Presentation on theme: "Chapiter 8 (part II) SITE CHARACTERIZATION"— Presentation transcript:
1Chapiter 8 (part II) SITE CHARACTERIZATION Isabelle MajkowskiSCK●CENIsabelle Majkowski, SCK●CEN and chapter 7
2“Recycling and reuse” route Decommissioning of nuclear facilities induces a huge amount of valuable material such as concrete and metal (very low cont.).Fundament:Risk: “mining & processing” versus “recycling & reuse”.Reduce waste to disposal facilities when risk is trivial.
3Clearance measurements 1. Terminology - International scene2. Development of clearance methodologies‘How to verify compliance to clearance level’Example:metal & material (plastic, small concrete elements)Buildingspecific examples4. Conclusions
4Terminology ICRP - 60 Practice: 2. Intervention: Dir. 96/29 Nuclear fuel cycleExemption & Clearance2. Intervention:Materials contaminated as a result of past practices which f.i. were not subject to regulatory control for any reason (e.g. military applications) or which were contaminated as a result of an accident.do NOT apply !e.g. PhosphateindustryDir. 96/29Third category:Work activitiesPresence of natural radiation sources.e.g. radon indwelling
5Clearance, exemption and exclusion 1. Different ways of avoiding regulatory resources being wasted2. Minimizing the radiological risk to the population and the workers.RadioactivesourceNo reportingif < E.L.Consumer productnot in nuclear fuel cycleNo reportingdue to naturenatural radiation sourcesExclusionExemptionRegulatory controlResidual materialNoyesClearanceradioactive waste managementGeneral clearanceSpecific clearanceDestinationdefined
6Aim of recommendations: minimise the radiological risks to workers and public The Safety Series N°89 that was issued jointly by the IAEA and the OECD-NEA in 1988 suggests:a maximum individual dose/practice of about 10 µ Sv/year (50 mSv/y skin dose)a maximum collective dose/practice of 1 manSv/yearto determine whether the material can be cleared from regulatory control or if other options should be examined.
7Scenario ’s and pathways E.g. Metal scenario 1. Takes into account the entire sequence of scrap processingTransport & handlingscrap yard, smelting or refineryconsumer goodsmanufacturing industry…2. Looks at the exposure pathway:ingestion inhalation external g radiation b-skin irradiationW: handlingW+P: fumeresuspended dustpublic
8Specific Clearance Level > General Clearance Level Destination NOT defined.Most restricted values – set of CL in RP 122.Specific Clearance Level:Destination defined – clear the material for a particular use.Only the first step of clearance is defined (concept of clearance = release from regulatory control – no traceability)Impact analyses – demonstrate through scenarios of exposure that the dose impact is acceptable for a health point of viewSpecific clearance pathway should be recognised and approved by the regulatory authorities.
9Clearance level (Bq/g) CL < EL RP 89 (metal scrap) + RP 113 (building rubble)Criterium 10 µSv/a:Choice of scenariosPathway of exposureChoice of parameter valuesCalculation of individual doses per unit activity concentrationIdentification of the limiting scenario and pathwayReciprocal individual doses yield activity concentrations corresponding to 10 µSv/a, rounded to a power of ten.Criterium 1 manSv/a:Takes into account the number of people exposed.For each radionuclide CL leads to collective dose <<< 1 manSv
10Need for international consensus 1. Transboundary movement2. NORM industry3. Car industry - waste industry
11Transboundary movement General clearance:destination is not defined(Unconditional release)Specific clearance:traceability of the first step
12Phosphate industry - Oil industry. NORM industryNaturally Occurring Radioactive MaterialPhosphate industry - Oil industry.Activity levels in NORM industry ~ very low level waste. But quantities are much higher.Strong campaign to regulate exposure to workers and public from both nuclear and Non-nuclear industries under the same radioprotection criteria.BNuclearBqBNORMBq
14International / EU recommendations and guidelines IAEA guidelines and recommendationsSafety Series No. 89 (Principles for the exemption of radiation sources from regulatory control)IAEA TEC DOC 855 recommends a set of unconditional clearance levels (in solid material).Council directive 96/29 EURATOMhad to be implemented in national legislation by May (few months ago)does not prescribe the application of clearance levels by competent authorities.RP N°122: Practical use of the concepts of clearance and exemption (recommendations of the Group of Experts established under the terms of Article 31 of the Euratom Treaty).
15EC publications - general 122: Practical Use of the Concepts of Clearance and exemption:part I: ‘Guidance on General Clearance Levels for practices’Part II: ‘Application of the Concept of exemption and Clearance to Natural Radiation Sources’.NuclearNORM
16EC publications - concrete Average in concrete:Ra-226: 0.04 Bq/gTh-232: 0.03 Bq/gK-40: 0.4 Bq/gIndex:112: Radiological protection principles concerning the natural radioactivity of building materials.113: Recommended radiological protection criteria for the clearance of building and building rubble from the dismantling of nuclear installations.114: Definition of Clearance Levels for the Release of Radioactivity Contaminated Building and Building Rubble3 sets of CL:reuse of demolition ?demolition (M – D)demolition (D – M)Approch to calculation of CL for building
17EC publications - metal Recycling:1 Bq/g Co & CsReuse:1 Bq/g Co& 10 Bq/g Cs89: Recommended radiological protection criteria for the recycling of metals from the dismantling of nuclear installations117: Methodology and Models used to calculate individual & collective doses from the recycling of metals from the dismantling of nuclear installations.
18EC publications - restauration 115: Investigation of a possible basis for a common approach with regard to the restoration of areas affected by lasting radiation exposure area result of past or old practice or work activity.124: Radiological protections with regard to the Remediation of areas affected by lasting radiation exposure as a result of a past or old practice or work activity
19Implementation of the council directive 96/29 in the Belgium legislation - clearance Annex 1B:art. 35:art. 18:‘ Set of Clearance level ’ ~ CL in RP 122’NO Ba-133 !!!!!Concentration Activity Level < CL (1B)measurement procedures conform to the Agency directives or approved by the Agency (and by C.P)(1st of march, list of released material to ONDRAF and Agency) Solid waste from nuclear installation of class 1, 2 or 3 or natural sources under art 9 that does NOT satisfy CL (given in annex 1B) request an authorisation by the agency. ’
20RP 88: Recommendations for the implementation of Title VII BSS Implementation of the council directive 96/29 in the Belgium legislation - NORMRP 88: Recommendations for the implementation of Title VII BSSart. 4:art. 9:art. 20.3:Defines 3 groups of professional activities using Natural SourcesDeclaration - decision - authorisationLevelprofessional activities involving exposition risk to the daughter product of radon (underground, caves, water treatment installation and place in a risk zone):effective dose > 3 mSv/year (worker & public)annual exposition to radon > 800 kBq.m-³.h (W & P)professional activities involving a risk of external exposition, ingestion or inhalation to natural radioactive sources (phosphate industry, extraction of earth…):effective dose >1 mSv/year (W&P)dose public > general dose limit for the public.Air craft industry1 mSv/year (worker)
21= Grey zone… RP 122 part I Nuclear 10 µSv/a RP 122 part II NORM Zone of freeinterpretationby the competentauthorityRP 122 part INuclear10 µSv/aRP 122 part IINORM300 µSv/a !!!Exemption level(K Bq/g)Clearance level(K-40 1 Bq/gRa Bq/g)(K-40oil-gas 100 Bq/gothers 5 Bq/g)Ra-226+oil-gas 5 Bq/gothers 0.5 Bq/g)=
22Trend… Full harmonization: Clearance = Exemption NORM = Nuclear One unique set ofClearance-exemption levelBack to more SpecificityCase by case clearance
23Other risk health aspect: Other consideration…Other risk health aspect:Chemical toxicity (industrial waste)Infectious riskDisposal:Management of materials should comply with the specific relevant regulations;
24Forbidden practices‘Deliberated dilution with non radioactive material to reach the clearance level is forbidden’RP 122 part I:“two factors generally lead to mitigate the radiological risk as time passes:spontaneous or technological dilutionradioactive decay”‘Hot spot’ - Averaging value ?Good practices
25Clearance measurements Chapter 3. Development of clearance methodologiesGeneral approach ‘to verify compliance to clearance level’Examples of methodologiesMetal & material (plastic, wood, concrete)BuildingSpecific examples
26Chapter 3: Development of clearance methodologies General approach ‘to verify compliance to clearance level’
27Optimizing the development of Clearance methodologies Phase 1: Preliminary surveyPhase 2: establishing methodologies that ensure compliance to clearance levelDevelopment of methodologiesSelection of the instrumentValidation of the instrumentQAMaterial management program (before clearance)
28Phase 1: Preliminary survey Planning: Inventory and distribution of the radionuclides likely to be present:Those data are obtained through:a good knowledge of the plant and its process streamstheoretical calculations of induced activitymeasurement samples taken during operational and maintenance tasksafter shut down of the plant -> preliminary monitoring survey.
29Finger print – Scaling factor Purpose is:to define nuclide to be measured to calibrate your instrument (gross gamma counting system or handheld monitor)to link between:nuclides that are easy to measure like Co-60 or Cs-137and DTM nuclides (Difficult To Measure), like pure alpha or beta emitters (Ni-63, C-14)Measuring DTM nuclides can be costly -> SF not to waste resources.
30Finger print – Scaling factor Observations – ISO norm Corrosion product nuclides (Ni-63, Nb-94 & Co-60)They originate from activation of reactor material released into the reactor coolant.They are insoluble metal element - deposited onto the surface of the plant systemsSame generation/transportation behaviorFission products nuclides,They originate from the fuel (nuclear fission or n° capture). So the scaling factor is not as constant.Cs-137 (easily soluble element – deposit less on the surface of heterogeneous waste) Sr-90 & alpha-emitters (low solubility)If Cs-137 = key nuclide (2 categories of waste (homo & heterogeneous waste)If Co-60 = key nuclide (Co-60 is insoluble like the DTM nuclide -> same transportation) – Cs-137 is easy to measure. Still need a fuel failure history to define the generation mechanism. No separation between homo & hetero.Co-60key nuclideratio constantCo-60 orCs-137 askey nuclide ?
31Phase 1: Preliminary monitoring survey- Instrumentation localization of radioactive sources, allowing perfect superimposition of the gamma and video images of the observed site:Gamma cameraCollimatedDigital image resolution: 768 x 572 pixelsStandard field of view: 50°Spatial resolution: from 1° to 2.5° depending on energy and field of viewCSI(Tl) detectorGamma scanthe camera moves to scan the surfaceNaI(Tl)
32Phase 1: Preliminary monitoring survey- Instrumentation localization of the depth of the radioactive sourcesContamination ()Gamma spectrometry analyses- pic to pic- compton frontPaintingmigration Cs-137or washing with water,or inhomogeneneity in the wall
33Phase 1: Preliminary monitoring survey- Instrumentation Samples – smear test:taken on a representative way or at places where the risk of contamination/activation is maximum.treatment of the samplemeasurement of the sampleUse to:confirm calculation, gamma cam. or historic knowledgeEvaluate the scaling factorverification of the migration of radionuclide
34Chapter 3: Development of clearance methodologies
37Methodology request for clearance Chapter 1 : CertificatScope (which material)Quantity of materialTracability systemHistory (accident, leak,…)Radio elements to be measuredActivation / contamination,Physico /chemical propretiesDecontamination processDestination of the waste (code)Classical risk (asbestos)Clearance level (general or specific)Chapter 2: Methodology (flowshart + description)Chapter 3: Justification – validationChapter 4: QAChapter 5: Info to give in the requestChapter 6: Comments from FC, FANC & OA
38Chapter 3: Development of clearance methodologies Examples:1. Metal & material
39methodology – flat & clean material dec.new pathAgent R.P.IDPBWmeasurego – no go ?yesNoGo – no go ?no goGomeasure mentformSurface contamination measure- beta- 100 cm²
40Flat surface with 2 hand held monitors No categoriesof material:1. water or air astransportation vector2. decontamination..CertificateScope: flat clean surfacesratio: 80% Co % Cs-137 (worst case assumption !!!)Measurement methodologysurface measured 2 times with 2 distinct handheld monitors and by 2 distinct operators.Release measurement procedure based on:ISO 11932: "Activity measurements of solid materials considered for recycling, re-use, or disposal as non-radioactive waste"ISO 7503: "Evaluation of surface contamination – Part 1: Beta-emitters (maximum beta energy greater than 0.15 MeV) and alpha-emitters".
41Hand held monitor (dual probe) Setting of optimal HV
42Mode: simultaneous Mode a part Gaz detector… cps Volt Va+b Va plateau betaVaplateau alphacpsVoltMode: simultaneousMode a part
43Hand held monitor (dual probe) Calibration Wide area reference sourceClass 2 reference source (ISO 8769)C-14, Co-60, Cs-137, Cl-36, Sr-90/Y-90 and Am-241.Instrument efficiency (ISO ) at 5 mm.42q1q2q3q4q5q6
44Hand held monitor (dual probe) Measurement Control with check sourcesISO 7503: deviation < 25 % expected valueSCK-CEN: deviation < 10 % beta emitters - 20 % alpha emitters
45Justification & validation Detection limit (cps) < Clearance level (cps)Detection limit - ISO 11929:k1-a, k1-b : function of alpha and beta errorR0 : back-ground level (cps),t0 : duration of the BG measurement (s),tb: duration of the measurement (s).Clearance level (cps) = alarm level (cps)CL: Clearance Level (Bq/cm²),Svue: surface ’sees' by the probe (cm²),4hglob: global efficiency of the instrument !!!!!!!!!
47Definition of the K factor ISO : k factorSurface density of absorbent layerDistance between source and detectorSCK data bankmaximum and minimum diameter that can be measured for a defined measurement durationInternalexternalattenuation with distance for our own probemeasurement of concrete
48Specific cases.. Measurement of tiles – ceramic Level of contamination very close to the clearance level in Bq/cm² -> so permanent alarm.According to RP 113, Natural radioactivity can be neglectedIt is easy to discriminate when measuring by gamma spectrometry but not with an Handheld monitorSo when measuring with an handheld monitor we need aReference BG level
49Painting & coverings in general Biggest nightmare..Painting & coverings in general
50Assumption of the ratio… Assumption of the ratio (control beta)BG = 10 cps, no attenuation, beta probeAssumption of the ratio (control alpha + beta)BG = 10 cps, no attenuation, dual probe
55Calibration & control Every 6 month: Before use: 8791011121314Every 6 month:Fine adjustment of the HVCalibration with Co-60 and Cs-137 linear sources in a mass of metal tube of 17.5 kgBefore use:control with point sources on a bloc of 7 kgcriteria: deviation < 10 % expected value
56Validation of the system Principle 1: As straight forward as possibleConditions of validation tests as close as possible to the measurement conditions
57Validation of the system Test in extreme conditions (point source)Test in measurement conditions (17.5 kg)safe side: always overestimation of the activityif mass < 17.5 kg -> overestimation – less shieldingif mass > 20 kg -> alarm in Bqalarm = detection limit -> software calculates the measurement time in function of the BG.Algorithm to calculate Cs-137 value do not work – With a Co-60 source the values measured in the Cs canal varies from – 280 % and + 40 %
58Validation of the system Statistic approach Calculate (efficiency)on a less conservativeassumptionsCalculate (efficiency)on conservativeassumptionsAlarm = CLAlarm = CLuncertainty stat measureuncertainty position sourceuncertainty ratiouncertainty material - shieldingActual alarm levelreal activitymeasured activity
59Extention of the scope to concrete Activation product: Ba-13380 keV (37 %)360 keV (56 %)300 keV (22 %)efficiency: 16 % integralNatural element: K-401.46 MeV (11 %)efficiency: 6 % integral !!!As = 0.05 Bq/g
60Alarm in Bq/g fct of the ratio in the integral channel Efficiency correction factorratioAlarm:
61Alarm level if function of the isotopic ratio Assumption of more Co-60 than Cs-137:If in reality there is more Cs-137 alarm level could had been higher.Radioelement with low efficiency have high CL, there is a kind of equilibrium.
62Step 3: Spectroscopy HPGe detectors Q² HPGe cooled by liquid nitrogen (2 fillings/week)Relative detection efficiency 20 % per detectorMeasurement chamber:shielding with 15 cm low BG steelturntable (10 rpm)drum 220 lload cell to measure weight from 10 to 400 kgTotal weight: 8000 kgSystem already incorporated in QA approach (validation done)100796736
65Spectroscopy HPGe detectors Q² calibration Adjustment of the amplifiers gainGamma peaks of the 3 spectraare in the same ROIROI2. Calibration with 4 reference drumsfilled with material density 0.02 g/cm³ g/cm³approximation of homogeneous distribution of activity
66Spectroscopy HPGe detectors Q² Errors Error due to systematic variation of the background.Error due to the unknown material compositionError caused by activity distributionError caused by the filling height of the drum.Errors are much more important for:low energy gamma emittershigh density of matrixand is mainly due to unknown activity distribution.The energy of the gamma emitted by Cs-137 and Co-60 are high, and the general error will be small.The detection limit for Co-60 and Cs-137 is of the order of some mBq/g for a 10 minutes count of a 200 l waste drum. Which is well below the Clearance Level.
67Other devices… In Situ Object Counting System ISOCS:portable Ge detector,flexible portable shielding/collimator system,mathematical efficiency calculation software that requires no radioactive sourcesand data analysis software.Modelisation of the object to be measuredSimple geometry of the objectAssessment of the position of the source (homogeneous, linear punctual)
71113 - 114: ‘Building & building rubble’ For the 3 options:NORM material have to be ignoredNo dilution ! Remove high level act. on the surface of the wall before demolishingNo limit on max total activity per year !1. building for reuse or demolition:tot A. in the structure/surface (1 Bq/cm² Co-60 & Cs-137)max averaging value = 1 m²2. buildings for demolition only:tot A. in the structure/surface (1 Bq/cm² Co-60 – 10 Bq/cm² Cs-137)1&2So only 1 criteria (Bq/cm² and not 2 bulk + surface)3. building rubble:Bq/g (0.1 Bq/g Co-60 & 1 Bq/g Cs-137)max averaging value = 1 Ton – if < 100 Tons/year -> C.L. x 10.Activity projected on the surface
72Phase 1: Preliminary monitoring survey- Building Contamination ()PaintingLonger phase than for metal & materialCombination of Carrots& gamma spectrometry analysesmigration Cs-137or washing with water,or inhomogeneneity in the wall
73Methodologie based on sampling & laboratories measurement used when contamination consists mainly of low energy beta or alpha emitters on surface that are difficult to access. (3H, 14C, 55Fe, 59Ni, 63Ni and 99Tc)Difficult to validate their representativity: taken & treatment.statistical analyses would be necessary to calculate the sampling density necessary to demonstrate compliance:Guidance: DIN 25457: ‘Activity measurement methods for the release of radioactive waste materials and nuclear facility components – part 6: Buiiding rubble & building.ISO : Accuracy of measurement methods and results – part 2: Basic method for the determination of repeatability and reproducibility of standard measurement method.smear test : efficiency ???
74Chapter 3: Development of clearance methodologies Examples:3. Specific exampleslead
75Special methodologie Clearance of activated lead.
76Special methodologie Clearance of activated lead.
77Special methodologie Clearance of activated lead.
78Special methodologie Clearance of activated lead.
79Special methodologie Clearance of activated lead. Activation of:Lead 971 mg/g (> 97%)Copper 315 µg/g (0.031%)Silver 8 µg/g (0.008%)Bismuth 200 µg/g (0.02 %)Other elements pewter (Sn) < 5µg/gContamination:Co-60 & Cs-137 in the water.
80Activated nuclides + contamination: Co-60 & Cs-137 Activation for 25 years & 16 years decay:Ag-108m & Ag-108 (CL Ag-108 m+: 0.1 Bq/g)Sb-125 & Te-125m (CL Sb-125+: 1 Bq/g)Sn-121m (T½ 55 ans) & fils Sn-121 (T½ 27 heures)spectrobêta
81Chapter 3: Development of clearance methodologies Other instruments…
82Other devices… Air ionisation measurement Passing a anode wire in the center of the tube -> use the tube as an ionisation chamber:detection: few Bq in 2 m in 30 secondes ~ Bq/cm³
83Passive & active neutron measurement Passive Neutron Drum Assay SystemUsing large efficiency cell, instrumented by 3He counters,measurement of Pu mass - Mass range covered 0 to 50 g of 240Pu equivalentDetection limit: < 1 mg of 240Pu equivalentAccuracy: better than 10% at 1g.
84Conclusions… Still a lot of international discussion on: Exemption / ClearanceNORM / nuclear industryInstrumentation market offers instruments that measure at Clearance level.Unknown (preliminary phase) -> worse case scenario:longer measurementless clearanceAlpha contamination !!!