ULNRC-06493, Supplemental Response to Notice of Violation, Inspection Report No. 50-483/2016002

Supplemental Response to Notice of Violation, Inspection Report No. 50-483/2016002

ML19101A319
Person / Time
Site:	Callaway
Issue date:	04/11/2019
From:	Herrmann T Ameren Missouri, Union Electric Co
To:	Document Control Desk, NRC Region 4
References
ULNRC-06493 IR 2016002
Download: ML19101A319 (6)

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ULNRC-06493 April 11, 2019 Page 2 of 6 In Reference 2, Ameren Missouri committed to perform an Essential Service Water (ESW) system transient analysis and identify non-conforming structural components by April 30, 2017. In addition, a supplemental response identifying actions required as a result of the transient analysis was committed to be provided by June 30, 2017.

In Reference 4, Ameren Missouri reported that, as of April 201 7, the preliminary results from the ESW system transient analysis were still being finalized. It was noted that the commitment to provide a supplemental response identifying actions required as a result of the transient analysis would still be met for the originally identified due date of June 3 0, 2017.

In Reference 5, Ameren Missouri provided a supplemental response to the subject NOV, including identification of actions required as a result of the analyses that were performed for the ESW system.

The information that was provided addressed each of the three concerns/actions that were identified as requiring further resolution in Ameren Missouris September 9, 201 6 NOV response. Of those three concerns, the first two have been resolved via cooling coil replacements for the identified heat exchangers. For the third concern, involving the completion of system transient analyses to determine what additional actions (i.e., plant design changes) are needed, it was reported that progress was being made on a conceptual design for a plant modification. It was noted that an engineering change package would be developed and that the design change(s) would be fully implemented and tested no later than completion ofRefuel 23, which is now in progress at Callaway.

In 201 8, significant progress was made on finalizing the design for the modification selected to resolve the ESW system pressure transient concern. In December 201 8, however, a previously unanalyzed failure mode for either of the UHS cooling tower bypass valves (EFHVOO65 for the A train and EFHVOO66 for the B train) was recognized. It was then determined that the additional failure mode would affect the previously completed transient analysis.

The previously unanalyzed failure mode identified for the normally open EFHVOO65/66 valves is that with either valve in an initially closed position, which is the case only during certain plant evolutions such as when using the ultimate heat sink (UHS) cooling tower to cool the UHS retention pond for temperature control, a failure of the valve(s) to open could occur following activation of the load sequencer in the event of a loss-of-coolant accident (LOCA) and/or a loss of offsite power (LOOP).

The failure ofthe valve to open may be postulated to occur during the time when, following the onset of the accident/event, load shedding has already occurred and the sequencing/re-energizing of loads is ongoing, specifically when the sequencer re-energizes the motor control center that supplies the EFHVOO65/66 valve operator motor.

ULNRC-06493 April 11, 2019 Page 3 of 6 Preliminary analysis of such a failure indicates that a pressure transient event is more severe for the affected train when the EFHVOO65/66 valve is closed (i.e., failed closed) at the time of E$W pump restart in the associated train. Since the previously completed transient analysis is no longer bounding (i.e., without the additional failure mode taken into account), the original modification planned for installation in Refuel 23 will not alone be sufficient to completely resolve the nonconforming condition (in regard to Code/design margins for structural components needed to withstand the postulated ESW pressure transient). Based on this new information, an additional plant modification(s) will likely be needed to fully resolve the issue.

It should be noted that although the need for an additional plant modification(s) is likely, sufficient analysis has been performed to assess the acceptability of the plant configuration that existed going into the current plant outage as well as the configuration that will exist following the outage (i.e.,

following implementation of the originally planned modification during the outage). In regard to the former, a Past Operability evaluation (POPE) was performed for the time period over the last three years, which includes the time periods before and after implementation of the corrective actions taken in response to initial identification of the system pressure transient issue in early 20 1 6 (as reported per Licensee Event Report 1 6-001 (and 1 6-001 -01) and as addressed by the NOV). From the analysis performed in support of the POPE, no new or previously unrecognized inoperability was identified for the period of time before the 201 6 corrective actions were taken. For the period subsequent to that, although some non-conforming conditions (i.e., reduced design margins) were identified, past Operability was confirmed to have existed for the ESW system and its loads, as well as for the UH$.

In regard to the plant configuration that will exist subsequent to the current plant outage, the originally intended modification is still being installed during the outage (as noted above), and sufficient post-modification testing will be performed during the outage to demonstrate that upon ESW actuation following a LOCA and/or LOOP, all plant components remain capable of performing their required functions, even with the EfHVOO65/66 valve(s) in the closed position upon ESW pump start.

At present, there is insufficient time to precisely analyze, design and implement a revised/additional modification to fully restore design margins prior to the completion ofRefuel 23. However, in light of the improved pressure transient mitigation capability afforded by the modification being installed during the outage, a basis exists to enable completion of an operability determination with the originally designed modification installed. The ESW system will thus be considered operable but degraded or non-conforming when the plant is returned to operation at the end of Refuel 23 The .

justification for operability will be documented in a Prompt Operability Determination in accordance with NRC-accepted guidance (IMC 0326).

ULNRC-06493 April 11, 2019 Page 4 of 6 The additional modification(s) for restoring the E$W system and/or affected components to their intended design (i.e., with all design margins fully restored) will be implemented and tested no later than completion ofRefuel 24 (Fall 2020).

None of the information in this supplemental response is proprietary. Further, this letter does not contain new commitments.

If there are any questions concerning this letter, please contact Mr. Eric Olson, Director, Engineering Design & Projects at (573) 676-8280.

Sincerel ,

7 T.E. Herrmann Site Vice President

ULNRC-06493 April 11, 2019 Page 5 of 6 cc: Mr. Scott A. Morris Regional Administrator U. S. Nuclear Regulatory Commission Region IV 1600 East Lamar Boulevard Arlington, TX 76011-4511 Senior Resident Inspector Callaway Resident Office U.S. Nuclear Regulatory Commission 8201 NRC Road Steedman, MO 65077 Mr. L. John Klos Project Manager, Callaway Plant Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop 09E3 Washington, DC 20555-0001

ULNRC-06493 April 11, 2019 Page 6 of 6 Index and send hardcopy to QA File A160.0761 Hardcopy:

Certrec Corporation 6100 Western Place, Suite 1050 FortWorth,TX 76107

( Certrec receives ALL attachments as long as they are non-safeguards and may be publicly disclosed.)

Electronic distribution for the following can be made via Responses and Reports ULNRC Distribution:

F. M. Diya T. E. Herrmann B. L. Cox S.P. Banker S. L. Abel E. C. Olson R. C. Wink T. B. Elwood NSRB Secretary RRA Department File STARS Regulatory Affairs Mr. Jay Silberg (Pillsbury Winthrop Shaw Pittman LLP)

Missouri Public Service Commission