ML13011A382
| ML13011A382 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 12/07/2012 |
| From: | O'Brien K Division of Reactor Safety III |
| To: | Bahadur S Division of Policy and Rulemaking |
| Caroline Tilton | |
| References | |
| TIA 2012-11 | |
| Download: ML13011A382 (5) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION REGION III 2443 WARRENVILLE ROAD, SUITE 210 LISLE, IL 60532-4352 December 7, 2012 MEMORANDUM TO:
Sher Bahadur, Deputy Director Division of Policy and Rulemaking Office of Nuclear Reactor Regulation FROM:
Kenneth G. OBrien, Acting Director /RA/
Region III Division of Reactor Safety
SUBJECT:
TASK INTERFACE AGREEMENT - LICENSING BASIS FOR DONALD C. COOK NUCLEAR POWER PLANT, UNITS 1 AND 2, DURING A STEAM GENERATOR TUBE RUPTURE EVENT COINCIDENT WITH A LOSS OF OFFSITE POWER (TIA 2012-11)
INTRODUCTION This Task Interface Agreement (TIA), documents the staffs position as determined through consultation between Region III and the Office of Nuclear Reactor Regulation (NRR) regarding the licensing basis for the steam generator tube rupture (SGTR) analysis, with respect to a loss of offsite power (LOOP) for the Donald C. Cook Nuclear Power Plant, Units 1 and Unit 2.
This TIA is submitted using the concurrence method as described in NRR Office Instruction COM-106, Control of Task Interface Agreements, Revision 3.
BACKGROUND During the 2012 Component Design Basis Inspection, the inspectors reviewed the licensing bases and plant response to a SGTR event. During this postulated design basis event (SGTR),
operators prevent overfill of the ruptured Steam Generator (SG) using the SG Power Operated Relief Valves (PORVs). Assuming a concurrent loss of offsite power (LOOP), the only available source of immediate motive power for the SG PORVs is the unit-specific control air compressor (CAC), which can be powered from on-site emergency power. The CACs are not safety-related.
For a LOOP with the CAC unavailable, the SG PORVs would be unavailable to mitigate the SGTR event described in the Updated Final Safety Analysis Report (UFSAR).
CONTACT:
(630) 829-9718
The licensee stated that their licensing bases assumed a LOOP for the unit with the SGTR (i.e., the affected unit) only, and the D. C. Cooks licensing basis does not require consideration of a single failure for components credited with mitigation for the SGTR analysis. Therefore, the non-safety-related Plant Air Compressor (PAC), which is shared between both units, would provide the motive power for the PORVs.
The inspectors disagreed with the licensees interpretation of their licensing bases with respect to a SGTR concurrent with a LOOP.
LICENSEE POSITION In response to a request from regional staff, the licensee provided their position on these issues in writing. A detailed description of the licensees position is provided in the licensees White Paper (Reference 1).
In Section 5 of their White Paper, Electrical Power Description, D. C. Cook states the following:
Normally, auxiliary power is supplied via the Unit Aux Transformers 1AB (2AB), as well as, 1CD (2CD) powered via the associated units Main Generator. A loss of offsite power to the affected units Plant Air Compressor is likely to result in a loss of the Technical Specification related source of offsite power to the unaffected units Plant Air Compressor. The loss of Technical Specification source of offsite power to the unaffected unit does not result in a loss of power to the unaffected units Plant Air Compressor. The unaffected unit will remain in operation with power supplied to the Plant Air Compressor and its Aux Oil Pump via the Unit Aux Transformers.
The licensees statement, that the unaffected units PAC will have power supplied via the Unit Aux Transformers, implies that they do not have to assume a loss of offsite power in the unaffected unit.
Furthermore, in Section 6 of their White Paper, Licensing Implications from the Postulated Scenario, the licensee states:
Because no single failure is considered in the D. C. Cooks licensing basis, the unaffected units Plant Air Compressor is assumed to be available and functional. If the postulated scenario precludes the use of compressed air supplied from the unaffected unit Plant Air Compressor, relative to the D. C. Cooks licensing basis, which would be considered a single failure, as well as considered beyond the D. C. Cooks design basis.
The licensees position that the unavailability of the unaffected units PAC would be considered a single failure again, implies that they do not have to assume a loss of offsite power in the unaffected unit or the failure of the non-safety related PAC.
S. Bahadur EVALUATION The original licensing basis for the SGTR analysis for D. C. Cook, similar to many of the earlier Westinghouse plants, did not include a computer analysis to describe the plant transient behavior following a SGTR. Instead, simplified calculations were performed based upon expected transient response to determine the primary-to-secondary break flow. Additionally, the analysis of record did not explicitly model the required operator actions to terminate the break flow, but rather assumed the operators actions could be completed within 30 minutes from the event initiation. During the licensees Expanded System Readiness Reviews that occurred in 1999, the lack of justification for the operator actions and 30 minute duration of the break flow was identified and documented in condition report CR-99-7284. The licensee contracted with Westinghouse to develop calculations based on the LOFTTR2 computer modeling code, using validated time critical operator actions from simulator runs performed by the licensee. These calculations demonstrated that although times in excess of the 30 minutes are required to terminate the SGTR break flow, a positive margin to SG overfill exists and the resulting offsite radiation doses are still bounded by the original licensing basis dose analysis.
The licensee subsequently submitted a license amendment request to the NRC (Reference 2),
which proposed incorporating the LOFTTR2 computer code into the SG overfill analysis. The NRC subsequently issued a Safety Evaluation and license amendment (Reference 3), which concluded that, although the incorporation of WCAP-10698-P-A into D. C. Cooks licensing basis is not acceptable, the licensee can use the LOFTTR2 code, with the current licensing basis assumptions as inputs for the overfill analysis of SGTR accidents.
The inspectors noted that the Updated Final Safety Analysis Report (UFSAR) Section 14.2.4, Steam Generator Tube Rupture, incorporated the LOFTTR2 computer code and one of the assumptions for the analysis included a LOOP. The inspectors noted the following:
Donald C. Cooks UFSAR Section 1.3.7, Electrical System, states, The main generators are 1800 rpm, Phase III, 60 cycle, hydrogen and water cooled units. The main transformers deliver generator power to the 345 kV and 765 kV switchyards. The station auxiliary power system consists of auxiliary transformers [emphasis added], 4160 v and 600 v switchgear, 600 v motor control centers, 120 v a-c vital instrument buses and 250 v d-c buses. Also, Section 1.3.8, Safety Features, describes the safety features incorporated in the design of the plant, including the fact that, even if external auxiliary power to the station [emphasis added] is lost concurrent with an accident, power is available for the engineered safeguards from on-site diesel-generator power to assure protection of the public health and safety for any loss-of-coolant accident.
The inspectors noted Section 1.3.7 describes the auxiliary power system in the station and not individually for each unit. Section 1.3.8 further amplifies a loss of offsite power to the station and not individual to each unit. The inspectors also noted that part of the safety features incorporated in the design of D. C. Cook included the reliability of on-site emergency diesel generators (EDGs) for a postulated loss of external auxiliary power to the station (i.e., both units) concurrent with an accident (i.e., SGTR). Therefore, the inspectors concluded that the accident in question, a SGTR, needs to be evaluated with a LOOP at the station (i.e., LOOP to both units).
Donald C. Cooks UFSAR Section 14.1.12.1, Identification of Causes and Accident Description, as related to UFSAR Section 14.1.12, Loss of All AC Power to the Plant Auxiliaries, states A complete loss of all (non-emergency) AC power (e.g., offsite power) may result in the loss of all power to the plant auxiliaries, i.e., the RCPs, condensate pumps, etc. The loss of power may be caused by a complete loss of the offsite grid accompanied by a turbine generator trip at the station, or by a loss of the on-site AC distribution system.
It should be noted that D. C. Cook has two UFSAR Sections 14.1.12.1 - one for Unit 1 and one for Unit 2.
The inspectors concluded that the licensing basis of D. C. Cooks AC power to plant auxiliaries (e.g., offsite power) allows for a complete loss of the offsite grid and that loss of all (non-emergency) AC power to the station (i.e., both units) is a credible event and part of D. C. Cooks design and licensing basis.
Based on the above, the inspectors concluded a LOOP is a station event, not a unit specific event. Furthermore, as applicable to the SGTR analysis, a LOOP is an initial condition of the event and should not be considered as a single failure.
CONCLUSION The staff concludes the licensing bases for D. C. Cook requires an assumption of a SGTR concurrent with a LOOP at the station (i.e., LOOP to both units). The scope of this TIA was limited to the licensing basis as related to offsite power only. The staff did not evaluate other assertions in the licensees white paper.
REFERENCES
- 1) Letter from W. Hodge (D. C. Cook ) to C. Tilton (NRC), D. C. Cook Steam Generator Tube Rupture Margin to Overfill Licensing Basis Position, (ADAMS Accession No. ML12320A544).
- 2) Letter from Indiana Michigan Power to NRC, License Amendment Request for Changes in Steam Generator Tube Rupture Analysis Methodology, dated October 24, 2000, (ADAMS Accession No. ML003762982).
- 3) Letter from NRC to Indiana Michigan Power, Issuance of Amendment, dated October 24, 2001, (ADAMS Accession No. ML012690136).
Docket Nos. 50-315 and 50-316 License Nos. DPR-58 and DPR-74
- 2) Letter from Indiana Michigan Power to NRC, License Amendment Request for Changes in Steam Generator Tube Rupture Analysis Methodology, dated October 24, 2000, (ADAMS Accession No. ML003762982).
- 3) Letter from NRC to Indiana Michigan Power, Issuance of Amendment, dated October 24, 2001, (ADAMS Accession No. ML012690136).
Docket Nos. 50-315 and 50-316 License Nos. DPR-58 and DPR-74 DISTRIBUTION:
Christopher Jackson Andersen, James Elliott, Robert Cruz, Holly Stuchell, Sheldon Wengert, Thomas Sun, Summer Miranda, Samuel Grover, Ravinder Waig, Gerald Parks, Benjamin Mathew, Roy Carlson, Robert Bahadur, Sher McGinty, Timothy Pelton, Dave Matharu, Singh, Gurcharan
NAME CTilton:ls
- AMStone for RBaker AMStone