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76 C.J. \Vooo
solidification practices by producing an inert organlc-free solid residue. None of these
techniques has been fleld tested yet, and it will probably be two to three years before
they are implemented. The oxidizing decontamination processes using ozone are a promising
method of producing a low volume of waste. Studies of one such process are being carried
out by the Empire State Electric Energy Research Corporation (ESEERCO). The main problem
with processes using ozone in the past has concerned the production, stabillty and control
of the ozone itself; although hlghly effective on a laboratory scale, seallng up major
plant systems has been thought difficult.
9.3 Possible future strategies
The importance of decontamination technology to the utility industry in future years
will depend primarily on two issues: radiation exposure limits and major repair
requirements.
Regulations imposing lifetime exposure limits and reductions in annual exposure limits
to below 5 rem per indivldual worker are probably going to be introduced. These will
severely restrict the use of key workers who currently receive doses above 2 rems/year.
Even in situations where outage work can be carried out within a reasonable total dose
limit, decontamination may be beneficial as it will increase the productivity of key
workers ( 6__00 ) •
Up to the present time, steam generator replacements have been achieved without large
scale decontaminations, but recent estimates (61) show that considerable dose savings can
be achieved, particularly with full-system decontamination. In fact, decontamination may
prove to be essential at many plants, Just to keep within mandated dose limits.
Requirements for the inspection of BWR core internals may give added Justification for
full-system decontamination.
Improvements in other areas of radiation control technology also affect decontamination
considerations. Replacement of major in-core cobalt sources and improved water chemistry
specifications will result in lower radiation field buildup rates in the future. This
conclusion applies to both BNRs and PWRs. The cobalt-60 already deposited on out-of-core
surfaces is essentially fixed - the only significant removal process in normal operation is
decay at less than 15% per year. The net result is that fields in most plants older than 3
years have leveled off, but are not declining to any great extent. With full-system
decontamination, radiation fields will probably re-estsbllsh and level off at significantly
lower values than are currently typical.
It is concluded that utilities should consider chemical decontamination in the following
circumstances:
o Part-system decontamination in conjunction with significant outage work (typical
situation at the present time).
o Routine part-system decontamination at every outage to minimize individual
exposures (as at Commonwealth Edison BWR plants).
Assuming successful completion o£ work currently in progress to qualify full-system
decontamination, after 1990:
o Full-system decontamination with fuel removed in conjunction with major
repalr/replacement work.
o Full-system decontamination to achieve permanent reduction in fields. This would
involve one application with fuel in place or two with fuel removed. In the
latter case, the second application should be made two refueling outages after the
first. Assuming that relatively little activity is transferred from the dirty
fuel to new fuel after the first decontamination (which would seem to be a
particularly valid assumption for a ~ operating at elevated pH), all remaining
cobalt-60 on the system surfaces should be removed by the second
decontamination. Activity on the fuel is removed when the fuel is replaced.
Plant-specific cost-benefit assessments will be necessary to determine if either
of these options is Justified.