The INL, an applied
engineering national laboratory dedicated to supporting the U.S. Department of
Energy's missions in nuclear and energy research, is currently disposing of
spent fuel rods from one of its reactors. Currently, it takes about 2 weeks to
process 6 baskets (546 Fuel rods) of fuel rods. The laboratory has 43,000 fuel
rods to process. The process follows the following steps:
1. Fuel rods (pins) are removed
from the reactor core and placed into baskets holding 91 pins.
2. The basket is placed into a
“Hot Cell”. The hot cell
is a room, full of argon gas, that is exposed to high levels of radiation.
Because of the high levels of radiation, people cannot be in the room. Any work
done in the hot cells must be done by a master slave manipulator (MSM) – a sort
of robotic arm controlled by an operator on the other side of a 5 foot thick
piece of lead glass.
3. The fuel rods consist of a
cylindrical stainless steel cladding, that is filled with uranium fuel pellets.
To prevent fuel rods from touching inside of the reactor, each rod has a spacer
wire wound helically around it and welded at each end. This wire must be
removed before the fuel is processed (chopped into small pieces for
electrorefiner). After the basket is placed into the hot cell, each element is removed individually (by
the MSM) and carried to the shearing device.
4. The shearing device consists of two
blades, one to hold the wire/pin and another to shear the wire near the weld.
These blades are driven by solenoids that are controlled by a foot pedal
outside of the hot cell. When the pin is
in position, the wire is sheared on one end. The fuel pin is then flipped (by
MSM) and reinserted into the shearing device, where the wire is sheared again,
near the weld.
5. The wire is removed and taken to the wire chopper (by MSM), where it is
cut into 2”-3” pieces.
6. The fuel pin is taken (by MSM) to the fuel element chopper, where it is
cut into small pieces.
The overall goal is to reduce manual input required from operator.
The following areas can be improved by adding automation and/or modifying
1. Wire shearing (most time consuming)
2. Wire separation
3. Loading elements into cassettes
4. Element feed basket
new equipment must be designed to be remotely maintained/installed (by
has very poor heat transfer properties (low conductivity/convection), all
electronic devices must be rated for high temperatures.