The pure sodium is shipped to the plant in Newton in 55 gallon
steel drums, each of which contains 400 lbs. of reactor grade (more than 99.9 percent pure) sodium metal in a fused (solid) state. The solid mass of
sodium occupies all but a few inches at the top of the drum and the
remaining space is filled with argon, an inert gas, to avoid contamination of
the product in transit or storage.
To extract the sodium, the steel drum is placed in a special heater
jacket that warms the contents until the sodium liquefies. A bayonet pickup
tube is then inserted into the drum and additional inert gas is
introduced at the top of the drum, to displace the liquefied sodium. The
sodium is drawn up into the tube and directly into the closed processing
system. The entire process takes place in a sealed atmosphere, since even
the moisture and other contaminants in the outside ambient air can
contaminate the sodium, creating a risk of explosion and making it
unusable for the process.
The normal procedure is to extract all of the sodium from the drum,
sometimes over a period of several days, down to the point that it can no
longer be drawn into the pick-up tube. This usually leaves two to five
pounds of sodium at the bottom of the drum which is allowed to cool and
solidify after the tube is withdrawn. The residual sodium, referred to as a
“heel,” usually occupies less than l/2 inch at the bottom of the drum. This
amount of sodium is impractical to extract or recycle; burning-off is a
common practice in the industry to dispose of small quantities of residual
sodium.
Burning-off the residual sodium avoids having to dispose of the
drums as a hazardous waste. This is practical, because the sodium can be
completely consumed and converted to sodium oxide ash, which is
collected by a filter system and can be disposed of much more easily. The
plant routinely has several drums with residual sodium to bum off each
week. The task is usually performed during the second or third shift.
The waste sodium is burned-off in a special enclosure that was built
for cleaning drums. The room is approximately 8 ft. X 10 ft., with an
exhaust system built into the roof to draw out the smoke. The burning
sodium produces large quantities of smoke which is passed through a
scrubber system to capture the sodium oxide ash and prevent atmospheric
contamination. The room has concrete block walls, with a large blowout
explosion relief panel in the exterior wall to allow the force of an explosion
to be vented to the outside. The blowout panel consists of a plywood
sheet, held in place by a metal framework.
The access to the enclosure is a double doorway opening into a
maintenance area of the plant. The doors are “blast doors” reinforced to stay closed while the force of an explosion is directed to the outside
through the blowout panel, instead of through the doorway to the interior
of the plant.
In addition to being designed for the disposal of waste sodium, the
room was also designed for wet washing drums and equipment that had
contained other products and other items used in the process. Spray
nozzles are located in one part of the room and the floor is a heavy metal
grate, which allows any runoff to drain into a system of shallow troughs
that lead to a holding tank and waste treatment system. Drums and
equipment can be placed in the room and flushed, with all runoff draining
down through the grates and into the troughs. There is often residual
water under the floor grates, after the room has been used for wet washing.
To bum-off a sodium drum, the near-empty drum is placed in a
special cradle that sets it at a slight angle inside the room (diagram
appears on the following page). The cradle has a rocker end to allow the
drum to be tilted from a vertical position to an almost horizontal position.
A metal drip pan is placed under the drum cradle to catch anything that
might drip out of the drum and keep it from contacting the floor grates or
falling into the troughs. The top of the drum is completely removed and
the drum is positioned with the open end facing toward the blast doors.
After the blast doors are closed and secured with a vertical bar, a
worker ignites the sodium with a MAPP gas lance, which is inserted
through an access hole in the blast doors and directly into the drum. Any
residual sodium coating the sides of the drum is melted and forms a pool
at the low end of the drum. When the sodium is ignited, the lance is
removed and the product is allowed to bum itself out, which usually takes
one to two hours. The sodium first melts and forms a puddle in the low
end of the drum, then the liquid usually bums calmly with a glowing red
combustion.
The burning sodium sometimes sputters and emits small flares of
glowing metal which are contained within the room. A heavy gray/white
smoke is produced, which is drawn immediately up into the exhaust system
and out through the scrubbers. When the sodium is completely burned-out
and the drum has cooled, it can be removed and sent out for disposal as a
non-hazardous waste.
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