ML24358A228
| ML24358A228 | |
| Person / Time | |
|---|---|
| Site: | Technical Specifications Task Force |
| Issue date: | 12/26/2024 |
| From: | Shivani Mehta NRC/NRR/DSS/STSB |
| To: | Technical Specifications Task Force |
| Shared Package | |
| ML24358A224 | List: |
| References | |
| EPID L-2024-PMP-0003, TSTF-597, Rev. 0 | |
| Download: ML24358A228 (8) | |
Text
DRAFT SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION TECHNICAL SPECIFICATIONS TASK FORCE TRAVELER TSTF-597, REVISION 0, ELIMINATE LCO 3.0.3 MODE 2 REQUIREMENT USING THE CONSOLIDATED LINE ITEM IMPROVEMENT PROCESS (EPID: L-2024-PMP-0003)
1.0 INTRODUCTION
By letter dated March 15, 2024 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML24075A080) as modified by supplement dated September 16, 2024 (ML24260A221), the Technical Specifications Task Force (TSTF) submitted traveler TSTF-597, Revision 0, Eliminate LCO 3.0.3 Mode 2 Requirement. Traveler TSTF-597, Revision 0, proposed changes to the Standard Technical Specifications (STS) for boiling-water reactor (BWR) designs. These changes would be incorporated into future revisions of NUREG-1433 and NUREG-1434.
U.S. Nuclear Regulatory Commission, Standard Technical Specifications, General Electric Plants, BWR/4, NUREG-1433, Volume 1, Specifications, and Volume 2, Bases, Revision 5, September 2021 (ML21272A357 and ML21272A358, respectively).1 U.S. Nuclear Regulatory Commission, Standard Technical Specifications, General Electric Plants, BWR/6, NUREG-1434, Volume 1, Specifications, and Volume 2, Bases, Revision 5, September 2021 (ML21271A582 and ML21271A596, respectively).2 The proposed change would revise the shutdown requirements in STS Limiting Condition for Operation (LCO) 3.0.3 by removing the requirement to place the unit in MODE 2 prior to entering MODE 3. This STS change will be made available to licensees through the Consolidated Line Item Improvement Process (CLIIP).
1.1 Description of the Current Limiting Condition for Operation 3.0.3 Requirement In NUREG-1433 and NUREG-1434, LCO 3.0.3 requires the unit to be placed into a MODE or other specified condition outside the currently applicable modes when an LCO is not met, and any of the following conditions are true: 1) the associated actions are not met, 2) an associated action is not provided, or 3) LCO 3.0.3 entry is directed by the associated actions. LCO 3.0.3 requires that action shall be initiated within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> to place the unit in MODE 2 (Startup) within 7 hour8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />s3, MODE 3 (Hot Shutdown) within 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />, and MODE 4 (Cold Shutdown) within 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />.
1 NUREG-1433 provides the STS for BWR/4 plant designs but is also representative of the BWR/2, BWR/3, and, in this case, of the BWR/5 plant design.
2 NUREG-1434 provides the STS for BWR/6 plant designs but is also representative in some cases of the BWR/5 plant design.
3 A reviewers note in NUREG-1433 states that plants may extend this time from 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> to a plant-specific time, if the licensee supports the extended time with plant-specific data.
The intent of each time limit to enter subsequently lower modes of operation is to ensure an orderly and timely shutdown when operation cannot be maintained within the limits for safe operation as defined by the LCO and its ACTIONS. Several LCOs identify these conditions and direct entry into LCO 3.0.3, such as when there is a loss of function of either low or high pressure ECCS (STS LCO 3.5.1) and inoperable offsite and onsite AC sources (STS LCO 3.8.1).
1.2 Description of Boiling Water Reactor Modes of Operation Table 1.1-1 shown below from NUREG-1433 and NUREG-1434 describes the conditions required for each mode of operation. The position of the reactor mode switch position and reactor coolant temperature are the main parameters that determine reactor MODE.
Additionally, reactor power also drives the reactor MODE during startup and shutdown operations.
During a typical BWR unit startup, the plant starts in MODE 4 (Cold Shutdown) with all control rods inserted and average reactor coolant temperature below 200 F. The mode switch is then moved to the Startup/Hot Standby position and MODE 2 (Startup) is entered. Control rods are withdrawn to bring the reactor critical, and the reactor coolant heats up. Control rods are further withdrawn, and reactor power is increased to approximately 10% when the mode switch is taken to Run and the reactor enters MODE 1 (Power Operation) as the unit is eventually taken to full power.
During a typical BWR unit shutdown, reactor power is reduced by inserting control rods and reducing core flow with the recirculation system. Upon reducing power to approximately 10%,
there are two methods to continue the shutdown.
The first and most frequently performed method involves inserting a low-power reactor SCRAM by placing the reactor mode switch to Shutdown. This action transitions the unit from MODE 1 directly to MODE 3 (Hot Shutdown) and skips entering MODE 2. The shutdown then continues by cooling the reactor down further until the average reactor coolant temperature is reduced to less than or equal to 200 F, at which time the unit enters MODE 4. This is typically the quicker method of shutting down a BWR.
The second method of shutting down a BWR is referred to as a soft shutdown. Upon reaching 10% reactor power, the reactor mode switch is moved to Startup/Hot Standby and MODE 2 is entered. Control rods continue to be inserted individually until all rods have been inserted. At that point, the reactor mode switch is moved to the Shutdown position and MODE 3 is entered.
The reactor is cooled down as in the first method and MODE 4 is entered when the average reactor coolant temperature is reduced to less than or equal to 200 F. This method is utilized to avoid a hydraulic transient on the control rod drive (CRD) system from the SCRAM and improve CRD reliability.
1.3 Proposed Changes to the Standard Technical Specifications Traveler TSTF-597, Revision 0, proposed revisions to LCO 3.0.3 for NUREG-1433 and NUREG-1434 to remove the requirement to be in MODE 2 prior to entering MODE 3.
1.3.1 Proposed Changes to Volume 1 of NUREG-1433 and NUREG-1434 The proposed change would modify STS LCO 3.0.3 in NUREG-1433 and NUREG-1434 as follows:
LCO 3.0.3 When an LCO is not met and the associated ACTIONS are not met, an associated ACTION is not provided, or if directed by the associated ACTIONS, the unit shall be placed in a MODE or other specified condition in which the LCO is not applicable. Action shall be initiated within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> to place the unit, as applicable, in:
- a.
MODE 2 within [7] hours, ab. MODE 3 within 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />, and bc. MODE 4 within 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />.
Exceptions to this Specification are stated in the individual Specifications.
Where corrective measures are completed that permit operation in accordance with the LCO or ACTIONS, completion of the actions required by LCO 3.0.3 is not required.
LCO 3.0.3 is only applicable in MODES 1, 2, and 3.
REVIEWER'S NOTE-------------------------
The brackets around the time provided to reach MODE 2 allow a plant to extend the time from 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> to a plant specific time. Before the time can be changed, plant specific data must be provided to support the extended time.
The effect of the change would be to better support the use of the low-power SCRAM method of shutting down the plant when shutting down in accordance with LCO 3.0.3. The proposed change would remove from NUREG-1433, the Reviewers Note at the end of LCO 3.0.3 that discusses the reason for the brackets around the MODE 2 time requirement and the process by which licensees can extend the time. This change would only apply to NUREG-1433; this note is not in NUREG-1434 due to the capability of BWR/6 plants to shut down more quickly.
1.3.2 Proposed Changes to the STS Bases The proposed change would modify the example in the STS Bases for LCO 3.0.3 (i.e., in Volume 2 of NUREG-1433 and NUREG-1434) as shown below:
For example, if MODE 2 is entered in 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, then the time allowed for entering MODE 3 is the next 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br />, because the total time for entering MODE 3 is not reduced from the allowable limit of 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />.
would be replaced with For example, if MODE 3 is entered in 9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br />, then the time allowed for entering MODE 4 is the next 28 hours3.240741e-4 days <br />0.00778 hours <br />4.62963e-5 weeks <br />1.0654e-5 months <br />, because the total time for entering MODE 4 is not reduced from the allowable limit of 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />.
The proposed STS Bases change would clarify the application of LCO 3.0.3 by using an example that is consistent with the revised LCO 3.0.3 requirements.
2.0 REGULATORY EVALUATION
As described in the Commissions Final Policy Statement on Technical Specifications Improvements for Nuclear Power Reactors (58 FR 39132, dated July 22, 1993), the NRC and industry task groups for new STS recommended that new STS include greater emphasis on human factors principles in order to add clarity and understanding to the text of the STS, and provide improvements to the Bases of the STS, which provide [] the purpose for each requirement in the STS. The improved vendor-specific STS were developed and issued by the NRC in September 1992.
The Commissions Final Policy Statement states that each LCO, Action, and Surveillance Requirement (SR) should have supporting Bases, and [t]he Bases should, at a minimum, address [certain] questions and cite references to appropriate licensing documentation (e.g.,
FSAR or Topical Report) to support the Bases.
The regulation at Title 10 of the Code of Federal Regulations (10 CFR) Section 50.36(b) requires that:
Each license authorizing operation of a utilization facility will include technical specifications. The technical specifications will be derived from the analyses and evaluation included in the safety analysis report, and amendments thereto, submitted pursuant to [10 CFR] 50.34 [Contents of applications; technical information]. The Commission may include such additional technical specifications as the Commission finds appropriate.
10 CFR 50.36(c) states the categories of items that must be included in TS. Among other items, the regulation requires that TS include LCOs. 10 CFR 50.36(c)(2)(i) states that:
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.
The NRC staffs guidance for the review of TSs is in NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR [light-water reactor]
Edition (SRP), Chapter 16.0, Technical Specifications, Revision 3, dated March 2010 (ML100351425).
3.0 TECHNICAL EVALUATION
In traveler TSTF-597, Revision 0, the TSTF proposed to modify STS 3.0.3 for NUREG-1433 and NUREG-1434 to remove the MODE 2 requirement. The requirements to be in MODE 3 within 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br /> and MODE 4 within 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br /> would remain unchanged. The NRC staff reviewed the proposed change to determine if: 1) the shutdown requirements in the proposed LCO 3.0.3 are consistent with those contained in other LCOs in the STS, 2) there is a significant safety benefit to requiring entry into MODE 2 while shutting down the plant, and 3) the proposal meets all applicable regulatory requirements.
The STS Bases for LCO 3.0.3 state, Upon entering LCO 3.0.3, 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> is allowed to prepare for an orderly shutdown before initiating a change in unit operation. This includes time to permit the operator to coordinate the reduction in electrical generation with the load dispatcher to ensure the stability and availability of the electrical grid. The time limits specified to reach lower MODES of operation permit the shutdown to proceed in a controlled and orderly manner that is well within the specified maximum cooldown rate and within the capabilities of the unit, assuming that only the minimum required equipment is OPERABLE.
When accounting for the initial hour, LCO 3.0.3 requires the plant to be in MODE 2 within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> (for a total of 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> from the time the LCO is entered), MODE 3 within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> (for a total of 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br /> from the time the LCO is entered) and MODE 4 within the next 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> (for a total of 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br /> from the time the LCO is entered). This means that the total time to place the unit in MODE 4 once the shutdown begins is 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.
Each LCO in STS Sections 3.1 through 3.10 specifies the operating modes or other conditions in which the LCO must be met (referred to as the mode of applicability). Typically, the Actions in other LCOs (other than LCO 3.0.3) require a plant to exit the mode of applicability by placing the plant in an operating MODE where the LCO does not apply when a significant degradation of safety-related plant SSC(s) occurs or if the LCO Required Actions are not completed within the specified Completion Time (CT). Accordingly, the NRC staff reviewed other STS LCOs to determine if the LCO 3.0.3 MODE 2 requirement was consistent with other plant conditions that require exiting the mode of applicability. Specifically, the NRC staff reviewed whether other LCOs required going to MODE 2 when exiting the mode of applicability requires entry into MODE 3 or MODE 4. The staff found that the MODE 2 requirement in LCO 3.0.3 is not consistent with the requirements for all other LCOs where the Actions require placing the plant in MODE 3 or MODE 4. The staff found that even for plant conditions that represent significant degradation in plant safety, the STS do not require going to MODE 2 before going to MODE 3.
In addition, in all cases where the STS Required Actions direct entry into MODE 3 or MODE 4, the CTs allowed for placing the unit in MODE 3 and MODE 4 are the same as allowed in LCO 3.0.3 (after accounting for the above-discussed one-hour preparation period built into LCO 3.0.3).
For example, LCO 3.6.1.1, Primary Containment, Required Action B, requires primary containment to be operable in MODES 1, 2, and 3. If primary containment is inoperable and not restored to operable within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, then Required Action B requires the plant be placed in a MODE in which the LCO does not apply (i.e., place the plant in MODE 4). There is no requirement to enter MODE 2 while shutting down the plant. Another example is LCO 3.4.3, Safety/Relief Valves (S/RVs), Required Action C in NUREG-1433. When the minimum number of required S/RVs are inoperable, Required Action C requires the plant to be placed in a MODE in which the LCO does not apply (i.e., MODE 4). In both examples, the plant is significantly degraded, and the STS requires entering MODE 3 (Hot Shutdown) within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and MODE 4 (Cold Shutdown) within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> which is the same time allotted in LCO 3.0.3 once accounting for the one-hour preparation time incorporated into LCO 3.0.3. Neither of these plant conditions have a requirement to enter MODE 2 within any amount of time. The staff found that entry into MODE 2 is not required in any LCOs that require entry into MODE 3 or MODE 4 when exiting the mode of applicability is required.
The NRC staffs review of the STS also found a small number of LCOs that only apply in MODE 1. An example of these is LCO 3.3.4.2, Anticipated Transient Without Scram Recirculation Pump Trip (ATWS-RPT) Instrumentation, in NUREG-1433. When the LCO is only applicable in MODE 1, then the STS require entry in MODE 2 when exiting the mode of applicability. The staff considered whether the removal of the MODE 2 requirement in LCO 3.0.3 could potentially have a nonconservative effect on these LCOs. The staffs review found that each of these LCOs have their own condition which directs entry into MODE 2 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> if the Required Actions and associated CTs are not met. Accordingly, the staff concludes that entry into LCO 3.0.3 when these LCOs are not met is not likely. However, if the plant did have to enter LCO 3.0.3 due to one of these LCOs not being met, the proposed LCO 3.0.3 would conservatively require the plant to be placed in MODE 3. MODE 3 would serve the same purpose as entering MODE 2 because both require leaving MODE 1. Accordingly, the staff concludes that the proposed change to LCO 3.0.3 would have negligible safety impact on LCOs that are only applicable in MODE 1.
The NRC staff also evaluated LCO 3.0.3s basis for requiring the plants be in MODE 2 within 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> and determined it is based on one hour to prepare for shutting the plant down plus engineering judgement that six hours is a reasonable amount of time to reduce power and enter MODE 2 in a controlled and orderly manner. There is no specific regulatory or safety basis in any safety analysis requiring entry into MODE 2 within a certain amount of time, so removal of the requirement would not invalidate any safety analysis. Further, the NRC staff did not identify any safety basis for including a requirement to enter MODE 2 before entering MODE 3 in LCO 3.0.3. In addition, except for LCOs that are only applicable in MODE 1 discussed above, the removal of the MODE 2 requirement in LCO 3.0.3 will not impact any LCO that requires entry into MODE 3 and/or 4 (i.e., be in MODE 3 within 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br /> and MODE 4 within 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />).
Based on this and the staffs analysis of other LCOs in the STS, the staff concludes there is no safety reason to require entry into MODE 2 prior to entry into MODE 3 and MODE 4 in LCO 3.0.3.
10 CFR 50.36(c)(2)(i) 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.
LCO 3.0.3 is the default condition for this requirement in that it directs shutting down the plant when an LCO is not met and either the LCO does not include remedial actions, or the licensee fails to complete the remedial actions within the specified CT. The regulation does not specify the time required to shut down. As noted above, the NRC staff has used engineering judgement to establish the LCO-required shut down times based on plant operational experience. Based on the staffs comparison of LCO 3.0.3 requirements with those contained in other STS LCOs, the staff concludes that the proposed revision to LCO 3.0.3 would continue to meet 10 CFR 50.36(c)(2)(i) since the LCO 3.0.3 requirements would align with all other LCOs on the times to reach MODE 3 and MODE 4 (after accounting for the above-discussed one-hour preparation period built into LCO 3.0.0) and in not requiring entry into MODE 2 while shutting down.
Finally, the LCO 3.0.3 MODE 2 requirement doesnt align with typical BWR shutdown operations. As stated in Section 1.2, the typical BWR shutdown process transitions from MODE 1 to MODE 3 via a low-power reactor SCRAM. As such, the proposed change to remove the MODE 2 requirement from LCO 3.0.3 would serve to better align with typical BWR shutdown operations, as well as remove an unnecessary distraction placing time pressure on the operators. Based on the evaluation above, the NRC staff concludes that the requirement to enter MODE 2 in LCO 3.0.3 can be removed since it alleviates unnecessary time pressure on licensees while still maintaining a reasonable assurance of safety. Therefore, the staff finds that removing the requirement for entry into MODE 2 in LCO 3.0.3 from NUREG-1433 and NUREG-1434 is acceptable.
3.1 Evaluation of Proposed STS Bases Changes This traveler will become part of the next major revision of the NRCs STS Bases NUREG documents. As such, the NRC staff assessed the proposed Bases changes included in TSTF-597 to determine if they addressed the items in the Commissions Final Policy Statement described in Section 2.0 above. For the reasons below, the NRC staff found that the proposed STS Bases changes sufficiently met the Final Policy Statement.
The Final Policy Statement says that Bases should provide the justification for the TS, i.e., discuss which Policy Statement criterion requires it to be in the TS. This standard continues to be met because the proposed STS Bases changes are consistent with the proposed LCO 3.0.3 change.
Additionally, they did not affect the discussion of which Policy Statement criterion required this to be in the STS.
4.0 CONCLUSION
The NRC staff reviewed traveler TSTF-597, Revision 0, which proposed changes to STS found in NUREG-1433 and NUREG-1434. The NRC staff determined that the proposed changes to the STS continue to meet the Commissions Final Policy Statement on Technical Specifications Improvements for Nuclear Power Reactors and 10 CFR 50.36. Additionally, the NRC staff reviewed the changes to the STS and found them to be technically clear and consistent with customary terminology and format in accordance with SRP Chapter 16.0. The NRC staff reviewed the proposed changes to the actions required by LCO 3.0.3 and concludes that the changes continue to provide reasonable assurance of adequate protection of the health and safety of the public. Therefore, the NRC staff concludes that the proposed STS changes are acceptable.
Principal Contributors: C. Rojas, NRR/DSS R. Elliott, NRR/DSS Date: December 26, 2024