ORNL-4191 - the Molten Salt Energy Technologies Web Site

Some delays were encountered in the retrieval
operation because of the necessity of building
shielded carriers into which to pull the contaminated
tools. As a result a very convenient arrangement
was developed. A hollow lead cylinder,
24 ft long with 1- to 11/2-in. walls, strapped to a
steel I-beam formed the body of the carrier. A
24-ft length of l>2-in. pipe, with a gate valve at
the lower end, fitted into the shield and could
easily be dropped out at the burial ground with
the contaminated tool safely contained inside.
Figure 2.2 shows the containment enclosure
around the restricted work area, with the shielded
carrier suspended from the crane bridge. The
workers on the bridge are in position to pull a
tool out of the sampler tube with a cable dropped
through a seal on the upper end of the pipe liner.
This system was used for five hot pulls, with no
spread of contamination or excessive radiation.
When the replacement sampler drive unit was
installed, some difficulties were encountered in
fitting up pipe and tubing connections, but containment
joints were made up leak-tight.
The procedures and tools developed for this
shutdown proved effective. The tool retrieval
shield, in particular, was a useful development.
Measures for control of contamination and radiation
prevented spread of activity outside the
restricted work zone, and the highest quarterly
dose for any worker was only 300 millirems. In
view of the intense sources involved, this record
attests to the effectiveness of the controls.
2.3 DECONTAMINATION STUDIES
T. H. Mauney
The maintenance scheme for molten-salt breeder
reactors proposes that components which can be
easily decontaminated will be repaired and reused
as spare parts. As an aid in evaluating this
proposal, a study was started to determine the
effectiveness of decontamination procedures in
reducing the activity of contaminated parts from
the MSRE.
The first item used in the study was the manip-
ulator hand which had been used in the sampler-
enricher system during months of power operation,
until it was replaced because of a leak in the
boot. When removed from the sampler-enricher,
the unit was contaminated by mixed fission prod-
ucts to a level of approximately 300 r/hr at 3 in.
40
It was necessary to first remove the two-ply
plastic boot which had provided fission product
containment for the manipulator while in use.
Since the ORNL facility used for routine decontami-
nation can handle only up to 50 r/hr of gamma
radiation, it was necessary to use a facility at
the High-Radiation -Level Analytical Laboratory.
This facility was equipped with remote handling
equipment and high-pressure sprays which were
used in the procedure.
The decontamination began with spraying the
manipulator hand with a 500-psi jet of detergent.
The unit was then soaked in several solutions.
After the radiation level was reduced to less than
3 r/hr, the manipulator was removed to a laboratory
hood and hand scrubbed with a wire brush and
another detergent. The radiation level was finally
reduced from the initial reading of -300 r/hr to a
final level of 300 mr/hr, which was low enough to
permit controlled direct contact for repair. The
detailed results of the various treatments in re-
ducing the radiation level are shown in Table 2. 1.
One of the complicating factors affecting the
decontamination of the manipulator hand was the
presence of many crevices in the linkages and
pins which could not be reached by the jet spray.
Extending the cleaning time per step might have
resulted in greater decontamination factors. Fur-
ther studies will be made of this effect as other
components become available.
The decontamination of the manipulator hand
served a dual purpose. It not only helped de-
termine the effectiveness of decontamination
procedures in reducing the activity of MSRE con-
taminated components, but also made available at
a decontamination cost of $300 a spare part that
would have cost about $2000 to duplicate.
2.4 DEVELOPMENT OF A SCANNING DEVICE
FOR MEASURING THE RADIATION
LEVEL OF REMOTE SOURCES
Robert Blumberg T. H. Mauney
Dunlap Scott
A method for locating and evaluating concentra-
tions of radioactive materials in areas having
high background radiation would be useful in fol-
lowing the deposition of fission products in com-
ponents of circulating fuel reactors and in chemi-
cal process plants. Location of unusual deposits
would aid in understanding the operation of the