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Selective Removal of C-14 from Resins

Investigation of various methods for C-14 removal from IX resins
C-14 is typically present on IX resins in carbonate and/or bicarbonate form. It is one of the key radionuclides, which determine waste classification both in CANDU, as well as in PWR / BWR plants.
Kinectrics has investigated various methods for C-14 removal from IX resins including:
·         Thermal stripping with air, air + 10% CO2, O2 or N2 as carrier gas
·         Acid stripping
·         Caustic stripping, and
·         Extraction using super-critical CO2 (SCC).
Each method has its pros and cons. For example, efficiency of thermal stripping is low unless the temperature is raised above 70ºC.  Acid stripping is effective, but is not selective, and strips all radionuclides from the resin: C-14 is released as CO2 while the bulk of the other radionuclides are stripped into the acid. Thus, the acid waste, as well as the stripped resins which contain low levels of residual activity, must both be managed. 
Extraction using SCC has the advantage that while C-14 undergoes isotopic exchange with C-12, the other radionuclides present remain bound on the resin. 
CO2 is non-toxic, inexpensive and recyclable. Contaminants dissolved in SCC can be separated out by expansion of the fluid to a subcritical pressure where CO2 is a gas, thus causing the dissolved materials to precipitate out.
At the end of the SCC process extraction cycle, the C-14 is present in the CO2 at an isotopic ratio of 10-6 to 10-9.  Because of this extremely low value, the CO2 can be reused for additional extractions.
Finally, when the C-14 level is sufficiently high, the CO2 can be immobilized (in calcium hydroxide solutions or solid lime) or alternately, reduced to CO which can then be cryogenically distilled to recover C-14 for sale.