Presentation is loading. Please wait.

Presentation is loading. Please wait.


Similar presentations

Presentation on theme: "Chapiter 8 (part II) SITE CHARACTERIZATION"— Presentation transcript:

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: 2. Intervention: Dir. 96/29
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. 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 No yes 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 pathways E.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: handling W+P: fume resuspended dust public

8 Specific 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 Phosphate industry - Oil industry.
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. B Nuclear Bq B NORM Bq

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
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 RP 88: Recommendations for the implementation of Title VII BSS
Implementation of the council directive 96/29 in the Belgium legislation - NORM RP 88: Recommendations for the implementation of Title VII BSS art. 4: art. 9: art. 20.3: 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)

21 = Grey zone… RP 122 part I Nuclear 10 µSv/a RP 122 part II NORM
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) Clearance level (K-40 1 Bq/g Ra Bq/g) (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 risk health aspect:
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 key nuclide ratio constant 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 Contamination () Gamma spectrometry analyses - pic to pic - compton front 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

35 Phase 2: Development of methodologies

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

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 Go – no go ? no go Go measure ment form Surface contamination measure - beta - 100 cm²

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

43 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 ) at 5 mm. 4 2 q1 q2 q3 q4 q5 q6

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 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 Painting & coverings in general
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

51 methodology – scrap material
GO No-GO Other evacuation route - Waste - Decontamination HPGe ~200 kg 20 kg Hot spot check

52 Detectable ‘Hot spot activity’ = …. Bq
Step 1: Control k1-a, k1-b ,R0  en t0 are fixed tb = 1 s hglob is fixed Detectable ‘Hot spot activity’ = …. Bq

53 ‘ Improved ’ Gross gamma counting CCM ESM FHT 3035

54 ESM - 4 channels Cobalt Coincidence Measurement

55 Calibration & control Every 6 month: Before use:
8 7 9 10 11 12 13 14 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 < 17.5 kg -> 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
Calculate (efficiency) on a less conservative assumptions Calculate (efficiency) on conservative assumptions Alarm = CL Alarm = CL uncertainty stat measure uncertainty position source uncertainty ratio uncertainty material - shielding Actual alarm level real activity measured activity

59 Extention of the scope to concrete
Activation product: Ba-133 80 keV (37 %) 360 keV (56 %) 300 keV (22 %) efficiency: 16 % integral Natural element: K-40 1.46 MeV (11 %) efficiency: 6 % integral !!! As = 0.05 Bq/g

60 Alarm in Bq/g fct of the ratio in the 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
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) 100 79 67 36

63 Step 3: Spectroscopy HPGe detectors Q²

64 Step 3: Spectroscopy HPGe detectors Q²

65 Spectroscopy HPGe detectors Q² calibration
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
Error due to systematic variation of the background. Error due to the unknown material composition Error caused by activity distribution Error caused by the filling height of the drum. Errors are much more important for: low energy gamma emitters high density of matrix and 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.

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
10 cm position 1 position 2 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 °

69 Chapter 3: Development of clearance methodologies
Examples: 2. Building

70 113 - 114: ‘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) 1. Clearance – massique TABLE 3 (Cs-137: 1 Bq/g; Co Bq/g) 1. Demolition (rubble) NO DILUTION ! group 2 group 3

71 113 - 114: ‘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) 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 < 100 Tons/year -> C.L. x 10. Activity projected on the surface

72 Phase 1: Preliminary monitoring survey- Building
Contamination () Painting Longer phase than for metal & material Combination of Carrots & gamma spectrometry analyses 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. (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 ???

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.

80 Activated 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) spectro bêta

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 3He counters, measurement of Pu mass - Mass range covered 0 to 50 g of 240Pu equivalent Detection limit: < 1 mg of 240Pu equivalent Accuracy: better than 10% at 1g.

84 Conclusions… Still a lot of international discussion on:
Exemption / Clearance NORM / nuclear industry Instrumentation market offers instruments that measure at Clearance level. Unknown (preliminary phase) -> worse case scenario: longer measurement less clearance Alpha contamination !!!

Download ppt "Chapiter 8 (part II) SITE CHARACTERIZATION"

Similar presentations

Ads by Google