Monitoring of different radiation exposure

pathways

National Institute for NBC Protection (SÚJCHBO, v.v.i.)

Eliska Fialova, Petr PS Otahal

fialovaeliska@sujchbo.cz

InterregionalWorkshop on Case Study of Conventional Uranium

Production from Exploration to Closure

14 – 18 October 2019

IAEA Technical Cooperation Project INT2019

Legislative framework

Czech legacy require measurement and determination of effective dose at

workplaces (Atomic law and it´s implementing regulation)

Czech State Office for Nuclear Safety (SONS) – many activities in the field of

radiation protection (among other) aimed to the protection of health and

environment against an unfavourable effect of ionizing radiation - supervision of

whole process

SONS control and regulate the using of nuclear energy and ionizing radiation

PERMISSION for all these activities

Recommendation of SONS for some special activities (for the concrete

permission) – free available

SUJCHBO:

Ensure the service of personal dosimetry for uranium miners

Ensure the service of measuring and determining of effective dose of workers

(„Radon“ and „NORM“ workplaces)

Type of measured workplaces

Activities regarding

uranium mining

(GEAM)

Remaining after

uranium mining

(SUL, HAMR)

„Rn“ workplaces

Workplaces with the possibility of

higher exposition to radon

„NORM“ workplacesWorkplaces with the possibility of

higher exposition to natural sources

of radiation

Potential exposure pathways

Long-lived RN αinhalation

Thoron (220Rn) inhalation

Radon (222Rn) inhalation

Skin contaminationsurface irradiation

Gammaexternal irradiation

Radon and RnDP

Radionuclide Half-lifeMajor radiation alpha energies

(MeV)

222Rn 3.82 d 5.49

218Po 3.05 min 6.00

214Pb 26.8 min -

214Bi 19.7 min -

214Po 164 µs 7.69

Units in radon (RnDP) measurement

Potential alpha energy The total alpha energy ultimately emitted during the decay of 222Rn progeny through

its decay chain, up to (but not including) 210Pb. The term potential then refers to the

fact that a given atoms (222Rn) has a potential to produce a certain amount of energy, if

it decays through the rest of the decay chain. It could be released in the lung if an atom

underwent the entire decay series after depositing in the lung.

Potential alpha energy concentration (PAEC) It is a sum of all the potential alpha energy in a volume of air, divided by the volume of

that air

A common unit is J·m-3. The conventional unit and the one often used for potential

alpha energy concentration is MeV·l-1. (1 MeV = 1.6 x 10-13 J)

Any atom of 218Po (one of the radon decay products – RnDP) emits during its decays

to long lived radionuclide (210Pb) two alphas of total energy of 13.2 MeV. The product

of this energy and concentration of 218Po in air therefore represent potential energy

deposited in lungs if breathing a unit of volume.

Units in radon (RnDP) measurement

Equilibrium equivalent activity concentration (EEC) In most situations the equilibrium between the parent radon isotope and the

progeny does not exist, and a single quantity is needed to describe the activity

concentration for such a non-equilibrium collection of atoms. The symbol is EEC

(Bq·m-3).

EEC presents the activity concentration of the parent that would have to exist in

complete equilibrium with the progeny if the short-lived progeny had the same

potential alpha energy concentration (J·m-3) as in the non-equilibrium mixture.

Equilibrium factor F The equilibrium factor is the ration of equilibrium equivalent activity

concentration Ceq and the radon activity concentration CRn.

F = Ceq/CRn

Units in radon (RnDP) measurement

Working level (WL) is the historical unit of potential alpha energy concentration.

1 WL was originally defined as the concentration of potential alpha energy

associated with the radon rogeny in equilibrium with 100 pCi·l-1 (3700 Bq·l-1).

1WL = 20.8 x 10-3 μJ·m-3

Working Level Month (WLM) is the cumulative exposure to an individual from breathing an atmosphere, at

concentration of 1 WL of radon progeny, over a time period of 1 working month

(170 working hours). 1WLM = 3.54 mJ∙h∙m-3.

WLM is not an SI unit, but it is important to undestand the historical publications

(Epidemiological studies).

Recapitulation of units

Intake

Exposition

Concentration

Bq, 1 MeV = 1.6 x 10-13 J

Bq·h/m3, J·h/m3,WLM

Bq/m3, J/m3, MeV/l, WL

WL –Working Level

1.3 x 105 MeV/m3 = 20.8 µJ/m3

WLM – RnDP exposition of PAEC 3.54 mJ·h·m-3

ICRP – 137, basic assumption for effective

dose calculation

• The working month has 170 hours

• The working year has 2000 hours

• The worker respiratory rate is 1.2 m3/h

Conversion coefficient – ICRP 137

MeasurementOld approach

[mSv/year]

New approach

[mSv/year]

Gama 0,85 [uSv/h] 1,7 1,7

RnDP 130 [Bq.m-3] 2,1 4,4

Rad. dust 0,12 [Bq.m-3] 3,1 1,8

Total effective dose 6,9 8

Uranium mine

Example of different contribution to the total

effective dose depends on a different coefficient

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

351 335 332 329 324 321 122 302 299 290 282 268

Eff

ecti

ve d

ose

(mSv

)

Uranium mine 2016

alfa

gama

Rn

E

Example of different contribution to the total

effective dose depends on a different coefficient

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

94 90 97 91 87 87 74 90 86 93 82 85

Eff

ecti

ve d

ose

(mSv

)

Uranium mine 2018

alfa

gama

Rn

E

Personal dosimetry

Sampling head of ALGADE

Completed head Decompleted head

Assessment of personal dosimeters

TLD type MCP-N (LiF: Mg,Cu,P) + Harshaw 3500

Membrane filter + alfa-beta automat / PSDA

KODAK LR 115 + microscop

H Effective dose (mSv)

Eext Effective dose from external gamma irradiation

Eint,Rn

Contribution to the effective dose from internal irradiation caused by inhalation

of RnDP (derived limit in the Czech Republic is 17 mJ/year)

Eint,dl.alfa

Contribution to the effective dose from internal irradiation caused by inhalation

of long-lived radionuclides emitted alpha radiation of uran-radium decay series

(derived limit in the Czech Republic is 3200 Bq/year)

Effective dose calculation (personal dosimeter)

H = Eext + Eint,Rn + Eint,long alfa

Effective dose calculation(workplace monitoring)

E Effective dose per year (mSv)

āv,Rn

Measured average of radon activity

concentration at workplace (Bq/m3)

T Duration of worker´s stay at workplace (h)

RamaRn

EECRadon gas

concentration

Detection efficiency [m] 0.0122 ± 0.0004 0.0062 ± 0.0003

Measuring range [MBqhm-3] 0.04 – 100 0.08 – 160

MDV [MBqhm-3] 0.015 0.027

Optimal measuring period 2 – 14 month 2 – 14 month

RAMARN is a Solid-State Nuclear

Track Detector (SSNTD) placed in a

diffusion chamber. It consists of a

plastic chamber which has a conically

cylindrical shape and about 0.5 l of

inner volume. Radon gas diffuses

into the chamber during the whole

exposure period. The plastic box

serves as a barrier for RnDP.

Thanks for your attention!