Www.gel.com problem solved Preservation of Samples for RETS, REMP and RW Bob Litman Radiochemistry...

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Preservation of Samples forRETS, REMP and RW

Bob LitmanRadiochemistry Laboratory Basics

Presented in coordination with

GEL Laboratories, LLC


AbstractNuclear 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.


What is Preservation?

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


What is a Holding Time?

Can be defined in two different ways (both are correct and apply to radionuclides):

• Time period during which the preserved sample will have negligible loss of analyte (radionuclide)

• Time period during which the radionuclide (analyte) will retain enough activity so that detection limits can be achieved (also referred to as radiological holding time)


Loss Mechanisms

• Precipitation

• Adsorption

• Volatilization

• Chemical reaction producing one of the first three

• DecayDecay


Preservation Categories

Radionuclides fall into three categories:– Metals– Volatiles– Non-metals

The chemical forms of each radionuclide are important when deciding preservation technique


Matrices Considered

• Liquids – Waste liquids– Surface water– Well water

• Air Particulate Filters– Glass fiber– Polymeric

• Solids– Soils– Resins– Vegetation


Who Decides How Samples Should Be Preserved?

• The project team (i.e., you!)

• Know the standard preservation techniques

• Communicate – the technique chosen should be coordinated

with the laboratory, before collection


Liquids

• Filtered or not filtered?

• Do you want the lab to filter?

• What micron size filter?

• Analyze residual matter on the filter?

• Whose decision is all this?


LiquidsRadionuclide 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


Liquids

The available ionic surface Area within a 1-liter container is large (it isn’t just A=πdh…).

Why?

Thus the potential for loss on surfaces is substantial…


LiquidsSamples containing metals are commonly preserved

by adding acid to pH < 2.0:

• Prevents precipitation of hydroxides• “Fills” sites* on sample bottle surfaces with H+

[Site]-M+ + H+ ↔ M+ + [Site]-H+

• Check the sample stream to ensure that pH is in the range you want it before you send it!

• Tell the lab which acid was added (usually nitric or hydrochloric)

*Any container material has “sites”. In some cases it may be advisable to pre-treat the sample container.


Liquids-Iodines

Iodine has 6 different oxidation states and each one is different chemical form

I-, I2, I3-, IO-, IO3

-, IO4-

But,

Don’t Add Acid!O2 + 2H2O + 4I- ↔ 2I2 + 4OH-

If necessary, preserve with S4O62-, SO3

2-, or HSO3-

(add NaI as Carrier?)


Liquids - Carbon

What is the chemical form of 14C in the RCS?

Formed from 17O(n, α)14C,

In the presence of lots of H●,14CH4? 14C2H6?

What about other samples like groundwater?

Oxidized (bacterially) to HCO31-


Liquids - Carbon

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


Liquids – 55Fe and 90Sr

• Preservation with either nitric or hydrochloric acid is most effective– Ensure pH is < 2.0

• Waste liquids have combinations of plant liquid wastes and may be buffered basic

• Most waste liquids have some ‘native’ iron content. Fe(OH)3 can precipitate even in acidic solutions

• Prevents carbon dioxide absorption and precipitation of SrCO3


Liquids - TRU

• Nitric acid preservation is recommended– Ensure pH is < 2.0

• Carrier addition is recommended– La, Ce, Nd

• Do not delay transport as the mass concentration is far less than that of the activation products


Liquids - Tritium

• Preservation Required?

• What is the chemical form?


Liquids – General

Preserve:

• As soon as practicable after collection

• If compositing samples, preserve at the beginning not at the end

• If storing prior to analysis for extended period of time consider adding tracers/carriers (tell the lab!)


Summary - Liquids


Solids - Soils

In order to assess how to preserve, you first need to know:– Will the entire sample be used?– Will the sample be homogenized at the lab?– Should miscellaneous detritus (sticks, stones,

worms) be removed?


Solids - SoilsDepending on the radionuclide needed:• Should the sample be frozen?• Shipped under nitrogen?• Freeze or refrigerate?• Wet weight or dry weight for results?

– Drying temperature?– Freeze drying acceptable?

• Total digestion or leaching to be used?


Solids - Soils

What about the following?

– 129,125,131I– 3H– 14C

Anything special required?


Solids - Resins• Think “estimate”*

• Think “non-homogeneous”*

• Whole Sample?

• Preserve dry, wet or semi-wet?

• If stored before shipment, under inert atmosphere?

• Don’t freeze…

*especially when analysis is on 10CFR61 radionuclides


Solids - Vegetation

• Critical factors:– Moisture content is high (75-98%)– Material changes quickly (hours to days)– Distinguish surface from internal

contamination?

• Refrigerate or freeze?


Solids- Summary

• No universal preservation techniques– Specified by Project

• If frozen, care needs to be taken to ensure sub-sampling is representative

• Wet or dry weight?– Will determine preservation– Project specific

• Volatiles are a concern with solids as well


Particulate Filters

• Fold filter in half (sample on itself)

• Slide filter into glassine-style envelope

• Ship between two blank filters (could be polymeric, or glass fiber) in Petri-style container


Particulate Filters

• Avoid situations which can induce a static charge on the sample

• Avoid adhering to another medium for shipment as the adhesive may affect the analysis


Summary

• Choose a preservation technique that ensures minimal loss of radionuclide

• Identify requirements to laboratory (holding times, preservation techniques used, carriers added, etc.)

• Several aliquants of the sample may be required as different radionuclides require different preservation

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