Preservation of Samples for RETS, REMP and RW. Bob Litman Radiochemistry Laboratory Basics Presented in coordination with GEL Laboratories, LLC. Abstract.
Radiochemistry Laboratory Basics
Presented in coordination with
GEL Laboratories, LLC
Nuclear Power Plants have special radioanalytical needs for several different classes of samples required by their operating licenses. The general sample categories can be characterized by the amount and type of radionuclides they contain. In order from highest to lowest activity they are radioactive waste (and associated characterization samples), routine liquid and gaseous effluent samples, and radiological environmental monitoring samples. Each step in the overall chain of information from sampling plan to final results is important. One of the elements that is often taken for granted is sample preservation. In order to provide assurance that the radionuclide of interest is not compromised during sampling, storage and transport of the sample the proper preservation must be performed for each radionuclide in each particular matrix. The preservation requirements for radionuclides (in particular 14C, iodines, tritium, 55Fe, TRUs and 90Sr) most commonly analyzed for the three general categories of samples and the different matrices that comprise these categories will be discussed.
A physical or chemical process that minimizes the potential for loss of the analyte (in this case a radionuclide) during the time period from sampling to aliquanting for analysis
Can be defined in two different ways (both are correct and apply to radionuclides):
Radionuclides fall into three categories:
The chemical forms of each radionuclide are important when deciding preservation technique
Radionuclide masses can be VERY small,
1μCi/mL of 58Co = 3.19x10-5 ppm
0.03 micrograms of material in one liter!
At the same activity concentration, mass concentration decreases linearly with half life
Thus for TRUs the mass is much, much smaller
The available ionic surface Area within a 1-liter container is large (it isn’t just A=πdh…).
Thus the potential for loss on surfaces is substantial…
Samples containing metals are commonly preserved by adding acid to pH < 2.0:
[Site]-M+ + H+↔ M+ + [Site]-H+
*Any container material has “sites”. In some cases it may be advisable to pre-treat the sample container.
Iodine has 6 different oxidation states and each one is different chemical form
I-, I2, I3-, IO-, IO3-, IO4-
Don’t Add Acid!
O2 + 2H2O + 4I-↔ 2I2 + 4OH-
If necessary, preserve with S4O62-, SO32-, or HSO3- (add NaI as Carrier?)
What is the chemical form of 14C in the RCS?
Formed from 17O(n, α)14C,
In the presence of lots of H●,
What about other samples like groundwater?
Oxidized (bacterially) to HCO31-
Preservative for 14C?
Don’t add acid!
HCO3- + H+ ↔ 14CO2 + H2O
Consult with laboratory on method.
If necessary, use NH3 or NaOH to pH ~9
Refrigeration can help minimize volatility
In order to assess how to preserve, you first need to know:
Depending on the radionuclide needed:
What about the following?
Anything special required?
*especially when analysis is on 10CFR61 radionuclides