ML23010A259
| ML23010A259 | |
| Person / Time | |
|---|---|
| Site: | Technical Specifications Task Force |
| Issue date: | 01/11/2023 |
| From: | Michelle Honcharik NRC/NRR/DSS/STSB |
| To: | Technical Specifications Task Force |
| References | |
| EPID L-2022-PMP-0011 | |
| Download: ML23010A259 (1) | |
Text
January 11, 2023 Technical Specifications Task Force 11921 Rockville Pike, Suite 100 Rockville, MD 20852
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION RE: TRAVELER TSTF-592, REVISION 0, REVISE AUTOMATIC DEPRESSURIZATION SYSTEM (ADS)
INSTRUMENTATION REQUIREMENTS (EPID L-2022-PMP-0011)
Dear Members of the Technical Specifications Task Force:
By letter dated July 19, 2022 (ADAMS Accession No. ML22200A080), you submitted a request to the U.S. Nuclear Regulatory Commission (NRC) to incorporate Traveler TSTF-592, Revision 0, Revise Automatic Depressurization System (ADS) Instrumentation Requirements, into the standard technical specifications.
Upon review of the information provided, the NRC staff has determined that additional information is needed to complete the review. Mr. Brian Mann, Vice President of Industry Programs, EXCEL Services Corporation, agreed that the NRC staff will receive your response to the enclosed request for additional information questions within 60 calendar days of the date of this letter.
The review schedule that was provided in the acceptance letter dated September 28, 2022 (ADAMS ML22256A212), has not changed.
MILESTONE DATE Issue Draft Safety Evaluation August 31, 2023 Issue Final Safety Evaluation December 22, 2023 If you have any questions, please contact me at (301) 415-1774 or via email to Michelle.Honcharik@nrc.gov.
Sincerely, Michelle C. Honcharik, Senior Project Manager Technical Specification Branch Division of Safety Systems Office of Nuclear Reactor Regulation Project No. 753 Michelle C.
Honcharik Digitally signed by Michelle C. Honcharik Date: 2023.01.12 11:34:46 -05'00'
Enclosure:
Request for Additional Information cc: See next page
Technical Specifications Task Force Project No. 753 cc:
Technical Specifications Task Force c/o EXCEL Services Corporation 11921 Rockville Pike, Suite 100 Rockville, MD 20852 Attention: Brian D. Mann Email: brian.mann@excelservices.com Drew Richards STP Nuclear Operating Company 12090 FM 521 Mail Code: N5016 Wadsworth, TX 77483 Email: amrichards@stpegs.com Kevin Lueshen Constellation Energy Generation 4300 Winfield Road Warrenville IL 60555 Email: kevin.lueshen@constellation.com Jordan L. Vaughan Duke Energy EC07C / P.O. Box 1006 Charlotte, NC 28202 Email: jordan.vaughan@duke-energy.com Ryan M. Joyce Southern Nuclear Operating Company 3535 Colonnade Parkway / Bin N-274-EC Birmingham, AL 35243 Email: rmjoyce@southernco.com Wesley Sparkman Southern Nuclear Operating Company 3535 Colonnade Parkway / Bin N-226-EC Birmingham, AL 35242 Email: wasparkm@southernco.com
ML23010A259 NRR-106 OFFICE NRR/DSS/STSB NRR/DSS/STSB NAME Vic Cusumano Michelle Honcharik DATE 12/12/2022 1/10/2023
Enclosure REQUEST FOR ADDITIONAL INFORMATION TECHNICAL SPECIFICATIONS TASK FORCE TSTF-592 REVISE AUTOMATIC DEPRESSURIZATION SYSTEM (ADS)
INSTRUMENTATION REQUIREMENTS (EPID L-2022-PMP-0011)
By letter dated July 19, 2022 (ADAMS Accession No. ML22200A080), the Technical Specifications Task Force (TSTF) submitted to the U.S. Nuclear Regulatory Commission (NRC)
Traveler TSTF-592, Revision 0, Revise Automatic Depressurization System (ADS)
Instrumentation Requirements. TSTF-592 would revise Technical Specification (TS) 3.3.5.1, Emergency Core Cooling System (ECCS) Instrumentation, Actions related to the Automatic Depressurization System (ADS) initiation instrumentation to correct several overly restrictive requirements, and to treat less significant channel inoperabilitys consistently. The proposed change modifies NUREG-1433, Standard Technical Specifications - General Electric BWR/4 Plants, and NUREG-1434, Standard Technical Specifications, General Electric BWR/6 Plants (the STS).
The purpose of the ECCS instrumentation is to initiate appropriate responses from systems to ensure that the fuel is adequately cooled in the event of a design basis accident or transient.
The ECCS is designed to cool the reactor core following a loss of coolant accident (LOCA). The typical boiling water reactor (BWR) ECCS has low-pressure and high-pressure subsystems. The low pressure ECCS subsystems are designed to mitigate a large break LOCA where reactor vessel pressure rapidly decreases to the point at which the low-pressure ECCS pumps can inject water. There are two redundant divisions for each of the low-pressure ECCS subsystems.
For example, BWR/4 plants typically have two Low Pressure Coolant Injection (LPCI) subsystems and two Core Spray (CS) subsystems. BWR/6 plants typically have one Low Pressure Core Spray (LPCS) subsystem and three LPCI subsystems. There is a single high-pressure ECCS subsystem. For example, BWR/4 plants have High Pressure Coolant Injection (HPCI), and BWR/6 plants have High Pressure Core Spray (HPCS). The high-pressure ECCS subsystem is designed to mitigate small break LOCAs during which reactor vessel pressure remains higher than the ability of the low-pressure ECCS pumps to inject water.
The ECCS instrumentation actuates in part, the Automatic Depressurization System (ADS). The ADS provides redundancy for the single high-pressure ECCS subsystem. In the event of failure of the high-pressure ECCS subsystem, the ADS valves open to rapidly reduce the reactor vessel pressure to the point at which a low-pressure ECCS pump can inject water.
To complete its review of TSTF-592, the NRC staff has determined that additional information is needed. The regulatory basis and the requested additional information are as follows.
REGULATORY BASIS FOR REQUEST 10 CFR 50.36(a)(1) states in part: A summary statement of the bases or reasons for such specification shall also be included in the application but shall not become part of the technical specifications.
10 CFR 50.36(c)(2) states: Limiting conditions for operation are the lowest functional capability or performance levels of equipment required for safe operation of the facility. When a limiting condition for operation of a nuclear reactor is not met, the licensee shall shut down the reactor or follow any remedial action permitted by the technical specifications until the condition can be met.
REQUESTS FOR ADDITIONAL INFORMATION
- 1. TSTF-592 proposed to renumber BWR/4 and BWR/6 STS 3.3.5.1, Emergency Core Cooling System (ECCS) Instrumentation, Condition H to Condition I. In the ECCS Instrumentation Bases B 3.3.5.1 markup, it appears that TSTF-592 did not change Condition H to Condition I in every instance. The NRC staff requests that TSTF-592 be reviewed and updated as appropriate. Applies to BWR/4 and BWR/6 STS Bases B 3.3.5.1.
- 2. TSTF-592 provided markups to the ECCS Instrumentation Bases B 3.3.5.1 for the ADS Functions associated with new Actions H.1, H.2, and H.3. Required Action H.1 is intended to ensure appropriate action when initiation capability is lost in both trip systems. The first paragraph in the BWR/6 ECCS Instrumentation Bases B 3.3.5.1 description for Actions H.1, H.2, and H.3 states, Required Action H.1 is intended to ensure that appropriate actions are taken if one or more Functions 4.e and 4.f channels, and one or more Function 5.e channels are inoperable. However, it would take at least two and possibly three Function 5.e channels to be inoperable before Trip System B would lose initiation capability. The BWR/4 STS states, Required Action H.1 is intended to ensure that appropriate actions are taken if a combination of Function 4.e, 4.f, 5.e, and 5.f channels are inoperable such that neither ADS Trip System A or B has two -Pressure High channels associated with one low pressure ECCS pump. Given that the proposed remedial actions (i.e., Condition H and associated Required Actions and Completion Times) are nearly identical for BWR/4 and BWR/6, it appears that the wording from the BWR/4 STS Bases (modified for the appropriate BWR/6 ADS Function designators) is more appropriate for the BWR/6 STS Bases: - H.1 is intended to ensure that appropriate actions are taken if a combination of Function 4.e, 4.f, and 5.e channels are inoperable such that neither ADS Trip System A or B has two Operable Discharge Pressure Therefore, based on the above, High channels associated with one low pressure ECCS pump. Therefore, based on the above, the NRC staff requests clarification on what specific conditions would require entering into Condition H and Required Action H.1. As part of the clarification, the NRC staff requests information that would explain why there is different wording in the first paragraph of the BWR/6 ECCS Instrumentation Bases B.3.3.5.1 for Actions H.1, H.2, and H.3 as compared to the BWR/4 ECCS Instrumentation Bases B 3.3.5.1 for Actions H.1, H.2, and H.3.
The NRC staff believes that diagrams would facilitate understanding of the ADS Trip System logic described in TSTF-592. Therefore, the NRC staff requests that TSTF-592 include simplified logic diagrams for the ADS Trip System. The diagrams should depict relays, contacts, and any other devices necessary to achieve ADS actuation, as well as any descriptive information to help interpret the diagrams.
- 4. The NRC position in NUREG-0737, Item II.K.3.18 states in part, The automatic depressurization system (ADS) actuation logic should be modified to eliminate the need for manual actuation to assure adequate core cooling. In response, many licensees made modifications which would extend ADS operation to events which do not result in a release of steam to the drywell, but which may require depressurization of the reactor pressure vessel (RPV) to maintain adequate core cooling. Modifications included the addition of a timer that bypasses the existing high drywell pressure trip logic if RPV water level is low for a sustained period of time (hereafter, referred to as bypass timer). The current STS Actions related to channel inoperability for the high drywell pressure function and the bypass timer function are similar regarding completion times (e.g., up to 8 days). TSTF-592 does not propose any STS changes related to the high drywell pressure function, but it does propose changes to the bypass timer, which bypasses the high drywell pressure trip logic.
From a logic perspective, inoperability of the bypass timer has the same effect as inoperability of the high drywell pressure. The inoperability of one bypass timer channel will prevent one of the ADS trip systems from automatic initiation capability unless there is a concurrent high drywell pressure signal. Likewise, the inoperability of a high drywell pressure channel will prevent one of the ADS trip systems from automatic initiation capability, unless there is a concurrent bypass timer signal. Bypass timer channel inoperability in both trip systems will prevent ADS automatic initiation capability unless there are concurrent high drywell pressure signals. Likewise, high drywell pressure channel inoperability in both trip systems will prevent ADS automatic initiation capability, unless there are concurrent bypass timer signals. TSTF-592 proposed to change the completion time for situations where bypass timer(s) is(are) inoperable from up to 8 days to 30 days (i.e., ADS Low Level Actuation Timer in BWR/4 (Function 4g and 5g) and ADS Bypass Timer High Drywell Pressure in BWR/6 (Function 4g and 5f)). STS Table 3.3.5-1, Emergency Core Cooling Instrumentation, specifies an Allowable Value for the bypass timer where according to the STS Bases, the Allowable Value serves as the limiting safety system setting (LSSS).
Technical Specifications are required by 10 CFR 50.36 to include LSSSs for variables that have significant safety system functions. LSSS are defined by regulation (50.36) as Where a LSSS is specified for a variable on which a safety limit has been placed, the setting must be chosen so that automatic protective actions will correct the abnormal situation before a safety limit is exceeded. The NRC staff considers that different treatment (i.e., completion times) in the STS for the bypass timer function as compared to the high drywell pressure function may not be responsive to the NRC position expressed in NUREG-0737 and the current STS, because ADS is part of the primary success path for automatic mitigation of a design basis accident. Based on the discussion above, the NRC staff requests that the TSTF 1) provide additional information that justifies why the proposed changes to the Actions for the bypass timer are appropriate or 2) return the bypass timer Actions to those found in the current STS (or equivalent to those in the current STS). Applies to STS for BWR/4 and BWR/6.
- 5. TSTF-592 provided markups to ECCS Instrumentation Bases B 3.3.5.1 related to Actions G.1 and G.2. However, the markup did not include a discussion regarding what Required Action G.2 is intended to ensure. For example, proposed Bases language for Required Action H.2 states, Required Action H.2 is intended to ensure that appropriate actions are taken if [], which results in automatic initiation capability being lost for that ADS trip system. The NRC staff requests that TSTF-592 includes a discussion in ECCS Instrumentation Bases B 3.3.5.1, Actions G.1 and G.2, that describes what Required Action G.2 is intended to ensure. Applies to STS BWR/4 and BWR/6.
- 6. TSTF-592 provided markups to ECCS Instrumentation Bases B 3.3.5.1 related to new Actions H.1, H.2, and H.3. While describing Required Action H.1, TSTF-592 states in part, In this situation (loss of automatic initiation capability), the 96 hour0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> or 8-day allowance, as applicable, of Required Action H.2 is not appropriate, and all ADS valves must be declared inoperable within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> after discovery of loss of ADS initiation capability (emphasis added). The Bases description for Required Action G.1 has a similar statement but clarifies the loss of ADS initiation capability by adding the following expression after capability: in both trip systems. Therefore, the NRC staff requests information that explains why ECCS Instrumentation Bases B 3.3.5.1, Actions H.1, H.2 and H.3 description did not include the expression in both trip systems, after capability. Applies to STS BWR/4 (BWR/6 Bases included this expression).
- 7. TSTF-592 provided markups to ECCS Instrumentation Bases B 3.3.5.1 related to new Actions H.1, H.2 and H.3. In the BWR/6 markup for that Bases section, the third paragraph begins with The Completion Time and ends with time for restoration or tripping of channels (emphasis added). The BWR/4 markup for new Actions H.1, H.2, H.3 did not include the expression or tripping. Its not clear to the NRC staff why there is a difference between the BWR/4 STS and BWR/6 STS regarding the expression or tripping. Therefore, the NRC staff requests information that explains the different treatment of ECCS Instrumentation Bases B.3.3.5.1 for Actions H.1, H.2, and H.3 regarding the expression or tripping.
- 8. TSTF-592 proposed to change the Completion Time from up to 8 days to 30 days for several ADS Trip System Functions (see remedial actions associated with proposed Condition H). Based on the NRC staffs review of TSTF-592 STS Bases markups, the NRC staff did not identify a clear discussion in the STS Bases that justifies continued operation at the reduced state from the state specified in the LCO for the proposed Completion Time of 30 days. Therefore, the NRC staff requests information be provided in the STS Bases that explains why 30 days is an appropriate Completion Time.
- 9. TSTF-592 proposed Condition H is associated with three Required Actions: H.1, H.2, and H.3. According to the ECCS Instrumentation Bases B 3.3.5.1 markup, Required Action H.3 is intended to ensure that appropriate actions are taken if inoperable channels within one ADS trip system do not result in loss of automatic initiation capability to respond to a design basis event but require restoration per Table 3.3.5.1-1 (emphasis added). It appears that the intended purpose of H.3 asstated above may not be appropriate for all associated Functions. For example, there are ADS Functions subject to Condition H and Required Action H.3, where it appears that inoperable channels within one ADS Trip System would result in loss of automatic initiation capability to respond to a design basis event. In the BWR/4 STS, proposed Required Action H.3 applies to Functions 4.e, 4.f, 4.g, 4.h, 5.e, 5.f, 5.g, and 5.h. Similarly, in the BWR/6 STS, proposed Required Action H.3 applies to Functions 4.e, 4.f, 4.g, 4.h, 5.e, 5.f, and 5.g. For the sake of this discussion BWR/4 Functions 4.g and 5.g, and BWR/6 Functions 4.g and 5.f, are referred to as bypass timers.
Required Action H.1 and H.2 are only applicable to Functions 4.e, 4.f, 5.e, and 5.f (BWR/4) and 4.e, 4.f, and 5.e (BWR/6). As a result, Required Action H.3 is the only Required Action that applies to the bypass timers. From the ADS logic as described in TSTF-592, one inoperable bypass timer channel will prevent one of the ADS trip systems to initiate and would result in loss of automatic initiation capability to respond to a design basis event (e.g.,
events which do not result in a release of steam to the drywell but which may require depressurization of the reactor pressure vessel (RPV) to maintain adequate core cooling) and therefore would not meet the intended purpose for Required Action H.3 as described in the STS Bases. In addition, an inoperable bypass timer channel in both ADS Trip Systems will prevent ADS actuation. Therefore, its unclear to the staff how the ADS bypass timer Function can be subject to Required Action H.3 based on not meeting the intended purpose of Required Action H.3 (i.e., an inoperable bypass timer channel within one ADS Trip System would result in loss of automatic initiation capability to respond to a design basis event). Based on the above, the NRC staff requests information that justifies why it is appropriate to associate an inoperable ADS bypass timer channel with the remedial actions provided by Condition H and Required Action H.3.
- 10. For the ADS low pressure ECCS pump discharge pressure switch (PS) instrument to perform its ADS Trip System Function (pump discharge pressure high), it relies on the pump itself to be OPERABLE and in operation. For example, based on TSTF-592 markups for BWR/6, if one of the PSs from the LPCI Pump A is inoperable, Condition H is entered, and the 30-day Completion Time clock starts for Required Action H.3. Required Action H.2 Completion Time clock does not start because the LPCS Pump has both of its PSs OPERABLE. Subsequently, if the LPCS pump is declared inoperable, its pressure switches would not be available and ADS Trip System A will not initiate ADS on a valid signal even if LPCI Pump A starts. The NRC staff requests information that explains how this situation would be addressed. As part of the response, address whether credit should be given for the pressure switches associated with an inoperable low-pressure injection/spray pump.
- 11. The current BWR/4 and BWR/6 STS 3.3.5.1 for the ADS Trip System Function has a remedial action for when a low pressure ECCS pump discharge pressure high channel is inoperable that states, Restore channel to OPERABLE status (see current Required Action G.2). TSTF-592 proposed a new remedial action (see Required Action H.3) for when a low pressure ECCS pump discharge pressure high channel is inoperable that states, Restore all channels to OPERABLE status (emphasis added). The NRC staff requests information that provides the basis for changing remedial action wording from channel to all channels.
- 12. TSTF-592 proposed Condition H is associated with three Required Actions: H.1, H.2, and H.3. From the proposed change to the TS Bases, Action H.2 is required when a trip system does not have at least one low-pressure injection/spray pump with both Discharge Pressure High channels OPERABLE. Therefore, Action H.2 is only required if there are multiple pressure switches inoperable in a Trip System. As such, the Completion Times for H.2 would necessarily have a modified time zero. The 96-hour completion time would only start when a switch becomes inoperable, concurrent with other inoperable switches, that results in no pumps in that trip system having two OPERABLE Discharge Pressure High channels concurrent with HPCI or RCIC inoperability. Likewise, the 8-day Completion Time would only start when a switch becomes inoperable, concurrent with other inoperable switches, that results in no pumps in that trip system having two OPERABLE Discharge Pressure High channels. The proposed wording for the 96-hour Completion Time has inoperable channel when it actually starts when multiple channels become inoperable such that no low-pressure pump in a Trip System has both pressure switches operable concurrent with HPCI or RCIC inoperability. The proposed wording for the 8-day Completion Time implies that it would start when Action H.2 is required, which again requires multiple, inoperable pressure switches.
Based on the discussion above, the NRC staff requests clarification on the conditions required to start the 96 hour0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> and 8-day completion times of Action H.2.