ML19179A133
| ML19179A133 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 06/27/2019 |
| From: | Ed Miller Special Projects and Process Branch |
| To: | Aitken D Dominion Energy Co |
| References | |
| L-2018-LLA-0132 | |
| Download: ML19179A133 (4) | |
Text
1 NRR-DRMAPEm Resource From:
Miller, Ed Sent:
Thursday, June 27, 2019 4:03 PM To:
diane.aitken@dominionenergy.com
Subject:
Discussion items for OPC Public Teleconference Attachments:
North Anna OPC Discussion Points for Public Telecon.pdf
- Diane, Attached are the discussion points for the July 9 teleconference to discuss the OPC LAR. Please let me know if you have any trouble opening the file. Thanks.
Ed Miller 301-415-2481
Hearing Identifier:
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Subject:
Discussion items for OPC Public Teleconference Sent Date:
6/27/2019 4:03:14 PM Received Date:
6/27/2019 4:03:00 PM From:
Miller, Ed Created By:
Ed.Miller@nrc.gov Recipients:
"diane.aitken@dominionenergy.com" <diane.aitken@dominionenergy.com>
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NORTH ANNA POWER STATION, UNITS 1 AND 2 QUESTIONS FOR DISCUSSION WITH THE LICENSEE REGARDING OPEN PHASE PROTECTION PER NRC BULLETIN 2012-01 (EPID NO. L-2018-LLA-0132)
By application dated April 30, 2018 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML18127A073), Virginia Electric and Power Company (Dominion Energy Virginia), the licensee for North Anna Power Station, Units 1 and 2, proposed to revise Technical Specifications (TS) 3.3.5 for Loss of Power (LOP) Emergency Diesel Generator Start Instrumentation. The license amendment request (LAR) addresses the potential for an open phase condition (OPC) that could exist on one or two phases of a primary off-site power source and that would not currently be detected and mitigated by the existing station electrical protection scheme. In response to the NRC Staffs request, the licensee provided additional information on March 24, 2019 (ML19156A207).
The NRC staff would like to discuss the following questions with the licensee in a public meeting or public conference call, which may be followed by Request for Additional Information:
Question # 1 In the letter dated May 24, 2019 (in response to RAI-EEOB-3), the licensee stated that because BE1-47N relay operates with an inverse time characteristic, which would result in a range of time delays for various OPC events, the inclusion of the allowable values for the full range of time delays in TS is not considered practical. The North Anna Technical Requirements Manual is being revised to incorporate the setpoint for the BE1-47N relay, which will include the time dial setting.
The staff would like to discuss why the inclusion of the allowable values of time delay(s) or time dial setting in TS is not practical for the BE1-47N relay. Also, if the TS does not include time delay(s) or time dial setting, how it can be ensured that the relay will not exceed the time limits of engineering safeguards actuation assumed in the safety analyses.
Question # 2 The staff would like to discuss the following underlined apparent discrepancies in statements made in the LAR, and the statement made in the mark-up of UFSAR (Page 8.3-4, Insert A) provided in response to RAI-EEOB-12:
According to statement in the LAR (Attachment 1, Page 8): At a minimum of 4 percent negative sequence, the BE1-47N relay will energize [trip] and send a start signal [to EDG] in approximately 11 seconds.
According to statement in the LAR (Attachment 1, Page 14): Analysis results show that for most open phase events in which the BE1-47N relays trip, the tripping time is less than 6 seconds after the open phase event occurs.
According to statement in the mark-up of UFSAR (Page 8.3-4, Insert A): A time dial setting is used which results in a typical trip time delay of less than 6 seconds for any open phase condition sensed at an emergency bus.
Question # 3 In the LAR, Attachment 1, Page 10, the licensee stated that the following open phase conditions were considered:
x Single open phase without a ground connections x
Single open phase with a 350 ohm grounded connection x
Single open phase with a solid grounded connection Regarding the 350 ohms ground connection, in the letter dated May 24, 2019 (in response to RAI-EEOB-5), the licensee stated that the total fault impedance of a high resistance fault was calculated based on an empirical model as discussed in the Surry Open Phase Condition Detection Analysis calculation and IEEE paper, Typical Expected Values of the Fault Resistance in Power Systems. Using the most conservative method discussed in the IEEE paper, a total fault impedance of 173.4 ohms was calculated. This value was doubled to 346.8 ohms and rounded to 350 ohms for use in North Annas calculation.
Since the documents mentioned above are not readily available, the staff would like to discuss the calculation related to the 173.4 ohms value.
Also, the staff would like to discuss which of the above Open Phase Ground Connection conditions are represented in Table-1 provided in the LAR, Attachment 1, Page 15 (which summarizes the results of studies with Open Phase Conditions on each transformer).
Question # 4 In the letter dated May 24, 2019 (in response to RAI-EEOB-8), the licensee stated that for a voltage unbalance greater than 5%, the BE1-47N relays should isolate the motor loads from the OPC condition prior to the 22 x value reaching 20 pu. To validate this condition was met for the BE1-47N relays, a model was created in EMTP-RV to calculate the time until the 22 x value for each monitored motor reached 20 pu. This value was compared to the trip time of the BE1-47N relay for each event modeled.
The staff would like to discuss the time until the 22 x value for each typical safety-related motor reached 20 pu, and its comparison to the trip time of the BE1-47N relay for each event modeled. The staff would like to understand which of the cases will result in an automatic action taken by the BE1-47N, and in which cases a manual action (alarm) will be acceptable, and whether the operator will have adequate time to perform the manual actions.