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Examples of ALARA evaluation at the SCK•CEN

Vermeersch Fernand

Head of the Unit, Safety, Control and Environment

SCK•CEN, Hermann Debrouxlaan 40, Brussel October 5, 2007

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General overviewThe BR3 decommissioningThe REBUS projectAlmaraz site characterisation in the VRIMOR project

Content

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ALARAput into practice

Planner• Work description• Site information

Radiation protection

• Radiological characterisation of the site

Workers and Technicians

• Work duration• Technical realisation

ALARA analyst BrainstormingEvaluate options

Dec

isio

n

Dose follow upALARA database

REX

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ALARA problems evaluated with the use of VISIPLAN

1. BR3 decommissioning site2. IRMM Geel, Gelina accelerator3. HADES underground laboratory4. BR2 reactor5. BR2 Heat exchangers6. CELL 10 dismantling7. CORALUS dose calculations8. BP hot cell dismantling9. BR3 decontamination area10. REBUS loading study11. Filter replacement study12. Fuel pond decommissioning study13. BR2 sub pile room14. Decom. Cel 40….

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Decommissioning of BR3Operations under the operation deck

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Radiological Characterisation

• 4π dose measurements• Source location measurements with RadScan 800• Historic information on the site.

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Characterisationdose rate measurements

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Gamma Scanning at the BR3 decommissioning site

Areas of the detected hotspots in scan 5 (Composite picture).

Steam generatorcable guide

Deuterium dump tank

Pressuriser tubepump 1

A

BC

D

E

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Intensity map scan5

range 10 to 35 cps, from purple over blue to red

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Example decommissioningactivities at BR3 (1)

Geometric and material data takenfrom paper plans

Model Building and validation Comparison contacts

0.001

0.01

0.1

1

10

Tyau

bru

n 1

Tyau

bru

n 2

PR le

vel 7

GV

leve

l 7

GV

leve

l 3

PR le

vel 3

Spra

y ta

nk le

vel 3

SP M

95

PR su

rge

line

mix

ed b

ed

MC1

MC2

CL M

C2

SPH

X

RC 2

060

Her

pi

PU 5

01 SC1

SC2

V17

V18

PU57

1

strai

ner

HD

T

floor

HD

TDD

T tu

be

Sources

Dos

e (m

Sv/h

)

MetingenVISIPLAN

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Example decommissioningactivities at BR3 (2)

A. Situation before the operations. B. Hot spot removal on level 0 m C. Hot spot removal around DDT lower part

D. Removal of the rotors. E. Removal of the SPHX F. Removal of the shutdown circuit

General planning

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Example decommissioningactivities at BR3 (3)

"Préparation" du chantier man h� obturation des fenêtres de la piscine RC (7) 2 5� Ventilat ion mobile BR2 3 8� Stand de découpe (installat ion / check) 3 4� Marquage tuyauteries 2 12

Modifications des circuits� Eau de service 2 10� Air comprimé � SOD 3 24 � OD (niet) 2 10

Mise en sécurité NST 2 5 vase d'expansion 2 2

Démantèlement points chauds + autres opérations� Pompe MC n°2 2 2� Herpi's 2 2� Ligne collecte d'effluents 2 3� Déshabillage DDT supérieur 2 4� Déshabillage SPHx 2 4� Spray System 2 5� Déshabillage DDT inférieur (dont L.O. + HDT) 2 3� Piquages tuyauteries primaires 2 3� Déshabillage MBT + évacuation 2 4� Piquages GV 2 3� Démantèlement ligne N² 2 2

man hÉvacuation chemins de câbles 2 5

Montage échafaudages (firme extérieure) � niv - 4,805 m 4 6 � sur balançoires MC 4 9

Modification état des boîtes à ressort � MK7 (GV) 3 12 � Autres MK3 - MK6 (balançoires MC, TP) 3 12

Évacuation des rotors des pompes primaires 2 4

Évacuation des SPHx (optionnel) 2 5

Detailed planning

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Example decommissioningactivities at BR3 (4)

Scenario comparison

Direct operation without dose reducing actions

Operation with hot spots removed

Operation with hot spots and small heat

exchangers removed

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The REBUS project

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The REBUS project

• Loading of a spent fuel bundle in a critical facility

First of a kindNeed for radiation protectionTechnical boundary condition

Limited lifting power of the hoist 1.5 ton

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Basic riskThe spent fuel bundle

• Spent fuel adequate shielding is needed

• Source term determined through Origen calculation based on the irradiation history

• Photon spectrum generated for dose calculations with VISIPLAN 3D ALARA planning tool

• Cross verification of dose calculation with MicroShield

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Design of the shielding

• Shielding in two partsDouble shielding for slow operationsSingle cylindrical shielding for fast operations and lifting

• Cross verification of the shielding calculations

Point-kernel 4.3-5.5 mSv/h in contactMCNP 3.4 mSv/h in contact

Fig. 2. Dosistempo rond de REBUS container (25 pins van 1 m, 60 GWd/ton burn-up, 5 jaar koeltijd).

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Loading of spent fuel in a critical facility Simulation in VISIPLAN

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Loading of spent fuel in a critical facility Reality

Spent fuel is shielded by a lead container. The inner container is lifted to the reactor top.

Sequence of events

Different geometries

Different exposure rates

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Loading of spent fuel in a critical facility Dose prognoses

man.mSvman.hman.min

0.0580.59335.6

0.0000.0100.60.0004CMoving the container

0.0350.267160.131BMan attachingthe hooks

0.0230.267160.086ACraneoperator

0.0000.05030.008FFork lift driver

mSvDuration(man.h)

Duration(man.min)

Average dose rate(mSv/h)Pers.Function

Dose evaluation could be made beforehand.

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Loading of spent fuel in a critical facility Dose Results for the loading

00.0050.01

0.0150.02

0.0250.03

0.0350.04

0.0450.05

Hoist Operator Hook operator Radiationprotection

Function

Gam

ma

dose

(mSv

)

Dose measurement(mSv)

Doseprognosis using VISIPLAN(mSv)

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What if analysis ?

• The bundle is lowered out of the shielding with a remote system, what can we do when

this system fails ?

• Backup plan• Development of a manual recovery, based on

a gear box system and a long handling tool

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Gear box and long handling tool position

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Dose map (bundle in the reactor)

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Intervention

Dosis REBUS BR3 bundle

1

10

100

1000

0 50 100 150

z(cm)

H(m

Sv/h

) Metingen

Berekening meting ophet rooster

Opening of the shielding door to place the long handling tool

Estimation of the radiation field

Estimation of the dose during the lift operation 2 min dose of 0.090 mSv

Dosis REBUS BR3 bundle

0.001

0.01

0.1

1

10

0 50 100 150

z(cm)

H(m

Sv/h

)

Ber. aan de deur

Aan de deur van de kazemat

Meting op het rooster

Meting op de werkvloer

Aan de deur van de kazemat

Meting op het rooster

Meting op de werkvloer

Dose rate near the fuel Dose rate at the door

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Cleaning the HLLW tanks

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Cleaning the HLLW tanksModeling the sources (1)

Dose measurement

Source model

Source strength calculation

Dose calculation

Source inference technique based on measured dose rates and 3D modeling of the sources and the site.

HLLW: High Level Liquid Waste tanks need to be cleaned before decommissioning.

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Cleaning the HLLW tanksModeling the Cleaning scenario (2)

Placement of the scaffolding Placement of the hose Cleaning source intact

Cleaning source at 75 % Cleaning source at 50% Cleaning source at 10 %

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Cleaning the HLLW tanksScenario dose assessment (3)

Nr Workers Take Trajectory SSA set

Work Time (min)

Collective Dose

(mSv)

Minimum Work Time

(min)

Minimum Coll. Dose

(mSv)

Maximum Work Time

(min)

Maximum Coll. Dose

(mSv)1 ABC TAKE28 Installing the hose FitValues 15 3.03E-02 12 2.42E-02 18 3.64E-022 AB TAKE28 Cleaning source 100% FitValues 15 2.75E-02 12 2.20E-02 18 3.29E-023 AB TAKE28 Cleaning source 75% Percent75 15 2.38E-02 12 1.90E-02 18 2.85E-024 AB TAKE28 Cleaning source 50% Percent50 15 2.01E-02 12 1.61E-02 18 2.41E-025 AB TAKE28 Cleaning source 10% Percent10 15 1.42E-02 12 1.13E-02 18 1.70E-026 AB TAKE28 Removing the hose Percent10 15 1.05E-02 12 8.39E-03 18 1.26E-02

Total 90 1.26E-01 72 1.01E-01 108 1.52E-01

Result from the simulation in VISIPLAN

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Simulation of the dose near a steam generator

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Steam generatorEvaluation of the dose in

different situations

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Dose evaluation

00.10.20.30.40.50.60.70.80.9

1

0 200 400 600 800 1000 1200

z (cm)

H (m

Sv/h

) Calculation for 45000 random pointsA=1.9E13 Bq (filled empty)Calculation for 55000 random pointsA=1.9E13 Bq (empty, empty)Calculation for 30000 random pointsA=1.9E13 Bq (filled, filled)

Pijpenbundel leeg

ijzer 0.6 g.cm-3

rel. dichtheid 0.077

Stoomgenerator wand

ijzer 7.8 g.cm-3

Lucht0.00122 g.cm-3

Pijpenbundel gevuld

ijzer 0.88 g.cm-3

rel. dichtheid 0.11

Stoomgenerator wand

ijzer 7.8 g.cm-3

Lucht0.00122 g.cm-3

Pijpenbundel gevuld

ijzer 1.52 g.cm-3

rel. dichtheid 0.19

Stoomgenerator wand

ijzer 7.8 g.cm-3

Water1 g.cm-3

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Decommissioning of the hot cell 41

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The dismantling campaign of cell 41 started in 2000

• Steel profiles • Working table• Vertical wall• Tanks• Shielding walls in

Pb• Remote handling

arm• Travelling crane• Several wastes

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Dose prognoses with VISIPLAN

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Different procedures were written

• Intervention zone before the entrance of the cell

Working zone

Waste docking station

Passage for the personnel

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Different procedures were written

• Means of protectionVentilated pressurized suit Mask filter P3TLDElectronic Dosimeters EPD

• Procedure Nose-blowMeasure Whole Body Counter

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Decommissioning Cell 40

VISIPLAN Dose prognoses: 21 man.mSvMeasured 26 man.mSv

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Almaraz site characterisation in the VRIMOR project

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Integrated approach

SCK••CEN's VISIPLAN 3D ALARAplanning tool performing doseassessment in a 3D multi-sourceenvironment on trajectories and workscenario's

Geometric environment determinedusing the laser scanner and the

LFM tool of Z+F ltd UK (VRIMOR)

HesPI human motion simulationtool from UPM, Spain(VRIMOR)

ErgoDose from NNC ltd UKhuman motion simulation

tool (VRIMOR)

EDR gamma scanner fromCIEMAT, Spain(VRIMOR)

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Geometric Information

LFM VISIPLAN 3D ALARA planning tool

Geometry interface

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Scan position 1

Scan position 2

Drain pipe shieldedwith lead

Position of a hot spot confirmed in the two scans

Gamma scan takenfrom two locations

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Application on siteGamma Scans

Two scans from different positions

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Gamma Scan Analysis with the VISIGAMMA tools

Scan 1 Scan 2 VISIPLAN plan view

of the two scans

Interpretation and analysis based on the geometric, gamma scanning and technical information acquired.

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Technical and materials information

Fondo superior = 9,8 mmVirola = 8,2 mmFondo inferior =10 mm Fondo superior = 10,3 mm

Virola = entre 7,9 y 8,4 mmFondo inferior =10,2 mm

Fondo superior = 10,3 mmVirola = entre 8,2 y 8,3 mmFondo inferior =10,3 mm

ESPESORES MEDIDOS

1-It is a pipe of the drainage system. its function is to collect the drainage from upper plants

2- It is a 6 inches pipe: DA-x-135-155G. Made of stainless steal. External Diameter: 168,3 mm. Wallthickness: 7,11mm . It is shielded with lead of 3 cm thickness.

3- This pipe contains leaks, drains, and any other thing coming from the floor.

4- The tanks are filled with pressurized air. The thickness is indicated in the picture.

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Source Model

Source A

Source B

Source C

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Source model and source strength fitting.

0.00E+00

5.00E-05

1.00E-04

1.50E-04

2.00E-04

2.50E-04

0 20 40 60 80 100 120 140 160 180

Measurement number

IDR

(mSv

/h) Meas.

abcSimulated

0.00E+00

5.00E-05

1.00E-04

1.50E-04

2.00E-04

2.50E-04

0 20 40 60 80 100 120 140 160 180

Meas.abcSim

Scan 1

Scan 2

Derived source model simulating

the drainage system.

ABC

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Modeling ResultsComparison with dose

measurements.

Source Scan 1 Scan 2

A (Co-60 eq) 2.78 107 Bq 3.78 107 Bq

B (Co-60 eq) 5.37 107 Bq 2.46 108 Bq

C (Co-60 eq) 8.41 108 Bq 9.84 108 Bq

Position Measured dose rate Simulated

Scan 1

Simulated

Scan 2

Contact

hotspot

0.6-0.8 mSv/h 0.6-1 mSv/h 0.8-1.4 mSv/h

Detector

position

0.010-0.020 0.009-0.010 mSv/h 0.010-0.013 mSv/h

2

60-80 mR/h in contact

2.5-3.5 mR/h at 1 meter

1.1-1.9 mR/h in contactPOSITION ISAPPROXIAMATE

1-2 mR/h in contactat detector position

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Dose plot basedon the fitted sources

Main dose contribution is not caused by the hotspot.

The main contribution is due the contaminated drainage lines.

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Conclusion

• ALARA is a methodology to reduce risks• It is a multidisciplinary approach• Different tools are available to assist

you to assess the dose

• But it al begins with an adequate characterisation of the workplace

Planner• Work description• Site information

Radiation protection

• Radiological characterisation of the site

Workers and Technicians

• Work duration• Technical realisation

ALARA analyst BrainstormingEvaluate options

Dec

isio

n

Dose follow upALARA database

REX