ML18075A025
| ML18075A025 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 03/08/2018 |
| From: | Daugherty J Dominion Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 17-420A | |
| Download: ML18075A025 (5) | |
Text
Dominion Nuclear Connecticut, Inc.
Rope Ferry Rd., Waterford, CT 06385 Mailing Address: P.O. Box 128 Waterford, CT 06385
<lorn.com U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 DOMINION NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 3 s, Dominion MAR tt*s 2018 Serial No.
NSS&L/WEB Docket No.
License No.
17-420A RO 50-423 NPF-49 REVISION TO 30-DAY SPECIAL REPORT FOR AN RCS PRESSURE TRANSIENT On November 7, 2017, in accordance with Technical Specification 3.4.9.3.f, Dominion Nuclear Connecticut, Inc., (DNC) submitted a 30-day special report for a Reactor Coolant System (RCS) pressure transient which occurred at Millstone Power Station Unit 3 (MPS3) on October 13, 2017 (ADAMS Accession No. ML17319A089). In this report, DNC reported a peak pressure at the reactor vessel beltline of 498.7 pounds per square inch absolute (psia) for one reactor coolant pump running. Subsequent review of the calculation identified a computational error.
The corrected calculation determined the correct reactor vessel beltline pressure value was 555.3 psia. Since the corrected value of 555.3 psia is below the allowable pressure limit of 625 psia, the conclusion by DNC that the 1 OCFR50, Appendix G limit was not exceeded and the structural integrity remains intact, is still valid.
If you have any questions or require additional information, please contact Mr. Jeffry Langan at (860) 444-5544.
Sincerely, Cir!1-.rot cs-~
J. R. Daugherty Site Vice President - Millstone
Attachment:
None Commitments made in this letter: None
cc:
U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd. Suite 100 King of Prussia, PA 19406-2713 R. V. Guzman Senior Project Manager - Millstone Power Station U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 C2 11555 Rockville Pike Rockville, MD 20852-2738 NRG Senior Resident Inspector Millstone Power Station Serial No. 17-420A Docket No. 50-423 Revised 30-Day Special Report Page 2 of 2
ATTACHMENT 30-DAY SPECIAL REPORT RCS PRESSURE TRANSIENT DOMINION NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 3 Serial No. 17-420A Docket No. 50-423
30-DA Y SPECIAL REPORT RCS PRESSURE TRANSIENT Serial No. 17-420A Docket No. 50-423 In accordance with the Millstone Power Station Unit 3 (MPS3) Technical Specifications (TSs), Section 3.4.9.3.f, Dominion Nuclear Connecticut, Inc., hereby submits this 30 Day Special Report documenting conditions surrounding a Reactor Coolant System (RCS) pressure transient.
Event Details:
On October 13, 2017 at approximately 21 :20 hours, with the plant in Mode 5, Cold Shutdown, and the RCS at a temperature of 169 degrees F, an unplanned RCS pressure transient occurred. To support an on-going modification, instrument air was isolated to a portion of the Auxiliary Building.
This resulted in a loss of air to the positioner for charging flow control valve 3CHS*FCV121. This resulted in the charging
. flow control valve failing full open resulting in an unplanned increase in charging flow into the RCS. This event occurred while the RCS was in a water solid condition. The increase in charging flow resulted in a rapid rise in RCS pressure. Over the course of approximately 18 seconds, the RCS wide range indicated pressure increased from an initial pressure of approximately 350 pounds per square inch absolute (psia) to a peak pressure of approximately 472 psia before returning to its previous value. The peak pressure of 472 psia exceeded the Technical Specification Pressure/Temperature limit of 435 psia. The Residual Heat Removal (RHR) System suction relief valves opened as designed to mitigate the pressure increase.
Control Room operators observed the charging flow control valve failing open and directed instrument air to be restored. This restored control of the charging flow control valve to the control room. RCS pressure was restored to below the TS limit. This event was entered into Millstone Power Station's (MPS's) Corrective Action Program (CAP)
(CR1080842, RCS Overpressure Event Due to 3CHS*FCV121 Failing Open.)
Engineering performed an evaluation of the pressure transient to determine if 1 OCFR50, Appendix G or ASME XI, Appendix G limits were exceeded. At 169 degrees F, the 1 OCFR50, Appendix G limit is bounding.
This limits pressure at the reactor vessel beltline to 20% of the preservice hydrostatic test pressure, or 625 psia. The wide range pressure of 4 72 psia corresponds to a pressure at the reactor vessel beltline of 555.3 psia when corrected for instrument uncertainty and dynamic pressure differential between the reactor vessel downcomer region and the wide range pressure transmitter for one reactor coolant pump running. Therefore, the 1 OCFR50, Appendix G limit was not exceeded and structural integrity remains intact.
Corrective Actions to Preclude Repetition:
Serial No. 17-420A Docket No. 50-423 Plant procedures are being revised to implement Infrequently Conducted or Complex Evolutions (ICCE) controls during water solid plant operations and linked to new procedure OP 3211 (Solid Plant Pressure Control (ICCE)).