Presentation on theme: "1 Chapiter 8 (part II) SITE CHARACTERIZATION Isabelle Majkowski SCKCEN Isabelle Majkowski, SCKCEN and chapter 7."— Presentation transcript:
1 Chapiter 8 (part II) SITE CHARACTERIZATION Isabelle Majkowski SCKCEN Isabelle Majkowski, SCKCEN 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: 1.Risk: mining & processing versus recycling & reuse. 2.Reduce waste to disposal facilities when risk is trivial.
3 Clearance measurements 1. Terminology - International scene 2. Development of clearance methodologies How to verify compliance to clearance level Example: -metal & material (plastic, small concrete elements) -Building -specific examples 4. Conclusions
4 Terminology ICRP Practice: Nuclear fuel cycle Exemption & Clearance 2. 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. Exemption & Clearance do NOT apply ! Dir. 96/29 Third category: Work activities Presence of natural radiation sources. e.g. radon in dwelling e.g. Phosphate industry
5 Clearance, exemption and exclusion Radioactive source Regulatory control Residual material Clearance yes General clearance Specific clearance No radioactive waste management ExclusionExemption 1. Different ways of avoiding regulatory resources being wasted 2. Minimizing the radiological risk to the population and the workers. No reporting if < E.L. Consumer product not in nuclear fuel cycle No reporting due to nature natural radiation sources Destination defined
6 Aim 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: 1.a maximum individual dose/practice of about 10 µ Sv/year (50 mSv/y skin dose) 2.a maximum collective dose/practice of 1 manSv/year to determine whether the material can be cleared from regulatory control or if other options should be examined.
7 Scenario s and pathways E.g. Metal scenario 2. Looks at the exposure pathway: ingestion inhalation external g radiation b-skin irradiation 1. Takes into account the entire sequence of scrap processing Transport & handlingconsumer goods … scrap yard, smelting or refinery manufacturing industry publicW: handling W+P: fume resuspended dust
8 Specific Clearance Level > General 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 view Specific clearance pathway should be recognised and approved by the regulatory authorities.
9 Clearance level (Bq/g) Criterium 10 µSv/a: Choice of scenarios Pathway of exposure Choice of parameter values Calculation of individual doses per unit activity concentration Identification of the limiting scenario and pathway Reciprocal 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 CL < EL RP 89 (metal scrap) + RP 113 (building rubble)
10 Need for international consensus 1. Transboundary movement 2. NORM industry 3. Car industry - waste industry
11 Transboundary movement General clearance: destination is not defined (Unconditional release) Specific clearance: traceability of the first step
12 NORM industry Naturally Occurring Radioactive Material Phosphate 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. NORM Nuclear
13 Car industry
14 International / EU recommendations and guidelines IAEA guidelines and recommendations Safety 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 EURATOM had 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).
15 EC 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. Nuclear NORM
16 EC publications - concrete 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 Rubble Average in concrete: Ra-226: 0.04 Bq/g Th-232: 0.03 Bq/g K-40: 0.4 Bq/g Index: 3 sets of CL: -reuse of demolition ? -demolition (M – D) -demolition (D – M) Approch to calculation of CL for building
17 EC publications - metal 89: Recommended radiological protection criteria for the recycling of metals from the dismantling of nuclear installations 117: Methodology and Models used to calculate individual & collective doses from the recycling of metals from the dismantling of nuclear installations. Recycling: 1 Bq/g Co & Cs Reuse: 1 Bq/g Co & 10 Bq/g Cs
18 EC 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
19 Implementation of the council directive 96/29 in the Belgium legislation - clearance 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. Annex 1B: art. 35: art. 18:
20 Implementation of the council directive 96/29 in the Belgium legislation - NORM Defines 3 groups of professional activities using Natural Sources Declaration - decision - authorisation Level professional 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 industry 1 mSv/year (worker) art. 4: art. 9: art. 20.3: RP 88: Recommendations for the implementation of Title VII BSS
21 Grey zone… Zone of free interpretation by the competent authority RP 122 part I Nuclear 10 µSv/a RP 122 part II NORM 300 µSv/a !!! Exemption level (K Bq/g) Exemption level Clearance level (K-40 1 Bq/g Ra Bq/g) Clearance level (K-40 oil-gas 100 Bq/g others 5 Bq/g) Ra-226+ oil-gas 5 Bq/g others 0.5 Bq/g) =
22 Trend… Full harmonization: Clearance = Exemption NORM = Nuclear One unique set of Clearance-exemption level Back to more Specificity Case by case clearance
23 Other consideration… Other risk health aspect : Chemical toxicity (industrial waste) Infectious risk Disposal: Management of materials should comply with the specific relevant regulations;
24 Forbidden 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 dilution -radioactive decay -Hot spot - Averaging value ? - Good practices
25 Clearance measurements Chapter 3. Development of clearance methodologies General approach to verify compliance to clearance level Examples of methodologies Metal & material (plastic, wood, concrete) Building Specific examples
26 Chapter 3: Development of clearance methodologies General approach to verify compliance to clearance level
27 Optimizing the development of Clearance methodologies Phase 1: Preliminary survey Phase 2: establishing methodologies that ensure compliance to clearance level Development of methodologies Selection of the instrument Validation of the instrument QA Material management program (before clearance)
28 Phase 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 streams theoretical calculations of induced activity measurement samples taken during operational and maintenance tasks after shut down of the plant -> preliminary monitoring survey.
29 Finger 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-137 and 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.
30 Finger 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 systems Same generation/transportation behavior Fission 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-60 or Cs-137 as key nuclide ? Co-60 key nuclide ratio constant
31 Phase 1: Preliminary monitoring survey- Instrumentation Gamma camera Collimated Digital image resolution: 768 x 572 pixels Standard field of view: 50° Spatial resolution: from 1° to 2.5° depending on energy and field of view CSI(Tl) detector Gamma scan the camera moves to scan the surface NaI(Tl) localization of radioactive sources, allowing perfect superimposition of the gamma and video images of the observed site:
32 Phase 1: Preliminary monitoring survey- Instrumentation Gamma spectrometry analyses - pic to pic - compton front localization of the depth of the radioactive sources Painting Contamination ( ) migration Cs-137 or washing with water, or inhomogeneneity in the wall
33 Phase 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 sample measurement of the sample Use to: confirm calculation, gamma cam. or historic knowledge Evaluate the scaling factor verification of the migration of radionuclide
34 Chapter 3: Development of clearance methodologies Methodologies….
37 Methodology request for clearance Chapter 1 : Certificat Scope (which material) Quantity of material Tracability system History (accident, leak,…) Radio elements to be measured Activation / contamination, Physico /chemical propreties Decontamination process Destination of the waste (code) Classical risk (asbestos) Clearance level (general or specific) Chapter 2: Methodology (flowshart + description) Chapter 3: Justification – validation Chapter 4: QA Chapter 5: Info to give in the request Chapter 6: Comments from FC, FANC & OA
38 Chapter 3: Development of clearance methodologies Examples: 1. Metal & material
39 methodology – flat & clean material dec. new path Agent R.P. IDPBW measure go – no go ? yes No measure Go – no go ? no go Go measure ment form Surface contamination measure - beta cm² Surface contamination measure - beta cm²
40 Flat surface with 2 hand held monitors Certificate Scope: flat clean surfaces ratio: 80% Co % Cs-137 (worst case assumption !!!) Measurement methodology surface 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". No categories of material: 1. water or air as transportation vector 2. decontamination..
41 Hand held monitor (dual probe) Setting of optimal HV
42 Gaz detector… Va+bVa+b plateau beta VaVa plateau alpha cps Volt Mode: simultaneous Mode a part
43 Hand held monitor (dual probe) Calibration Wide area reference source 1.Class 2 reference source (ISO 8769) 2.C-14, Co-60, Cs-137, Cl-36, Sr-90/Y-90 and Am Instrument efficiency (ISO ) at 5 mm. 4 2 q1q2q3q4q5q6
44 Hand held monitor (dual probe) Measurement Control with check sources ISO 7503: deviation < 25 % expected value SCK-CEN: deviation < 10 % beta emitters - 20 % alpha emitters
45 Justification & validation Detection limit (cps) < Clearance level (cps) Detection limit - ISO 11929: k 1-a, k 1-b : function of alpha and beta error R 0 : back-ground level (cps), t 0 : duration of the BG measurement (s), t b :duration of the measurement (s). Clearance level (cps) = alarm level (cps) CL: Clearance Level (Bq/cm²), S vue : surface sees' by the probe (cm²), 4 h glob :global efficiency of the instrument !!!!!!!!!
46 Justification and validation ISO 11929
47 Definition of the K factor ISO : k factor Surface density of absorbent layer Distance between source and detector SCK data bank maximum and minimum diameter that can be measured for a defined measurement duration Internal external attenuation with distance for our own probe measurement of concrete
48 Specific 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 neglected It is easy to discriminate when measuring by gamma spectrometry but not with an Handheld monitor So when measuring with an handheld monitor we need a Reference BG level
49 Biggest nightmare.. Painting & coverings in general
50 Assumption of the ratio… Assumption of the ratio (control alpha + beta) BG = 10 cps, no attenuation, dual probe Assumption of the ratio (control beta) BG = 10 cps, no attenuation, beta probe
51 methodology – scrap material HPGe GO No-GO Hot spot check ~200 kg Other evacuation route - Waste - Decontamination 20 kg
52 Step 1: Control k 1-a, k 1-b,R 0 en t 0 are fixed t b = 1 s h glob is fixed Detectable Hot spot activity = …. Bq
55 Calibration & control Every 6 month: Fine adjustment of the HV Calibration with Co-60 and Cs- 137 linear sources in a mass of metal tube of 17.5 kg Before use: control with point sources on a bloc of 7 kg criteria: deviation < 10 % expected value
56 Validation of the system Principle 1: As straight forward as possible Conditions of validation tests as close as possible to the measurement conditions
57 Validation of the system Test in extreme conditions (point source) Test in measurement conditions (17.5 kg) safe side: always overestimation of the activity if mass overestimation – less shielding if mass > 20 kg -> alarm in Bq alarm = 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 %
58 Validation of the system Statistic approach Alarm = CL uncertainty stat measure uncertainty position source uncertainty ratio uncertainty material - shielding Actual alarm level Alarm = CL Calculate (efficiency) on conservative assumptions Calculate (efficiency) on a less conservative assumptions real activity measured activity
59 Extention of the scope to concrete Activation product: Ba keV (37 %) 360 keV (56 %) 300 keV (22 %) efficiency: 16 % integral Natural element: K MeV (11 %) efficiency: 6 % integral !!! As = 0.05 Bq/g
60 Alarm in Bq/g f ct of the ratio in the integral channel Integral channel: Efficiency correction factor ratio Alarm:
61 Alarm 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.
62 Step 3: Spectroscopy HPGe detectors Q² Detectors: HPGe cooled by liquid nitrogen (2 fillings/week) Relative detection efficiency 20 % per detector Measurement chamber: shielding with 15 cm low BG steel turntable (10 rpm) drum 220 l load cell to measure weight from 10 to 400 kg Total weight: 8000 kg System already incorporated in QA approach (validation done)
63 Step 3: Spectroscopy HPGe detectors Q²
64 Step 3: Spectroscopy HPGe detectors Q²
65 Spectroscopy HPGe detectors Q² calibration 1.Adjustment of the amplifiers gain Gamma peaks of the 3 spectra are in the same ROI ROI 2. Calibration with 4 reference drums filled with material density 0.02 g/cm³ g/cm³ approximation of homogeneous distribution of activity
66 Spectroscopy HPGe detectors Q² Errors 1.Error due to systematic variation of the background. 2.Error due to the unknown material composition 3.Error caused by activity distribution 4.Error caused by the filling height of the drum. Errors are much more important for: 1.low energy gamma emitters 2.high density of matrix 3.and is mainly due to unknown activity distribution. 4.The energy of the gamma emitted by Cs-137 and Co-60 are high, and the general error will be small. 5.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.
67 Other devices… In Situ Object Counting System ISOCS: portable Ge detector, flexible portable shielding/collimator system, mathematical efficiency calculation software that requires no radioactive sources and data analysis software. Modelisation of the object to be measured Simple geometry of the object Assessment of the position of the source (homogeneous, linear punctual)
68 Other devices… Tunnels 2 detectors: position 1: 60° + 60° = 120° position 2: 180° + 60° = 240° 4 detectors position 1: 60° + 60° + 180° + 60 °= 360° position 2: 180° + 60° + 60°+60°= 360 ° 10 cm position 1 position 2
69 Chapter 3: Development of clearance methodologies Examples: 2. Building
: Building & building rubble Reuse or demolition ? (any purpose) Clearance – surfacique TABLE 1 (Cs-137: 1Bq/cm²; Co-60 1 Bq/cm²) Demolition Clear Demolished 1. Clearance – surfacique TABLE 2 (Cs-137: 10 Bq/cm²; Co-60 1 Bq/cm²) group 1 2. Demolition (rubble) Demolition Demolished Clear 1. Clearance – massique TABLE 3 (Cs-137: 1 Bq/g; Co Bq/g) 1. Demolition (rubble) NO DILUTION ! group 2 group 3
: Building & building rubble For the 3 options: NORM material have to be ignored No dilution ! Remove high level act. on the surface of the wall before demolishing No 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 m² 2. buildings for demolition only : tot A. in the structure/surface (1 Bq/cm² Co-60 – 10 Bq/cm² Cs-137) max averaging value = 1 m² 1&2 So 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 C.L. x 10. Activity projected on the surface
72 Phase 1: Preliminary monitoring survey- Building Longer phase than for metal & material Combination of Carrots & gamma spectrometry analyses Painting Contamination ( ) migration Cs-137 or washing with water, or inhomogeneneity in the wall
73 Methodologie based on sampling & laboratories measurement used when contamination consists mainly of low energy beta or alpha emitters on surface that are difficult to access. ( 3 H, 14 C, 55 Fe, 59 Ni, 63 Ni and 99 Tc) 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 ???
74 Chapter 3: Development of clearance methodologies Examples: 3. Specific examples -lead
75 Special methodologie Clearance of activated lead.
76 Special methodologie Clearance of activated lead.
77 Special methodologie Clearance of activated lead.
78 Special methodologie Clearance of activated lead.
79 Special 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/g Contamination: Co-60 & Cs-137 in the water.
81 Chapter 3: Development of clearance methodologies Other instruments…
82 Other 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
83 Passive & active neutron measurement Passive Neutron Drum Assay System Using large efficiency cell, instrumented by 3 He counters, measurement of Pu mass - Mass range covered 0 to 50 g of 240 Pu equivalent Detection limit: < 1 mg of 240 Pu equivalent Accuracy: better than 10% at 1g.
84 Conclusions… 1.Still a lot of international discussion on: Exemption / Clearance NORM / nuclear industry 2.Instrumentation market offers instruments that measure at Clearance level. 3.Unknown (preliminary phase) -> worse case scenario: longer measurement less clearance 4.Alpha contamination !!!