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Chapiter 8 (part II) SITE CHARACTERIZATION

Chapiter 8 (part II) SITE CHARACTERIZATION. Isabelle Majkowski SCK●CEN. Isabelle Majkowski, SCK●CEN and chapter 7. “Recycling and reuse” route. Decommissioning of nuclear facilities induces a huge amount of valuable material such as concrete and metal (very low cont.). Fundament:

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Chapiter 8 (part II) SITE CHARACTERIZATION

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  1. Chapiter 8 (part II)SITE CHARACTERIZATION Isabelle Majkowski SCK●CEN Isabelle 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.

  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 - 60 • 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 ! e.g. Phosphate industry Dir. 96/29 Third category: Work activities Presence of natural radiation sources. e.g. radon in dwelling

  5. Clearance, exemption and exclusion 1. Different ways of avoiding regulatory resources being wasted 2. Minimizing the radiological risk to the population and the workers. Radioactive source No reporting if < E.L. Consumer product not in nuclear fuel cycle No reporting due to nature natural radiation sources Exclusion Exemption Regulatory control Residual material yes No Clearance radioactive waste management General clearance Specific clearance 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: • a maximum individual dose/practice of about 10 µ Sv/year (50 mSv/y skin dose) • 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 pathwaysE.g. Metal scenario 1. Takes into account the entire sequence of scrap processing Transport & handling scrap yard, smelting or refinery consumer goods manufacturing industry … 2. Looks at the exposure pathway: ingestion inhalation external g radiation b-skin irradiation W+P: fume resuspended dust W: handling public

  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) CL < EL RP 89 (metal scrap) + RP 113 (building rubble) • 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

  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. Nuclear NORM B B Bq Bq 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.

  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 2000 - (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 Average in concrete: Ra-226: 0.04 Bq/g Th-232: 0.03 Bq/g K-40: 0.4 Bq/g Index: • 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 • 3 sets of CL: • reuse of demolition ? • demolition (M – D) • demolition (D – M) Approch to calculation of CL for building

  17. EC publications - metal Recycling: 1 Bq/g Co & Cs Reuse: 1 Bq/g Co & 10 Bq/g Cs • 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.

  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 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. ’

  20. Implementation of the council directive 96/29 in the Belgium legislation - NORM RP 88: Recommendations for the implementation of Title VII BSS 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:

  21. Zone of free interpretation by the competent authority Grey zone… =

  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 factorObservations – ISO norm Co-60 key nuclide ratio constant 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 ?

  31. Phase 1: Preliminary monitoring survey- Instrumentation localization of radioactive sources, allowing perfect superimposition of the gamma and video images of the observed site: 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)

  32. Phase 1: Preliminary monitoring survey- Instrumentation localization of the depth of the radioactive sources Gamma spectrometry analyses - pic to pic - compton front Contamination () Painting 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….

  35. Phase 2: Development of methodologies

  36. Methodologyrequest for clearance Methodology 1 request 1 request 2 request n Methodology 2 request 1 request 1 Methodology 3 request 2

  37. Methodologyrequest 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. Surface contamination measure - beta - 100 cm² measure Agent R.P. dec. new path yes go – no go ? Surface contamination measure - beta - 100 cm² No measure no go Go – no go ? Go measure ment form IDPBW methodology – flat & clean material

  40. Flat surface with 2 hand held monitors No categories of material: 1. water or air as transportation vector 2. decontamination.. • Certificate • Scope: flat clean surfaces • ratio: 80% Co-60 - 20% 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".

  41. Hand held monitor (dual probe)Setting of optimal HV

  42. cps plateau beta plateau alpha Volt Va Va+b Gaz detector… Mode: simultaneous Mode a part

  43. 2 4 q1 q2 q3 q4 q5 q6 Hand held monitor (dual probe) Calibration • Wide area reference source • Class 2 reference source (ISO 8769) • C-14, Co-60, Cs-137, Cl-36, Sr-90/Y-90 and Am-241. • Instrument efficiency (ISO 7503-1) at 5 mm.

  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: • k1-a, k1-b : function of alpha and beta error • R0 : 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), • 4 hglob: global efficiency of the instrument !!!!!!!!!

  46. Justification and validationISO 11929

  47. Definition of the K factor • ISO 11929 : 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 beta) • BG = 10 cps, no attenuation, beta probe • Assumption of the ratio (control alpha + beta) • BG = 10 cps, no attenuation, dual probe

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