Historical waste

Different types of historical waste can be distinguished:

⎯ tanks with liquids

⎯ waste to be decontaminated before decommissioning

⎯ workshops to be decommissioned

⎯ waste sites (near surface, interim storage sites) 4.7.1. Tanks with liquids

4.7.1.1. General aspects

⎯ There can be different subcases

• one liquid phase

• two different, immiscible liquid phases (organic and mineral)

• a mixture of liquids and solids

⎯ These radioactive wastes have to be treated before immobilization;

⎯ The aim of the characterization here is to wisely choose the right processes considering safety and transportation.

4.7.1.2. Specific recommendations for the different subcases

⎯ One liquid phase

The assumption of homogeneity can be confirmed based on interviews with operational personnel, knowledge of history and processes. Mixing is recommended if possible before sampling.

⎯ Two or more immiscible phases

1. determine the interface(s) and the volume of each phase 2. assume each phase is homogeneous

3. sampling has to be made in the middle of each phase

⎯ Mixture of liquid and solid

The ratio solid/liquid should be determined, and each phase must be characterized.

− If the tank can be mixed, sampling must be conducted during the mixing process at different depths. At each depth, a sample must be made consisting of several subsamples, one of which is to be sent to the laboratory.

• All other subsamples are mixed, filtered and the ratio of solid to liquid and its composition are determined.

• For all samples taken at different depths, the laboratory performs a first evaluation,

• If chemical and physical analytical results are similar, it is assumed that the mixing process was correct and it is possible to calculate easily the S/L ratio and the composition of each.

• If not, it is necessary to change the mixing process, requiring additional energy and time.

− If it is not possible to mix the tank, then recognized specialists should study this difficult case to determine the risks and difficulties of further processing.

4.7.2. Historical waste to be decontaminated before decommissioning 4.7.2.1. General aspects

⎯ When a chemical decontamination process is applied, one has to be aware that the initial radiochemical and chemical compositions will be modified to completely analyze the waste characteristics.

⎯ The aim of the initial characterization is to determine the chemical, physical, and rheological properties, considering that they will significantly influence the choice of the conditioning process, to check the efficiency of the decontamination process and to determine when the clearance level is achieved. Using both NDA and DA analysis is recommended.

4.7.2.2. Recommended analytical methodology

⎯ Measure the efficiency of the decontamination process by

• Taking samples of the decontamination liquid waste and performing destructive analysis, and/or

• Performing non-destructive assay

⎯ In case of difficulties, the object (e.g. walls, counters, drains, piping) to be decontaminated should be observed with a camera and/or NDA device such as γ-camera to determine the specific location and type of contamination,

⎯ Use historical records (process data sheets, chemical inventory lists, purchase records, interviews with operational personnel) and/or NDA measurements (spectrometry, neutron counting), and determine risks due to fissile materials,

⎯ Decide for mechanical decontamination in order to reduce the final waste volume,

⎯ Use previous data to determine the sampling plan,

⎯ Make the chemical and radiochemical DA,

⎯ Determine the first (chemical) decontamination process All actions mentioned are done frequently and repeatedly.

4.7.3. Workshops to be decommissioned 4.7.3.1. General aspects

It is assumed that in this case, the radioactive waste resulting from the decommissioning will be directly conditioned and immobilized in drums. The drums will be measured to determine the concentration of key nuclides. The aim of the characterization is to determine the scaling factors with sufficient accuracy together with the key nuclides. Checking for homogeneity and representation of the sampling and subsampling process are therefore crucial points.

4.7.3.2. Recommended methodology

NDA, DA, calculation and modelling will be used. Modelling is necessary for radionuclides at or below detection limits. Three complementary steps are proposed. The first deals with measurements made in situ, the second with analytical measurements, and the third is related to the calculation and modelling step.

In situ measurements

If the historical data are accurate and well known, it will be possible to start the first two actions given here:

⎯ Determine and locate hot spots by using a γ-camera, (or dose rate measurement);

⎯ Check the consistency of the nuclide vector to decide about the location and choice of the representative active samples by using a gamma spectrometer with a counting system software;

⎯ Take representative samples and classify them by type (metal, concrete, chemotoxic elements).

Analytical measurements (for each type of sample)

⎯ dissolution by qualified procedures and check the representativeness of the solutions by processing standard samples of similar matrices;

⎯ chemical separation needed prior to the measurement, depending on the measurement device (liquid scintillation, ICP-MS);

⎯ measurement and calculation for each radionuclide of the mass and radioactivity;

⎯ consider appropriate chemical toxicity testing.

Final checking and calculation of the DTM radionuclides

⎯ Validation of the different DA results

• Coherence between different samples;

• Coherence between DA results and NDA results from the in situ measurements

⎯ Calculation of the DTM radionuclides;

• Study the workshop history (where was the fuel processed and so on);

• Choose a key nuclide for each hard measurable radionuclide;

• Calculate the ratios between DTM radionuclides and the chosen KN using computer codes (ORIGEN, CESAR) on fuels processed in the workshop before decommissioning;

• Consider process chemistry that may alter these calculated ratios and make corrections.

⎯ Fingerprint calculation

• Determine for each type of sample the associated fingerprint;

• Establish the global fingerprint of the workshop by calculating it proportionally to the weight of each type of waste inside the workshop.

4.7.4. Historical waste sites (near surface, interim storage sites)^∗

Several questions are to be answered and information must be provided when preparing the characterization strategy for such wastes.

⎯ What is the extent (site/volume) of the waste?

• Determine the physical boundary of the waste site that will be retrieved and processed by physical sampling and analysis (refer to sampling standards).

• Use any historical information and interview individuals who can provide information.

⎯ Apply NDA to assess safety requirements for workers

⎯ What is the condition of the waste?

• Drummed

* Intact

* Breached/corroded

* Solid/liquid/both

• Contaminated equipment/supplies

• Contaminated soil.

• Use information to determine retrieval, transport, characterization plans

⎯ Determine the best methods to sort the waste into similar waste streams based upon waste minimization, disposal path and anticipated waste form;

⎯ Determine a representative sampling plan to include witness samples for archival purposes (based upon heterogeneity of waste stream). Samples should be archived until there is an approved waste conditioning process, waste form and disposal site.

⎯ Apply detailed NDA/DA characterization of waste sorted into similar waste streams for safety, transportation and general knowledge of nuclear, chemical and physical properties.

⎯ Based upon characterization data, determine if further processing of sorted waste streams would be beneficial for safety, waste minimization or regulatory purposes.

⎯ Determine final waste conditioning process, waste form and disposal site.

∗Historical waste disposal sites near the surface (trenches) or interim storage (drum waste) are considered. For very specific site cases that deal with difficult to retrieve waste, a site specific risk analysis would need to be performed to determine the waste retrieval process waste forms.