RS-23-111, Additional Information Supporting Request for License Amendment to Revise Technical Specifications Section 3.8.3
| ML23289A069 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 10/16/2023 |
| From: | Humphrey M Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| RS-23-111 | |
| Download: ML23289A069 (1) | |
Text
4300 Winfield Road Warrenville, IL 60555 630 657 2000 Office RS-23-111 October 16, 2023 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Clinton Power Station, Unit 1 Facility Operating License No. NPF-62 NRC Docket No. 50-461
Subject:
Additional Information Supporting Request for License Amendment to Revise Technical Specifications Section 3.8.3
References:
- 1. Letter from P. R. Simpson (Constellation Energy Generation, LLC) to U.S.
NRC, "Request for License Amendment to Revise Technical Specifications Section 3.8.3, 'Diesel Fuel Oil, Lube Oil, and Starting Air'," dated March 1, 2023
- 2. Email from J. Wiebe (U.S. NRC) to K. M. Nicely (Constellation Energy Generation, LLC), "Clinton Power Station, Unit 1, Preliminary Requests for Additional Information (RAIs) Related to the Amendment Request to Revise Diesel Generator Starting Air Technical Specifications," dated August 18, 2023 In Reference 1, Constellation Energy Generation, LLC (CEG) requested an amendment to Facility Operating License No. NPF-62 for Clinton Power Station, Unit 1. Specifically, the proposed change revises Technical Specifications Section 3.8.3, "Diesel Fuel Oil, Lube Oil, and Starting Air," to delete Condition E that allows a required Diesel Generator to be considered operable with reduced starting air capability, and to clarify that only one air start receiver with adequate pressure is required for the associated starting air system to be considered operable.
The NRC requested additional information that is needed to complete review of the proposed change in Reference 2. In response to this request, CEG is providing the attached information.
CEG has reviewed the information supporting a finding of no significant hazards consideration, and the environmental consideration, that were previously provided to the NRC in Attachment 1 of Reference 1. The additional information provided in this submittal does not affect the bases for concluding that the proposed license amendment does not involve a significant hazards consideration. In addition, the additional information provided in this submittal does not affect
October 16, 2023 U.S. Nuclear Regulatory Commission Page 2 the bases for concluding that neither an environmental impact statement nor an environmental assessment needs to be prepared in connection with the proposed amendment.
There are no regulatory commitments contained in this letter. Should you have any questions concerning this letter, please contact Mr. Kenneth M. Nicely at (779) 231-6119.
I declare under penalty of perjury that the foregoing is true and correct. Executed on the 16th day of October 2023.
Respectfully, Mark Humphrey Sr. Manager Licensing Constellation Energy Generation, LLC
Attachment:
Response to Request for Additional Information cc:
NRC Regional Administrator, Region III NRC Senior Resident Inspector - Clinton Power Station Illinois Emergency Management Agency - Division of Nuclear Safety Humphrey, Mark D.
Digitally signed by Humphrey, Mark D.
Date: 2023.10.16 07:46:17 -05'00'
ATTACHMENT Response to Request for Additional Information Page 1 NRC Request 1 The licensee requests changing Surveillance Requirement (SR) 3.8.3.4 from "Verify each required DG air start receiver pressure is 200 psig to "Verify each air start pressure is 200 psig." As indicated in the LAR, each DG has an air start system with adequate capacity for five successive start attempts of the DG without recharging the air start receiver(s).
The intent of air starting system SR 3.8.3.4 is contained in NUREG-1434 (Standard Technical Specifications (STS)) which reads in part, "This Surveillance ensures that, without the aid of the refill compressor, sufficient air start capacity for each DG is available. The system design requirements provide for a minimum of five engine start cycles without recharging." The proposed change removes the pressurized requirement for the individual receiver and requires the overall system to remain above the pressure required for five starts ( 200 psig). With the SR revised as proposed, both receivers will not be required to meet the five-start requirement and could meet TS requirements with only one receiver operable.
Section 9.5.6.1.1 of Clinton's Final Safety Analysis Report (FSAR) states, "The diesel-generator starting systems for the Divisions I, II, and III diesel engines are independent and redundant for each division. Each diesel generator starting system consists of two full capacity air starting subsystems. Each subsystem has a rated capacity capable of starting its respective engine set five times without recharging the associated air receiver. The rated air capacity of each subsystem is 93 ft.3 at 250 psig for the Division I and II DGs and 64 ft.3 at 240 psig for the Division III DG. All three DGs are capable of multiple successive starts without recharging the air receiver tank when the air receiver pressure is below the rated air pressure but above 200 psig."
The staff understands the terminology of "diesel generator air starting system" contained in FSAR Section 9.5.6.1.1 to represent the overall air start system (containing 2 receivers) suppling it's respective DG (Div I, II, or III). Additionally, each "diesel generator air starting system" consists of two redundant air starting "subsystems". The FSAR indicates each subsystem has a rated capacity for starting its respective engine set five times.
The staff requests that the licensee:
- 1.
Provide a description of what components define the "system" and "sub-system" and their operability requirements with the proposed TS changes.
- 2.
Describe how the system is normally aligned for the DG for the Divisions I, II, and III.
Also, define independence and redundancy within each division containing full capacity subsystems/systems and how the TS change impacts redundancy, as defined in FSAR 9.5.6.
Response
The CPS Class 1E AC Electrical Power Distribution System AC sources consist of the offsite power sources and the onsite standby power sources (i.e., DGs 1A, 1B, and 1C). The three air start systems for the Divisions I, II, and III diesel engines are independent and redundant for each division. Failure of one system will not prevent the other two systems from starting their
ATTACHMENT Response to Request for Additional Information Page 2 respective DG. Each DG starting air system consists of two full capacity air starting subsystems, as discussed below.
Figure 1 shows a simplified diagram of the air start systems for the Division I and Division II DGs.
Figure 1: Air Start Systems for Divisions I and II DGs The Division I and II DGs are tandem mounted 12 and 16 cylinder engines with a center mounted generator. The Division I and II DGs have independent starting air systems, with each system containing two 100% capacity AC motor driven air compressors, one starting air dryer, two air receiver tanks, six air motors, and associated piping, valves, and controls. The air start systems for each division have two motor driven air compressors that are cross-connected on the inlet side of the receivers. Therefore, each air compressor can supply air to both air receiver tanks. The starting air receivers ensure an adequate supply of air is available to start the DGs using three air start motors mounted on each tandem engine. When the DG starting logic is actuated, four air start solenoids open the pilot valves allowing air from the starting air header to actuate and open the main air start valves. This provides a flowpath for air from the starting air receivers to the three air start motors on each tandem engine. The air start motors rotate the pinion gears and the pinion gears, in turn, engage with and drive the engine flywheel ring gear, causing the engine to crank. Two air start motors on one engine and a single motor on the other engine are required to engage in order to start the engines.
Each air start system, for the Division I and II DGs, consists of two full capacity subsystems that contain one air receiver, two divisional air start solenoids, three air motors, and associated piping, valves, and controls. As stated above, two air start motors on one engine and a single
ATTACHMENT Response to Request for Additional Information Page 3 motor on the other engine are required to engage in order to start the engines. Periodic surveillance testing is performed with one of the two air receivers isolated; therefore, the ability of each subsystem to start the Division I and II DGs is confirmed during surveillance testing.
A simplified diagram of the air start system for the Division III DG is shown in Figure 2.
Figure 2: Air Start System for Division III DG The Division III DG has a single 16 cylinder engine. The Division III air system contains two 100% capacity AC motor driven air compressors, one starting air dryer, two air receiver tanks, four air motors, and associated piping, valves, and controls. The Division III air start system has two motor driven air compressors that are cross-connected on the inlet side of the receivers. Therefore, each air compressor can supply air to both air receiver tanks. When a start signal is received, the air start solenoids on both trains energize and cause the associated valves to open. The starting air passes through these valves and enters the lower air start motors. The starting air causes the pinion gear of each motor to jog forward until it engages with the engine flywheel ring gear. Engagement of the lower pinion gear uncovers a port, which provides an air flowpath to the upper air motor pinion gear piston, causing it to jog forward and engage the ring gear. When the upper air start motor pinion gear engages it uncovers a port that allows air to open the main air supply valve. This provides a flowpath from the air receiver to the pair of air start motors. Only one pair of air start motors is required to start the Division III DG.
The Division III air start system consists of two full capacity subsystems that contain one air receiver, one divisional air start solenoid, two air motors, and associated piping, valves, and controls. As stated above, one pair of air start motors is required to start the engine. Periodic surveillance testing is performed with one of the two air receivers isolated; therefore, the ability of each subsystem to start the Division III DG is confirmed during surveillance testing.
ATTACHMENT Response to Request for Additional Information Page 4 Based on the redundant design of the starting air systems (i.e., with two full capacity subsystems containing one air receiver connected to one starting air motor train), each DG is considered operable when the pressure is greater than or equal to 200 psig in at least one of the two air receivers for the respective DG. As discussed above, periodic surveillance testing for all three DGs is performed with one of the two air receivers isolated; therefore, the capability of starting the DG with a single air receiver is periodically verified.
The proposed change removes the allowance permitting the DG to remain operable (i.e., for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />) with reduced starting air capability. Therefore, following implementation of the proposed change, the DG will be declared inoperable when the pressure in both of the associated air receivers is less than 200 psig. The DG will remain operable when the pressure in at least one of the two air receivers for the respective DG is greater than or equal to 200 psig.
This is consistent with CPS annunciator response procedures for all three DGs, which direct the operators to declare the DG inoperable if the pressure in both its air start receivers is below 200 psig. The proposed change has no impact on DG air start system redundancy and independence.
NRC Request 2 The DG air start system safety function is to assure reliable starting of the emergency diesel engines in the event of a loss of offsite power. SRP 9.5.6 states the consequences of a single active failure in a starting air system will not lead to a loss of more than one diesel generator.
Consistent with SRP criteria, FSAR Section 9.5.6.1.1.c indicates "A failure of a single active or passive component for one division will not prevent another division from performing its intended function."
GDC 17 requires the onsite electric power supplies, including the batteries, and the onsite electric distribution system, shall have sufficient independence, redundancy, and testability to perform their safety functions assuming a single failure.
SRP 9.5.6 further indicates "Piping interconnections between the dedicated air start systems are reviewed for whether a failure in the interconnecting piping could lead to the loss of starting for more than one diesel engine."
The staff requests that the licensee confirm that failure of single receiver will not result in multiple DGs being inoperable.
Response
As discussed above, the three DG starting air systems are independent and redundant for each of the Division I, II, and III DGs. A failure of a single receiver, alone, will not result in the associated DG being inoperable because each DG starting air system consists of two full capacity air starting subsystems and each subsystem includes an air receiver. Furthermore, a complete failure of an air system (i.e., both air starting subsystems) will not result in multiple DGs being inoperable because the starting air systems are independent for each of the Division I, II, and III DGs.
ATTACHMENT Response to Request for Additional Information Page 5 NRC Request 3 GDC 17 requires the onsite electric power supplies, including the batteries, and the onsite electric distribution system, shall have sufficient independence, redundancy, and testability to perform their safety functions assuming a single failure. Specific criteria and guidance necessary to meet GDC 17 requirements are indicated in Section 9.5.6 of NUREG-0800 (Standard Review Plan (SRP)) as follows: "C. As a minimum, the air starting system should be capable of cranking a cold diesel engine five times without recharging the receiver(s). The air starting system capacity should be determined as follows: (i) each cranking cycle duration should be approximately three seconds, (ii) consist of two to three engine revolutions, or (iii) air start requirements per engine start provided by the engine manufacturer, whichever air start requirement is larger."
Current SR 3.8.3.4 requires that EDG starting air receiver pressure be maintained greater than or equal to 200 psig. This value is based on capacity as defined in FSAR Section 9.5.6.1.1 which specifies "Each subsystem has a rated capacity capable of starting its respective engine set five times without recharging the associated air receiver."
Current TS 3.8.3 allows operating for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> when pressure requirements are met for only one of the two starting air receivers. That is, up to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> is allowed to restore the pressure of the DG receiver prior to declaring the DG inoperable. TS 3.8.3 further requires receiver pressure remain greater than 140 psig. NUREG-1434 defines lower specified pressure as allowance for an extension of 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> prior to having to declare the EDG inoperable based on the assessment that the minimum pressure will be sufficient for a reliable start with one attempt.
The licensee's basis for current TS criteria is defined in the Bases for TS 3.8.3 (Condition E) as, "With the required starting air receiver pressure < 200 psig, sufficient capacity for multiple DG start attempts may not exist. However, as long as the receiver pressure is 140 psig, there is adequate capacity for at least one start attempt, and the DG can be considered OPERABLE while the air receiver pressure is restored to the required limit. A period of 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> is considered sufficient to complete restoration to the required pressure prior to declaring the DG inoperable. This period is acceptable based on the remaining air start capacity, the fact that most DG starts are accomplished on the first attempt, and the low probability of an event during this brief period."
The licensee proposed to delete Condition E that allows a required DG to be considered operable with reduced starting air capability. The LAR indicates "This determination was made because the capability of one successful start attempt cannot be assured when starting air receiver pressure falls to the lower limit of 140 psig." With the proposed change, licensee removes the ability to consider the impacted DG operable with a minimum TS pressure requirement ensuring one start. As a result, overall air starting system pressure falling below the 200 psig SR requirement results in immediate entry into LCO 3.8.1 and declaring the impacted DG inoperable.
The NRC staff requests that the licensee confirm that the system meets the 5-start criteria (12 second fast start) with air receiver pressure at the proposed SR 200 psig and how the pressure is defined, calculated, tested, and monitored.
ATTACHMENT Response to Request for Additional Information Page 6
Response
For the Division I DG, the ability to start the engine set five times without recharging the associated air receivers was demonstrated as part of initial plant startup testing, and subsequently as part of post-modification testing following implementation of a design change in 1998. As such, no calculation was performed related to the 5-start criteria.
The results concluded that the air-start system is capable of performing five starts, which meets the established design criteria. The Division I DG successfully started on the fifth attempt using the 'A' receiver; however, the time to achieve rated speed was 12.6 seconds. This was dispositioned as acceptable because as stated in USAR Section 9.5.6.1.1, each subsystem has a rated capacity capable of starting its respective engine set five times without recharging the associated air receiver. In addition, the requirement to start the DG and reach rated speed, voltage, and frequency within 12 seconds after receipt of the start signal was confirmed in accordance with USAR Section 9.5.6.1.1. Fast start capability is not required for successive starts because the accident analyses assume a successful start on the first attempt.
The Division I DG test results are considered bounding for the other DGs due to the physical differences between the three DGs. For example, the Division I DG has a much larger generator rotor compared to the other DGs. In addition, the Division III DG consists of a single engine; whereas, the Division I and Division II DGs consist of two tandem engines.