ML25044A244
| ML25044A244 | |
| Person / Time | |
|---|---|
| Site: | Technical Specifications Task Force |
| Issue date: | 04/15/2025 |
| From: | Vijay Goel, Khadijah West Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| EPID L-2024-PMP-0000 | |
| Download: ML25044A244 (8) | |
Text
DRAFT SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION 1
TECHNICAL SPECIFICATIONS TASK FORCE TRAVELER 2
TSTF-599, REVISION 1 3
ELIMINATE PERIODIC SURVEILLANCE TEST OF SIMULTANEOUS START OF 4
REDUNDANT DIESEL GENERATORS 5
USING THE CONSOLIDATED LINE ITEM IMPROVEMENT PROCESS 6
(EPID: L-2024-PMP-0000) 7 8
1.0 INTRODUCTION
9 10 By letter dated April 3, 2025 (Agencywide Documents Access and Management System 11 (ADAMS) Accession No. ML25093A204), the Technical Specifications Task Force (TSTF) 12 submitted Traveler TSTF-599, Revision 1, Eliminate Periodic Surveillance Test of 13 Simultaneous Start of Redundant Diesel Generators (TSTF-599), to the U.S. Nuclear 14 Regulatory Commission (NRC). TSTF-599 proposed changes to the Standard Technical 15 Specifications (STS) for boiling-water reactor (BWR) and pressurized-water reactor (PWR) 16 designs under the consolidated line item improvement process (CLIIP). Upon approval this 17 Traveler will be made available for adoption and the changes will be incorporated into future 18 revisions of the following NRC STS1:
19 20 NUREG-1430, Standard Technical Specifications, Babcock and Wilcox Plants, Volume 1, 21 Specifications, and Volume 2, Bases, Revision 5, September 2021 (ML21272A363 and 22 ML21272A370, respectively).
23 NUREG-1431, Standard Technical Specifications, Westinghouse Plants, Volume 1, 24 Specifications, and Volume 2, Bases, Revision 5, September 2021 (ML21259A155 and 25 ML21259A159, respectively).
26 NUREG-1432, Standard Technical Specifications, Combustion Engineering Plants, 27 Volume 1, Specifications, and Volume 2, Bases, Revision 5, September 2021 28 (ML21258A421 and ML21258A424, respectively).
29 NUREG-1433, Standard Technical Specifications, General Electric BWR/4 Plants 30 Volume 1, Specifications, and Volume 2, Bases, Revision 5, September 2021 31 (ML21272A357 and ML21272A358, respectively).
32 NUREG-1434, Standard Technical Specifications, General Electric BWR/6 Plants 33 Volume 1, Specifications, and Volume 2, Bases, Revision 5, September 2021 34 (ML21271A582 and ML21271A596, respectively).
35 36 1NUREG-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.
NUREG-1434 provides the STS for BWR/6 plant designs, but is also representative in some cases of the BWR/5 plant design.
The proposed change would delete a surveillance requirement (SR) in STS 3.8.1, AC 1
[alternating current] Sources - Operating, to verify that diesel generators (DGs) achieve a 2
specific frequency and voltage within a specified time period when started simultaneously.
3 Associated changes were also proposed for STS 3.8.2, AC Sources - Shutdown, and Bases 4
5 6
1.1
System Description
7 8
The Class 1E AC electrical power distribution systems onsite standby power sources provide 9
independence and redundancy to ensure an available source of power to the engineered safety 10 feature (ESF) systems when the offsite or preferred power sources are unavailable. Specifically, 11 the onsite standby power source consists of emergency DGs to power ESF buses. A DG starts 12 automatically on a safety injection (SI) signal or on a loss of offsite power (i.e., an ESF bus 13 degraded voltage or undervoltage) signal. The DG will start and automatically tie to its 14 respective ESF bus after offsite power is tripped due to an ESF bus undervoltage or degraded 15 voltage, independent of or coincident with an SI signal. The DGs will also start and operate in 16 the standby mode without tying to the ESF bus on an SI signal alone. Following the trip of offsite 17 power, nonpermanent loads are stripped from the ESF bus. When the DG is tied to the ESF 18 bus, emergency loads are then sequentially connected to its respective ESF bus by the 19 automatic load sequencer. The sequencing logic controls the permissive and starting signals to 20 motor breakers to prevent overloading the DG by automatic load application.
21 22 In the event of a loss of preferred (offsite) power, the ESF electrical loads are automatically 23 connected to the DGs in sufficient time to provide for safe reactor shutdown and to mitigate the 24 consequences of a design basis accident such as a loss of coolant accident.
25 26 1.2 Proposed Changes to Standard Technical Specification 3.8.1, AC Sources - Operating 27 28 The proposed changes revise STS 3.8.1 by deleting SR 3.8.1.20 from NUREG-1430 through 29 NUREG-1434. The current requirements differ slightly by NUREG and are as follows:
30 31 For NUREG-1430, SR 3.8.1.20 states:
32 33 NOTE: All DG starts may be preceded by an engine prelube period.
34 35 Verify, when started simultaneously from standby condition, each DG achieves, in 36
[10] seconds, voltage [3740] V and [4580] V, and frequency [58.8] Hz and 37
[61.2] Hz.
38 39 Frequency: [10 years OR In accordance with the Surveillance Frequency Control 40 Program]
41 42 For NUREG-1431, SR 3.8.1.20 states:
1 2
NOTE: All DG starts may be preceded by an engine prelube period.
3 4
Verify when started simultaneously from standby condition, each DG achieves:
5
- a. In [10] seconds, voltage [3740] V and frequency [58.8] Hz and 6
- b. Steady state voltage [3744] V and [4576] V, and frequency [58.8] Hz and 7
[61.2] Hz.
8 9
Frequency: [10 years OR In accordance with the Surveillance Frequency Control 10 Program]
11 12 For NUREG-1432, SR 3.8.1.20 states:
13 14 NOTE: All DG starts may be preceded by an engine prelube period.
15 16 Verify, when started simultaneously from standby condition, each DG achieves:
17
- a. In [10] seconds, voltage [3740] V and frequency [58.8] Hz and 18
- b. Steady state voltage [3740] V and [4580] V, and frequency [58.8] Hz and 19
[61.2] Hz.
20 21 Frequency: [10 years OR In accordance with the Surveillance Frequency Control 22 Program]
23 24 For NUREG-1433, SR 3.8.1.20 states:
25 26 NOTE: All DG starts may be preceded by an engine prelube period.
27 28 Verify, when started simultaneously from standby condition, [each] [2A and 2C] DG 29 achieves:
30
- a. In [12] seconds, voltage [3740] V and frequency [58.8] Hz and 31
- b. Steady state voltage [3740] V and [4580] V and frequency [58.8] Hz and 32
[61.2] Hz.
33 34 Frequency: [10 years OR In accordance with the Surveillance Frequency Control 35 Program]
36 37 For NUREG-1434, SR 3.8.1.20 states:
38 39 NOTE: All DG starts may be preceded by an engine prelube period.
40 41 Verify, when started simultaneously from standby condition, [each] [Division 1, 2, and 3]
42 DG achieves:
43
- a. In [10] seconds, voltage [3744] V and frequency [58.8] Hz and 44
- b. Steady state voltage [3744] V and [4576] V and frequency [58.8] Hz and 45
[61.2] Hz.
46 47 Frequency: [10 years OR In accordance with the Surveillance Frequency Control 48 Program]
49 50 1.3 Proposed Changes to Standard Technical Specification 3.8.2, AC Sources - Shutdown 1
2 For NUREGs -1430, -1431, and -1432, STS SR 3.8.2.1 would be modified as follows (emphasis 3
added):
4 5
NOTE------------------------------
6 The following SRs are not required to be performed:
7 SR 3.8.1.3, SR 3.8.1.9 through SR 3.8.1.11, 8
SR 3.8.1.13 through SR 3.8.1.16, and [SR 3.8.1.18].
9 10 11 For AC sources required to be OPERABLE, the SRs 12 of Specification 3.8.1, "AC Sources - Operating,"
13 except SR 3.8.1.8, SR 3.8.1.12, SR 3.8.1.17, and 14 SR 3.8.1.19, and SR 3.8.1.20, are applicable.
15 16 Frequency: In accordance with applicable SRs 17 18 1.4 Proposed Changes to Standard Technical Specification Bases 19 20 The associated STS Bases are affected in this manner:
21 22 The STS SR 3.8.1.20 Bases discussion would be deleted.
23 In the STS 3.8.1 Bases References section, brackets would be added to the referenced 24 revision number to Regulatory Guide (RG) 1.9, Revision 3, Selection, Design, 25 Qualification, and Testing of Emergency Diesel Generator Units Used as Class 1E 26 Onsite Electric Power Systems at Nuclear Power Plants, to indicate that the revision is 27 plant-specific. Brackets would also be added to the entire reference to RG 1.108, 28 Revision 1, Periodic Testing of Diesel Generator Units Used as Onsite Electric Power 29 Systems at Nuclear Power Plants.
30 In STS SR 3.8.2.1 Bases, a sentence would be deleted that describes the exclusion of 31 this SR for the DGs that are not required to be operable per LCO 3.8.2.
32 33 1.5 Reason for Proposed Change 34 35 Currently, STS SR 3.8.1.20 requires the simultaneous fast start (e.g., starts and achieves 36 required voltage and frequency in the required time, typically 10 seconds) of all redundant DGs 37 and verification that the DGs reach the required voltage and frequency in order to verify that the 38 DG starting independence has not been compromised. The SR is required to be performed in 39 10-year intervals or in accordance with the Surveillance Frequency Control Program (SFCP),
40 with an initial frequency of every 10 years.
41 42 As stated in TSTF-599, at least four sites have extended the frequency to 20 years. The TSTF 43 members stated that past successful performance during surveillances, actual events, and the 44 other tests performed on the DGs outweigh the potential detrimental effects on plant safety and 45 DG reliability. Therefore, the TSTF members have deemed the performance of the SR is not 46 warranted by the safety benefit of the test. As a result, they proposed to eliminate SR 3.8.1.20 47 from the STS in TSTF-599.
48 49
2.0 REGULATORY EVALUATION
1 2
As described in the Commissions Final Policy Statement on Technical Specifications 3
Improvements for Nuclear Power Reactors (58 FR 39132, dated July 22, 1993), [t]he new STS 4
should include greater emphasis on human factors principles in order to add clarity and 5
understanding to the text of the STS, and provide improvements to the Bases Section of the 6
Technical Specifications which provides the purpose for each requirement in the specification.
7 The improved vendor-specific STS were developed and issued by the NRC in September 1992.
8 9
The Summary section of the Final Policy Statement on Technical Specifications Improvements 10 for Nuclear Power Reactors states, in part:
11 12 Implementation of the Policy Statement through implementation of the improved 13 STS is expected to produce an improvement in the safety of nuclear power 14 plants through the use of more operator-oriented Technical Specifications, 15 improved Technical Specification Bases, reduced action statement induced plant 16 transients, and more efficient use of NRC and industry resources.
17 18 Section IV, The Commission Policy, of the Final Policy Statement on Technical Specifications 19 Improvements for Nuclear Power Reactors states, in part:
20 21 The purpose of Technical Specifications is to impose those conditions or 22 limitations upon reactor operation necessary to obviate the possibility of an 23 abnormal situation or event giving rise to an immediate threat to the public health 24 and safety by identifying those features that are of controlling importance to 25 safety and establishing on them certain conditions of operation which cannot be 26 changed without prior Commission approval.
27 28
[T]he Commission will also entertain requests to adopt portions of the 29 improved STS [(e.g., TSTF-599)], even if the licensee does not adopt all STS 30 improvements. The Commission encourages all licensees who submit 31 Technical Specification related submittals based on this Policy Statement to 32 emphasize human factors principles.
33 34 In accordance with this Policy Statement, improved STS have been developed 35 and will be maintained for each NSSS [nuclear steam supply system] owners 36 group. The Commission encourages licensees to use the improved STS as the 37 basis for plant-specific Technical Specifications. [I]t is the Commission intent 38 that the wording and Bases of the improved STS be used to the extent 39 practicable.
40 41 The regulations in Title 10 of the Code of Federal Regulations (10 CFR) paragraph 50.36(a)(1) 42 require that:
43 44 Each applicant for a license authorizing operation of a utilization facility shall 45 include in his application proposed technical specifications in accordance with 46 the requirements of this section. A summary statement of the bases or reasons 47 for such specifications, other than those covering administrative controls, shall 48 also be included in the application, but shall not become part of the technical 49 specifications.
50 51 The regulations in 10 CFR 50.36(b) require that:
1 2
Each license authorizing operation of a utilization facility will include 3
technical specifications. The technical specifications will be derived from the 4
analyses and evaluation included in the safety analysis report, and amendments 5
thereto, submitted pursuant to [10 CFR] 50.34 [Contents of applications; 6
technical information]. The Commission may include such additional technical 7
specifications as the Commission finds appropriate.
8 9
The categories of items required to be in the TS are listed in 10 CFR 50.36(c). The regulation at 10 10 CFR 50.36(c)(3) requires that TS include SRs, which are requirements relating to test, 11 calibration, or inspection to assure that the necessary quality of systems and components is 12 maintained, that facility operation will be within safety limits, and that the limiting conditions for 13 operation will be met.
14 15 The NRC staffs guidance for the review of TS is in NUREG-0800, Standard Review Plan for 16 the Review of Safety Analysis Reports for Nuclear Power Plants: LWR [Light-Water Reactor]
17 Edition (SRP), Chapter 16.0, Technical Specifications, Revision 3, dated March 2010 18 (ML100351425). As described therein, as part of the regulatory standardization effort, the NRC 19 staff has prepared STS for each of the LWR nuclear designs.
20 21 STS Bases for SR 3.8.1.20 reference guidance to perform simultaneous start DG testing in 22 RG 1.108, Revision 1. RG 1.108, Revision 1, Regulatory Position C.2.b states:
23 24 Testing of redundant diesel generator units during normal plant operation should 25 be performed independently (nonconcurrently) to minimize common failure 26 modes resulting from undetected interdependences among diesel generator 27 units. However, during reliability demonstration of diesel generator units during 28 plant preoperational testing and testing subsequent to any plant modification 29 where diesel generator unit interdependence may have been affected or every 30 10 years (during a plant shutdown), whichever is the shorter, a test should be 31 conducted in which redundant units are started simultaneously to help identify 32 certain common failure modes undetected in single diesel generator unit tests.
33 34 RG 1.108 was withdrawn in 1993 and superseded by RG 1.9. RG 1.108 continues to be 35 referenced in the STS Bases because the majority of operating plants, which were licensed 36 before 1993, reference this guidance in their plant-specific Bases and have commitments based 37 on its use.
38 39 RG 1.9, Revision 3, incorporated the simultaneous start test. RG 1.9, Revision 3, Regulatory 40 Position C.2.2.14 (Redundant Unit Test) states:
41 42 Demonstrate that, by starting and running both redundant units simultaneously, 43 potential common failure modes that may be undetected in single emergency 44 diesel generator unit tests do not occur.
45 46 Revision 3 of RG 1.9 is referenced in the STS Bases due to a majority of operating 47 plants currently holding commitments to this revision. Subsequently, RG 1.9, Revision 4, 48 Application and Testing of Safety-Related Diesel Generators in Nuclear Power Plants 49 was issued in 2007 (ML070380553). As stated in section 1.3 of this safety evaluation, 50 the licensee will have the option to reference the revision of RG 1.9 that is applicable to 1
its plant.
2 3
3.0 TECHNICAL EVALUATION
4 5
The NRC staff reviewed Traveler TSTF-599, which proposed changes to NUREG-1430 through 6
NUREG-1434. The regulatory framework the NRC staff used to determine the acceptability of 7
the proposed changes consists of the requirements and guidance listed in section 2.0 of this 8
safety evaluation. The NRC staff reviewed the proposed changes to the STS to determine 9
whether they meet the standards for TS in 10 CFR 50.36(c)(3) and conform to the Final Policy 10 Statement on Technical Specifications Improvements for Nuclear Power Reactors.
11 12 Depending on the reactor type, two or more redundant DGs are required to be operable by STS 13 limiting condition for operation (LCO) 3.8.1.b. Several SRs in STS 3.8.1 are used to establish 14 the operability of the DGs to meet the LCO. SR 3.8.1.20 requires a simultaneous start of the 15 redundant DGs to be performed every 10 years or in accordance with the SFCP. This 16 surveillance test is consistent with the guidance in RG 1.108 (withdrawn in 1993) and RG 1.9 to 17 test for common cause failure.
18 19 The STS 3.8.1 DG SRs that test for achieving the required frequency and voltage ranges within 20 a specified time are the following:
21 22 Related Diesel Generator Surveillance Requirements Frequency 3.8.1.7 (each DG starts from standby) 184 days (6 months) 3.8.1.11 (each DG auto-starts on loss of offsite power signal) 18 months 3.8.1.12 (each DG auto-starts on SI signal from standby) 18 months 3.8.1.19 (each DG auto-starts on loss of offsite power signal in conjunction with SI signal from standby) 18 months 3.8.1.20 (simultaneous start of DGs from standby) 10 years 23 These SRs also have the option to modify the frequency in accordance with the SFCP. During 24 the performance of SR 3.8.1.20, no components are tested that are not already covered by one 25 or more of the other related SRs. The DGs are designed to start on either a loss of offsite power 26 signal, ESF signal, or both signals concurrently, which is verified by SR 3.8.1.11, SR 3.8.1.12, 27 and SR 3.8.1.19, respectively. The main focus of the performance of SR 3.8.1.20 is to test the 28 independence of the starting logic and mechanisms of the redundant DGs.
29 30 With respect to DG operating experience, the TSTF members stated in TSTF-599 that they 31 conducted a survey of licensees and determined that, for each unit, plants entered the condition 32 of one inoperable DG an average of 27 times per year. When in this condition, the STS require 33 the licensee to evaluate for a common cause failure. This is to determine whether or not the 34 cause of the inoperable DG exists on the other DGs. Additionally, the TSTF determined that for 35 the 104 units operating between 2005 and 2010 that licensees performed around 14,000 36 common cause failure evaluations with no common cause failure mechanisms identified on the 37 other DGs. These common cause failure evaluations covered various DG failure mechanisms.
38 Specific to simultaneous DG starts, the NRC staff reviewed Licensee Event Reports from 39 January 1, 2000, through August 29, 2021, and identified 43 loss of offsite power events at 40 30 sites (ML25051A225). Each event resulted in the redundant DGs starting as required with no 41 instance in which a redundant DG was found to be inoperable due to a common cause failure.
42 Performance of SR 3.8.1.20 at many plants requires rendering the DGs inoperable during their 1
surveillance, which includes test preparation, performance, and recovery. This would result in 2
reduced availability of the DGs because during the performance of SR 3.8.1.20 the automatic 3
DG functions (e.g., starting, load rejection, load sequencing, etc.) are rendered inoperable.
4 Accordingly, if one or more DGs are rendered inoperable during preparation or performance of 5
this SR and an accident were to occur, the plant may not be able to meet the accident analysis 6
assumptions; most accident analyses assume a concurrent loss of offsite power and a limiting 7
single failure (e.g., failure of one DG to start). The performance of SR 3.8.1.20 does not 8
enhance safety over increased risk of equipment inoperability, considering common cause 9
failure is a very low likelihood event. Therefore, NRC staff finds the proposed deletion of 10 SR 3.8.1.20 from STS acceptable.
11 12 The proposed changes to STS 3.8.2, AC Sources - Shutdown, are editorial in nature to reflect 13 the deletion of SR 3.8.1.20. Therefore, the NRC find the proposed changes to STS 3.8.2 14 acceptable.
15 16
4.0 CONCLUSION
17 18 The NRC staff reviewed Traveler TSTF-599, which proposed changes to STS found in 19 NUREG-1430 through NUREG-1434. The NRC staff determined that the proposed changes to 20 the STS continue to meet the Commissions Final Policy Statement on Technical Specifications 21 Improvements for Nuclear Power Reactors and 10 CFR 50.36(c)(3) because the remaining 22 STS 3.8.1 DG SRs provide assurance that the necessary quality of systems and components 23 are maintained, and that STS LCO 3.8.1.b will be met. This is in combination with the fact that in 24 recent decades, industry operating experience during loss of offsite power events has 25 demonstrated consistent performance of the DG simultaneous start function. Additionally, the 26 NRC staff found the changes to the STS to be technically clear and consistent with customary 27 terminology and format in accordance with SRP Chapter 16.0. In summary, the NRC staff 28 reviewed the proposed deletion of STS SR 3.8.1.20, along with the associated changes to 29 STS 3.8.2 and the STS Bases, and concludes that the STS continue to provide reasonable 30 assurance of adequate protection of the health and safety of the public. Therefore, the NRC 31 staff concludes that the proposed STS changes are acceptable.
32 33 Principal Contributors:
K. West, NRR/DSS/STSB 34 V. Goel, NRR/DEX/EEEB 35 36 Date: April 15, 2025 37