05000400/LER-2020-002, Re Manual Reactor Trip Due to Control Rod Drop During Surveillance Testing
| ML20286A166 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 10/12/2020 |
| From: | Maza K Duke Energy Progress |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RA-20-0275 LER 2020-002-00 | |
| Download: ML20286A166 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv), System Actuation |
| 4002020002R00 - NRC Website | |
text
(DUKE ENERGY Kim E. Maza Vice President Shearon Harris Nuclear Power Plant 5413 Shearon Harris Road New Hill, NC 27562-9300 10 CFR 50.73 October 12, 2020 Serial: RA-20-0275 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Shearon Harris Nuclear Power Plant, Unit 1 Docket No. 50-400/Renewed License No. NPF-63 Subject: Licensee Event Report 2020-002-00 Ladies and Gentlemen:
Duke Energy Progress, LLC, submits the enclosed Licensee Event Report 2020-002-00 in accordance with 10 CFR 50.73 for Shearon Harris Nuclear Power Plant, Unit 1 (HNP). On August 13, 2020, a control rod dropped during control rod drive system surveillance testing, which required a manual reactor trip in accordance with plant procedural guidance. All safety systems functioned as expected. The cause of the control rod drop has been addressed and the unit has been restarted. This event had no significance with respect to the health and safety of the public.
There are no regulatory commitments contained within this report.
Please refer any questions regarding this submittal to Sarah McDaniel at (984) 229-2002.
Sincerely, Kim E. Maza Enclosure: Licensee Event Report 2020-002-00 cc:
J. Zeiler, NRC Senior Resident Inspector, HNP M. Mahoney, NRC Project Manager, HNP NRC Regional Administrator, Region II
Abstract
Shearon Harris Nuclear Power Plant, Unit 1 400 3
Manual Reactor Trip Due to Control Rod Drop During Surveillance Testing 08 13 2020 2020 002 00 10 12 2020 1
100
Sarah McDaniel, Regulatory Affairs Engineer (984) 229-2002 X
AA 75 F183 Y
On August 13, 2020 at 09:38 Eastern Daylight Time, with Shearon Harris Nuclear Power Plant, Unit 1 (HNP), in Mode 1 at 100 percent power, a control rod dropped during control rod drive (CRD) system surveillance testing. This required a manual reactor trip in accordance with plant procedural guidance. The reactor protection system (RPS) and auxiliary feedwater system (AFWS) actuated as designed. Based upon troubleshooting, it was determined that the control rod drop was due to the accumulation of crud in the dashpot region of the control rod drive mechanism (CRDM) movable gripper latch support assembly, which prevented the stationary gripper from latching onto the CRD shaft when the movable gripper was released. Three full-length exercises for each control rod bank were completed to remove crud from the CRDM surfaces that restored the CRDM to operable for unit startup. The dropped control rod was recovered from the reactor core and restored to the fully withdrawn position. A preventative maintenance activity to exercise the control rod banks 10 steps on a weekly frequency was implemented. Coil current traces will be obtained periodically during rod exercises to monitor for crud presence. After review, the CRD system surveillance test procedure was revised to remove the instruction to trip the reactor if a dropped rod is present with any control rods inserted into the core other than the controlling bank. In the next refueling outage, full length control rod exercises and flushing of applicable CRDMs will be completed. Due to actuation of the RPS and AFWS, this event is reportable per 10 CFR 50.73(a)(2)(iv).
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guidance in InfoGram 05-4, Westinghouse plants have not experienced untrippable control rods due to crud accumulation.
C. Causal Factors The cause of the CRDM F2 malfunction was crud accumulation on CRDM internal components, which resulted in the lower stationary gripper not engaging on the CRD shaft when the RCCA was being withdrawn from the fuel assembly.
Informal (unwritten) operational experience obtained from CRDM original and current manufacturers following the event indicates that periodic cycling of control rods following a RVH replacement return to service will minimize crud build-up until a passivation layer is established and crud may be monitored through coil current traces during control rod cycling.
Following this event, the surveillance test procedural guidance to trip the reactor if a dropped rod is present with any control rods inserted into the core other than the controlling bank was determined to be overly conservative since this condition is analyzed by the HNP safety analysis. This guidance was added to the procedure in 2008.
D. Corrective Actions
The Westinghouse rod control diagnostic flow charts were implemented to support the causal analysis of the control rod drop. Three full-length exercises for each control rod bank were completed that restored the CRDM to operable for unit startup. Coil current traces were obtained during these exercises, which were later determined by the CRDM original equipment manufacturer to indicate the presence of crud on the CRDMs. The RCCA F2 was recovered from the reactor core and restored to the fully withdrawn position.
A preventative maintenance activity to exercise the control rods 10 steps on a weekly frequency was implemented upon reactor startup. Coil current traces will also be obtained periodically during rod exercises to monitor for crud presence. The CRD system surveillance test procedure was revised to remove the instruction to trip the reactor if a dropped rod is present with any control rods inserted into the core other than the controlling bank.
Coil current trace data from control rod exercises will be evaluated to determine if any changes to the rod exercising frequency or scope are warranted. During the next refueling outage, full length control rod exercises and flushing of applicable CRDMs through rod drops will be completed to remove crud. Coil current trace data will also be obtained. The results of the outage CRDM exercising and flushing activities will be evaluated to determine if a change in the preventative maintenance strategy is needed.
E. Safety Analysis
The primary function of the CRDM is to insert or withdraw RCCAs within the core to control average core temperature and to shutdown the reactor. The trippability of the shutdown and control rods is an initial assumption in all safety analyses that assume rod insertion upon reactor trip. At no point during this event was the trippability of the shutdown rods or control rods questionable. The dropped control rod fell normally to the bottom. There was no loss in function of safety systems, structures, or components. There were no significant equipment abnormalities. The condition did not result in a safety system functional failure and had no adverse impact on the health and safety of the public.
F. Additional Information
There have been no events similar to the event documented in this LER in the past three years.
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