|Gamma assay of radioactive waste packages|
|Off-site radiochemical separation and measurement of DTM isotopes|
|Determination of Scaling Factors for DTM isotopes|
|Special applications, e.g. gas/heat generation monitoring of various rad.waste types|
In the execution of the disposal of low and intermediate level radioactive wastes, it is important toevaluate accurately the kind and quantity of each radionuclide in the waste packages. For such an evaluation,correlation of non-gamma-emitting nuclides based on gamma-emitting nuclides is recommended andregarded as a practical method. This method necessitates a completion of a highly accurate and reliablenondestructive assay system of gamma-emitting nuclides for practical use.
However, severalof the radionuclides considered significant are non-gamma-emitting isotopes,consequently are not easily measured by routine techniques.Thus, they are termed "difficult to measure" (DTM). To estimate the concentrations ofDTM nuclides indirect measurement methods are used. The method mostcommonly used by utilities is theapplication of scaling factors (SF). This method is based on the determination and consequent application of correlation factors between those critical nuclides and socalled key nuclides, which can be easily measured and are representative for theoccurrence of certain type of isotopes in the waste packages.
Scaling factors for DTM isotopes can be derived from sub-samples collected fromthe waste packages, sent to an off-site analytical laboratory for radiochemical analysis and
measurement of the radionuclides. The method of deriving SF is known to be vulnerable to problemswith sampling representatives, analytical detection limits and an inability to account for changing conditions, which may shift the radionuclide ratios.
In case of waste packages intended for long-term underground deposition, gas generation has to be considered as well. During the storage, the coupled processes of metal corrosion and microbial degradation of organic, particularly cellulosic wastes may generate significant quantities of gas within the drums or vaults. It is likely that a small proportion of the generated gas will be radioactive, principally as a result of the incorporation of the isotopes 3H and 14C that are present within the waste. Our company has experience in the construction and maintenance of complex systems for the monitoring of such processes.