05000237/LER-2016-001

LER-2016-001, Secondary Containment Differential Pressure Transient

Dresden Nuclear Power Station, Unit 2
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material
2372016001R00 - NRC Website

LER 16-001-00 for Dresden Nuclear Power Station, Unit 2 and 3 Regarding Secondary Containment Differential Pressure Transient

ML16104A031
Person / Time
Site:	Dresden
Issue date:	04/08/2016
From:	Karaba P J Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
SVPLTR 16-0013 LER 16-001-00
Download: ML16104A031 (4)

Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by intemet e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

PLANT AND SYSTEM IDENTIFICATION

Dresden Nuclear Power Station (DNPS), Unit 2, is a General Electric Company Boiling Water Reactor with a licensed maximum power level of 2957 megawatts thermal. The Energy Industry Identification System codes used in the text are identified as [XX].

A. Plant Conditions Prior to Event:

Unit: 02 Reactor Mode: 1 Event Date: 02/09/2016 Event Time: 1900 CST Mode Name: Power Operation Power Level: 100 percent

B. Description of Event:

On 2/9/16 at 19:00, the operating heating boiler [LV] shutdown. At 19:15, the Main Control Room (MCR) received alarms indicating that Reactor Building (RB) [NG] DP was below -0.3" wc. An Equipment Operator (EO) was dispatched to take local RB DP readings on the Refuel Floor. Local readings were averaged to be -0.35" wc. Operations verified that all Secondary Containment interlock doors, RB blowout panels and reactor building ventilation [VA] (RBV) exhaust hatches were in the proper configuration.

Following the loss of the heating boiler, Operations entered the associated response procedure. This procedure directed field operators to block open all doors of both the U2 and U3 RBV supply plenums to prevent freezing of the ventilation filters and heating coils within the plenums.

At 21:42, another step change in RB DP was noticed by Operations. Main Control Room RB DP indication degraded from -0.25" wc to -0.12" wc. An EO was dispatched to obtain local readings on the Refuel Floor. Local readings were averaged at -0.24" wc which required entry into Tech Spec 3.6.4.1.A due to RB DP being greater than Tech Spec required -0.25" wc by local average on the refuel floor.

At 22:05, U3 RBV was secured, and at 22:07 Tech Spec 3.6.4.1.A was exited when RB DP returned to below -0.25" wc.

An 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> non-emergency notification was made via Emergency Notification System #51721 in accordance with 10 CFR 50.72(b)(3)(v)(C) for the loss of Secondary Containment.

Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by intemet e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

C. Cause of Event:

The apparent cause of the event was determined to be the system operating with an out of tolerance (00T) U3 Area DP controller that degraded total system margin.

D. Safety Analysis:

With the exception of the degraded area differential pressure controller, all equipment responded as designed. Operator action to secure Unit 3 RBV in accordance with proceduralized guidance prevented the further degradation of the reactor building differential pressure, maintaining the negative differential pressure and preventing loss of safety function.

This event is of very low safety significance.

This event is being reported under 10 CFR 50.73(a)(2)(v)(C) "Any event or condition that could have prevented the fulfillment of the safety function of ... systems that are needed control the release of radioactive material.

E. Corrective Actions:

The degraded area DP controller was calibrated and the Unit 3 RBV restored to operation.

Gaps in the maintenance strategy will be identified and eliminated. System upgrades will be reviewed for implementation. The operational response procedure for the loss of plant heating steam will be reviewed for enhancements.

F. Previous Occurrences:

A previous event in 2009 was found during the investigation where a degraded area DP controller caused a loss of secondary containment differential pressure. This event was used in the development of corrective actions.

G. Component Failure Data:

Manufacturer Model S/N Type Johnson Controls T-5312 RY10812 Pneumatic Conroller