July 12, 1955 letter from F.W. Gilbert to Dr. Clifford Beck, with enclosure

Cable address "MOTA"
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Industrial Operation - July 12, 1955

Dr. Clifford Beck
North Carolina State College
Raleigh, N.C.

Dear Dr. Beck;

Attached you will find my comments on the
recent trip to see your reactor. I would like to
state that I had a very enjoyable trip. It was a
pleasure to work with you and your associates.

Yours very truly,

F. W. Gilbert
Reactor Operations


[ enclosure]


The North Carolina State University Nuclear reactor
is of the water boiler type and consists of reacting vessel
of 14 litre capacity containing about 13 litres of uranium
sulphate solution. It is water cooled through four cooling
coils. Connected to the reacting vessel is a recombination
system consisting of an entrainment trap, two catalyst beds,
a condenser and a positive displacement gas pump.

On May 6th the reactor operated satisfactorily.
However, on May 9th it was found that it no longer had a
negative pressure although normally the pressure was maintained
at 10" w.g. below atmospheric. It was later found to have a
leak in the reacting vessel and also possibly one in one of
the water cooling coils. The leakage from the reacting vessel
was contained in an outer aluminum envelope. It was decided
to replace the reacting vessel and the recombination system.
On my arrival on July 6th, the following conditions existed:

The main portion of the uranium sulphate had been
removed and stored. The reacting vessel and the envelope had
been flushed. An air purge had passed through the reacting
vessel and the recombination unit for about six weeks. The
shielding blocks were removed from the top of the reactor.
The covering plate in the plenum chamber immediately above the
reactor had been removed. The control rod lifting mechanism
was removed. The shim rods had also been removed. Preparations
were going forward for the removal of the reactor vessel itself.

[page 2]

Questions brought out the information that the total power
that had been developed by the reactor was about 60,000 kw.
hours. About 40,000 of this had been generated in the last
six months of operation. This meant that in the total volume
of the solution there had been about 2.5 grams of fission
products. The subsequent draining and washing of the vessels
should have reduced this to less than 1%. The remaining
activity was probably trace fission products plated on to the
surfaces plus the stainless steel induced activity.

Indications from instrument reading were that the
activity was relatively soft. The maximum activity in the
plenum chamber was about 60 mr, most of which was coming from
the catalyst beds. It would have been possible to shield this
from the working space in the plenum chamber but a suitable
sheet of lead was not available. It was obvious that consider-
able care had been taken in dismantling to this stage as there
was no spread of measurable contamination. The preparations
that had been made for the shipment of the vessel to Oak Ridge
were as follows:

A drum had been lined with a ceramic tile and
concrete. The tile had an inside diameter large enough to take
the vessel plus a sheet of plastic. There was about six inches
of concrete around the tile. This appeared somewhat low but
as the drum was to be shipped by truck it was thought that
suitable care could be exercised to make the shipment safe.
The subsequent removal of the reacting vessel was very well
planned and executed. Air contamination was about 50% above
background. On removal the activity from the vessel was 1 r,
36% from the centre. In the shipping drum it was 3 r on contact.

[page 3]

Later the recombination unit was removed. The last
operation that I saw was the cutting out and removal of the
catalyst beds. This was done without incident.

My comments on the operations are as follows:
1. The steps that were taken were well planned and executed
in view of the activity that was present.

2. Had the activity been higher it was doubtful whether the
control would have been sufficient.

3. Although there is no criticism whatsoever of the operation
to date, I feel that to obtain maximum efficiency and at
the same time safe operation from this reactor, a full-
time supervisor should be employed. This person would
then have the time to study thoroughly all operating
problems including contamination control.

4. A good chemist, versed in the problems of the reactor
operation, whould be available for consultation purposes.
For example, I believe that there was probably trace
quantities of nitric acid formed which could probably be
found in the solution. Although the nitrate would not be
serious it could promote pit corrosion.

5. It is suggested that consideration be given to the use of
a paladium aluminum catalyst instead of the platinum
alumina. Dr. H.S. Taylor of Princeton has design a very
efficient material for combining hydrogen and oxygen. It
appears to be much less affected by moisture than the
platinum catalyst. Also regardless of material the
catalyst should be checked in the laboratory before it
is used.