Arkansas Nuclear One: Pictures of an Accident
Fission Stories #181
Dave Lochbaum, director, Nuclear Safety Project
Union of Concerned Scientists
Fission Stories #139 described the March 31, 2013, event at Arkansas Nuclear One where a heavy load dropped during a refueling
outage on Unit 1 caused the automatic shut down of the Unit 2 reactor from full power. The accident killed one worker and injured
several others. The damage to the plant by the dropped stator took weeks to repair.
In response to a request under the Freedom of Information Act, the NRC recently released several dozen photographs showing the
consequences from the dropped load and the steps taken to fix the damage it caused. This post updates the original description using
several photographs released by the NRC. Links to the NRC’s FOIA documents containing these and many other photographs (more
than 400 photographs in all) are provided towards the bottom of this post.
The operators shut down the Unit 1 reactor on March 24, 2013, to enter a routine refueling outage. In addition to removing some of
the irradiated fuel assemblies from the reactor core and replacing it with new fuel assemblies, workers planned to replace the main
generator’s stator.
Like all the nuclear power reactors currently operating in the US, the Unit 1 reactor at Arkansas Nuclear One used the heat produced
from splitting atoms in the reactor core to boil water. The steam flowed into the main turbine to spin its blades. The turbine shaft was
connected to the main generator’s rotor.
Page 1
Source: Bob Lochbaum
This photograph shows the rotor and the stator for the Unit 1 reactor at the Watts Bar nuclear plant in Tennessee. The rotor is in the
foreground, partially inserted into the stator. The low pressure turbines can be seen in the upper left background behind the stator. The
rapidly turning rotor within the stator generates electricity.
Page 2
Source: NRC Flickr Gallery
The two reactor containment buildings at Arkansas Nuclear One appear in the center of this picture. Unit 1 is on the left and Unit 2 is
on the right. The turbine buildings appear in front of the containment building in this picture as one long, rectangular structure. A large
door inside the red circle provides entrance to an area called the train bay. As implied by the name, the train bay has tracks for a railcar
to enter. Heavy equipment can be offloaded from the railcar for use in the plant. Similarly, heavy equipment can be loaded into an
empty railcar for removal offsite. Eighteen-wheel trailer truckers and other haulers also use the train bay for deliveries and pickups.
Page 3
Source: NRC ADAMS ML003747839
The train bay is circled in red on this map of the Arkansas Nuclear One site. In addition to the main turbine and generator, the turbine
building contains associated equipment like the condensers, condensate pumps, feedwater heaters, and feedwater pumps. Immediately
to the left of the turbine building are the auxiliary buildings. To their left are the reactor containment buildings. The auxiliary
buildings contain much of the safety equipment needed to mitigate reactor accidents. The containment buildings house the reactor
pressure vessels, reactor coolant pumps, steam generators, pressurizer, and containment coolers.
Page 4
Source: NRC FOIA Document ML13213A270
The plan called for workers to remove the rotor from the stator and unconnect the stator from its mounting on the turbine building
floor. The stator weighed over 500 tons—too heavy for the turbine building’s permanent crane to handle. A temporary lifting device
(including the dark object) was installed to pick up the stator and carry it over the turbine building floor to the train bay opening.
Page 5
Source: NRC FOIA Document ML13213A270
The stator would then be rotated 90 degrees and slowly lowered down to a heavy duty hauler parked on the ground floor of the train
bay. A truck rather than a train engine would tow the hauler and stator away.
Page 6
Source: NRC FOIA Document ML14219A431
This view shows the Unit 1 turbine building floor and the opening occupied by the main generator stator before its removal. Several
vertical pegs are visible that matched holes in alignment and mounting plates on the stator to aid installing it in the proper position.
The train bay is located behind the camera. The low pressure and high pressure turbines are located behind the blue blocks.
Page 7
Source: NRC FOIA Document ML14219A433
This view through the train bay door shows the stator where it came to rest on the hauler after being dropped. The blue beam resting at
an angle is part of the temporary lift device that broke to cause the drop.
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The stator dropped onto the hauler and fell to the
side. This view shows a corner of the stator
gouging a masonry block wall inside the train bay.
The dropping stator caused significantly more
damage before this last hole.
Source: NRC FOIA Document ML14219A433
Page 9
Source: NRC FOIA Document ML14219A431
The blue beams in the center of this photograph are part of the temporary lift device. The Unit 2 main generator and turbine are in the
background. The stator rests on the damaged hauler in the train bay below these beams. The masonry wall to the upper right of the
beams shows signs of damage. Damage to the concrete floor and structural steel is partially visible behind the beams.
Page 10
Source: NRC FOIA Document ML14219A431
This photograph shows the damage to the concrete floor and structural steel caused by the dropped stator striking the turbine building
floor on the Unit 2 side of the train bay opening.
Page 11
Source: NRC FOIA Document ML14219A423
The dropped stator cause more extensive damage upon striking the turbine building floor on the Unit 1 side of the train bay opening.
In additional to crumbing the concrete floor, the impact deformed and displaced a large structural steel support beam.
Page 12
Source: NRC FOIA Document ML14219A425
This photograph shows the structural steel beam displaced from its connection to the vertical I-beam illustrating the amount of force
imparted by the dropped stator.
Page 13
Source: NRC FOIA Document ML14218A607
This photograph was taken from the turbine building floor looking down into the train bay at the stator resting on the damaged hauler.
Damage to the Unit 2 side is evident on the left while more extensive damage to the Unit 1 side appears on the right side.
Page 14
Source: NRC FOIA Document ML14218A607
The deformation of the turbine building floor on the Unit 1 side compressed the wall from the ground floor of the train bay up to the
turbine building floor.
Page 15
Source: NRC FOIA Document ML14219A433
The dropped stator (partially shown on the right) created a lot of debris before coming to rest on the hauler in the train bay.
Page 16
Source: NRC FOIA Document ML14219A428
“Coming to rest on the hauler” understates what happened to the hauler when the 500-plus ton stator arrived. The stator smashed and
broke the hauler. This photograph shows the hydraulic jacks being used to lift the stator off the hauler so it can be removed and
replaced with an undamaged hauler.
Recall that this accident began when the temporary lift device transporting the stator in the turbine building broke. A temporary lift
device was being used because the permanent crane lacked sufficient capacity to lift the stator. Without means to lift the stator from
above, workers used hydraulic jacks to push the stator upward.
Page 17
Source: NRC FOIA Document ML14219A428
Once the weight of the stator was removed using the hydraulic jacks, workers used a fork lift to tug the damaged hauler from the train
bay.
Page 18
Source: NRC FOIA Document ML14219A427
The hauler had lots of wheels to distribute the load from heavy objects like the stator, but not all of the tires were properly inflated and
pointing in the same direction after the stator fell on it.
Page 19
Source: NRC FOIA Document ML14219A426
Rather than rolling the hauler out from beneath the jacked up stator, the fork life dragged it away.
Page 20
Source: NRC FOIA Document ML14219A426
As shown within the cyan circles in the photograph, the cylinders of the hydraulic jacks holding the stator off the train bay floor were
nearly fully extended. Workers needed to raise the stator higher to allow the replacement hauler to move in underneath it. Workers
used an iterative process to raise the stator to the desired height.
Page 21
Source: NRC FOIA Document ML14219A426
The cylinder of the hydraulic jacks had a finite length and couldn’t extend farther. So workers used stands (like the one circled in red
on the right) to support the stator. With the stator supported on the stands, workers retracted the hydraulic jacks’ cylinders. As shown
within the cyan circle to the left, wood beams were then placed under the hydraulic jacks. Workers extended the hydraulic jacks’
cylinders again, lifting the stator up a few inches. Workers repositioned the stands to the new height, too.
Page 22
Source: NRC FOIA Document ML14219A426
Repeating this process, workers slowly and steadily raised the stator higher and higher off the train bay floor.
Page 23
Source: NRC FOIA Document ML14219A426
The raised stator was now ready for the replacement hauler to be moved underneath it.
Page 24
Source: NRC FOIA Document ML14219A426
Not coincidentally, the replacement hauler was just outside ready to do its thing.
Page 25
Source: NRC FOIA DocumentML14218A737
Workers didn’t need a fork lift to move the self-propelled replacement hauler into place beneath the stator.
Page 26
Source: NRC FOIA Document ML14218A736
Once the replacement hauler was in place, workers needed to remove the hydraulic jacks and their supporting beams. This photograph
shows the turbine building crane about to be used to lift a support beam.
Page 27
Source: NRC FOIA Document ML14218A737
And so the hydraulic jack support beams were removed.
Page 28
Source: NRC FOIA Document ML14218A605
The stator begins its overdue departure from the train bay on board the replacement hauler.
Page 29
Source: NRC FOIA Document ML14218A605
The stator continues its overdue departure from the train bay on board the replacement hauler.
Page 30
Source: NRC FOIA Document ML14218A605
The stator on the replacement hauler outside the train bay. The stator is resting partially on its top side. Running left to right across the
middle of the photograph (or running right to left it you prefer) is a metal plate with numerous holes. The holes in this plate, along
with a companion plate not visible on the opposite side, match up with the vertical metal pegs in the turbine building floor shown in an
earlier picture.
Page 31
Source: NRC FOIA Document ML14220A162
The stator on its way from the site. Like Elvis, the stator has left the building. But workers still had to repair the damage caused within
the building on its way out.
Page 32
Source: NRC FOIA Document ML14218A737
The most extensive repairs were needed to the damaged turbine building floor and associated structural supports on the Unit 1 side of
the train bay. The photograph shows the crumbled and broken concrete removed from where the stator impacted the floor. The force
overstressed and damaged other concrete and steel, requiring this area to be significantly enlarged.
Page 33
Source: NRC FOIA Document ML1419AA424
Workers chipped away concrete and removed material damaged or potentially damaged by the dropped stator. This task had to be
performed carefully as it was similar to cutting a tree limb while perched on the limb.
Page 34
Source: NRC FOIA Document ML14220A092
This overhead view shows the turbine building floor under repair. The Unit 1 low pressure turbine appears in the upper center flanked
on either side by moisture separator reheaters (these components receive the steam leaving the high pressure turbine and strive to
remove water droplets before the steam enters the low pressure turbines.) Across the bottom of the photograph is the deformed and
dislodged structural steel beam.
Page 35
Source: NRC FOIA Document ML14219A425
With the suspect floor area removed, workers turned to removing the damaged structural steel beams. Note the worker tethered to an
anchor spot for protection against falling into the train bay on the left.
Page 36
Source: NRC FOIA Document ML14219A434
This overhead view shows the turbine building floor under repair. The Unit 1 low pressure turbine appears in the upper center flanked
on either side by moisture separator reheaters. Note that the deformed and dislodged structural steel beam has been removed from its
former location toward the bottom of the photograph. Also note that the cross beams have been removed.
Page 37
Source: NRC FOIA Document ML14219A434
This photograph looks down into the train bay from the turbine building floor on the Unit 2 side. When the stator dropped onto the
floor on the Unit 1 side, the force depressed the floor downward. In the center of this photograph is a vertical steel beam that
supported the floor. The downward movement of the floor tore its connections to the vertical support beam and crumbled the masonry
block wall below it. The damaged section of the train bay wall has been removed.
Page 38
Source: NRC FOIA Document ML14219A425
This photograph was taken from the train bay’s floor. In the center of the photograph is the vertical support beam that was torn loose
from the turbine building floor when it moved downward due to the stator’s impact. The damaged section of the masonry block wall
lining the train bay has been removed.
Page 39
Source: NRC FOIA Document ML14218A736
This 3D schematic shows the structural steel beams that were replaced during the repairs of the damaged caused when the stator
dropped onto the turbine building floor. The Unit 1 turbine and generator would be to the lower right while the Unit 2 turbine and
generators would be to the upper left. Using the grid system on the schematic, the train bay includes areas A-9 and A-10.
When the temporary lift device failed, the stator fell while positioned over the train bay. The dropped stator struck the turbine building
floor on both sides of the train bay opening, causing more extensive damaged on the Unit 1 side. The stator twisted and fell through
the train bay opening onto the hauler. The stator caused significant damage to the hauler. The stator fell over to the side atop the hauler
and further damaged the train bay’s walls before coming to a stop.
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Our Takeaway
Fission Stories #139 described this event. Our takeaway now is the same as expressed then:
Gravity never takes a minute off. Neither can vigilance to safety or tragedy can occur.
Links to the documents in NRC’s ADAMS online electronic library containing the photographs:
ML003747839
ML13213A270
ML14218A605
ML14218A607
ML14218A736
ML14218A737
ML14219A424
ML14219A425
ML14219A426
ML14219A427
ML14219A431
ML14219A433
ML14219A434
ML14220A092
ML14220A162
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