Healthy discussion of the Arkansas Nuclear One accident

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ANO Stator 2

Early Easter Sunday morning, an industrial accident at the Arkansas Nuclear Power Plant killed one worker and injured 8 others and left the unit without offsite power.  At the time of the accident, workers were moving the Main Turbine Generator Stator out of the turbine building when the lift crane failed and dropped the load.  In the days after the event it was announced that the United States Occupational & Health Administration would investigate the incident and the NRC later announced that they would investigate the licensee’s response to the event.

While the event was immediately picked up by headlines around the world, very little information has been released in the meantime. Our readers have been sharing different opinions on the accident, describing two distinct scenarios which may have resulted in the accident.  We would like to share these two scenarios, not to imply which may or may not be the most likely, but to help communicate the difficulty of the operation being performed and encourage healthy discussion of safety-related accidents to ensure that lessons are learned.

ANO stator 3

[dropcap]1[/dropcap]In the first scenario, it was noted that the Bigge equipment did not look severely damaged, that the stator had made it from the turbine deck to the hatchway and was in the process of being turned correctly to be lowered to the transport below.  It appears that the front left leg of the gantry crane was positioned on a floor beam. That beam is bent. A rational hypothesis could be posed asking whether or not the floor which supported the front two legs of the gantry beams was strong enough, and if the under-beam buckled and the gantry came apart.  The turbine deck was strong enough to support the back two legs of the gantry, and may have had jack plates built into the foundation. The legs of gantry may have been positioned right above foundation columns under the turbine deck, while the front legs were on building floor. This could like the fatal flaw for this scenario, and even though the floor beam held for a while, it may have then deflected.

[dropcap]2[/dropcap]In the second scenario, it was noted that the end of the long travel beams over the hoist well were fully supported on two vertical beams from a beam in the rail bay with a horizontal beam at the turbine floor level and two further verticals to the main long travel beams (this could be a standard arrangement for Bigge systems). In this scenario, the accident could have been the result of the vertical supports tilting, stopping the load too quickly as it was being rotated to align with the hoist well and causing the whole rig to collapse.

ANO stator 4

ANO stator

Source: Efin Engineer

Source: Frank Bailey

Source: SteamShovel2002

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