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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: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 - 60
1. 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 & Clearancedo NOT apply !
Dir. 96/29
Third category:
Work activities
Presence of natural radiation sources.
e.g. radon indwelling
e.g. Phosphateindustry
5
Clearance, exemption and exclusion
Radioactivesource
Regulatory control
Residual material
Clearanceyes
General clearanceSpecific clearance
No
radioactive waste
management
Exclusion Exemption
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 pathwaysE.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 & handling consumer 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 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
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: 32.03.0KThRa CCC
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 INuclear10 µSv/a
RP 122 part IINORM300 µSv/a !!!
Exemption level(K-40 100 Bq/g)
Exemption level
Clearance level(K-40 1 Bq/gRa-226+ 0.01 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 = ExemptionNORM = Nuclear
One unique set ofClearance-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
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
PaintingContamination ()
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
HPGe
HPGe
HPG
Instruments
Validations
Characterisation- Assumptions- conditions
Methodology:1. Certificate2. Methodology3. Validation4. QA
36
Methodologyrequest for clearance
Methodology 1
Methodology 3
Methodology 2
request 1
request 2
request n
request 1
request 1
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
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 mentform
Surface contamination measure- beta- 100 cm²
Surface contamination measure- beta- 100 cm²
40
Flat surface with 2 hand held monitors
• 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".
No categories
of material:
1. water or air as
transportation vector
2. decontamination..
41
Hand held monitor (dual probe)Setting of optimal HV
0
10
20
30
40
50
60
70
80
500 700 900 1100 1300
alpha source
beta channel
alpha channelHV
cps
0
10
20
30
40
50
60
70
80
500 600 700 800 900 1000 1100 1200 1300
beta source
beta channel
alpha channel
HV
cps
42
Gaz detector…
Va+b
plateau beta
Va
plateau alpha
cps
Volt
Mode: simultaneous
Mode a part
43
Hand held monitor (dual probe)
CalibrationRadionuclide Energy MeV Efficiency 4
C14 0,158 0% - 7 %
Co60 0,31 4% - 16%
Cs137 0,51 12% - 21%
Cl36 0,714 17% - 23%
Sr90 0,54+2,27 18% - 24%
Am241 5,48 13% - 0%
Wide area reference source1. Class 2 reference source (ISO
8769)2. C-14, Co-60, Cs-137, Cl-36, Sr-
90/Y-90 and Am-241.3. Instrument efficiency (ISO
7503-1) at 5 mm.
42
q1 q2 q3 q4 q5 q6
q2π
-nnη BGbrut
instrument
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 emittersControl with U-Source n°XQA number from to-channel ... cps ... cps-channel ... cps ... cps
Without Background!!!
45
Justification & validation
b0
2β1α1
b00β1α1 t
1
t
1.kk
4
1
t
1
t
1R.kklimitDetection
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 !!!!!!!!!
global.vue S CL(Bq/cm²) (cps)CL
46
Justification and validationISO 11929
Duration of the measurement - beta contamination
1. Clearance Level (CL) 5. Duration of the measurement (via curves)NL: 0,4 Bq/cm²
Alarm level: 6,8 cps
2. Probe:2.1 Identification:
QA n°: FC_IDP6.107
2.2 Surface probe (S)S: 100 cm²
2.3 Global efficiencyRadioisotopes: 80%Co-60, 20%Cs-137
hinstrument: 0,17 cps/Bq
Justification
K: 1 hglob: 0,17
2.4 Maximum back-groundR0: 12 cps
3. Mesurement3.1 Duration of the back-ground measurement
t0: 60 s
3.2 Facteur probability errork1-a 1,645
k1-b 1,645
4. Détermination du temps de mesure (si t0 est >>> tb)
tb: 3,56 seconds tb: 3 seconds
0
2
4
6
8
10
12
14
16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
cps
alarm
detection limit
47
Definition of the K factor
r
L
S2
rectangle
a
4L²
r²a²a2L
r²a4L²
r²2L
2rL
r²arcsin2aL
12aLtriangle2S1
hmoy
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
4L²
r²a²a2L
r²a4L²
r²2L
2rL
r²arcsin-)4L²
r²(r2a)(L2aL
1hmoy
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 Efficiency Duration (s) Alarm (cps)20 % Cs-137 17 % 3.1 s 6.8 cps100 % Cs-137 21 % 2.1 s 8.4 cps0 % Cs 137 16 % 3.4 s 6.4 cps
Assumption Efficiency Duration (s) Alarm (cps)20 % Cs-137 6 % 21 s 2.4 cps100 % Cs-137 12 % 6 s 4.8 cps0 % Cs 137 4 % 46 s 1.6 cps
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
HPGe
HPGe
GONo-GO
Hot spot check
~200 kg
Other evacuation route
- Waste
- Decontamination
20 kg
52
Step 1: Control
globb0
2β1α1
b00β1α1 η(Bq) hotspot'A'
t
1
t
1.kk
4
1
t
1
t
1R.kklimitDetection
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
Spectra of Plastic-Detectors (22x22cm2; d=10cm)
0
5
10
15
20
25
30
35
40
45
50
0 500 1000 1500 2000 2500
Energy in keV
Rn
et(C
o),
Ba
ckg
rou
nd
in
1/s
0
20
40
60
80
100
120
140
160
180
200
Rn
et(C
s) i
n 1
/s
7*Background Co-60 Cs-137
Co-60
1
Detect. 1
2
Detect. 2
Cobalt Coincidence Measurement
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
8
7
9
10
11
12 13
14
7
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
Point source CCM Co-60 ROI Cs-137 IntegralCentre of detector 170 % 150 % 150 % 140 %in the blind corner 30 % 50 % 50 % 60 %
Test in extreme conditions (point source)
Source CCM Co-60 ROI Cs-137 Integral mass 13 – 23 kg 90 % to 190 % 100 % to 150 % 100 % to 140 % 100 % to 120 % wood 160 % to 230 % 130 % to 160 % 130 % to 160 % 120 % to 140 % cable 150 % to 230 % 130 % to 160 % 130 % to 160 % 120 % to 140 % plastic 90 % to 200 % 100 % to 160 % 130 % to 160 % 100 % to 140 %
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 systemStatistic approach
Alarm = CLuncertainty 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
Co-ROI
Intergal
60 %K-40
40 %K-40
10 %Ba-13390 %
Ba-133
KeV
cpsActivation 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 ratioin the integral channel
0.10
0.11
0.12
0.13
0.14
0.15
0.16
0.17
0.18
0.19
0.20
%Co
CL
In
t
) 1ε and 14.0ε ; 4.0ε CoBaCs
)A(AA
Aet r
)A(AAA
r; )A(AA
Ar
BaCsCo
CoCo
BaCsCo
BaBa
BaCsCo
CsCs
Integral channel: Efficiency correction factor
ratio
Alarm:
y
y
x
x
Co
Co
yyxxCoscreen
CL
r
CLr
CLr
εrεrr
(g) massA
61
Alarm level if function of the isotopic ratio
CL rCo rCs rBa AlarmBq/g
AlarmBq
Real activityBq
RealactivityCo
Realactivity Cs
Realactivity Ba
prev. 0.8 0.2 0 0.21 4190 4762 3810 952 0prev. 0.6 0.4 0 0.22 4471 5882 3529 2353 0prev. 1 0 0 0.20 4000 4000 4000 0 0prev. 0 1 0 0.40 8000 20000 0 20000 0prev. 0.8 0.1 0.1 0.21 4141 4848 3879 485 485prev. 0.3 0.5 0.2 0.26 5151 9756 2927 4878 1951Act. 0.8 0.2 0 0.21 4293 4878 3902 976 0Act. 0.6 0.4 0 0.24 4750 6250 3750 2500 0Act. 0.8 0.1 0.1 0.21 4191 4908 3926 491 491Act. 0.3 0.5 0.2 0.29 5867 11111 3333 5556 2222
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
67
36
100
79
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 Q²calibration
1. Adjustment of the amplifiers gainGamma 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 - 1.83 g/cm³
• approximation of homogeneous distribution of activity
66
Spectroscopy HPGe detectors Q²Errors
1. Error due to systematic variation of the background.
2. Error due to the unknown material composition3. Error caused by activity distribution4. Error caused by the filling height of the drum.
Errors are much more important for:1. low energy gamma emitters 2. high density of matrix3. 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
10 cmposition 1
position 2
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)
Demolition
Demolished
Clear
1. Clearance – massique
TABLE 3 (Cs-137: 1 Bq/g; Co-60 0.1 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) 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 < 100 Tons/year -> 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. (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 5725-2: 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
108-Ag activity of lead samples
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
0701
0707
0713
0716
0403
0409
0412
0103
0109
0115
0118
0305
0311
0315
0501
0507
0513
0516
0605
0611
0614
0205
0210
0213
R103
R202
R301
R305
Sample number
108-
Ag
(Bq/
kg)
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)
Sb-125 activity in lead samples
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0701
0707
0713
0716
0403
0409
0412
0103
0109
0115
0118
0305
0311
0315
0501
0507
0513
0516
0605
0611
0614
0205
0210
0213
R103
R202
R301
R305
Sample number
Sb-1
25 (
Bq/
kg)
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 ~ 0.001 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…
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 !!!
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