05000348/LER-2016-005

LER-2016-005, Toxic Gas Event

Joseph M. Farley Nuclear Plant, Unit 1
Event date:	11-01-2016
Report date:	12-28-2016
Reporting criterion:	10 CFR 50.73(a)(2)(x)
3482016005R00 - NRC Website

LER 16-005-00 for Joseph M. Farley Nuclear Plant, Unit 1, Regarding Toxic Gas Event

ML16363A397
Person / Time
Site:	Farley
Issue date:	12/28/2016
From:	Pierce C R Southern Nuclear Operating Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NL-16-2479 LER 16-005-00
Download: ML16363A397 (6)

Reported lessons leamed 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 e-mail to Infocollects.Resource@nrc.goy, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means 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.

A. PLANT IDENTIFICATION

Westinghouse - Pressurized Water Reactor

B. DESCRIPTION OF EVENT

On 11/1/2016 at 1743, Farley declared an Alert based on ammonia levels on the radiation side of the Auxiliary Building in the Recycle Evaporator (REV) Room. The declaration was based on toxic gas emergency action level (EAL) HA3 which states, "Release of Toxic, Asphyxiant or Flammable Gases Within or Contiguous to a VITAL AREA Which Jeopardizes Operation of Systems Required to Maintain Safe Operations or Establish or Maintain Safe Shutdown." The toxic gas was identified as ammonia. The source was identified as a failed valve [ISV] in the auxiliary steam system [SA] supply to the REV system [WD], which had previously been abandoned in place. The ammonia leak was subsequently isolated.

Ammonia levels were reduced and the event was terminated at 2340 on 11/1/2016. The event was entered into the corrective action program as Condition Report 10293519.

C. UNIT STATUS AT TIME OF EVENT

Farley Unit 1 was in Mode 2, 1% power Farley Unit 2 (unaffected unit) was in Mode 1, 100% power

D. CAUSE OF EVENT

The direct cause of the event was determined to be degradation of valve [ISV] N1P20V0913, "Condensate Return from Recycle Evaporator Strainer Blowdown Valve." The valve degradation was determined to be due to ammonia induced copper corrosion. Ammonium hydroxide and Hydrazine are added to the secondary side of the steam generators during outage and non-outage conditions. The Hydrazine reacts in the steam generators and produces ammonia, which is carried over in steam. Steam traps in the steam system provide influent flow to the Auxiliary Steam Condensate Tank (ASCT) [TK]. The ASCT vents to atmosphere on the Main Steam Valve Room roof. In addition, the ASCT has a flow path to valve N1P20V0913 due to leak by of a check valve [ISV]. Valve N1P20V0913 is a brass component and the ammonia reacts with the copper in the brass, which degraded the valve over time to provide a flow path the environment. Start-up activities led to additional input flow to the ASCT. This additional input and backflow to N1P20V0913 caused ammonia to enter Room 180 of the Unit 1 Auxiliary Building.

The root cause (RC-1) of this event was inadequate isolation and abandonment of the REV system allowing a backflow path to valve N1P20V0913. When the REV system was abandoned in place in approximately the 1992 timeframe, the guidance for abandonment was not clear. With no maintenance or monitoring of the abandoned system, leak-by from check valve N1P20V005 allowed the flow path to valve N1P20V0913. If the REV system had been effectively abandoned the in place, this backflow path would not have been available. Since that time the process has been improved; however, the need to employ that process for the REV system was not previously recognized.

A second root cause (RC-2) of this event was determined to be the legacy process which allowed for installation of a brass valve N1P20V0913 in a steam system. Operating experience existed as early as 1984, though no formal review process appeared to be in place at the time. A Significant Event Notification (SEN) was published in 1992 describing the ability of ammonia in steam carry-over to react with copper and co

• er allo s. The SEN does not appear to have been considered for this system.

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 e-mail to Infocollects.Resource@nrc.goy, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. It a means 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.

This event was determined to be reportable under 10 CFR 50.73(a)(2)(x), "Any event that posed an actual threat to the safety of the nuclear power plant or significantly hampered site personnel in the performance of duties necessary for the safe operation of the nuclear power plant including fires, toxic gas releases, or radioactive releases," because plant personnel were evacuated from the area. During normal operation, this area is required to be entered to perform rounds and fire watch duties. Equipment in the area is not typically required to be operated for normal plant operation.

Under accident conditions, multiple means are available to provide emergency boration of the reactor coolant system via actions taken in the Control Room. However, in beyond design basis scenarios, operators may need to enter the area to manually operate valves to provide emergency boration if operation from the control room is not available.

The safety significance of this event is considered to be very low because plant personnel were evacuated from the area; there were no radioactive or toxic gas releases to the public; and, the risk of an accident requiring emergency boration via manual actions in the affected area is low.

F. CORRECTIVE ACTION

Immediate corrective action was to evacuate plant personnel, locate and secure the source of the ammonia leak, and ventilate the area.

The REV system will be properly mechanically isolated per current plant modification and configuration change processes.

The engineering design change process will be revised to provide enhanced guidance on material interactions.

G. ADDITIONAL INFORMATION

1) Previous Similar Events: None 2) Commitment Information: No commitments are made in this correspondence.