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sewer disposal
Regardless of low risk arguments we are faced with ....
1. The political issues of sewer treatment plants that accumulate
significant quantities of licensed materials (presumably long lived isotopes,
e.g., Co-60). NRC, being a politically appointed agency, must respond to
these concerns, almost regardless of actual risks. So, IMHO, sewer release
of persistent radionuclides will soon be a closed option. The fact that
some areas of the country have large Ra-226 source terms in their water that
is also accumulated in these plants is irrelevent (although mildly amusing).
2. Treatment to remove solids will render many 'soluble' compounds
insoluble. So simply meeting the current regulatory solubility requirement
is not a good long-term plan.
3. Decay in storage technically does not satisfy the solubility requirement.
NRC has clearly and repeatedly stated that the solubility requirement applies
regardless of the radioactive concentration. Even if it is a low enough
concentration to dump on your lawn it cannot be put into the sewer without
meeting the solubility requirement. On the other hand, if after decay you
run it through a nominal cleanup process, assay the result at an adequate
sensitivity (e.g., 10% of the Table 3 linits for your nuclide), and if the
result shows no detectable activity then it can be released as 'clean'.
The solubility rule in this instance no longer applies.
It is likely that in the near future (near in this instance means the next
4-8 years since it requires a rule change) that the sewer release rules will
change dramatically. So if you are planning a new operation it would be best
to be very conservative (or at least flexible) in your plans for usinf the
sewer release pathway.
Note: These are my personal views, not those of my agency or of any known
or hypothetical government body.
SLABACK@MICF.NIST.GOV
...a little risk, like a bit of spice, adds flavor to life
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