Joint ICTP/IAEA Workshop on radiation COMPARATIVE STUDY FOR C-14 MEASUREMENT IN OPERATIONAL SOLID RADIOACTIVE WASTE L.Bujoreanu D. Bujoreanu , Radioactive Waste Department, Institute for Nuclear Research Str . Campului no 1, POB 78, Pitesti, Romania Joint ICTP/IAEA Workshop on radiation effects in nuclear waste forms and their consequences for storage and disposal 12 - 16 September 2016 Miramare, Trieste, Italy

INTRODUCTION According with to the National Nuclear Program, The Institute for Nuclear Research Pitesti (ICN) is the main support for implementation of the methods for characterisation of radioactive waste generated by Cernavoda NPP. Over the past few years, Waste Department from the Institute for Nuclear Research, Pitesti has been focusing on the experimental methods for measurement of radioactivity of various categories of waste generated by Cernavoda NPP. Because the radionuclide C-14 is present in almost all radioactive waste streams generated by a CANDU nuclear power plant, it is very important to determine the concentration of this radionuclide into radioactive wastes. The objective of this study was to recovery of 14C by means of combustion and digestion methods of the solid waste and to measurement the radioactivity using a Tri-Carb 3110 TR liquid scintillation analyzer.

NUCLEAR FACILITIES IN ROMANIA In Romania there are : The nuclear power plant, Cernavoda NPP, has five PHWR - CANDU-6 Canadian type reactors with a 705 MW(e) gross capacity each, in different implementation stages. Units 1 and 2 are in commercial operation since December 1996, respectively November 2007; Nuclear Fuel Plant (FCN) Pitesti as a CANDU 6 fuel manufacturer; The Institute for Nuclear Research Pitesti (ICN), has an American TRIGA -type research reactor in operation; A VVR-S research reactor located in Magurele owned by National Institute for Research and Development of Physics and Nuclear Engineering-Horia Hulubei (IFIN-HH). VVR-S research reactor is now under decommissioning. A near surface repository (DIDR), in geological formations, at Baita-Bihor;

Romanian map - The main organizations involved in radioactive waste and spent fuel management

Spent fuel from Cernavoda NPP BRIEF OVERVIEW OF THE TYPES OF WASTE FROM NUCLEAR FACILITIES IN ROMANIA Spent fuel from Cernavoda NPP Cernavoda NPP-Units 1 and 2, has the following spent fuel management facilities: The Spent Fuel Handling System (for each unit); The Interim Spent Fuel Dry Storage Facility – DICA; The facilities are located on NPP site. Spent fuel from TRIGA reactor ICN Pitesti, the operator of TRIGA reactor, has the following spent fuel management facilities:   The Spent Fuel Pool; The Dry Storage Pits. Spent fuel from VVR-S research reactor VVR-S reactor which is now under decommissioning . The spent nuclear fuel has been shipped and back into origin country, in Russian Federation.

DICA and the storage pits at LEPI for irradiated experimental fuel rods and fragments

Operational wastes Cernavoda NPP has own facilities for liquid (aqueous and organic), spent resins and solid operational radioactive wastes; After pretreatment (collection, segregation, decontamination) and treatment, the solid wastes are confined in 218L stainless steel drums and transported to the Solid Radioactive Waste Interim Storage Facility (DIDR), located on the plant site; The Spent resins are stored into three tanks for spent resins located in the basement of the Service Building. Management of operational radioactive waste at ICN Pitesti The Institute for Nuclear Research Pitesti has its own Radioactive Waste Treatment Plant - STDR. The activity of this department is to treatment and conditioning the operational radioactive wastes resulted from: the operation of the TRIGA reactor; the operation of the Post Irradiation Examination Laboratory; the secondary radioactive waste from operation of STDR; research laboratories.

Solid Radioactive Waste Interim Storage Facility (DIDR) – Cernavoda NPP

Management of institutional radioactive waste at IFIN-HH The management of the institutional radioactive wastes is performed at IFIN–HH and processing all institutional radioactive waste (excepting nuclear fuel cycle waste) generated from nuclear techniques and technologies applications in areas as industry, agriculture, research, education and medicine. Spent sealed radioactive sources are collected and radiological characterized at the Radioactive Waste Treatment Plant from IFIN–HH. Disposal of the radioactive waste In the NW part of the country, at Baita-Bihor, is located a near surface repository, in geological formations, which is licensed for disposal of the low and intermediate level radioactive wastes and the institutional radioactive waste. The Baita-Bihor repository was designed to accommodate around 5,000 m3 of conditioned wastes disposed in about 21,000 standard containers. The first waste disposals were made in 1985 and it is assumed that disposals will continue until 2040.

Disposal Galleries at DNDR Baita - Bihor

Maximum admissible activity for packages disposal at baita-bihor repository

C-14 MEASUREMENT IN OPERATIONAL SOLID RADIOACTIVE WASTE Over the past few years, Waste Department from the Institute for Nuclear Research, Pitesti has been focusing on the experimental methods for measurement of radioactivity of various categories of waste generated by Cernavoda NPP. The objective of this study was to recovery of 14C using the combustion and digestion methods of the solid waste and to measurement the radioactivity using a Tri-Carb 3110 TR liquid scintillation analyzer. The paper describes the efficiency of treating the solid waste within combustion and microwave digestion. Combustion of the solid waste using a Sample Oxidizer Model 307 The equipment Sample Oxidizer Model 307 burns the waste sample in an oxygen atmosphere and separate carbon-14 radionuclide into vial for counting, using PERMAFLUOR E+ that liquid scintillation cocktail and Carbo-Sorb E that is a strong quenching agent.

TABLE 2: Sample composition for simulated contaminated paper Three samples of contaminated paper (labelled as H1, H2 and H3) were prepared using the C-14 stock solution with activity of 87.2x103 DPM/ml. . In table 2 is listed the manner of preparation of the samples used in experiments. Three samples of contaminated textile (labelled as T1, T2 and T3) were prepared using the C-14 stock solution. In table 3 is listed the manner of preparation of the samples used in experiments. TABLE 2: Sample composition for simulated contaminated paper Sample ID Solution A [ml] Sample weight [g] Carbo-Sorb-E PermaFluorE+ H1 0.05 0.2040 10 H2 0.2034 H3 0.2050 TABLE 3: Sample composition for simulated contaminated textile Sample ID Solution A [ml] Sample weight [g] Carbo-Sorb-E PermaFluorE+ T1 0.05 0.1905 10 T2 0.1927 T3 0.2236

TABLE 4: Sample composition for simulated contaminated paper 2. Digestion of the solid waste using a BERGHOF SpeedWave4 The speed wave microwave digestion system has been used to perform chemical digestion procedures under extreme pressure and temperature conditions for digestion of the solid waste. To prepare the simulated solid radioactive waste a stock solution (A) with C-14 activity of 4.87x104DPM/ml was prepared. Three samples of contaminated paper (labelled H7, H8 and H9) were prepared using the C-14 stock solution and they were placed in three pressure vessels (Table 4). In order to perform the digestion step of paper type sample, the procedure presented in Table 5 was adopted. TABLE 4: Sample composition for simulated contaminated paper Sample ID Sample weight [mg] Solution A [ml] HNO3 H2O H2O2 H7 250 0.1 8 6 2 H8 H9 TABLE 5: Digestion procedure Temp [0C] Press [bar] Ramp [min] Time [min.] Power [%] Step1 150 80 15 70 Step2 180 Step3 200 5

TABLE 6: Sample composition for each bubbler The check of C-14 retention in the off gas system : The first bubbler (B1 ) containing demineralized water in order to retain the soluble contaminants; The second bubbler (B2 ) containing NaOH solution to capture any emission of carbon. Samples from the bubblers were measured by liquid scintillation spectrometry and one sample for background - B (Table 6). TABLE 6: Sample composition for each bubbler Sample ID Sample bubbler 1 [ml] Sample bubbler 2 Ultima Gold XR Hionic-Fluor B1 10 B2 1 19 B

TABLE 7: Sample composition for simulated contaminated textile Three samples of contaminated textile (labelled T7, T8 and T9) were prepared using the C-14 stock solution and they were put in three pressure vessels (Table 7). For the digestion of textile samples, the procedure presented in Table 8 was adopted. TABLE 7: Sample composition for simulated contaminated textile Sample ID Sample weight [mg] Solution A [ml] HNO3 H2O H2O2 T7 250 0.1 10 6 2.5 T8 T9 TABLE 8: Digestion procedure Temp [0C] Press [bar] Ramp [min] Time [min.] Power [%] Step1 120 80 10 70 Step2 150 5 Step3 180 Step4 200 Step5 50 60 1

TABLE 9: Sample composition for each bubbler The check of C-14 retention in the off gas system The first bubbler (B1 ) containing demineralized water in order to retain the soluble contaminants; The second bubbler (B2 ) containing NaOH solution to capture any emission of carbon. Samples from the bubblers were measured by liquid scintillation spectrometry and one sample for background - B (Table 9). TABLE 9: Sample composition for each bubbler Sample ID Sample bubbler 1 [ml] Sample bubbler 2 Ultima Gold XR Hionic-Fluor B1 10 B2 1 19 B

TABLE 10: Experimental data on 14C measurement in contaminated paper Analysis by LSC for liquid samples from combustion process The experimental results obtained for C-14 measurement by LSC after combustion of the samples simulating the contaminated paper are reported in Table 10. The relative errors between the measured values and the reference one are also reported in Table 10. TABLE 10: Experimental data on 14C measurement in contaminated paper Sample ID 14C Reference Activity [DPM] 14C Measured Activity 14C Measured Activity* tSIE Efficiency recovery [%]  H1 43600 43391 43126 125.8 98.9 1.08 H2 43160 42896 129.5 98.3 1.61 H3 43287 43022 121.3 98.6 1.32 *C-14 measured activity corrected for combustion recovery (99.39%)

TABLE 11: Experimental data on 14C measurement in contaminated textile The experimental results obtained for C-14 measurement by LSC after combustion of the samples simulating the contaminated textile are reported in Table 11. TABLE 11: Experimental data on 14C measurement in contaminated textile Sample ID 14C Reference Activity [DPM] 14C Measured Activity 14C Measured Activity* tSIE Efficiency recovery [%]  (%) T1 43600 41623 41369 120.4 94.8 5.1 T2 41889 41633 118.3 95.4 4.5 T3 41564 41310 126.3 94.7 5.2 *C-14 measured activity corrected for combustion recovery (99.39%)

TABLE 12: Experimental data on 14C measurement in contaminated paper Analysis by LSC for liquid samples from digestion process The determination of C-14 in the liquid samples resulted from digestion process was performed using Low Activity Count Mode (typical count rate between 50 and 500CPM and 1000 minutes count time); The experimental results obtained for C-14 measurement by LSC after digestion of the paper samples are reported in Table 12 and in Table 13 are reported the results from bubblers; For a more accurate assessment of the C-14 activity it was performed the decontamination of pressure vessels of the digestor and measurement by LSC (Table 14).   TABLE 12: Experimental data on 14C measurement in contaminated paper Sample ID Time [min.] 14C Reference Activity [DPM/ml] 14C Measured Activity [DPM//ml] [Bq/ml] Efficiency recovery [%] *%2s H7(1) 1000 302.48 185 5.04 3.08 61.1 0.63 H7(2) 186 3.10 61.4 H8(1) 206 3.43 68.0 0.60 H8(2) H9(1) 210 3.50 69.3 H9(2) 209 3.48 69.0 *%2s-represents the gross uncertainty in a count value (with 95% confidence limits)

TABLE 14: Experimental data measurement in the decontamination sample TABLE 13: Experimental data measurement in sample from bubbler Sample ID Measured Activity [DPM/proba] [Bq/ml] B1 18 0.03 B2 25 0.401 B 17 0.028 TABLE 14: Experimental data measurement in the decontamination sample Sample ID Solution C6H8O7 [ml] UltimaGold AB Measured Activity [DPM/ml] [Bq/ml] D7(H) 1 19 20 0.33 D8(H) 24 0.4 D9(H) 23 0.38

TABLE 15: Efficiency recovery 14C As it can be seen in Table 12 the efficiency recovery is between 61.1% and 69%, with an average value of 66.13%. If one takes into account the activities of C-14 presented inTables 13 and 14, the average value of efficiency recovey is 81.43% (Table 15). TABLE 15: Efficiency recovery 14C Sample ID 14C Reference Activity [Bq/ml] Measured Activity Efficiency recovery % H7(1) 5.04 3.81 75.5 H7(2) 3.83 75.9 H8(1) 4.23 83.9 H8(2) H9(1) 4.28 84.9 H9(2) 4.26 84.5 Where (*)=measured activity corrected for measured activity from bubller and from decontamination

TABLE 16 Experimental data on 14C measurement in contaminated textile The experimental results obtained for C-14 measurement by LSC after digestion of the textile samples are reported in the Table 16 and in the Table 17 are reported the results from bubblers; For a more accurate assessment of the C-14 activity it was performed the decontamination of pressure vessels of the digestion and measurement by LSC (Table 18). TABLE 16 Experimental data on 14C measurement in contaminated textile Sample ID Time [min.] 14C Reference Activity [DPM/ml] 14C Measured Activity [DPM//ml] [Bq/ml] Efficiency recovery [%] *%2s T7(1) 1000 261.82 212 4.36 3.53 80.9 0.60 T7(2) 214 3.56 81.7 0.59 T8(1) 195 3.25 74.4 0.62 T8(2) T9(1) T9(2) 208 3.46 79.4 *%2s-represents the gross uncertainty in a count value (with 95% confidence limits)

TABLE 18: Experimental data measurement in the decontamination sample TABLE 17: Experimental data measurement in sample from bubbler Sample ID Measured Activity [DPM/sample] [Bq/ml B1 18 0.03 B2 27 0.45 B 17 0.028 TABLE 18: Experimental data measurement in the decontamination sample Sample ID Solution C6H8O7 [ml] UltimaGold AB Measured Activity [DPM/ml] [Bq/ml] D7(H) 1 19 22 0.36 D8(H) 21 0.35 D9(H) 23 0.37

TABLE 19: Efficiency recovery 14C As it can be seen in Table 16 the efficiency recovery is between 74.4% and 81.7%, with average value of 79.7%. If one takes into account the activities of C-14 presented in Tables 17 and 18, the average value of efficiency recovery is 85.03% (Table 19).   TABLE 19: Efficiency recovery 14C Sample ID 14C Reference Activity [Bq/ml] Measured Activity Efficiency recovery % T7(1) 5.04 4.34 86.1 T7(2) 4.37 86.7 T8(1) 4.05 80.3 T8(2) 4.33 85.9 T9(1) 4.35 86.3 T9(2) 4.28 84.9   * measured activity corrected for measured activity from bubller and from decontamination

CONCLUSION The results obtained from measurements by liquid scintillation spectrometry on the samples acquired by combustion method show very good results with reference to efficiency recovery. The efficiency recovery for solid waste paper type is between 98.3% and 98.9% and for solid waste type textile is between 94.7% and 95.4%. The results obtained from measurements by liquid scintillation spectrometry on the samples acquired by microwave digestion method show slightly lower results with reference to efficiency recovery. The efficiency recovery for solid waste paper type is between 75.5% and 84.5% and for solid waste textile type is between 84.9% and 86.7%. The combination of combustion and LSC spectrometry is a more adequate method for C-14 measurement, comparatively with the combination of microwave digestion and LSC spectrometry. When analyzing waste samples, the combustion method offers numerous advantages as the following: sample processing time is rapid, there are no quench interferences, there is no interference from other low-energy beta emitters, as well as from the beta continuum of high-energy beta particles.

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