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Radon Measurement and

Mapping

Jiří Hůlka

SURO - National Radiation Protection Institute, Praha, Czech Republic

jiri.hulka@suro.cz

WORKSHOP ON THE CONTROL OF PUBLIC EXPOSURE IN COMPLI ANCE WITH THEINTERNATIONAL BASIC SAFETY STANDARDS

Cape town 4-7 May 2016

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DISCLAIMER

Neither the presenter nor the IAEA endorses the use of any of the commercially available

radon detectors presented here.

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Indoor radon variation in time and space

Diurnal variation seasonal variation

)(.)().(/)()(

tatatkVtQdt

tda −−= λRadon entry rate

Ventilation rate

Q,k are influenced by

– Meteorological changes (temperature difference, wind, b) → ∆p– human behaviour (ventilation and radon entry)– long-term changes (soil moisture below house , subsoil water level,

construction changes , window sealing, cracks …., global warming…

Reasons for indoor Rn variation

).(,.,,

λ+++

=kV

QQQa otherRnmatbuildRnsoilRn

Rn

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Radon variation at home influence the behavior of inhabitants

Workplaces, schools etcVentilation and heating habits differ and are expected to be different based on the purpose of the building or room (office, storeroom, school/kindergarten, etc.)

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Rad

on c

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tion

(Bq/

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Time

Radon concentration in kindergarten

Radon concentrationOccupancy

weekend

Source: SURO v.v.i

Radon measurement and „uncertainty“ of interpretation

Instrumental uncertainty (< 30%) …not a big problem

Spatial uncertainity (in the house)(How many and which rooms should be measured?)

Time factor (How long should we measure?

the most complicated for interpretation.

„seasonal correction factors“

Measurement techniques

passive (require no electrical power)active

Integrating technique (mostly passive)

– Provide averaged concentration over a period of a few days to a year

Continuous technique (active)

– provide information on the time course of Rnconcentration

Grab-sample (spot-sampling) technique– discrete samples of air taken over a short time at a single point

(great uncertainty!!!!) X

Summary: Measurement devices

DETECTOR TYPE PASSIVE

/ACTIVE

TYPICAL SAMPLING

PERIODCOST

Solid state nuclear track detectors(CR-

39 or LR115)Passive 1 - 12 months low

Electret IonizationChambers

Passive 2 days - 1 year medium

NEW: PIN Si diodecontinuousdetectors

Active(batery)/Passive

1 hour – 1 yearLow,

medium

Continuous Radon Monitor

Active 1 hour – 1 yearmedium,

high

Activated Charcoal Detector

Passive 1 – 3 days low

The type of detector should be carefully selected since it influences the cost of measurement per dwelling and therefore the cost of a radon programme on a national level.

Measurement strategy

2. Other need for measurement (sell-buy, pre/post reconstruction measurements, workplaces…)

Step 1 – cheap , short „ screening“ measurements ( some days), to avoid underestimation - be conservative : measurement under“close room condition” , at rooms in ground floor (conta ct withsoil), also look for suspicious construction material etc …

If the results are above reference level

Step 2 – more detailed, radon diagnosis : m easurement “in depth” : under normal living condition, fan working, to iden tify Rn entry etc

1. National Rn survey and mapping• based on long term measurements > 3 month (preferred 1 year)• cheap passive detectors (SSTD)• mostly 2 detectors /house (living area + bedroom)

Example : Workplaces, schools etc

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Rad

on c

once

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tion

(Bq/

m3 )

Time

Radon concentration in kindergarten

Radon concentrationOccupancy

weekend

Source: SURO v.v.i

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REMARK : Radon „Diagnosis“

sophisticated measurement for building professionalsto identify radon sources, radon routes

New promising techniques

– Blower Doors– Infrared Thermograph for radon entry identification– simultaneous continuous measurements in different

parts of house and in soil gas → mapping radon route– measurement of mean ventilation (trace gas)

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Blower doors technique (negative pressure and Rn entry investigation)

Sample of air measurement-

Lucas cell

Entry rate visualisation

by smoke

15,2°C

21,6°C

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SP01: 14,9°C

15,2°C

21,6°C

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SP01: 13,7°C

Infrared camera :

Cold-air as indicator of radon entry

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Rn „transport“ in the houseBlower doors technique and simultaneous Rn monitors:

Simultaneous Rn measurement in different parts of house radon „route“ analysis, (human activities in dwellings, ventilation and heating regime)

New cheap continuous Rn monitorswifi connection

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More sophisticated experiment different blower door operating modes (negative pressure)

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Time (hh:mm)

C (

Bq.

m-3

)

20 Pa

30 Pa

15,5 Pa

m

n

pkkk

pQQQ

).(

).(

10

10

∆+=

∆+=

Blower doors can “switch-off” meteorological ∆p

Source of photos: Radon v.o.s.

Measurement radon concentration in soil gasSufficient number of sampling points to cover the surface area of interest (sampling grid

10x10 m for large areas, single family house 15 sampling points)

+Measurement of soil permeability

Remark : Radon/thoron (and their progeny) measurement outdoor (in the atmosphere)

(average 5-10 Bq/m3) – need for more sensitive measurement

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• Standard Measurement Protocol• QA /QC measures are strongly recommended to assure

the reliability of radon measurements.

QA(Quality Assurance)The set of planned and systematic actions put in place at specified stages of the radon measurement process to ensure confidence and accuracy of the measurement results.

QC(Quality Control)The quality checks carried out within the radon measurement laboratory (Radon chamber) as part of the overall quality assurance system.

QA(Quality Assurance) /QC(Quality Control)

222Rn chamber 220Rn chamber

International intercomparison experiments of passive 222Rn/220Rn detectors in radon chambers

RADON SURVEYS

AND

MAPPING(RADON PRONE AREAS )

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National radon survey and mappingbased on indoor meassurement

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To estimate the average exposure (+ data distribution)– population-weighted survey by measuring indoor radon levels in

randomly selected homes

To identify radon prone areas (prepare national radon map)– geographically based survey (homes randomly selected to obtain a

minimum density of measurements per area unit chosen(more extensive survey depending on population and area of the country)

A carefully designed survey can, in principle, meet the requirements and objectives of both types of surveys

Radon prone areas

areas, where Rn concentrations are likely to be „significantly higher“ than national average

(ICRP 103, ICRP 115/126)

So far there has not been a uniform approach to the wayin which high radon areas are defined

Aim: to implement special RADON strategies (ACTION PLAN)

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As a first step the national authority should review any existing data onconcentrations of radon indoors, in particular, in areas where highconcentrations of radon indoors might be expected (e.g. geological criteriaindicated uranium).

NATIONAL RADON SURVEY AND MAPPINGHOW TO START ?

If no such data are available, authority should consider organizing localizedsurveys ….

……. and also evaluate the available information on radon indoors inneighbouring States.

The buildings with public access can be used as 1st step of radon survey, e.g. primary schools and kindergartens

• Usually easy to access through municipality

• Positive public perception of the measurement (protection of children)

• Classrooms are occupied with predictable pattern BUT nights, weekends and holidays the building is unoccupied � the average radon concentration for the whole exposure period may be higher than during occupation

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� Select homes randomly (using e.g. electoral registers, postal listings…..other similar representational data bases).

� Contact homes to invite them to participate.

� Stimulate participation using local media, local authority.

� Distribute and recover detectors (e.g.by post if possible).

� Accompany detectors with household questionnaire (at least basic information about the address, contact details of the house owner, position of each of the detectors in the house (detector code, room, floor).

� Inform householders of results but maintain confidentiality.( Prepare : How to present the results to the homeowner!)

SUMMARY: RN SURVEY METHODOLOGY

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(a) Quality standards for radon detectors

(b) The minimum measurement period;

(c) The measurement protocols to be applied (prepare database)

(d) Whether measurements should be limited to certain seasons;

(e) Whether or not seasonal correction factors should be applied

to the results;

(f) Quality standards for reporting results to owners of the

dwellings and other buildings

(g) The advice that should be offered to owners of that have

concentrations of radon in excess of the reference level.

National authority should specify

National radon database

Radon database (results from radon measurements) is an important tool for National Radon Action Plan (planning, evaluation)

Questions to solve:– Who will enter the results and has access to the database?– Consider confidentiality of (some) data !!!– What information should be stored in the database ?

results of radon measurements, information from the questionnaire on building characteristics, construction materials, etc., information on corrective actions (type, cost, radon concentration before/after), information on preventive measures (type, cost, radon concentration should be also collected for further analysis.

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Geogenic radon risk (radon index, …)(no harmonization up to now )

What is reasonable classification of Rn risk (index ) of the building site? By which procedure can it be done?

Up to now at CZ it was based on :• set of Rn soil gas measurement (15 probes in the building site, depth 0,8 m) • soil permeability measurements

Rn soil riskRn concentration in soil

(kBq/m3)Low

permeabilityMedium

PermeabilityHigh

permeabilityLow <30 <20 <10

Medium 30-100 20-70 10-30High >100 >70 >30

Average radon concentrations (geometric mean) in homes in Germany

Example : Radon in Germany Rn in soil (geogenic) Rn indoor

Radon Maps could be based on

• Indoor radon measurements

• „Geogenic radon risk“ (Rn in soil )

Geogenic radon vs. indoor radon

Source: Gruber, V., Bossew, P., De Cort, M., Tollefsen, T.: The European map of the geogenic radon potential, Radiol. Prot. 33 (2013), p. 51-6

Radon Maps - Display and Evaluation

Different forms of display

Average radon concentrations (geometric mean) in homes in Germany

Grid Geology boundariesMunicipalityboundaries

Different evaluation in unit

(indoor mean value, probability > reference level, Rn index of bedrock , Rn potential,…)

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1:500 0001:50 000

Radon risk maps development

Graded approach based on indoor data and geology prediction

Measured points

Remark: Simple gamma survey(SAFECAST)

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Thank you