions b. and c. of LCO 3.4.4 (which become actions d. and e. in the revised LCO) and to Surveillance Requirement 4.4.4.2 to reflect the addition of the new LCO actions discussed abovc.
A new item .B is added to the TS Bases Section 3/4.4.4 discussion of PORV function which states, " Automatic control ofPOR Vs to control reactor coolant system pressure. This is afunction that reduces challenges to the Code Safety Valvesfor an Inadvertent Safety Injection at Power event." The existing items B, C, and D are relabeled as items C, D, and E respectively. The relabeled item D is modified to include automatic control of reactor coolant system pressure 3 Attachment A. Safety Analysis
- _ _ . _ _ _ - _ _ _ _ _ - - - _ _ = _ _ _ -- _ n
as a function of the PORVs. In addition, the last paragraph of TS Bases Section 3/4.4.4 is revised tro state that the PORV function is credited for :he Inadvertent Safety Injection at Power Transient and that both manual and automatic operation capabilities are required for the PORVs to be considered operable. The Tc 3ases also indicate that if the automatic actuation circuitry of a PORV is inoperable, that PORV is inoperable. However, placing the PORV in manual control does not render the PORV inoperable as long as the automatic '
actuation circuitry is available.
F. SAFETY ANALYSIS OF THE PROPOSED CHANGES 1
As stated previously, one of the ANS Condition II transient acceptance criteria is that an incident of moderate frequency must not lead to a more serious incident without additional failures. The current safety analysis acceptance criteria for the Spurious SI at Power pressurizer overfilling case is that the transient must be terminated prior to the point at which the pressurizer becomes water solid. This conservative acceptance criteria precludes the potential for water relief through the PSRVs which are not currently qualified to pass subcooled liquid. _ UFSAR Section 15.5.1 currently states that it is difficult to prove that water relief through the PSRVs due to a water solid pressurizer does not result in a more significant event. The postulated scenario is that if the PSRVs were to pass subcooled RCS liquid and not reclose, the transient could potentially proceed to a more significant event due to the uncontrolled release path through the PSRVs. Note, however, that the statement in UFSAR Section 15.5.1 regarding water relief through a PSRV is somewhat inconsistent with information documented elsewhere in the B/B UFSAR. The scenario of an uncontrolled release of RCS inventory through.a stuck open PSRV or PORV is already analyzed in B/B UFSAR Section 15.6.1. The Section 15.6.1 transient has been determined by the NRC to meet all acceptance criteria and, per the NRC Standard Review Plan (Reference 2), is considered an ANS Condition II event and is not analyzed as representing a precursor to an ANS Condition III event (i.e., LOCA). The acceptability of the stuck open PSRV or PORV transient evaluated in UFSAR Section 15.6.1 is based on a comparison of the radiological consequences of the event compared to a LOCA (UFSAR Section 15.6.5). In general, the same arguments for UFSAR Section 15.6.1 with respect to radiological consequences apply to the Spurious SI at Power transient maximum overfill case in the event that water relief through a PSRV resulted in an uncontrolled release path from the RCS.
The revised design analysis for the Spurious SI at Power transient assumes that one pressurizer PORV is fully open for pressurizer pressure relief within 460 seconds after the reactor trip.
The 460 seconds includes a 40 second time delay to account for block valve and PORV stroke time. The revised design analysis is performed for the Byron and Braidwood Units assuming replacement steam generators. For the Spurious SI maximum overfill case, analysis for a unit l .with the replacement steam ge erators is bounding compared to the original steam generators. q l
l As currently stated in the TS Bases Section 3/4.4.4, "... the automatic mode is the preferred I i
configuration, as this provides pressure relieving capability without reliance on operator action." In this submittal, the basis requirement for PORV operability is changed to state that a PORV is operable when it is capable of being manually cycled and capable of being operated I
4 Attachment A. Safety Analysis
in automatic mode. This capability for automatic function could be met even if the PORV {
block valves were closed to isolate one or more PORVs with excessive seat leakage. Since the block valves are maintained energized in the event of excessive seat leakage, they can be l opened to make the PORVs available within the assumed time frame in the revised analysis. '
Existing Emergency Operating Procedures include steps to verify at least one PORV relief path is available; if the associated block valve is not open, the procedures specifically direct the operator to open the PORV isolation valve. In the event of PORV inoperability for any reason beside excessive seat leakage or automatic actuation circuitry in Modes 1,2 or 3, TS LCO 3.4.4 revised action statements d. and e. govern the appropriate operator actions.
The PORVs (1/2RY455A and 1/2RY456) at both Byron and Braidwood Stations are classified as safety related components. The PORVs are air-operated valves manufactured by Copes.
Vulcan. The valves are equipped with safety related actuators and safety related accumulator -
tanks which maintain valve function during a loss of instrument air. Note that the instrument air supply valves to the PORVs isolate upon a Phase A containment isolation signal which occurs concurrent with a safety injection signal. As dommented by the NRC in a safety evaluation report dated November 4,1988 (Reference .y, the pressurizer PORVs at Byron and Braidwood Stations are qualified to cycle at least 50 times in the event of a loss of instrument air. Based on a review of the pressurizer pressure history from the Spurious SI at Power transient analysis, Comed hu determined that 50 cycles is sufficient to allow RCS pressure centrol for the Spurious SI at Power transient. Pre-operational startup testing performed at the stations indicates that the PORVs will actually cycle in excess of 100 complete cycles in
. the event of a loss of instrument air. Therefore, sufficient air supply is available in the PORV accumulators to provide their mitigation function in automatic mode for this transient. Note that the transient would be terminated by plant operators when the ECCS safety injection pumps were secured from the injection mode. Implicit in the conclusion that sufficient air is
. available in the accumulators to allow the PORVs to mitigate this transient is the assumption that plant operators terminate the ECCS injection within 20 minutes after Spurious SI initiation. This 20 minute action time is consistent with the original licensing basis for Byron and Braidwood Stations for the Spurious SI at Power transient.
Comed recently performed review of the piping and support system documentation to verify that the PORV downstream piping systems are qualified to pass steam and/or subcooled liquid for this transient and are able to withstand the potential impact from repeated cycling of a PORV. The PORV discharge piping at Byron and Braidwood Stations was qualified per NUREG-0737, item II.D.1, to function under all design basis transients and accidents. This que.lification was reaffirmed by the recent review.
l, The PORV control circuits are classified as safety related. Specifically, the safety related components are as follows: a) the valve solenoids and limit switches, b) the 125 Volt DC power supplies, c) the control switches and valve position indicating lights on the board in the Main Control Room (MCR), d) the associated cabling, and e) the permissive auto control relays / isolation devices in the control circuits. Therefore, the manual portion of the PORV function is all safety related. In addition, the automatic portion of the PORV circuitry, the instrument channels from the process sensors, through the field wiring, and to the isolation 5 Attachment A. Safety Analysis l'
L
E 1 l
devices in the instrument cabinets are also safety related. The portion of the circuit that is ;
l classified as non-safety related is the portion between the instrument loop isolation relays and the control circuit isolation devices that process the automatic actuation signal. The isolation devices in this portion of the circuitry ensure that the General Design Criteria (GDC) requirements 17 and 18 of 10CFR50, Appendix A, are met for separation and isolation in the PORV circuitry. This configuration is consistent with the original design of the plants.
However, both stations have implemented modifications which ensure that automatic control of both PORVs is available during loss of offsite power conditions. These modifications were implemen:ed by both stations (Reference 4) in response to NRC Generic Letter (GL) 90-06,
" Power-Operated Relief Valve and Block Valve Reliability and Additional Low-Temperature Overpressure Protection for Light-Water Reactors."
Even though the equipment that comprises the non-safety related portion of the PORV circuitry was not purchased under 10CFR50, Appendix B, and 10CFR21 criteria, the j components, panels, and cables are the same type and quality as the safety related components elsewhere in the system. In addition, this portion of the PORV circuitry is maintained in the same manner as the safety related portions of the circuitry. Given that the power supply to all portions of the PORV component functions is reliable (i.e., Class 1E), there is high assurance that the automatic control function for the pressurizer PORVs would remain available under all normal and accident conditions to prevent challenges to the PSRVs. The conclusion that the automatic function of the pressurizer PORVs is available for mitigation of the Spurious SI at Power transient is consistent with the assumption that the automatic PORV function is also i available when the system is in ARM LO TEMP (i.e., low temperature overpressure {
protection). The signals for the at power portion are processed separately from the cold overpressure protection signals. However, the quality standards and safety grade status is similar. Therefore, it is as reasonable to credit the automatic function of the PORVs to mitigate the at power overpressure transient (Spurious SI at Power) as it is the cold overpressure transient.
l I
l In addition, the NRC performed a regulatory analysis which is documented in NUREG-1316 (Reference 1). This regulatory analysis was an evaluation of PORV and block valve reliability in PWR power plants. In that report, the staff concluded that "... it is not cost effective to ,
replace (backfit) existing non-safety grade POR Vs and block valves with POR Vs and block valves l that are safety gradefor the sole purpose ofmaking them safety grade when they have been determined to perform any ofthe safety-relatedfunctions discussed in Section 2.1 ofthis report or to i perform any other safety relatedfunction that may be identifiedin thefuture... " This regulatory analysis by the NRC provides additional support to the basis for allowing Byron and Braidwood Station to take limited credit for the automatic function of the PORVs to provide mitigation for the Spurious SI at Power transient. In NUREG-1316, the staff proposed three actions to increase tb reliability of PORVs and block valves to provide assurance they will function when required. These actions are summarized below:
- 1. Include PORVs and block valves within a quality assurance (QA) program in compliance with 10CFR50, Appendix B; 6 Attachment A-Safety Analysis
(; -
l 2. Ensure that TS require that electric power is maintained to the block valves when they are 1 closed so that the valves can be readily opened from the MCR; and
- 3. Place the block valves within the scope of NRC GL 89-10 (Reference 5).
l Byron and Braidwood Stations have previously implemented all three of the above actions.
L For example, the PORVs are currently on a periodic preventative maintenance and surveillance schedule. In addition, stroke time testing is performed on the PORVs to ensure that the valves function properly. The B/B TS do allow for operation with the block valves closed if the pressurizer PORVs are considered inoperable due to excessive seat leakage.
However, in this circumstance, power must be maintained to the block valves to ensure that they are available to be opened, if required. Finally, the PORV block valves (1/2RY8000A/B) at both stations are included within the scope of the GL 89-10 Program at the sites. The block r valves are subject to inspection and testing per Comed's commitment to GL 89-10 and are l considered fully capable of opening and/or closing, as required, under design basis conditions.
l Note that the overpressure protection function of the PORVs is within the scope of the l Maintenance Rule Program at both Byron and Braidwood Station, as required by 10CFR50.65 and implemented in accordance with NRC Regulatory Guide 1.160 (Reference 6). The overpressure protection function provided by the system (RY) is considered risk significant l and has specific performance criteria for reliability and availability. The performance criteria l encompass both the manual and automatic PORV function along with the other related components in the RY system.
There is additional justification to accept the revised status of the PORVs to mitigate the Spurious SI at Power maximum overfill case. The NRC Standard Review Plan, NUREG-0800 (Reference 2), does not have " overfill" acceptance criteria for this transient. The B/B UFSAR and associated Safety Evaluation Reports (SERs) do not have " overfill" acceptance criteria, either. The acceptance criteria of precluding a water solid condition in the pressurizer is very conservative with respect to the actual ANS Condition II acceptance criteria that an event of moderate frequency must not proceed to a more serious event without additional failures. The additional failure scenario would be the potential failure of the PORVs to open l in automatic. As stated previously in this section, an inadvertent opening of a PSRV is already evaluated in UFSAR Section 15.6.1 and is considered an ANS Condition II transient. The
' safety analysis for Section 15.6.1 of the B/B UFSAR demonstrates that the inadvertent opening of a PSRV accident meets appropriate ANS Condition II acceptance criteria. The transient analysis for the UFSAR section 15.6.1 analysis does not evaluate the transient as a j potential precursor to a more significant event. In addition, the' dose consequences are determined to be acceptable when compared to a LOCA. The same general arguments are applicable to the Spurious SI at Power transient maximum overfill case.
In effect, the revised design analysis for the Spurious SI at Power transient demonstrates that the NRC Standard Review Plan (SRP) acceptance criteria for the transient are met. The DNB and maximum RCS pressure limits are maintained in the minimum DNBR case. The analysis .
for the maximum pressurizer overfill case demonstrates that the event has acceptable l l
7 Attachment A. Safety Analy2is a_____________-_-__-_____-- _ _ _ _ - - _ _ _ - - .
r.
I consequences while crediting the automatic function of the PORVs to mitigate the transient.
The automatic function of the PORVs has demonstrated itself to be reliable over the operating life of the plants. The circumstance where both PORVs would fail to cycle in automatic mode does not necessarily represent a failure to meet the UFSAR acceptance I criteria for the Spurious SI transient which states that this Condition II transient must not proceed to an incident of greater magnitude without additional failures occurring. As stated previously, this scenario is functionally equivalent to the UFSAR Section 15.6.1 transient which is considered an ANS Condition II transient and not a Condition III transient.
l ' In the context of this submittal, the allowance of the pressurizer PORVs to be credited to j mitigate the consequences of the Spurious SI at Power transient is similar to the limited allowance that is credited to the PORVs for other accidents and transients that are contained in the current B/B licensing basis. For example, the PORVs are currently assumed to function in manual mode for the Steam Generator Tube Rupture (SGTR) accident in B/B L UFSAR Section 15.6.3. The PORVs are modeled to allow plant operators to reduce RCS l pressure following a SGTR event. For the Low Temperature Overpressure Protection I (LTOP) system, the automatic function of the pressurizer PORVs is specifically credited to
( mitigate this event. The circuitry that is used for the LTOP automatic function is similar in
! terms of quality and classification as the PORV at power automatic circuitry.
I In summary, the basis for crediting the automatic PORV function to provide mitigation for l
l the Spurious SI at Power transient is sound. The manual portion of the PORV function is all l safety related. A portion of the automatic actuation circuitry is considered non-safety related.
However, modifications have been implemented by both stations which ensure the automatic control function of the PORVs is maintained during a loss of offsite power event by supplying l Class 1E power to the isolation relays in the PORV automatic actuation circuitry. The basis i for revising the TS bases to credit the automatic function of the PORVs to mitigate the Spurious SI at Power transient is further supported by the fact that the safety analysis for this transient does not assume a concurrent loss of offsite power in the analysis assumptions. This assumption is consistent with the NRC SRP requirements. Additionally, the PORV !
overpressure protection function is included in the scope of the Maintenance Rule Program at I both Byron and Braidwood Stations. A regulatory analysis performed by the NRC and documented in NUREG-1316 concluded that it was not cost effective to upgrade existing non- ,
safety grade components in PORVs for the sole purpose of making them safety grade when
. they have been determined to perform various safety related functions. Finally, Comed believes that this proposed change is consistent with similar analyses that are currently in the i licensing basis for Byron and Braidwood Stations.
- Given the current operating status of the PORVs, including their reliable operating history at the plants, Comed has determined that that it is acceptable to credit the automatic function of
' the PORVs for mitigation of the Spurious SI at Power transient only.
l The new actions for PORV inoperability due to automatic circuitry inoperability are similar l- to the existing actions which address PORV inoperability due to causes other than excessive seat leakage with one exception, electrical power is maintained to the block valve for the 8 Attachment A. Safety Analysis
l l l affected PORV. Comed believes this proposed change is consistent with the i - recommendations of NUREG-1316 (Reference 1), for plants that run with the block valves closed, to maintain electrical power to the block valves so that they can be readily opened from the Main Control Room. This will ensure that the manual function of the PORVs remains available to perform other safety related functions required for mitigation of events
. such as a Steam Generator Tube Rupture (SGTR) or an Anticipated Transient Without Scram, i i
G. IMPACT ON PREVIOUS SUBMITTALS I On December 13,1996, Comed submitted a request for conversion from current Byron and Braidwood Technical Specifications to Improved Technical Specifications (ITS). The impact of the proposed change on the ITS conversion will be addressed in a separate submittal to l NRC.
H. SCHEDULE REQUIREMENTS There are no specific schedule requirements for this submittal. Byron and Braidwood Stations have performed operability assessments which determined that there is reasonable assurance of operability. Approval of this amendment request is required to allow the stations to close the open operability assessments by revising the appropriate sections of the UFSAR.
I. REFERENCES
- 1. R. Kirkwood, "Techniul Findings and Regulatory Analysis Related to Generic Issue 70, Evaluation of Power-Operated Relief Valve and Block Valve Reliability in PWR Nuclear Power Plants,". NUREG-1316, dated December 1989.
- 2. "NRC Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants, LWR Edition," NUREG-0800, July 1981.
- 3. " Byron Station Units 1 and 2 and Braidwood Station Units 1 and 2 Natural Circulation Cooldown (TAC NOS. 56199,63239,64018,64045)," NRC Safety Evaluation Report, dated November 4,1988.
- 4. Comed Response to NRC Generic Letter (GL) 90-06, " Power-Operated Relief Valve and Block Valve Reliability and Additional Low-Temperature Overpressure Protection for Light-Water Reactors," D. L. Taylor to NRC, dated December 6,1990.
- 5. NRC Generic letter 8910, " Safety-Related Motor Operated Valve Testing and Surveillance," dated June 28,1989.
- 6. " Monitoring the Effectiveness of Maintenance at Nuclear Power Plants," NRC Regulatory Guide 1.160, Rev. 2, dated March 1997.
9 Attachment A. Safety Analysis