Towards the application of electrokinetic remediation for nuclear site decommissioning.

This paper reports the results obtained in a Nordic Nuclear Safety Research project during the second intercomparison exercise for the determination of difficult to measure radionuclides in decommissioning waste. Eight laboratories participated by carrying out radiochemical analysis of 3H, 14C, 36Cl, 41Ca, 55Fe and 63Ni in an activated concrete. In addition, gamma emitters, namely 152Eu and 60Co, were analysed. The assigned values were derived from the submitted results according to ISO 13,528 standard and the performance assessments were determined using z scores. The measured results were compared with activation calculation result showing varying degree of comparability.

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Intercomparison exercise on difficult to measure radionuclides in activated concrete - statistical analysis and comparison with activation calculations

Development of 3H, 14C, 41Ca, 55Fe, 63Ni radiochemical analysis methods in activated concrete samples

A radiochemical method was developed for the accurate 55Fe determination in various radioactive waste, in particular samples contaminated with 241Pu. It consisted of three purification steps based on first ammonium hydroxide precipitation, and then anion exchange separation followed by TRU®-based extraction chromatography. It was characterized by an iron recovery yield of about 80% for all the studied samples and a 60Co decontamination factor of 106. In comparison to a standard protocol based on iron cupferrate extraction in chloroform, an improvement of a 30-fold factor was achieved towards plutonium. The developed TRU®-based procedure was validated by participating in interlaboratory exercises.

Accurate measurement of 55 Fe in radioactive waste

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Are molecular solvents, aqueous biphasic systems and deep eutectic solvents meaningful categories for liquid–liquid extraction?

This paper reports the results obtained during an intercomparison exercise for the determination of difficult to measure radionuclides in activated reactor pressure vessel (RPV) steel samples. In total, eight laboratories participated analysing 14C, 55Fe and 63Ni activity concentrations in RPV steel. In addition, some laboratories also analysed 60Co activity concentrations. Corresponding activity concentrations were also determined using activation calculations. Robust statistical techniques were utilised for the analysis of the results according to ISO 13528 standard. The results showed good agreement for 55Fe and 63Ni results whereas 14C results had significant differences. 60Co results were in quite good agreement.

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Intercomparison exercise on difficult to measure radionuclides in activated steel: statistical analysis of radioanalytical results and activation calculations

90Sr radiochemical method using nitric acid for Sr and Ca separation was optimized using design of experiments methodology. Nitric acid concentration and total volume of solution were determined as influencing factors applying Plackett–Burman design. These parameters were then optimized using Box–Behnken experimental design. An optimal nitric acid concentration of 63% and a total solution volume of 26 mL were found to achieve a Sr recovery of 93% with only 5% of Ca for a single precipitation. The developed procedure was applied on real radwaste samples: effluent, sludge and concrete. By comparison of the recovery and the 90Sr activity measurement with the results of the in-house standard method based on fuming nitric acid, the optimized method with concentrated nitric acid was validated. The fuming nitric acid can now be eliminated for 90Sr radioactive waste characterization.

Celine Gautier

Papers

Intercomparison exercise on difficult to measure radionuclides in activated steel: statistical analysis of radioanalytical results and activation calculations

Intercomparison exercise on difficult to measure radionuclides in activated concrete - statistical analysis and comparison with activation calculations

Optimization of Sr-90 precipitation in nitric acid using design of experiments for radioactive waste characterization method

Accurate measurement of 55 Fe in radioactive waste