Radiochemistry and Compliance Assessment of LLW The Waste Quality Checking Laboratory (WQCL) Chris Dale AMEC Nuclear UK Limited UKAEA Winfrith

Transcription

1 Radiochemistry and Compliance Assessment of LLW The Waste Quality Checking Laboratory (WQCL) Chris Dale AMEC Nuclear UK Limited UKAEA Winfrith

2 Overview of Presentation The Role of the Laboratory Facility and Staff The Waste Checking Process NDT DT / Radiochemistry Compliance Level Assessment of Waste Reporting Results and Quality Assurance Examples of Non-Compliant Waste Contact Details

3 The Role of the Laboratory

4 WQCL, A512, Winfrith

5 The WQCL Team

6 Initial Testing Process Receipt of Consignment QA Checks Segmented Gamma Scanning Real-Time X-Radiography Passive Neutron Coincidence Counting

7 Waste Receipt Typically Full-height or ISO Skip Containers

8 Non-Destructive Testing Waste Receipt QA Checks (all waste drums + ISO) β/γ dose rate, contamination checks, ISO seal integrity, corrosion, maintenance plate, labelling, ISO and drum weights etc. NDT (all waste drums) Each drum assigned unique ID number Real-Time X-Radiography (RTX) Visual image of drum contents Segmented Gamma Scanning Identify and quantify γ emitters in waste Passive Neutron Coincidence Counting Identify and quantify Pu in waste

9 Real-Time X-radiography (RTX) Used to examine contents of waste drum Identify any prohibited items Digital image handling Rapid dist n of photo evidence Video clips New X-ray Set: Higher power for dense waste Improved imaging Zoom & Jog

10 RTX Image Non-permitted Items which may contravene EA Transfer and Disposal Authorisations Or LLW Repository Conditions for Acceptance - Free liquids - Pressurised containers - Putrescible matter

11 Segmented Gamma Scanning (SGS) Identifies & quantifies γ emitters within waste Drums scanned in segments to locate sources We have more time to scan! Results corrected for attenuation by use of a transmission source Routinely calibrated and checked against traceable reference standards Method is UKAS accredited

12 Passive Neutron Coincidence Counting (PNCC) H2K Passive Neutron Coincidence Counter Built by SCK CEN in Belgium Installed at WQCL in 2002 Detects Pu in waste from emitted neutrons Sensitive to < 1mg 240 Pu

13 Stage Two Testing Process Which Drums? Consignor D4 Declaration Health Physics Results 5% Drums for DT SGS + RTX Drum Results

14 WQCL Active Lab

15 Sampling for Destructive Testing

16 Destructive Testing (DT) Aqueous solutions are prepared from solid samples by acid / alkaline leach & dissolution Radiochemical analysis: Total α α spectrometry Total β Liquid Scintillation Counting (LSC) Individual γ γ spectrometry Chemical Separation: Specific α emitters: U, Pu, Th, Am, Cm α spec Specific β emitters: 3 H, 90 Sr, 14 C, 99 Tc, 241 Pu LSC Specific γ & X-ray: 125 I, 129 I, 55 Fe γ spec / LSC

17 Total (Gross) Alpha Analysis Calibrated pipette 0.1ml sample volume Hot block or IR lamp < 1.5mg solid on stainless steel disc Total net counts MeV on Canberra Packard Alpha Analyst system QA standard

18 Total (Gross) Beta Analysis Calibrated pipette 0.1 or 1.0ml sample volume Ultima Gold AB + low 40 K vials Temp and dark adapt overnight Total net counts kev on Perkin Elmer Quantulus Cs internal CE standard QA standard

19 125/129 Iodine Analysis Calibrated pipettes for all methods 5.0ml sample + 50mg I carrier Initial Fe and Co hydroxide co-pptns 2-stage redox reactions to convert all I species to iodide Anion exchange absorbs iodide Elute I as periodate with NaOCl. Prepare in calibrated volumetric flask 50ml eluate counted on Canberra Packard BEGe γ spec QA standards for recovery for all methods

20 Actinide Separation ~ Activity levels from Total Alpha ml sample Bq per std Initial iron hydroxide co-precipitation then ether extraction of iron First anion exchange separation. Am/Cm and Th pass through, Pu and U retained. U and Pu then separated + clean-up column Second column separates Am/Cm from Th Electrodeposit on s/steel disc 400mA 2.5h with HCl + Amm Chloride or Amm Oxalate Typical count of 1 3 days, 8 chambers Pu α disc stripped with HNO 3 /HCl for 241 Pu measurement by LSC

21 14 C Analysis Separate solid sample taken when sampling Typically < 2g for analysis Blank and std sample using inactive matrix for C carrier Reflux sample with in-situ chromic acid mixture. All inorganic and organic carbon converted to 14 CO 2 Acid wash prior to absorption in Carbosorb (Perkin Elmer) Prepare in calibrated volumetric flask Count with Permafluor E+ scintillant on Quantulus 1220 above 3 H window Internal 14 C standardisation and re-count

22 55 Fe Analysis 5.0ml sample + blank and QA std Initial Fe separation from main 60 Co and 63 Ni activation products Separate 55 Fe by extraction with di-isopropyl ether from 8M HCl. Back extract into water Precipitation of iron hydroxide and dissolution in phosphoric acid. Colourless solution reduces colour quenching in LSC Prepare in calibrated volumetric flasks Initial leach γ spec shows if 59 Fe present Count 1ml aliquot with 10ml Ultima Gold AB scintillant by LSC, otherwise 50ml counted on Canberra Packard BEGe γ spec

23 90 Sr Separation 5.0ml sample + blank and QA std. Add calibrated Sr carrier for final weight yield Initial oxalate pre-concentration then flame to carbonate. Remove main impurities by co-precipitation with H 2 S Separate from 45 Ca with fuming HNO 3 in an ice bath. Sr(NO 3 ) 2 precipitates Remove secondary impurities with BaCrO 4 and Fe(OH) 3 co-precipitations Separate 90 Y daughter and note Time = 0 Final SrCO 3 precipitation. Weigh for yield Dissolve in 0.5M HNO 3 and allow 90 Y to grow-in over 20 days minimum Count 1ml aliquot with 10ml Ultima Gold AB scintillant by LSC. Spike and re-count

24 Drum Total Activities by Radiochemistry Analyses give individual leach nuclide activities Bq/ml Calibrated volumetric flasks and sample weights leached give sample specific activities Bq/g ( 14 C already Bq/g) Calculate package activity from total sample weight of hotspot or % scaling factor Sum individual packages for total drum nuclide inventory Determine wastestream fingerprint nuclide % composition

25 Waste Checking Criteria WQCL results are compared with site declaration and compliance documents RSA 93 waste transfer & disposal authorisations Form D4 and D5 where applicable Wastestream fingerprint information LLWR Limits and Conditions for Acceptance (CFA) Compliance Level Assessment of Waste (CLAW) Compares measured and declared activities with authorisation limits Based on the Waste Receipt Monitoring Results Assessment Procedure (WRAP) methodology developed by BNFL

26 Compliance Level Assessment of Waste (CLAW) Methodology 2 problems arise when assessing the accuracy of the consignor s declaration : NDT on the whole consignment only give results for γ & n emitters DT measurements only made on a small number of selected samples Methodology provides a means of comparing measured and declared activities with authorisation limits on a scale which becomes more demanding as activities approach the limits (4GBq/t α & 12GBq/t β/γ) Calculations are based on BNFL WRAP methodology but are extended to include radiochemical results and site specific annual limits

27 Derivation The measurement ratio (MR) is defined as measured activity declared activity (M/D) MR < 1 (activity over-declared c.f. WQCL measurement) MR = 1 (measured value = declared value) MR > 1 (activity under-declared c.f. WQCL measurement) This is compared with the Acceptable Range Factor (ARF) defined as Site Limit Measured activity ( Ls/M) The factor is arbitrary but ensures that greater significance is given to higher activities

28 ARF FAIL UNDER-DECLARED MR = M/D PASS 1/ARF FAIL OVER-DECLARED Activity Site Limit = Ls /10

29 Site Limits and Uncertainties Annual disposal limits are defined in Site Authorisations for each of the waste categories e.g. Uranium, Radium Thorium-232, Other alphas Carbon-14, Iodine-129, Tritium Cobalt-60, Other betas, Other short-lived betas The CLAW assumes a nominal 10 consignments/year unless otherwise specified and defines a consignment limit = Ls/10 The uncertainty (U) in the WQCL measurement is either added or subtracted to give a value for MR which is closest to unity this gives the benefit of the doubt to the Consignor

30 Extended Assessments Where measurements are possible for every drum in a consignment e.g. 60 Co and 137 Cs by SGS, the level of compliance is simple to assess In the example the amount of 60 Co in the waste was grossly over-estimated COBALT Results based on SGS total i.e no extrapolation Details Symbol Value (Bq) Declared (D4) D 3.00E+07 Measured M 4.75E+04 Uncertainty (+/-) on M U 1.54E+03 De minimis dm 2.00E+06 Calculations (M+U)/D MR (M-U)/D MR Measurement Ratio MR WRAP limit Ld 2.00E+09 CLAW limit Ls 3.00E+09 SQRT(Ld/M) ARF SQRT(M/Ld) 1/ARF SQRT(Ls/M) ARF SQRT(M/Ls) 1/ARF RESULTS M -U > D? NO WRAP Pass/Fail? WRAP FAIL CLAW Pass/Fail? CLAW FAIL

31 Extended Assessments (2) For DT results however, an assessment may still be made by extrapolating the result from a single drum to all other drums from the same wastestream in the consignment using the waste consignor s wastestream fingerprint In the following example 2 calculations are shown for 14 C The first assumes that all the 14 C is in the drums that were sampled (unlikely). Although the measured activity (15.3 MBq) was greater than declared (7.92 MBq) when the uncertainty is subtracted the MR lies just within the acceptable range In the second example the total 14 C is estimated by extrapolation using the consignor s wastestream fingerprint and a marker radionuclide, in this case 137 Cs

32 CARBON-14 Note: This radionuclide has been identified by the EA as potentially important for the LLWR post-closure risk 1. Results based on DT results of drums sampled only 2. Results based on extrapolation of DT samples i.e no extrapolation using consignors waste stream fingerprint doc Details Symbol Value (Bq) Details Symbol Value (Bq) Declared (D4) D 7.92E+06 Declared (D4) D 7.92E+06 Measured M 1.53E+07 Measured M 3.74E+07 Uncertainty (+/-) on M U 1.60E+06 Uncertainty (+/-) on M U 4.00E+06 De minimis dm 5.00E+04 De minimis dm 5.00E+04 Calculations Calculations (M+U)/D MR (M+E)/D MR (M-U)/D MR (M-E)/D MR Measurement Ratio MR Measurement Ratio MR WRAP limit Ld 5.00E+07 WRAP limit Ld 5.00E+07 CLAW limit Ls 5.00E+07 CLAW limit Ls 5.00E+07 SQRT(Ld/M) ARF SQRT(Ld/M) ARF SQRT(M/Ld) 1/ARF SQRT(M/Ld) 1/ARF SQRT(Ls/M) ARF SQRT(Ls/M) ARF SQRT(M/Ls) 1/ARF SQRT(M/Ls) 1/ARF RESULTS RESULTS Total (M-U) > D? YES Total (M-U) > D? YES WRAP Pass/Fail? WRAP PASS WRAP Pass/Fail? WRAP PROB' FAIL CLAW Pass/Fail? CLAW PASS CLAW Pass/Fail? CLAW PROB' FAIL

33 Reporting CLAW assessments are made for each of the radionuclide groups declared by the Consignor and measured by WQCL Key radionuclides for the LLWR post-closure safety case are highlighted Qualitative findings such as the presence of prohibited items such as aerosols and free liquids are included together with general aspects such as container/drum condition, labelling, documentation and weight or dose rate discrepancies The CLAW provides a way of assessing the level or degree of compliance of LLW assessed at WQCL A CLAW assessment is included as an appendix to the consignment report provided to the EA

34 Quality Assurance All operations at WQCL are carried out within a QA system The QA system and all key tests are accredited by UKAS to BS EN ISO/IEC 17025: 2005 Certificate of Test included as appendix The Laboratory is also accredited to ISO 9001: 2000 and ISO 14001: 2004

35 Non-Compliant Waste - Aerosols

36 Non-Compliant Waste Free Liquids, Solvents, Adhesives

37 Non-Compliant Waste Damaged Drums

38 Contact Details AMEC Nuclear UK Limited, UKAEA Winfrith Site, Waste Quality Checking Laboratory, Building A512, Dorchester, Dorset, DT2 8WQ Tel: Fax: Laboratory Manager Steve Daish ( ) Senior Radiochemist Chris Dale ( )