1 Chapiter 8 (part II) SITE CHARACTERIZATION Isabelle Majkowski SCKCEN Isabelle Majkowski, SCKCEN and chapter 7.

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


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


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


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


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


64


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


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


Examples:3. Specific examples- lead

75

Special methodologie Clearance of activated lead.

76


77


78


79


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


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 !!!

1 Chapiter 8 (part II) SITE CHARACTERIZATION Isabelle Majkowski SCKCEN Isabelle Majkowski, SCKCEN and chapter 7.

Documents

bqg clearance level

case clearance slide

clearance level example

concept of clearance

step of clearance

clearance measurements

clearance level bqg

unique set of clearance