ML23012A282
| ML23012A282 | |
| Person / Time | |
|---|---|
| Site: | Technical Specifications Task Force |
| Issue date: | 03/13/2023 |
| From: | Victor Cusumano NRC/NRR/DSS/STSB |
| To: | Technical Specifications Task Force |
| Shared Package | |
| ML23012A280 | List: |
| References | |
| EPID L-2022-PMP-0002 | |
| Download: ML23012A282 (8) | |
Text
Enclosure 1 DRAFT SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION 1
TECHNICAL SPECIFICATIONS TASK FORCE TRAVELER 2
TSTF-584, REVISION 0 3
ELIMINATE AUTOMATIC RWCU SYSTEM ISOLATION ON SLC SYSTEM INITIATION 4
USING THE CONSOLIDATED LINE ITEM IMPROVEMENT PROCESS 5
(EPID L-2022-PMP-0002) 6 7
8
1.0 INTRODUCTION
9 10 By letter dated February 23, 2022 (Agencywide Documents Access and Management System 11 (ADAMS) Accession No. ML22054A292), the Technical Specifications Task Force (TSTF) 12 submitted Traveler TSTF-584, Revision 0, Eliminate Automatic RWCU [reactor water cleanup]
13 System Isolation on SLC [standby liquid control] System Initiation, to the U.S. Nuclear 14 Regulatory Commission (NRC). Traveler TSTF-584, Revision 0, proposed changes to the 15 Standard Technical Specifications (STS) for boiling-water reactor (BWR) designs. 1 These 16 changes would be incorporated into future revisions of NUREG-1433 (BWR/4) and 17 NUREG-1434 (BWR/6).
18 19 The proposed changes would revise the Primary Containment Isolation Instrumentation, 20 specification by removing the requirement of automatic isolation of the RWCU system on 21 initiation of the SLC system. This STS change will be made available to licensees through the 22 consolidated line item improvement process (CLIIP).
23 24
2.0 REGULATORY EVALUATION
25 26 2.1 System Descriptions 27 28 2.1.1 RWCU 29 30 Section 2.1.1 of the TSTF letter dated February 23, 2022, briefly describes the RWCU system.
31 The TSTF listed the following automatic signals to the RWCU system supply and/or return 32 isolation valves in a typical BWR design that indicate that the RWCU piping or components 33 have been breached:
34 35 Low reactor vessel water level; 36 RWCU system high differential flow; 37 Main steam tunnel penetration area temperature high; and 38 RWCU heat exchanger/pump/filter demineralizer unit area high temperature.
39 40 The STS requires the above functions to be operable. The automatic closure of the supply 41 and/or return isolation valves, coupled with the dual check valves in each RWCU system return 42 line, isolates the RWCU system from the reactor coolant pressure boundary.
43 1U.S. Nuclear Regulatory Commission, Standard Technical Specifications, General Electric Plants, BWR/4, NUREG-1433, Volume 1, Specifications, and Volume 2, Bases, Revision 5.0, September 2021 (ML21272A357 and ML21272A358, respectively).
U.S. Nuclear Regulatory Commission, Standard Technical Specifications, General Electric Plants, BWR/6, NUREG-1434, Volume 1, Specifications, and Volume 2, Bases, Revision 5.0, September 2021 (ML21271A582 and ML21271A596, respectively).
The automatic signal for RWCU system isolation on SLC system initiation that is proposed to be 1
removed is not used to indicate any breach of RWCU piping or components.
2 3
2.1.2 Standby Liquid Control System 4
5 During an Anticipated Transient Without Scram (ATWS) event, the SLC system would bring the 6
reactor from full power to a subcritical condition without crediting the control rods. The SLC 7
system injects a quantity of borated water into the reactor core that adds negative reactivity 8
sufficient to compensate for all of the various positive reactivity effects that could occur during 9
shutdown. In addition to its use for ATWS mitigation, some plants credit manual actuation of the 10 SLC system following a loss of coolant accident (LOCA) to control primary containment acidity.
11 12 2.2 Proposed Changes to the Standard Technical Specifications 13 14 The proposed changes remove the requirement for automatic isolation of the RWCU system on 15 SLC system initiation. The following are the proposed changes in NUREG-1433 and 16 NUREG-1434:
17 18 NUREG-1433 19 20 Technical Change:
21 22 Table 3.3.6.1-1, Function 5.d, "Reactor Water Cleanup (RWCU) System Isolation - SLC 23 System Initiation," is deleted.
24 25 Editorial changes needed for consistency:
26 27 Table 3.3.6.1-1, Function 5.e, "Reactor Vessel Water Level - Low Low, Level 2," is 28 renumbered as Function 5.d.
29 Table 3.3.6.1-1, Function 5.f, "Manual Initiation," is renumbered as Function 5.e.
30 Table 3.3.6.1-1, Footnote (b), if present, is only referenced from Function 5.d, and is 31 deleted.
32 Table 3.3.6.1-1, Function 6.b, reference to Action J is revised to reference Action I.
33 TS 3.3.6.1, Action I, which is only referenced in Function 5.d, is deleted.
34 TS 3.3.6.1, Action J, is renumbered as Action I.
35 36 NUREG-1434 37 38 Technical Change:
39 40 Table 3.3.6.1-1, Function 4.l, "Reactor Water Cleanup (RWCU) System Isolation - Standby 41 Liquid Control System Initiation," is deleted.
42 43 Editorial changes needed for consistency:
44 45 Table 3.3.6.1-1, Function 4.m, "Manual Initiation," is renumbered as Function 4.l.
46 Table 3.3.6.1-1, Function 5.c, reference to Action J is revised to reference Action I.
47 TS 3.3.6.1, Action I, which is only referenced in Function 4.l, is deleted.
48 TS 3.3.6.1, Action J, is renumbered Action I.
49 TS 3.3.6.1, Action K, is renumbered Action J.
50 1
2.3 Applicable Regulatory Requirements and Guidance 2
3 As described in the Commissions Final Policy Statement on Technical Specifications 4
Improvements for Nuclear Power Reactors (58 FR 39132, dated July 22, 1993), the NRC and 5
industry task groups for new STSs recommended that improvements include greater emphasis 6
on human factors principles in order to add clarity and understanding to the text of the STSs and 7
provide improvements to the Bases of the STSs, which provides the purpose for each 8
requirement in the STSs. The improved vendor-specific STSs were developed and issued by 9
the NRC in September 1992.
10 11 Section IV, The Commission Policy, of the Final Policy Statement on Technical Specifications 12 (TSs) states, in part:
13 14 The purpose of Technical Specifications is to impose those 15 conditions or limitations upon reactor operation necessary to 16 obviate the possibility of an abnormal situation or event giving rise 17 to an immediate threat to the public health and safety by 18 identifying those features that are of controlling importance to 19 safety and establishing on them certain conditions of operation 20 which cannot be changed without prior Commission approval.
21 22
[T]he Commission will also entertain requests to adopt portions 23 of the improved STS [(e.g., TSTF-584)], even if the licensee does 24 not adopt all STS improvements. The Commission encourages 25 all licensees who submit Technical Specification related submittals 26 based on this Policy Statement to emphasize human factors 27 principles.
28 29 In accordance with this Policy Statement, improved STS have 30 been developed and will be maintained for each NSSS [nuclear 31 steam supply system] owners group. The Commission 32 encourages licensees to use the improved STS as the basis for 33 plant-specific Technical Specifications. [I]t is the Commission 34 intent that the wording and Bases of the improved STS be used 35 to the extent practicable.
36 37 The Summary section of the Final Policy Statement on TS states, in part:
38 39 Implementation of the Policy Statement through implementation of 40 the improved STS is expected to produce an improvement in the 41 safety of nuclear power plants through the use of more 42 operator-oriented Technical Specifications, Improved Technical 43 Specification Bases, reduced action statement induced plant 44 transients, and more efficient use of NRC and industry resources.
45 46 The Final Policy Statement on TS provides the following description of the scope and the 47 purpose of the STS Bases:
48 49 Each LCO [limiting condition for operation], Action, and 50 Surveillance Requirement should have supporting Bases. The 51 Bases should at a minimum address the following questions and 1
cite references to appropriate licensing documentation (e.g.,
2 FSAR [final safety analysis report], Topical Report) to support the 3
Bases.
4 5
- 1. What is the justification for the Technical Specification, i.e.,
6 which Policy Statement criterion requires it to be in the Technical 7
Specifications?
8 9
- 2. What are the Bases for each LCO, i.e., why was it determined 10 to be the lowest functional capability or performance level for the 11 system or component in question necessary for safe operation of 12 the facility and, what are the reasons for the Applicability of the 13 LCO?
14 15
- 3. What are the Bases for each Action, i.e., why should this 16 remedial action be taken if the associated LCO cannot be met; 17 how does this Action relate to other Actions associated with the 18 LCO; and what justifies continued operation of the system or 19 component at the reduced state from the state specified in the 20 LCO for the allowed time period?
21 22
- 4. What are the Bases for each Safety Limit?
23 24
- 5. What are the Bases for each Surveillance Requirement and 25 Surveillance Frequency; i.e., what specific functional requirement 26 is the surveillance designed to verify? Why is this surveillance 27 necessary at the specified frequency to assure that the system or 28 component function is maintained, that facility operation will be 29 within the Safety Limits, and that the LCO will be met?
30 31 Note: In answering these questions the Bases for each number 32 (e.g., Allowable Value, Response Time, Completion Time, 33 Surveillance Frequency), state, condition, and definition (e.g.,
34 operability) should be clearly specified. As an example, a number 35 might be based on engineering judgment, past experience, or 36 PSA [probabilistic safety assessment] insights; but this should be 37 clearly stated.
38 39 The regulation under paragraph 50.36(a)(1) of Title 10 of the Code of Federal Regulations 40 (10 CFR) requires that:
41 42 Each applicant for a license authorizing operation of a 43 utilization facility shall include in his application proposed technical 44 specifications in accordance with the requirements of this section.
45 A summary statement of the bases or reasons for such 46 specifications, other than those covering administrative controls, 47 shall also be included in the application, but shall not become part 48 of the technical specifications.
49 50 The regulation under 10 CFR 50.36(b) requires that:
1 2
Each license authorizing operation of a utilization facility will 3
include technical specifications. The technical specifications will 4
be derived from the analyses and evaluation included in the safety 5
analysis report, and amendments thereto, submitted pursuant to 6
[10 CFR] 50.34 [Contents of applications; technical information].
7 The Commission may include such additional technical 8
specifications as the Commission finds appropriate.
9 10 The categories of items required to be in the TSs are listed in 10 CFR 50.36(c). The regulation 11 at 10 CFR 50.36(c)(2) requires that TSs include LCOs. Per 10 CFR 50.36(c)(2)(i), LCOs are 12 the lowest functional capability or performance levels of equipment required for safe operation 13 of the facility. The regulation also requires that when an LCO of a nuclear reactor is not met, 14 the licensee shall shut down the reactor or follow any remedial action permitted by the TS until 15 the condition can be met.
16 17 The regulation at 10 CFR 50.62(b) defines an Anticipated Transient Without Scram (ATWS) as 18 an anticipated operational occurrence as defined in appendix A of this part followed by the 19 failure of the reactor trip portion of the protection system specified in General Design 20 Criterion 20 of appendix A of this part.
21 22 10 CFR Part 50 Appendix A, applicable General Design Criteria (GDCs) are as follows:
23 GDC 20 - Protection system functions. The protection system shall be designed (1) to 24 initiate automatically the operation of appropriate systems including the reactivity control 25 systems, to assure that specified acceptable fuel design limits are not exceeded as a 26 result of anticipated operational occurrences and (2) to sense accident conditions and to 27 initiate the operation of systems and components important to safety.
28 GDC 26 - Reactivity control system redundancy and capability. Two independent 29 reactivity control systems of different design principles shall be provided. One of the 30 systems shall use control rods, preferably including a positive means for inserting the 31 rods, and shall be capable of reliably controlling reactivity changes to assure that under 32 conditions of normal operation, including anticipated operational occurrences, and with 33 appropriate margin for malfunctions such as stuck rods, specified acceptable fuel design 34 limits are not exceeded. The second reactivity control system shall be capable of reliably 35 controlling the rate of reactivity changes resulting from planned, normal power changes 36 (including xenon burnout) to assure acceptable fuel design limits are not exceeded. One 37 of the systems shall be capable of holding the reactor core subcritical under cold 38 conditions.
39 The NRC staffs guidance for the review of TSs is in chapter 16.0, Technical Specifications, of 40 NUREG-0800, Revision 3, Standard Review Plan for the Review of Safety Analysis Reports for 41 Nuclear Power Plants: LWR [Light-Water Reactor] Edition (SRP), March 2010 (ML100351425).
42 As described therein, as part of the regulatory standardization effort, the NRC staff has 43 prepared STSs for each of the LWR nuclear designs.
44 45
3.0 TECHNICAL EVALUATION
1 2
3.1 Deletion of Table 3.3.6.1-1, Function 5.d (NUREG-1433) and 4.l (NUREG-1434) 3 4
For the reduction of risk from an ATWS event for BWRs, 10 CFR 50.62(c)(4) states that the 5
SLC system initiation must be automatic and must be designed to perform its function in a 6
reliable manner for plants granted a construction permit after July 26, 1984, and for plants 7
granted a construction permit prior to July 26, 1984, that have already been designed and built 8
to include this feature. The TSTF stated, and the NRC staff confirmed, that there are no BWRs 9
whose construction permits were issued after July 26, 1984, and no operating BWRs that credit 10 automatic initiation of the SLC system. The SLC system is manually initiated by the plant 11 operators as directed by the emergency operating procedures.
12 The TSTF stated that since the RWCU system isolation signal on SLC system initiation is a 13 fail-close signal for the RWCU system return isolation valves, it complicates plant maintenance 14 evolutions by interruption of power to the signal, resulting in isolation of the RWCU system.
15 Isolation of the RWCU system has an undesirable effect on reactor coolant system chemistry.
16 Restarting the RWCU system is a lengthy process that requires warming the of system prior to 17 starting the pump, typically requires control room and field actions, and diverts operator 18 attention from more safety significant tasks. Further, shutdown and restart of the RWCU system 19 increases wear on the pump motors. The RWCU system motors and pumps are typically 20 replaced together as a unit requiring extensive maintenance being conducted in a high radiation 21 area.
22 23 The NRC staff reviewed the proposal to eliminate automatic isolation of the RWCU system upon 24 the initiation of the SLC system and determined the following:
25 26 The RWCU system isolation signal is not designed to indicate any breach of RWCU system 27 piping or components.
28 The SLC system is not credited to mitigate any design basis accident (DBA).
29 Following an ATWS event, the SLC system is manually initiated, and therefore a manual 30 isolation of the RWCU system is acceptable because it will have a negligible effect on 31 operator response to an ATWS event.
32 Automatic RWCU system isolation on SLC initiation is not considered part of the primary 33 success path for the mitigation of a DBA.
34 During an ATWS event, the reactor water level would drop, and the reactor Level 2 signal 35 would automatically isolate the RWCU system. This is a backup to the proposed 36 procedurally-controlled, manual RWCU system isolation, and therefore removes the concern 37 of the RWCU system removing SLC system-injected boron from the reactor vessel.
38 For the plants that credit manual SLC system initiation following a LOCA for pH control, the 39 RWCU system would be isolated by the containment isolation signal originating from the 40 LOCA signal.
41 The automatic RWCU system isolation function upon initiation of the SLC system does not 42 satisfy any 10 CFR 50.36 criteria.
43 When the SLC system is taken out of service (e.g., for maintenance), unnecessary 44 automatic isolation of the RWCU system will be prevented.
45 Unnecessary interruption of the RWCU system operation due to the fail-close feature of the 46 SLC system initiation signal complicates maintenance.
47 48 The NRC staff finds the proposal to eliminate automatic isolation of the RWCU system upon 1
imitation of the SLC system acceptable based on the following NRC staff findings:
2 3
The manual initiation of the SLC system during an ATWS event remains unchanged. A 4
procedurally-controlled simultaneous manual isolation of the RWCU system during this 5
event removes the concern of the RWCU system removing the SLC system-injected boron 6
from the reactor vessel. Therefore, the specified acceptable fuel design limits will not be 7
affected during an ATWS event, and 10 CFR 50.62(b) and GDC 20 continue to be met.
8 The design of the SLC system as one of the two independent reactivity control systems for 9
the mitigation of an ATWS event remains unchanged. Therefore, the specified acceptable 10 fuel design limits will not be affected during an ATWS event and GDC 26 continues to be 11 met.
12 The regulation at 10 CFR 50.36(c)(2)(i) is met because STS 3.3.6.1 continues to provide 13 remedial actions and shuts down the reactor if the remedial actions cannot be met.
14 15 3.2 Editorial Changes to TS 3.3.6.1 16 17 TSTF-584 proposed renumbering and deletion of Functions and Actions in NUREG-1433 and 18 NUREG-1434, which are described above in section 2.2.
19 20 The NRC staff finds that these changes are acceptable because they are conforming changes 21 resulting from the deletion of Table 3.3.6.1-1, Function 5.d (NUREG-1433) and Function 4.l 22 (NUREG-1434), and do not alter the way the TS are implemented. Furthermore, the NRC staff 23 finds this change is acceptable since it is editorial and provides the correct number sequence.
24 25 3.3 Consideration of Changes to the STS Bases 26 27 The NRC staff reviewed the proposed changes to the STS Bases of STS 3.3.6.1. As discussed 28 in Section 2.3 of this SE, the Final Policy Statement on TS describes the scope and purpose of 29 the STS Bases. It does so by listing five questions the STS Bases must address. While the STS 30 Bases as a whole must address these questions, not every question will be relevant to every 31 change to the STS Bases. The second, fourth, and fifth questions are not relevant to this 32 evaluation because the STS changes proposed in TSTF-584, Revision 0, as evaluated above, 33 do not affect the LCO or its Applicability Bases, safety limits, or surveillance requirements. Since 34 the proposed change only affects Actions, the Policy Statement criterion that applies to the LCO 35 is not affected and the first question is not relevant to this evaluation. The proposed change 36 does not add any new actions or alter any remaining actions, it only deletes an action; therefore, 37 the third question is not relevant to the changes.
38 39 The STS Bases changes proposed in TSTF-584 are to reflect the deletion of Table 3.3.6.1-1, 40 Function 5.d (NUREG-1433) and 4.l (NUREG-1434) and STS renumbering. These changes are 41 acceptable since they are editorial and appropriately follow the structure of the document.
42 43 The NRC staff finds the proposed STS Bases changes acceptable as they are editorial in nature 44 and are consistent with the Final Policy Statement on TS and 10 CFR 50.36. Furthermore, the 45 NRC staff review determined that the proposed STS Bases changes enhance and/or clarify the 46 current STS Bases.
47 48
4.0 CONCLUSION
1 2
The NRC staff finds that the changes to STS 3.3.6.1 satisfy 10 CFR 50.36(c)(2)(i) and 3
10 CFR 50.62(b) because the specified acceptable fuel design limits will not be affected during 4
an ATWS event and remedial actions to be taken until each LCO can be met continue to 5
provide adequate protection to the public health and safety. Additionally, the NRC staff 6
determined that the changes are technically clear and consistent with customary terminology 7
and format in accordance with SRP chapter 16.0.
8 9
Therefore, the NRC staff concludes that all of the proposed changes in TSTF-584, Revision 0, 10 are acceptable, and thus, approved.
11 12 Principal Contributors: T. Sweat, NRR/DSS/STSB 13 M. Honcharik, NRR/DSS/STSB 14 A. Sallman, NRR/DSS/SNPB 15 16 Date:
17