ML25076A169
| ML25076A169 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 03/17/2025 |
| From: | NRC/NRR/DORL/LPMB |
| To: | |
| Bina S, NRR/DORL/LDATA | |
| References | |
| EPID L-2025-LLA-0049 | |
| Download: ML25076A169 (1) | |
Text
REQUEST FOR ADDITIONAL INFORMATION EMERGENCY LICENSE AMENDMENT REQUEST TO REVISE TS 3.7.8 CONTROL ROOM EMERGENCY VENTILATION SYSTEM (CREVS)
CALVERT CLIFFS NUCLEAR POWER PLANT, UNIT 1 CEG, LLC DOCKET NO. 50-317 By application dated March 15, 2025, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML25074A002) Constellation Energy Generation, LLC (the licensee) requested changes to the technical specifications (TSs) for Calvert Cliffs Unit 1. The proposed changes would allow a one-time extension to the Completion Time (CT) for TS 3.7.8, Control Room Emergency Ventilation System (CREVS), Required Action C.1 from 7 days to 17 days. The licensee stated the one-time extension is necessary to support ongoing modifications and return to service testing of the 13.8 kilo volts (kV) Service Bus 21.
Regulatory Requirements Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Section 36 (50.36), Technical specifications, requires, in part, that the operating license of a nuclear production facility include TS. Paragraph 50.36 (c)(2)(i) of 10 CFR requires that the TSs include limiting conditions for operation (LCOs), which are the lowest functional capability or performance levels of equipment required for safe operation of the facility. When an LCO of a nuclear reactor is not met, paragraph 50.36(c)(2)(i) requires that the licensee shall shut down the reactor or follow any remedial action permitted by the TSs until the condition can be met.
General Design Criterion (GDC) 17, Electric power systems, of 10 CFR Part 50, Appendix A, General Design Criteria for Nuclear Power Plants, requires, in part, that an onsite electric power system and an offsite electric power system shall be provided to permit functioning of structures, systems, and components important to safety. The safety function for each system (assuming the other system is not functioning) shall be to provide sufficient capacity and capability to assure that (1) specified acceptable fuel design limits and design conditions of the reactor coolant pressure boundary are not exceeded as a result of anticipated operational occurrences and (2) the core is cooled and containment integrity and other vital functions are maintained in the event of postulated accidents. The onsite electric power supplies and the onsite electric distribution system shall have sufficient independence, redundancy, and testability to perform their safety functions assuming a single failure. In addition, this criterion requires provisions to minimize the probability of losing electric power from any of the remaining supplies as a result of the loss of power from the unit, the transmission network, or the onsite electric power supplies.
The U.S. Nuclear Regulatory Commission (NRC) staff notes that Calvert Cliffs Nuclear Power Plant (Calvert Cliffs or CCNPP) was not licensed to the GDCs listed in 10 CFR Part 50, Appendix A, but was licensed based on the Atomic Energy Commission proposed GDCs published on July 10, 1967. The relevant principal design criteria for Calvert Cliffs are described in Appendix 1C of the Calvert Cliffs Updated Final Safety Analysis Report (UFSAR)
(ML21257A252) and are as follows:
Similar to GDC 17, UFSAR Appendix 1C.5 and 1C.8 include Criteria 24 and 39, respectively.
Criterion 24, Emergency Power for Protection Systems (Category B), states that in the event of loss of all offsite power, sufficient alternate sources of power shall be provided to permit the required functioning of the protection systems.
Criterion 39, Emergency Power for Engineered Safety Features (Category A), states that alternate power system shall be provided and designed with adequate independency, redundancy, capacity, and testability to permit the functioning required of the engineered safety features. As a minimum, the onsite power system and the offsite power system shall each, independently, provide this capacity assuming a failure of a single active component in each power system.
The NRC staff has reviewed the submittal and has determined that the following additional information is needed to complete its review.
Request for Additional Information (RAI) EEEB-1 The fourth paragraph of section 3.1, Safety Analysis, of the LAR states, in part:
In the current electrical line up, CCNPP has two of the four offsite power sources available (5051 and 5052). These sources are being supplied to downstream 4 kV buses through a single 13 kV Bus (11) and a single 13 kV/4 kV transformer (U-4000-12), including the 24 4 kV bus for 12 CREVS/CRETS [Control Room Emergency Temperature System]
Please clarify which single 13 kV Bus supplies power to the 12 CREVS/CRETS (i.e.,13 kV Bus (11) or 13 kV Bus (21).
RAI EEEB-2 The fifth paragraph of section 3.1 of the LAR states, in part:
As detailed in Section 3.2, Risk Assessment Insights and Compensatory Measures, to reduce the possibility that maintenance activities could contribute to a loss-of-offsite power, the protected equipment to prevent 11 CREVS being declared INOPERABLE includes 11 CR HVAC, 1A DG [diesel generator], and the 2B DG which is the emergency supply to the 12 CREVS. The main control room has placed protected equipment tags on the hand switch for 13 kV Bus (11) and will continue to protect the single 13 kV / 4 kV transformer (U-4000-12), including the 4 kV Bus 11 for 11 CREVS/CRETS.
However, the seventh paragraph of Section 3.1 of the LAR further states, in part:
During the electrical upgrade maintenance window in which the 4 kV Bus 11 (power to 11 CREVS) is protected, some work will be required on the bus.
Specifically, wiring will be required on the alternate feeder breaker for the 4 kV Bus 11. This breaker is on the bus and will be open as the normal feeder will be supplying power to the bus.
According to the above paragraphs, the licensee is protecting equipment including 13 kV Bus (11) and the single 13 kV / 4 kV transformer (U-4000-12) to reduce the possibility that maintenance activities could contribute to a loss-of-offsite power. However, it appears that the 13 kV Bus (11), the single 13 kV / 4 kV transformer (U-4000-12), and the 4 kV Bus 11 are not included in the list of protected equipment in section 3.2, Risk Assessment Insights and Compensatory Measures of the LAR.
Please explain why the 13 kV Bus (11), the single 13 kV / 4 kV transformer (U-4000-12), and the 4 kV Bus 11 are not listed as protected equipment in section 3.2 of the LAR or add this aforementioned equipment to Section 3.2 of the LAR as protected equipment.
RAI EEEB-3 LAR Section 2.1, CREVS Design and Operation states, in part, that the 12 CREVS train is normally powered from the Unit 2 4.16 kV ESF Bus 24, which is connected to the 13.8 kV Service Bus 21 offsite circuit and backed up by the 2B DG.
The third paragraph of Section 3.1 of the LAR states, in part:
The 12 CREVS train will be powered from its alternate offsite power supply during this period, and have its emergency onsite power supply, the 2B DG, available during this period. The non-safety related 0C DG is available as a backup emergency power source for the 12 CREVS.
LAR Section 3.2 states, in part, that wiring work on the 4 kV Bus 24 normal feeder breaker will be performed.
It appears that any potential failure of the 4 kV Bus 24 as the result of work on this bus would make it not available to receive power from the 2B DG. Consequently, 0C DG becomes a backup power source for the 12 CREVS train in the event of loss of offsite power.
Please clarify whether the 0C DG should be protected (i.e., added to protected equipment list in Section 3.2) during the proposed extended completion time for TS 3.7.8, Required Action C.1, given the stated wiring work to be performed.