Transcript 3.7 MB - eundetraf

Chapiter 8 (part II)
SITE CHARACTERIZATION
Isabelle Majkowski
SCK●CEN
1
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:
1. Risk: “mining & processing” versus “recycling &
reuse”.
2. Reduce waste to disposal facilities when risk is
trivial.
2
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
3
Terminology
ICRP - 60
1. Practice:
Nuclear fuel cycle
Exemption & Clearance
2. Intervention:
e.g. Phosphate
industry
Dir. 96/29
e.g. radon in
dwelling
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
4
do NOT apply !
Third category:
Work activities
Presence of natural
radiation sources.
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
due to nature
No reporting
if < E.L.
Exclusion
Exemption
Consumer product
Regulatory control
natural radiation sources
not in nuclear fuel cycle
Residual material
No
yes
Clearance
radioactive
waste
management
General clearance
Specific clearance
5
Destination
defined
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.
6
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
W: handling
W+P: fume
resuspended dust
external g radiation
7
public
b-skin irradiation
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.
8
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
9
Need for international
consensus
1. Transboundary movement
2. NORM industry
3. Car industry - waste industry
10
Transboundary movement
General clearance:
destination is not defined
(Unconditional release)
Specific clearance:
traceability of the first step
11
NORM industry
Naturally Occurring Radioactive Material
Phosphate industry - Oil industry.
•
•
Activity levels in NORM industry ~ very low
level waste. But quantities are much higher.
NORM
Nuclear
B
B
Strong campaign to regulate exposure to
workers and public from both nuclear and
Non-nuclear industries under the same
radioprotection criteria.
12
Car industry
13
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).
14
EC publications - general
122: Practical Use of the Concepts of
Clearance and exemption:
 part I: ‘Guidance on General Clearance Levels
Nuclear for practices’
 Part II: ‘Application of the Concept of
exemption and Clearance to Natural Radiation
NORM
Sources’.
15
EC publications - concrete
Average in concrete:
Ra-226: 0.04 Bq/g

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
Th-232: 0.03 Bq/g
K-40: 0.4 Bq/g
Index: C Ra  C Th  C K
0 .3
0 .2
3
3 sets of CL:
-reuse of demolition ?
-demolition (M – D)
-demolition (D – M)
Approch to
calculation of CL
for building
16
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.
17
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
18
Implementation of the council
directive 96/29 in the Belgium
legislation - clearance
Annex 1B: ‘ Set of Clearance level ’ ~ CL in RP 122’
NO Ba-133 !!!!!
art. 35:



art. 18:
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. ’
19
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
20
 1 mSv/year (worker)
Grey zone…
RP 122 part I
Nuclear
10 µSv/a
RP 122 part II
NORM
300 µSv/a !!!
Zone of free
Exemption level
(K-40 100 Bq/g)
interpretation
by the competent
authority
Clearance level
(K-40 1 Bq/g
Ra-226+ 0.01 Bq/g)
21
Exemption level
=
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)
Trend…
Full harmonization:
Clearance = Exemption
NORM = Nuclear
Back to more
Specificity
Case by case
clearance
One unique set of
Clearance-exemption level
22
Other consideration…
Other risk health aspect:
 Chemical toxicity (industrial waste)
 Infectious risk
Disposal:
 Management of materials should comply with
the specific relevant regulations;
23
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
24
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
25
Chapter 3: Development of
clearance methodologies
General approach ‘to verify
compliance to clearance
level’
26
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)
27
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.
28
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, C14)
Measuring DTM nuclides can be costly -> SF
not to waste resources.
29
Finger print – Scaling factor
Observations – ISO norm
Corrosion product nuclides (Ni-63, Nb-94 & Co-60)
Co-60
key nuclide
ratio constant
 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°
Co-60 or
Cs-137 as
key nuclide ?
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 &
30
hetero.
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
31 NaI(Tl)

Phase 1: Preliminary monitoring
survey- Instrumentation
localization of the depth of the radioactive sources
Contamination ()
Painting
Gamma
spectrometry
analyses
- pic to pic
- compton front
migration Cs-137
or washing with water,
or inhomogeneneity in the wall
32
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
33
Chapter 3: Development of
clearance methodologies
Methodologies….
34
Phase 2: Development of
methodologies
35
Methodology
request for clearance
Methodology 1
request 1
request 2
request n
Methodology 2
request 1
Methodology 3
request 1
request 2
36
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
Chapter
Chapter
Chapter
Chapter
2:
3:
4:
5:
6:
Methodology (flowshart + description)
Justification – validation
QA
Info to give in the request
Comments
from FC, FANC & OA
37
Chapter 3: Development of
clearance methodologies
Examples:
1. Metal & material
38
methodology – flat & clean
material
Surface contamination measure
- beta
- 100 cm²
measure
go – no go ?
Surface contamination measure
- beta
- 100 cm²
Agent R.P.
yes
dec.
new
path
No
measure
Go – no go ?
no go
Go
measure ment
form
39
IDPBW
Flat surface with 2 hand held
monitors
No categories
of material:
•
1. water or air as
Certificate


transportation vector
2. decontamination..•
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 nonradioactive waste"

ISO 7503: "Evaluation of surface contamination – Part 1:
Beta-emitters (maximum beta energy greater than 0.15
MeV) and alpha-emitters".
40
Hand held monitor (dual probe)
Setting of optimal HV
80
cps
alpha source
80
70
beta source
70
60
60
beta channel
50
50
40
40
30
30
20
20
alpha channel
10
0
50 0
cps
HV
70 0
900
110 0
13 0 0
41
beta channel
alpha channel
10
HV
0
50 0
600
70 0
800
900
10 0 0
110 0
12 0 0
13 0 0
Gaz detector…
cps
plateau beta
Mode: simultaneous
plateau alpha
Mode a part
Volt
Va
Va+b
42
Hand held monitor (dual probe)
Calibration
Radionuclide Energy M eV
C
14
 0,158
0% - 7 %
60
 0,31
4% - 16%
137
 0,51
12% - 21%
Cl
36
 0,714
17% - 23%
Sr
90
 0,54+2,27
18% - 24%
 5,48
13% - 0%
Co
Cs
Am
241
Wide area reference
source
Efficiency 4 
1.
2.
3.
2
q1
q2
q3
4
q4
q5
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.
η instrument 
q6
43
n brut -n BG
q2 π
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
C o ntr o l w ith U -So ur c e n°X
Q A nu m b er
fr o m
... c p s
 -c ha n ne l
to
... c p s
 -c ha n n el
... c p s
... c p s
W ithou t B a ck grou nd !!!
44
Justification & validation
Detection limit (cps) < Clearance level (cps)
Detection limit - ISO 11929:
Detection
 1
1  1
1 
2  1
  k 1  α  k 1  β  .

 k 1  α  k 1  β . R 0 




tb  4
t b 
 t0
 t0
k1-a, k1-b : function of alpha and beta error
limit
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 (cps)  CL(Bq/cm²)  S vue   global.
CL:
Clearance Level (Bq/cm²),
Svue:
hglob:
surface ’sees' by the probe (cm²),
global efficiency of the instrument !!!!!!!!!
4
45
Justification and validation
ISO 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
16
cps
detection limit
2. Probe:
2.1 Identification:
QA n°:
14
FC_IDP6.107
2.2 Surface probe (S)
S:
12
100 cm²
10
2.3 Global efficiency
Radioisotopes:
80%Co-60, 20%Cs-137
alarm
hinstrument:
0,17 cps/Bq
8
Justification
K:
2.4 Maximum back-ground
R0:
1
hglob:
6
0,17
12 cps
4
3. Mesurement
3.1 Duration of the back-ground measurement
t0:
60 s
3.2 Facteur probability error
k1-a
k1-b
2
1,645
0
1
1,645
2
3
4
5
6
7
8
4. Détermination du temps de mesure (si t0 est >>> tb)
tb:
3,56 seconds
tb:
46
3 seconds
9 10 11 12 13 14 15 16 17 18 19 20
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
rectan gle
L
S2
external
a

r
h moy 
h moy 
S1  2  triangle
L  2a


 r²arcsin  L   L
L  2a 
 2r  2
1 
(L  2a)  (r 
L  2a 

1
r² 
L²
4
r² 

 L  L
) -  r²arcsin 


 2r  2

L²
L

 a r²    a  ²  a r² 
4
4
2

L²
r² 
L²
4
L²  
L

 a r²    a  ²  a r² 
4  
 2


•
attenuation with distance for our own probe
•
measurement of concrete
47




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
48
Biggest nightmare..
Painting &
coverings in
general
49
Assumption of the ratio…
Assumption of the ratio (control beta)
BG = 10 cps, no attenuation, beta probe
A ssu m p tio n
E fficien cy
D uration (s) A larm (cp s)
2 0 % C s-137
17 %
3 .1 s
6 .8 cp s
1 00 % C s-13 7 2 1 %
2 .1 s
8 .4 cp s
0 % C s 137
16 %
3 .4 s
6 .4 cp s
Assumption of the ratio (control alpha + beta)
BG = 10 cps, no attenuation, dual probe
A ssum ption
20 % C s-137
100 % C s-137
0 % C s 137
E fficiency
6%
12 %
4%
D uration (s)
21 s
6s
46 s
50
A larm (cps)
2.4 cps
4.8 cps
1.6 cps
methodology – scrap material
GO
No-GO
Other evacuation route
HPGe
- Waste
HPGe
HPGe
- Decontamination
~200 kg
20 kg
Hot spot check
51
Step 1: Control
Detection
limit
 1
1  1
1 
2  1
  k 1  α  k 1  β  .
  A' hotspot' (Bq)  η glob
 k 1  α  k 1  β . R 0 


 4
t

t
t
t
b 
b 
 0
 0
k1-a, k1-b ,R0 en t0 are fixed
tb = 1 s
hglob is fixed
Detectable ‘Hot spot activity’ = …. Bq
52
‘ Improved ’ Gross gamma
counting CCM ESM FHT 3035
53
ESM - 4 channels
Spectra of Plastic-Detectors (22x22cm2; d=10cm)
7*Background
Co-60
Cs-137
200
45
180
40
160
35
140
30
120
25
100
20
80
15
60
10
40
5
20
0
0
0
500
Cobalt
Coincidence
Measurement
1000
1500
Ene rgy in ke V
2000
2500
Detect. 2
Detect. 1
1
2
Co-60
54
Rnet(Cs) in 1/s
Rnet(Co), Background in 1/s
50
Calibration & control
14
11
12
13
Every 6 month:


7
10
7
8
9
Fine adjustment of the HV
Calibration with Co-60 and Cs137 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
55
Validation of the system
Principle 1: As straight forward as
possible
• Conditions of validation tests as close as
possible to the measurement conditions
56
Validation of the system
Test in extreme conditions (point source)
P o int so urce
C entre o f d etecto r
in the b lind co rner
CCM
170 %
30 %
C o -6 0 R O I
150 %
50 %
C s-1 3 7
150 %
50 %
Integral
140 %
60 %
Test in measurement conditions (17.5 kg)
Source
mass 13 – 23 kg
wood
cable
plastic
CCM
90 % to 190 %
160 % to 230 %
150 % to 230 %
90 % to 200 %
Co-60 ROI
100 % to 150 %
130 % to 160 %
130 % to 160 %
100 % to 160 %
Cs-137
100 % to 140 %
130 % to 160 %
130 % to 160 %
130 % to 160 %
Integral
100 % to 120 %
120 % to 140 %
120 % to 140 %
100 % to 140 %
 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
57 in the Cs canal varies from – 280 %
and + 40 %
Validation of the system
Statistic approach
Calculate (efficiency)
Calculate (efficiency)
on a less conservative
on conservative
assumptions
assumptions
Alarm = CL
Alarm = CL
uncertainty stat measure
uncertainty position source
uncertainty ratio
uncertainty material - shielding
Actual alarm level
real activity
measured activity
58
Extention of the scope to
concrete
Activation product: Ba-133
cps
80 keV (37 %)
360 keV (56 %)
10 %
Ba-133
90 %
Ba-133
300 keV (22 %)
40 %
K-40
efficiency: 16 % integral
60 %
K-40
Natural element: K-40
1.46 MeV (11 %)
efficiency: 6 % integral !!!
Co-ROI
As = 0.05 Bq/g
Intergal
59
KeV
Alarm in Bq/g fct of the ratio
in the integral channel
Integral channel:

Efficiency correction factor ε Cs  0 . 4 ; ε Ba  0 . 14

ratio
rCs 
Alarm:
A Cs
A Co  A Cs (  A Ba )
A screen
mass (g)

r
Co
; r Ba 
A Ba
A Co  A Cs (  A Ba )
 rx  ε x  r y  ε y
 r
rx
Co


 CL
CL
Co


x
ry
CL
y
et r Co 
and ε Co  1 )
A Co
A Co  A Cs (  A Ba )





0.20
0.19
0.18
CL Int
0.17
0.16
0.15
0.14
0.13
0.12
0.11
0.10
0
0.1
0.2
0.3
0.4
0.5
%
Co
60
0.6
0.7
0.8
0.9
1
Alarm level if function of the
isotopic ratio
CL
rCo
p rev.
p rev.
p rev.
p rev.
p rev.
p rev.
A ct.
A ct.
A ct.
A ct.
rCs
0 .8
0 .6
1
0
0 .8
0 .3
0 .8
0 .6
0 .8
0 .3
0 .2
0 .4
0
1
0 .1
0 .5
0 .2
0 .4
0 .1
0 .5
rBa
0
0
0
0
0 .1
0 .2
0
0
0 .1
0 .2
A larm
Bq
A la r m
B q /g
0 .2 1
0 .2 2
0 .2 0
0 .4 0
0 .2 1
0 .2 6
0 .2 1
0 .2 4
0 .2 1
0 .2 9
R eal activity
Bq
4190
4471
4000
8000
4141
5151
4293
4750
4191
5867
4762
5882
4000
2 0 0 00
4848
9756
4878
6250
4908
1 1 1 11
R eal
activity
Co
3810
3529
4000
0
3879
2927
3902
3750
3926
3333
R eal
activity C s
R eal
activity B a
952
2353
0
2 0 0 00
485
4878
976
2500
491
5556
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.
61
0
0
0
0
485
1951
0
0
491
2222
Step 3: Spectroscopy HPGe
detectors Q²
Detectors:
• HPGe cooled by liquid nitrogen (2
fillings/week)
• Relative detection efficiency 20 %
per detector
100
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
79
Total weight: 8000 kg
67
36
System already incorporated in QA
approach (validation done)
62
Step 3: Spectroscopy HPGe
detectors Q²
63
Step 3: Spectroscopy HPGe
detectors Q²
64
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 1.83 g/cm³
approximation of homogeneous distribution
of activity
65
Spectroscopy HPGe detectors Q²
Errors
1.
2.
3.
4.
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:
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. 66
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) 67
Other devices…
Tunnels
position 2
10 cm
position 1
 2 detectors:

position 1: 60° + 60° = 120°
 position 2: 180° + 60° = 240°
10 cm
 4 detectors


68
position 1: 60° + 60° + 180° + 60 °= 360°
position 2: 180° + 60° + 60°+60°= 360 °
Chapter 3: Development of
clearance methodologies
Examples:
2. Building
69
113 - 114: ‘Building & building
rubble’
group 1
group 2
Reuse or
demolition ? (any
purpose)
Clearance – surfacique
Demolition
1. Clearance – surfacique
Clear
TABLE 2 (Cs-137: 10 Bq/cm²;
Co-60 1 Bq/cm²)
Demolished
Demolition
group 3
Demolished
Clear
TABLE 1 (Cs-137: 1Bq/cm²;
Co-60 1 Bq/cm²)
1. Demolition
(rubble) NO
DILUTION !
70
2. Demolition
(rubble)
1. Clearance – massique
TABLE 3 (Cs-137: 1 Bq/g; Co60 0.1 Bq/g)
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
Activity projected on the surface
 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.
71
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
72
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 ???
73
Chapter 3: Development of
clearance methodologies
Examples:
3. Specific examples
- lead
74
Special methodologie Clearance
of activated 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.
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.
79
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)
spectro
•Sb-125 & Te-125m (CL Sb-125+: 1 Bq/g)
108-Ag activity of lead samples
Sb-125 activity in lead samples
4.00
5
4.5
3.50
4
3.00
3.5
Sb-125 (Bq/kg)
108-Ag (Bq/kg)
2.50
2.00
1.50
3
2.5
2
1.5
1.00
1
0.50
0.5
Sample number
bêta
02
13
R1
03
R2
02
R3
01
R3
05
02
10
02
05
06
14
06
11
06
05
05
16
05
13
05
07
05
01
03
15
03
11
03
05
01
18
01
15
01
09
01
03
04
12
04
09
04
03
07
16
07
13
07
07
07
01
02
13
R1
03
R2
02
R3
01
R3
05
02
10
02
05
06
14
06
11
06
05
05
16
05
13
05
07
05
01
03
15
03
11
03
05
01
18
01
15
01
09
01
03
04
12
04
09
04
03
07
16
07
13
0
07
07
07
01
0.00
Sample number
•Sn-121m (T½ 55 ans) & fils Sn-121 (T½ 27 heures)
80
Chapter 3: Development of
clearance methodologies
Other instruments…
81
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
82
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.
83
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 !!!
84