ML20231A652

Summary of Teleconference with Pacific Gas & Electric Company Regarding an Exigent Amendment Request to Modify Diablo Canyon Power Plant, Units 1 & 2, Technical Specification 3.7.5, Auxiliary Feedwater (AFW) System EPID L-2020-LLA-017

ML20231A652
Person / Time
Site:	Diablo Canyon
Issue date:	08/24/2020
From:	Samson Lee Plant Licensing Branch IV
To:
Lee S, 301-415-3158
References
EPID L-2020-LLA-0176
Download: ML20231A652 (8)

Text

August 24, 2020 LICENSEE: Pacific Gas and Electric Company FACILITY: Diablo Canyon Nuclear Power Plant, Units 1 and 2

SUMMARY

OF AUGUST 14, 2020, TELECONFERENCE WITH PACIFIC GAS AND ELECTRIC COMPANY REGARDING AN EXIGENT LICENSE AMENDMENT REQUEST TO MODIFY TECHNICAL SPECIFICATION 3.7.5, AUXILIARY FEEDWATER (AFW) SYSTEM, FOR DIABLO CANYON NUCLEAR POWER PLANT, UNITS 1 AND 2 (EPID L-2020-LLA-0176)

On August 14, 2020, a Category 1 public teleconference was held between the U.S. Nuclear Regulatory Commission (NRC) and representatives of the Pacific Gas and Electric Company (the licensee). The purpose of the teleconference was to discuss an exigent license amendment request (LAR) for Diablo Canyon Nuclear Power Plant (Diablo Canyon), Units 1 and 2. Specifically, the proposed amendments would avoid an unnecessary plant shutdown during the expected time needed to perform potential repairs to the Diablo Canyon Unit 1, auxiliary feedwater (AFW) system piping that the licensee anticipates may be identified during Unit 1, Cycle 22, planned upcoming inspections to the AFW system. The licensee submitted the LAR by letter dated August 12, 2020 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML20225A303). In the LAR, the licensee requested NRC approval by August 25, 2020. The meeting notice and agenda, dated August 13, 2020, are available in ADAMS at Accession No. ML20226A447. A list of attendees is provided as .

Because of localized corrosion identified on Diablo Canyon, Unit 2, AFW piping during a recent Unit 2 maintenance outage, the licensee intends to perform inspections of Diablo Canyon, Unit 1, AFW piping in the near term to ensure that Unit 1 is not similarly affected. If similar below-minimum wall pipe thicknesses are found in the Unit 1 AFW system piping and elbows that were found in Unit 2, based on the estimated time-to-repair gained from the Unit 2 repair, it is likely that the current Diablo Canyon Technical Specification (TS) 3.7.5, Auxiliary Feedwater (AFW) System, Required Actions B.1 or D.1 would result in the required shutdown of Unit 1.

The licensees proposed one-time TS 3.7.5 change would avoid an unnecessary plant shutdown during the expected time needed to perform the potential repairs and associated post-maintenance inspections and testing to the Unit 1 AFW system piping.

During the meeting, the licensee discussed the corrosion identified on Diablo Canyon, Unit 2, AFW piping and the subsequent repairs. The licensee discussed its assessment of extent of condition for the Unit 1 AFW piping and its plan for inspection and repair, as necessary.

The NRC staff planned to issue requests for additional information (RAIs) on August 14, 2020, following the public teleconference. The NRC staff provided the licensee a list of discussion topics, which is provided as Enclosure 2, shortly before the public teleconference to facilitate discussion. The NRC staff noted that it intended to modify the discussion topics, as appropriate, and issue them as RAIs.

During the meeting, the licensee provided the following information regarding the topics in :

1. The AFW system consists of carbon steel piping. The licensee found one leak and a few areas where the Unit 2 AFW piping was below the Code minimum wall thickness, and performed repairs. The corrosion was found to be external surface corrosion; however, the licensee had not yet completed the root cause evaluation. The licensee plans to inspect five similar AFW piping locations in Unit 1. The licensee also plans to inspect all AFW piping in the upcoming Unit 1 outage in about 45 days.

2. The AFW piping is American Society of Mechanical Engineers (ASME) B31.1 Code piping (1967 Code Edition, with 1971 Addenda). Necessary repairs would be performed to Code requirements and would be inspected with ultrasonic testing and radiography.

3. The licensee discussed the configuration of the valves and pumps in the AFW system.

4. The AFW system would be ready to actuate. The related systems, such as steam generator level control instrumentation, are not impacted.

5. The licensee acknowledged it was a typographical error.

6. An updated computer code was used. The licensee was not changing the design basis events.

7. The licensee was providing risk insights with the risk management actions (RMAs). The 7-day extension numerical value was not tied to the RMAs. The licensee planned to maintain the RMAs during the duration of the requested completion time.

8. RMAs would protect equipment, such as doors, and existing processes.

9. The licensee discussed the risk significance of Pumps 1-1 and 1-3.

10. The licensee discussed the risk significance of feed-and-bleed.

11. The licensee performed a walkdown of Diablo Canyon Unit 1, 2 days after the leak was identified in Unit 2. The licensee had completed the operability determination for Unit 1.

Three members of the public were in attendance. The following comment was received:

Request to be added to the public distribution list and the importance of the NRC staff review of the AFW system.

No regulatory decisions were made at this meeting.

Please direct any inquiries to me at 301-415-3168 or Samson.Lee@nrc.gov.

/RA/

Samson S. Lee Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-275 and 50-323

Enclosures:

1. List of Attendees

2. Discussion Topics cc: Listserv

LIST OF ATTENDEES AUGUST 14, 2020, TELECONFERENCE REGARDING AN EXIGENT LICENSE AMENDMENT REQUEST TO MODIFY TECHNICAL SPECIFICATION 3.7.5, AUXILIARY FEEDWATER (AFW) SYSTEM PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON NUCLEAR POWER PLANT, UNITS 1 AND 2, U.S. Nuclear Regulatory Commission Pacific Gas and Electric Company S. Lee M. Richardson N. Chien R. Thatipamala N. Karipineni A. Lin A. Russell B. Mainini C. Moulton M. Sheppard T. Hilsmeier S. Williams B. Allik K. Schrader M. Breach R. Baradaran A. Tsirigotis J. Barbosa J. Seymour K. Bych J. Borromeo R. Berger T. Wengert R. OSullivan B. Waltos Public M. Lewis J. Swanson Y. Peng Enclosure 1

DISCUSSION TOPICS FOR AUGUST 14, 2020, PUBLIC CONFERENCE CALL DIABLO CANYON EXIGENT AMENDMENT REQUEST (EPID: L-2020-LLA-0176)

1. Corrosion : Please discuss:

a. Material type of the auxiliary feedwater (AFW) piping (e.g., carbon steel)

b. Degradation mechanism identified at Unit 2 (e.g., general corrosion)

c. Corrosion at Unit 2 was on the internal or external surfaces?

d. Corrosion at Unit 2 was at welds or piping?

e. Are there any differences between the AFW piping at Units 1 and 2 in terms of material type, corrosion protection (i.e., coatings), or environment (e.g., time of wetness, potential for contaminants such as chlorides to accelerate corrosion)?

2. Please identify the AFW piping design Code and the process that will be followed for the repair consistent with the Code requirements. Is the one-to-one repair/replacement method being utilize?

3. License amendment request (LAR), page 7 of 22, states that:

On July 23, 2020, with DCPP [Diablo Canyon Nuclear Power Plant] Unit 2 still in Mode 3, a 3.9 gallons per minute calculated through-wall leak was observed coming out of the elbow just downstream of Valve LCV-111 in the discharge line for Unit 2 AFW Pumps 2-1 and 2-2 to SG 2-2.

What role is Pump 2-1?

4. LAR, page 8 of 22, states that:

While in Condition G the SG [steam generator] 1-2 related TS [technical specification] required equipment will continue to remain operable.

Please explain what are the related TS required equipment.

5. LAR, page 9 of 22, states that:

Conditions B and GD are modified to add new Condition G as a Condition for which an inoperable Condition is applicable.

6. LAR page 10 states that:

Loss of Normal Feedwater Transient The condition 2 event of loss of normal feedwater is addressed in the FSARU [Final Safety Analysis Report Update] Section 15.2.8. This transient is modeled with an assumed single failure of the turbine-driven pump, resulting in the remaining two motor-driven pumps operable and feeding all four SGs with a total of 600 gallons per minute (gpm) flow. The proposed possible isolation of AFW flow to SG 1-2 means that the AFW system will have three available AFW pumps, which can provide well Enclosure 2

above 600 gpm, but only to the three unaffected SGs. There is an additional FSARU analysis of the loss of normal feedwater transient in Section 6.5.3.7, termed a better-estimate analysis, that is done for AFW reliability demonstration. FSARU Section 6.5.3.7 notes that the FSARU Section 15.2.8 analysis has considerable margin when 4 SGs are credited, and that the better-estimate analysis shows successful event mitigation with just two SGs receiving a total of 390 gpm. Therefore, the proposed SG 1-2 isolation case, with three available SGs, is bounded by the FSARU Section 6.5.3.7 better-estimate case which only credits AFW flow to 2 SGs.

FSARU 6.5.3.7 states that:

A better-estimate analysis is performed to address the reliability of the AFW system. This analysis is similar to that described above for the Chapter 15 analysis, but assuming that only a single motor-driven AFW system pump supplies a minimum of 390 gpm to two of the four SGs.

The cases considered in this additional analysis assume better-estimate conditions for several key parameters, including initial power level, decay heat, RCS temperature, pressurizer pressure, and low-low SG water level reactor trip setpoint. The results of this better-estimate analysis demonstrate that there is margin to pressurizer over-filling. While this analysis demonstrates that the AFW system remains highly reliable, the DCPP licensing basis requires that at least two AFW pumps delivering at 600 gpm to four SGs is required for this event.

The staff requests the licensee to explain the bases that a better-estimate analysis (two DGs receiving 390 gpm) can be used to cover a licensing based event (four SGs receiving 600 gpm).

7. The licensee proposed a completion time (CT) of 7 days for TS 3.7.5 Condition G One or two AFW trains inoperable in MODE 1, 2, or 3 due to inoperable AFW piping affecting the AFW flow path(s) to one steam generator for Unit 1 during repair of AFW piping.

The proposed Condition is modified by a note which identifies that the condition is only applicable to Unit 1 once during Unit 1 Cycle 22 during repair of AFW piping.

In the Enclosure of the LAR on pages 12-13, the licensee provides a list of risk management actions (RMAs) the licensee will implement during the TS 3.7.5 Condition G 7-day CT. It appears that part of the justification for the proposed temporary CTs relies on the RMAs listed in the Enclosure.

Provide further justification for the proposed note language, which does not currently mention the RMAs. Alternatively, consider rewording the proposed note language to indicate that the 7 day CT is contingent on implementation of the RMAs listed in the LAR.

In addition, clarify whether the identified risk management actions will be required to be in place for the duration of the extended completion time.

8. In the description of RMAs, the LAR describes protecting certain equipment during the extended completion time. Clarify whether this includes preventing the protected equipment from being taken out of service for testing and maintenance activities.

9. Based on the risk insights, the LAR identified RMAs to be implemented during TS 3.7.5 Condition G. The first RMA protects AFW Pump 1-3 and its supporting equipment (e.g.,

vital 4 kV and 480 V Bus F, vital DC Bus 1, Battery Charger 1-1 and Emergency Diesel Generator 1-3). However, the second RMA protects only AFW Pumps 1-1 and 1-2, and does not identify protecting the associated supporting equipment. Explain why the supporting equipment of AFW Pumps 1-1 and 1-2 will not be protected during proposed TS 3.7.5 Condition G.

10. The LAR proposes RMAs based on insights from the PRA to be implemented during proposed TS 3.7.5 Condition G. The staff notes additional actions that could potentially reduce the impact on risk from Condition G, which are in alignment with the proposed RMAs in the LAR. Explain whether the following actions would be effective at reducing the risk associated with Condition G, and if so, incorporated them as RMAs for this LAR.

Protect supporting equipment of AFW values (e.g., power, air/nitrogen),

Ensure the power-operated relief valve (PORV) block valves remain open to ensure feed-and-bleed availability, Protect the RHR [residual heat removal] pumps and centrifugal charging/intermediate head pumps to ensure feed-and-bleed availability, Protect RHR sump recirculation valves (and support systems) to ensure feed-and-bleed availability, Protect the steam-driven main feedwater pumps and the turbine to ensure feedwater availability.

11. The leak and degraded conditions on the Unit 2 AFW system were discovered on July 23rd. With the exception of a visual only walkdown by non-inservice inspection (ISI) trained personnel, the licensee has not yet conducted a formal extent of condition walkdown on similar Unit 1 AFW piping. The licensee had originally scheduled this Unit 1 AFW extent of condition walkdowns for this week (week of August 10th). Please justify, from a safety perspective, performing the walkdowns two additional weeks later in the week of August 24th , approximately one month after the Unit 2 leak, was identified?

ML20231A652 *via e-mail OFFICE NRR/DORL/LPL4/PM NRR/DORL/LPL4/LA* NRR/DORL/LPL4/BC* NRR/DORL/LPL4/PM*

PBlechman NAME SLee w/comment JDixon-Herrity SLee DATE 8/17/2020 8/23/2020 8/24/2020 8/24/2020