Junk Plant Brunswick: Double Preventable Explosion, Trip and LOOP

05000324/325

These guys are very dangerous. A double preventable event is one where say a high voltage cabinet leaks water inside. They discover it and fix it in a half ass manner. It should have created the explosion trip and LOOP but only luck intervened on the first shot. Then it leaks again cause the big explosion.         

Duke? Brunswick Steam Electric Plant: 

Electrical Bus Fault Results in Lockout of Startup Auxiliary Transformer and Loss of Offsite Power

On February 7, 2016, at 1312 Eastern Standard Time (EST), Unit 1 was in Mode 1 (i.e., Run) at 88 percent of rated power in end-of-cycle coastdown. At that time, an electrical fault occurred on a balance of plant 4160-volt bus, resulting in a lockout of the Startup Auxiliary Transformer (SAT) and a loss of both Reactor Recirculation pumps. Licensed personnel inserted a manual scram per procedure. Emergency Diesel Generators supplied emergency electrical busses until offsite power was restored at 1628 EST. The loss of power and reactor water level changes resulted in automatic closures of various Primary Containment Isolation Valves (PCIVs). The electrical fault resulted in an electrical explosion; therefore, an Alert was declared at 1326 EDT. The immediate cause of this event was a fault in a non-segregated electrical bus connected to the SAT. The root causes were insufficient detail in applicable maintenance instructions for inspecting the non-segregated bus housing and inadequate instructions for terminating electrical cables in a circuit breaker cubicle. Corrective actions include repairing equipment damaged by the electrical fault and revising the procedures and work instructions.

Event Causes

The initiating event was two arc flashes that occurred in a non-segregated bus (i.e., a bus in which all three phases lie within a single housing) and in a circuit breaker cubicle which powers the 18 VFD for a Reactor Recirculation system pump. The first arc flash occurred in an area of the bus housing outdoors where water had accumulated. The fault created a voltage imbalance which led to the second arc flash which occurred in the breaker cubicle where cable insulation was found to be degraded.

Water entered the non-segregated bus housing through a degraded seal and an area that had previously been repaired. The water created the conditions conducive to an arc flash. 

In the breaker cubicle for the 1 B VFD, it was found that during installation in 201 O of electrical stress relieving insulation (i.e., "stress cones"), the dielectric insulation on a cable jacket had been damaged when a piece of semiconducting material was being removed. The arc flash occurred at the point where the cable insulation had been damaged.

The root cause of the moisture intrusion into the non-segregated bus was inspection procedures did not contain sufficient specific detail based on highest risk locations (i.e., specifically, horizontal surfaces through which bars penetrate) to ensure that deficiencies that can lead to water intrusion are identified and corrected during its implementation. A contributing cause was that the design of the bus housing is not optimum for the application because it is susceptible to corrosion leading to water intrusion. The root cause of the damaged cable insulation was failure to specify and use a depth-limiting cutting tool for removing semiconducting material from cable insulation. 

When workers removed semiconducting material from the cable during initial installation of the cable termination stress cone, the underlying cable dielectric insulation was scored, reducing its insulating effectiveness. This contributed to conditions which led to an arc fault in the affected 4160-volt cable. A contributing cause was lack of a post-installation test method which would be adequate to detect insulation deficiencies...

They are depending on the electrical procedures being correct. When skill of the craft is missing, then good procedures are worthless. These guys didn't have the electrical high voltage basic engineering skills to do this job.

I doubt this would ever happen again on this piece of equipment. The problem is if this is systemic, they could be ignoring problem or just being to stupid to understand other problems are developing.   

Corrective Actions 

Any changes to the corrective actions and schedules noted below will be made in accordance with the site's corrective action program.

• Affected equipment related to the event has been repaired, including the affected non-segregated bus housing, conductors and stress cones, and circuit breaker. These actions are completed. 

• The procedure for splicing and terminating wires and cables will be revised to include lessons

learned from this event, including the use of depth-limiting cutting tools and inspections for damage

after cutting operations are performed. This action is expected to be completed by June 30, 2016. 

• The procedure and work instructions for inspecting and cleaning the non-segregated busses will be

revised to eliminate the root causes of the water intrusion. This action is expected to be completed

by August 25, 2016. 

• An improved cable testing methodology will be specified in appropriate maintenance procedures. 

This action is expected to be completed by June 30, 2016.

• The non-segregated bus housing design will be presented for action by the site's Modification 

Review and Prioritization Team (MRPT) for scheduling and design work. This action is expected to be completed by June 30, 2016.