Procedures for the Release of Sites

Transcription

1 Procedures for the Release of Sites Dr. J. Feinhals DMT Dr. M. Bothe VKTA IAEA Regional Workshop on Clearance of Decommissioning Waste Bangkok, 6-9 Nov. 2012

2 Research Site Rossendorf Verein für Kernverfahrenstechnik und Analytik Rossendorf e.v. (VKTA) Helmholtz Center Dresden-Rossendorf) 1,5 km 2

3 NPP Greifswald

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5 Radiation survey and site investigation process

6 radiation survey and site investigation process 6 principal steps: 1. site identification 2. historical site assessment 3. scoping survey 4. characterisation survey 5. remedial action support survey 6. final status support survey What is already available?

7 radiation survey and site investigation process 6 principal steps: 1. site identification 2. historical site assessment 3. scoping survey 4. characterisation survey 5. remedial action support survey 6. final status support survey Collection of data about installations, emissions, contamination, conceptual model

8 radiation survey and site investigation process 6 principal steps: 1. site identification 2. historical site assessment 3. scoping survey 4. characterisation survey 5. remedial action support survey 6. final status support survey Classification, estimation of effort for remediation

9 radiation survey and site investigation process 6 principal steps: 1. site identification 2. historical site assessment 3. scoping survey 4. characterisation survey 5. remedial action support survey 6. final status support survey Determination of extent of contamination, selection of instrumentation

10 radiation survey and site investigation process 6 principal steps: 1. site identification 2. historical site assessment 3. scoping survey 4. characterisation survey 5. remedial action support survey 6. final status support survey Support of remediation actions

11 radiation survey and site investigation process 6 principal steps: 1. site identification 2. historical site assessment 3. scoping survey 4. characterisation survey 5. remedial action support survey 6. final status support survey Proof of compliance with criteria for release of site

12 1. site identification site identification: typical performed before decommissioning known use of radioactive material potential former use of radioactive material environmental settings geology hydrogeology hydrology meteorology

13 radiation survey and site investigation process 6 principal steps: 1. site identification 2. historical site assessment 3. scoping survey 4. characterisation survey 5. remedial action support survey 6. final status support survey

14 2. historical site assessment collection of the knowledge about the installation particularly: kind of installation historic and current usage system boundaries buildings materials activated and contaminated areas migration pathways water cycles waste and waste water steam aerosols dust leakages

15 2. historical site assessment sources: licenses, permits, authorisations operating records interviews current employees previous employees

16 2. historical site assessment evaluation of historical site assessment data identify: potential contaminants potentially contaminated areas potentially contaminated media surface soil subsurface soil and media surface water ground water structures

17 potential contaminants (examples) activation nuclides: beta: H-3, C-14, Fe-55, Ni-63 gamma: Mn-54, Co-60, Ag-108m, Ag-110m, Sb-125, Cs- 134, Ba-133, Eu-152, Eu-154, Eu-155 fission products: beta: Sr-90 gamma: Cs historical site assessment actinides: alpha: isotopes of U, Pu, Am, Cm beta: Pu-241 gamma: Am-241

18 2. historical site assessment develop a conceptual model of the site site diagram known contamination suspected contamination potential reference areas classification similar areas current and past site characteristics anticipated future use identify data gaps

19 2. historical site assessment professional judgement Are data: unavailable unreliable conflicting too costly or time consuming to obtain? based on: technical knowledge professional experience assumptions, algorithms and definitions by experienced experts without potential conflict of interests with expertise in a required topic with objectiveness

20 radiation survey and site investigation process 6 principal steps: 1. site identification 2. historical site assessment 3. scoping survey and preliminary survey considerations 4. characterisation survey 5. remedial action support survey 6. final status support survey

21 valid for all surveys preliminary survey considerations decommissioning criteria regulatory agencies establish dose standards based on risk considerations clearance levels are calculated by analysis of various pathways and scenarios (direct radiation, ingestion, inhalation etc.) clearance levels are expressed as surface or mass specific activity (Bq/cm² or Bq/g) for each nuclide clearance levels may be general or site-specific additional conditions for implementing the clearance levels, e.g.: statistical criteria averaging area or mass consideration of background

22 preliminary survey considerations identify contaminants and establish clearance values identify potential radionuclide contaminants determine the relative ratios of nuclides (= nuclide vector ) calculate the clearance levels for nuclide mixtures according to relative ratios of nuclides (e.g. Sr-90 to Cs-137) relative ratios of 2 nuclides = scaling factors relative ratios of a mixture = nuclide vector application of the sum formula or unity rule : a 1 CL 1 + a 2 CL a n CL n 1 where a i CL i specific activity of nuclide i clearance level of nuclide i

23 preliminary survey considerations classification of areas by contamination potential Class 1: known or potential radioactive contamination above clearance level former contamination control areas areas with remedial actions locations with known leaks or spills burial or disposal sites waste storage sites Class 2: possible radioactive contamination below clearance level transport routes areas with handling of low concentrations of radionuclides perimeter of former contamination control areas Class 3: no radioactive contamination expected buffer zones around class 1 or class 2 areas

24 preliminary survey considerations select background reference areas some radionuclides may occur at significant levels as part of background in the media of interest (soil, building materials etc.) natural radionuclides K-40 decay series of U-238 U-235 Th-232 H-3 C-14 artificial radionuclides (nuclear weapons fallout, Chernobyl) Cs-137 Sr-90

25 preliminary survey considerations select background reference areas reference area should have similar characteristics as the survey unit: physical chemical geological radiological biological selected from: non-impacted areas not influenced by handling of radioactive materials pay attention to variation of background values different areas different materials

26 Example: NPP Greifswald Consideration of Cs-137 and Sr-90 from fallout (Chernobyl and nuclear weapon test ) According to German regulation (RPO) for the release of sites only those nuclides have to be considered, which have their origin in the operation of the site. Therefore, Cs-137 resulting from Chernobyl fallout and Sr-90 due to nuclear weapon tests can be neglected. But how can be distinguished between Cs-137 from operation and Cs-137 from fallout?

27 Example: NPP Greifswald Consideration of Cs-137 and Sr-90 from fallout (Chernobyl and nuclear weapon test ) NPP- Greifswald reference areas In-situ-gammaspectrometry measurements were performed around NPP Greifswald at 1. Westbogenstr. (close to monitored area) 2. side area of open ditch for release of liquid effluents (close to monitored area) 3. peninsula Struck (1 km north of turbine hall) 4. Peenemünde (island Usedom) approx. 25 km from NPP 5. Wackerow approx. 25 km distance from NPP

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29 Example: NPP Greifswald Consideration of Cs-137 and Sr-90 from fallout (Chernobyl and nuclear weapon test ) Requirements for selection of reference areas: reference areas identical to NPP areas (grass, distance to trees, sandy soil with density 1.3 g/cm³ definition of extension of reference areas ( m²) definition of measurement points in reference areas (4% of total area measured) In total 75 measurements were performed by in-situgammaspectrometry. In addition soil samples were analysed at every reference area.

30 Example: NPP Greifswald Consideration of Cs-137 and Sr-90 from fallout (Chernobyl and nuclear weapon test ) Results determination of effluents during operation for reference areas 300 Bq/m² average value on all reference areas reduced by value for effluents Bq/m² (0,31 Bq/cm² or 0,047 Bq/g) This value is approx 50% of the clearance value of Cs-137 for reuse of land areas. Measured values of areas on site can be reduced by this value!

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32 identify survey units preliminary survey considerations physical areas common radiological history consistent with exposure pathway modelling expect the same radiological characterisation

33 preliminary survey considerations select instruments and survey techniques depends on: radionuclides nuclide specific method gross measurement method direct measurements sampling detection sensitivities compared with clearance levels detection limit = % of clearance level best available technique materials and surfaces environmental conditions time costs

34 site preparation preliminary survey considerations consent for survey owners authority other affected parties marking the boundaries physical characteristics accessibility of the survey unit removing of equipment and materials accessibility to potentially contaminated surfaces underground objects pipes tanks possible contaminated material under buildings excavated areas before backfilling

35 clearing to provide access structures preliminary survey considerations remove of covers, disassembly, produce openings provide means to reach some surfaces (cranes, ladders etc.) remove furnishings and equipment special attention to piping, drains, sewers, sumps, tanks unsealed porous materials (e.g. concrete, wood) remove wall and floor coverings (including paint, wax or other sealer)

36 clearing to provide access land areas preliminary survey considerations remove ground covers (e.g. concrete) clearing of brush and weeds depends on potential contamination pay attention to underground structures contamination of materials to be cleared exposure of clearing personnel potential ecological damage

37 preliminary survey considerations reference coordinate system provide a level of reproducibility consistent with objectives of the survey grid of intersecting lines referenced to a fixed site location or benchmark types e.g. perpendicular pattern 3-dimensional polar intervals depend on objectives of the survey not dictate the spacing or location of measurement or sampling points

38 preliminary survey considerations reference coordinate system identification: e.g. alphanumerical distances to grid origin altitude or level in buildings GPS marking: e.g. paint (lines or intersections) wooden or metal stakes map or drawing of reference coordinate system

39 preliminary survey considerations reference coordinate system

40 preliminary survey considerations reference coordinate system

41 quality assurance quality assurance project plan preliminary survey considerations initiated at the start of a project objectives reproducibility accuracy precision factors of bias, error and uncertainty sample collection methods handling and preparation of samples homogenisation and aliquots of laboratory samples field methods for scanning and direct measurements laboratory analytical process

42 quality assurance preliminary survey considerations quality control measurements and analysis number depends on: degree of assurance (level of confidence) variability of survey unit complexity of investigation (duration, number of samples, methods, personnel, laboratories etc.) experience (personnel, methods, survey design etc.) level of radioactivity how close the clearance level is to detection limit potential uncertainty

43 health and safety preliminary survey considerations radiation protection unexpected radioactivity ingestion, inhalation particularly during sampling industrial hazards (similar to construction sites) exposed electric installations excavation enclosed work space hazardous atmosphere (tanks, underground buildings etc.) working at heights identify, eliminate, avoid or minimize potential safety hazards

44 documentation preliminary survey considerations records about all measurements and sampling to assure reproducibility reference all locations to grid coordinates or fixed site features records about all deviations from the survey programme records about all additional activities convert all measurement data into the same units as clearance levels prior to evaluation

45 3. scoping survey objectives preliminary risk assessment site priorisation check and correct classification estimate variability identify non-impacted areas (appropriate for reference areas?) estimate level of effort for remediation information for planning of more detailed surveys may used as final status survey for Class 3 areas if detection sensitivities are in compliance with release criterion

46 3. scoping survey methods surface scanning surface activity measurement (limited number) sampling (limited number to check the variability) background activity judgement measurements and sampling in areas likely to have accumulated radioactivity

47 3. scoping survey evaluating results identify radionuclides identify locations and general extent of radioactivity estimate variability adjust clearance levels (alarm values of device based on nuclide vector and average area) determine need for additional action (none, remediate, more surveys) prepare report

48 Using average parameter Standard geometry 1 m² always sufficient! Demolition Reuse

49 radiation survey and site investigation process 6 principal steps: 1. site identification 2. historical site assessment 3. scoping survey 4. characterisation survey 5. remedial action support survey 6. final status support survey

50 4. characterisation survey objectives determine the nature and extent of radioactive contamination evaluate remediation alternatives: unrestricted use restricted use onsite disposal off-site disposal input to pathway analysis, dose or risk assessment models for determination of site specific clearance levels (Bq/g, Bq/cm²) estimate occupational and public health and safety impacts during decommissioning re-evaluate the initial classification of survey units evaluate potential reference areas

51 4. characterisation survey objectives input to final status survey design radionuclides relative ratios of radionuclides ( nuclide vector ) concentration ranges and variances spatial distribution select instrumentation based on necessary detection limits

52 4. characterisation survey methods surface scanning measurements one category may sufficient surface activity dose rate in-situ-gammaspectrometry sensitivity appropriate to clearance levels data may be used for final status survey sampling (surface and subsurface) combination of direct measurements and sampling investigate the change of nuclide ratios to the depth lateral and vertical extent of contamination

53 4. characterisation survey methods site specific additional investigations surface water sediments ground water (also hazardous substances)

54 evaluating results 4. characterisation survey confirm and add radionuclides evaluate nuclide ratios ( nuclide vector ) identify locations and extent for remediation determine need for additional measurements prepare report

55 radiation survey and site investigation process 6 principal steps: 1. site identification 2. historical site assessment 3. scoping survey 4. characterisation survey 5. remedial action support survey 6. final status support survey

56 5. remediation action support survey objectives support remediation actions location of residual radioactivity extent of residual radioactivity depth of residual radioactivity determine when ready for final status survey update estimates for planning final status survey

57 5. remediation action support survey methods in real-time mode, because during waiting for results the environment can change typical one simple radiological parameter direct measurements are preferred but it depends on radionuclides field laboratories and screening techniques may be acceptable difficult to correlate scanning results with radionuclide concentration in soil measurement of excavated materials is possible to check the residual radioactivity in the soil in situ set investigation level for in-field decisions (< clearance level) for expediency and cost effectiveness no accurate data (but then you need the accurate data later) or designed to meet the objectives of final status survey (even you do not need it, because you have to remediate again)

58 evaluating results 5. remediation action support survey if measured parameter is above investigation level continue with remediation if measured parameter is below investigation level go to final status survey data for planning final status survey estimate variance, it may changed by remediation

59 radiation survey and site investigation process 6 principal steps: 1. site identification 2. historical site assessment 3. scoping survey 4. characterisation survey 5. remedial action support survey 6. final status support survey

60 6. final status survey objectives demonstrate compliance with criteria for release for unrestricted use for use with designated limitations demonstrate that all radiological parameters do not exceed clearance levels

61 6. final status survey survey design number and locations of measurements and sampling points depends on: variance confidence level nuclide in background or not selection and implementation of survey techniques selection of instrumentation quality assurance measures discussion with regulatory authority concerning logistics for confirmatory or verification surveys (performed by regulatory authority or independent expert contracted by regulatory authority

62 6. final status survey methods scanning Class 1: 100 % Class 2: % (systematically and judgement) Class 3: judgement (areas with greatest potential of contamination) activity measurements number according to statistical demands sampling and analysis values above investigation level further investigation reclassification remediation resurvey

63 6. final status survey evaluating results comparison with clearance levels application of statistical tests contaminant not in background: Sign test contaminant in background: Wilcoxon Rank Sum test define Type I decision error = false positive (α) define Type II decision error = false negative (β) if release criterion has been exceeded: remediation resurvey other actions in agreement with regulatory agency

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66 6. final status survey report stand alone document results of all measurements, sampling and analysis additional remediation actions all information for re-creation and evaluation should independently reviewed should be approved by designated person (or persons) capable of evaluation all aspects prior to release

67 Some examples 1. ditches before backfilling 2. areas after backfilling of ditches 3. areas after covering Helmholtz Center Dresden-Rossendorf

68 1. Area in front of building 91 after removal of pipes before backfilling the ditches Aim: release of area partly more than 80 cm below future level of surface Clearance measurements: total measurement by surface contamination monitor (LB 124) sampling on 7 areas with 45 to 96 m² mix of 10 to 13 single samples depth of sampling 20 cm analysing of samples gammaspectrometry (Co-60, Cs-137, Eu-152, Eu-154) LSC (Sr-90)

69 Area in front of building 91 after removal of pipes

70 Area in front of building 91 after removal of pipes

71 Area in front of building 91 after removal of pipes

72 Area in front of building 91 after removal of pipes

73 Result of all clearance measurements all samples are below clearance values (less than 10%)

74 2. Release of areas after backfilling of ditches Area behind building 8d after backfilling of ditches Aim: release of area after single case decision by authority clearance measurements by in-situ gammaspectrometry average area 100 m² average mass 1 Mg 65 measuring points 2 nuclide vectors

75 Area behind building 8d after backfilling of ditches

76 Area behind building 8d after backfilling of ditches

77 Area behind building 8d after backfilling of ditches

78 Area behind building 8d after backfilling of ditches

79 Area behind building 8d after backfilling of ditches Results of the clearance measurements: nuclide vector 1 (Co-60) only in one measurement all other nuclide vector 2 one measurement above clearance value (129%) 4 partial measurements all values below clearance value (9-81%) =>

80 3. Area behind building 8d after covering Aim: release of area after covering with material from other objects of the site

81 Area behind building 8d after covering Clearance measurements by in-situ gammaspectrometry average area max. 100 m² (special permit) average mass 5 Mg (special permit) nuclide vector nuclide percentage clearance value: 0,011 Bq/g necessary detection limit: 0,0025 Bq/g

82 Area behind building 8d after covering Alternative 1: measurement of the total area grid 4m x 4m area of measurement 25 m² average area 10 m² 283 measurement points

83 Area behind building 8d after covering

84 Area behind building 8d after covering Alternative 2: randomized measurement grid 4 m x 4 m area of measurement 25 m² average area 10 m² 60 measurement points (choosen by random generator)

85 Area behind building 8d after covering

86 Area behind building 8d after covering Results: detection limit 0,0016 Bq/g only 6 measurements were above detection limit all measured values did not exceed the clearance value (< 41%)

87 Alternatives for the release of buildings Problems release of buildings with higher level of contamination is complicated high effort for decontamination large amounts of radioactive waste, which have to be treated properly according waste acceptance criteria

88 Alternatives for the release of buildings Concept of remediation of buildings with following safe enclosure Basics: decontamination of the building derivation of a remediation value, i.e. value for surface contamination above RPO value (e.g. some 20 Bq/cm²) safe enclosure of the building until activity is decayed and in compliance with de minimis dose concept demolition after release conventional reutilisation of concrete debris

89 Alternatives for the release of buildings Concept of remediation of buildings with following safe enclosure (2) remediation value limiting value for contamination on building surfaces depending on time of safe enclosure and nuclide vector

90 Alternatives for the release of buildings Radiological conditions of the concept: compliance of the remediation value makes sure, that potential doses are below the dose concept of some 10µSv/a for clearance, below the dose limit of 1 msv/a for the public during demolition, below the dose limit of 1 msv/a for workers without medical surveillance, below 1 msv/a, so no monitoring area is necessary during demolition.

91 Alternatives for the release of buildings Radiological conditions of the concept: Example For derivation of the remediation value the following nuclide vector was used: Co-60 50% Cs % Sr-90 5% Am-241 2% Clearance value for demolition: 4,6 Bq/cm² Remediation value considering a time of safe enclosure of 30 years 23,1 Bq/cm² of 50 years 37,4 Bq/cm²

92 Thank you for your attention!