Safety Forum - Safety and Nuclear OPEX

Red Memo - ANO

This information is preliminary and should be treated as such. A Root Cause Evaluation will be performed and is
tracked by CR-ANO-1-2009-00254. Corrective actions based on the Root Cause will be issued.
Reset Criteria:
The Site Clock has been reset based on the following Nuclear Safety Event criteria outlined in EN-HU-101,
Human Performance Program procedure:
[1](a), Event requiring Emergency Plan activation.
[4](a), Misoperation, misposition, or improper configuration of equipment that results in power reduction >10%
[4](d), Property damage in excess of $100,000
What happened:
At 1046 the Unit 1 reactor was manually tripped due to a report of fire at the generator hydrogen addition station.
Following a pre-job brief from Operations Supervision, an Auxiliary Operator (AO) was adding hydrogen to the
main generator per Exhibit A of OP-1106.002, Generator Hydrogen System. The AO was performing step 1.2.2
of Exhibit A, which requires verifying the H2 Addition Station H2 to Generator PCV-8311 Inlet Isolation H2-109 in
the open position.
The AO attempted to open the valve and could obtain no movement by using both hands. The AO then attempted
to close the valve also using both hands and could not get the valve to move.
At this point the AO assumed that the valve was stuck on its closed seat and it would be necessary to use a
Torque Amplifying Device (TAD) to position this valve. OP-1015.001, Conduct of Operations contains detailed
instructions in Section 14, Guidelines for operation of manual valves. These instructions require Operations
Supervisor permission be obtained prior to use of a Torque Amplifying Device (TAD). OP-1015.001 provides the
following additional instruction to the Operations Supervisor.

What happened (cont.):
Supervisor permission prior to the use of the Torque Amplifying Device (TAD) was not obtained and the operator
proceeded to attempt to open the valve. Subsequent investigation has determined the valve was already in the
open position and on its backseat. The AO proceeded to turn the valve handwheel in the open direction using a
TAD, and stopped after initial motion in the open direction was obtained. The Operator again attempted by hand
to move the valve in the open direction and was unsuccessful, and then continued using the TAD. After turning
the handwheel ~5-6 revolutions the valve bonnet assembly (pictured below) ejected forcefully from the valve
body, striking the AO in the arm.
Hydrogen gas from the station gas storage facility flowed from the open bonnet of the valve under full supply
pressure (~100 psig). The AO immediately exited the area to isolate the H2 supply to the header. As the AO was
exiting the area, the H2 gas ignited. The AO was able to exit the area safely and was not injured. Operators
isolated the H2 supply at the station gas storage facility to stop the flow of gas to the fire. Control Room operators
manually tripped the reactor and dispatched the fire brigade. The fire brigade used a combination of CO2 and
chemical extinguishers to initially extinguish the fire and then used a small amount of water to cool an electrical
cable tray in the overhead to prevent reflash. The Shift Manager entered the emergency plan and declared a
Notification of Unusual Even (NUE) based on EAL 7.5 “fire within the Protective Area which is not extinguished
within 10 minutes”. Offsite fire fighting resources were dispatched to the site, but were not required to extinguish
the fire, which was out in less than 15 minutes. The NUE was terminated at 1238 hours.
Why it happened:
The procedural steps directing operation of H2 Addition Station H2 to Generator PCV-8311 Inlet Isolation H2-109
were not followed because the operator did not recognize that H2-109 was already open. Actions to attempt to
open the valve resulted in the valve being unscrewed from the body with the valve eventually being ejected.
What contributed to this incident?