ML21022A129

Reactor Vessel Level Monitoring System Special Report

ML21022A129
Person / Time
Site:	Calvert Cliffs
Issue date:	01/13/2021
From:	Laura Smith Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML21022A129 (2)

Text

Exelon Generation~ Larry D. Smith Regulato,y Assurance Manqer Calvert Cllffs Nuclear Power Plant 1650 Calvert Cllff1 Parlcway Lusby, MD 20657 410 495 5219 Office 410 610 9729 Mobile www.exeloncorp.com larry.sllllth2~1oncorp.com TS 3.3.10 and 5.6.7 January 13, 2021 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 Calvert Cliffs Nuclear Power Plant, Unit No. 1 Renewed Facility Operating License No. DPR-53 NRC Docket No. 50-317

Subject:

Reactor v,uet Level Monftorinc System Special Report This special report Is submitted in accordance with Calvert Cliffs Nuclear Power Plant Technical Spedflcation 3.3.10. The report is required due to the Unit 1 Reactor Vessel Level Monitoring System having less than the required minimum number of operable channels.

ACTION TAKEN On December 10, 2020 at 1517, Unit 1 Control Room received an unexpected alarm at window E-10 on 1C06, "RVLMS [Reactor Vessel Level Monitoring System] CH A 1C144A" and responded in accordance with the applicable alarm response procedure. The Channel A Post-Accident Monitoring Display at 1C06 System Health screen indicated a fan malfunction, and showed a Fan Fall Red light illuminated at the same time. In accordance with site procedure the associated cabinet should be considered Inoperable.

This rendered Channel A RVLMS inoperable. Calvert Cliffs Technlcal Specification "Post-Accident Monitoring (PAMS) Instrumentation/ Table 3.3.10-1, Function 5, requires two channels of RVLMS to be operable. Because of the subject failure, Calvert Cliffs entered Technical Specification 3.3.10, Condition A. When the Completion Time of Condition A expired, Calvert Cliffs entered Technical Specification 3.3.10, Condition B.1, which requires submission of this report In accordance with Technical Specification 5.6.7.

PREPLANNED ALTERNATE METHOD OF MONITORING The RVLMS Instrumentation is designated for post-accident monitoring use. It provides the plant operator with Information to assess void formation in the reactor vessel head region and the trend of llquld level In the reactor vessel plenum. The RVLMS consists of two redundant channels. Reactor Vessel Level Monitoring Channel B remains operable with all eight of its sensors functioning normally.

The removal of Channel A from operable status ellmlnates a means of redundant Indication. However, alternate methods of monitoring for core and Reactor Coolant System voiding, using pressurizer level,

Document Control Desk January 13, 2021 Page 2 Reactor Coolant System subcoollng, hot and cold leg temperature, and core exit thermocouple Instrumentation, were Initiated as required by plant procedures.

CAUSES OF INOPfRABIUTY The cause of inoperability is the failure of channel A RVLMS cabinet cooling fan. The most probable cause of this failure Is age-related degradation.

PLANS AND SCHEDULES FOR RESTORING THE SYSTEM TO OPERABLE STATUS Currently, Maintenance Is waiting on the replacement fan assembly to arrive onslte. The expected return to service date ls January 31, 2021.

There are no regulatory commitments contained in this correspondence.

• Should you have questions regarding this matter, please contact me at {410) 495-5219.

Respectfully, c;;4,l!JS.~a-,

Larry D. Smith Regulatory Assurance Manager LDS/KLG/lmd NRC Project Manager, Calvert dlffs S. Seaman, MD-DNR NRC Regional Administrator, Region I NRC Resident Inspector, Calvert Cliffs