Strategies for Optimisation of Protection against Internal Exposure: SMOPIE Project

Strategies and Methods for Optimisation of Protection against Internal Exposure of workers from industrial natural sources (SMOPIE) 9th ALARA workshop; Augsburg, 18-21 October 2005

SMOPIE FP5 project (Contract no FIGM-CT-2001-00176) • Start: 1 November 2001 • End: 30 June 2004

SMOPIEResearch Partners • NRG; Arnhem/Petten, Netherlands (Co-ordinator) • J. van der Steen, A.W. van Weers, C.W.M. Timmermans • CEPN; Fontenay-aux-Roses, France • C. Lefaure, J.-P. Degrange • NRPB; Leeds, United Kingdom • P.V. Shaw • IRSN; Fontenay-aux-Roses, France (subcontractor to CEPN) • O. Witschger

SMOPIEIndustrial Partners • Thermphos International; Netherlands • Phosphorus production • Kerr-McGee; Netherlands • TiO2 production • COMURHEX: France • U concentrates • UK Heavy Mineral Sands Association: United Kingdom • Zircon sand • TiO2 production

SMOPIEOrigin of the Project Project originates from recommendations of the 3rd European ALARA Workshop

SMOPIERecommendations of 3rd EAN Workshop • …. there was limited data, at the national regulatory body level, on the number of workers exposed to intakes and the profile of the dose received. It is recommended that the Commission and the regulatory bodies pursue efforts to improve the data. Of particular concern is the area related to doses from the use of Naturally Occurring Radioactive Materials (NORM) • …. need to improve the quality and accuracy of internal dose monitoring techniques (particularly personnel air samplers) to fit with the specifications needed for analytical task dosimetry

SMOPIEObjective To arrive at recommended monitoring strategies and methods for optimising protection against internal exposure in a wide range of predictable occupational exposure situations

SMOPIE Introduction • Work activities with NORM can involve significant exposure of workers, due to internal contamination by inhalation • However, there can be considerable differences in work place conditions, radionuclides involved and the physical and chemical matrices in which the radionuclides are incorporated • The study covers a variety of practical exposure situations in industries with NORM

SMOPIE Introduction (2) • For optimisation of the protection of workers, it is necessary to answer the following questions • What doses have been received by whom? • Where has it been received (work places)? • When has it been received (jobs, tasks)?

SMOPIE Introduction (3) • This determines the monitoring methodology for optimisation • Bioassays do not allow to answer all the previous questions • Only way is by monitoring through air sampling • Personal air sampling • Static air sampling • Real time dust monitoring

SMOPIE Introduction (4) • The dose assessment requires: • Knowledge of dose coefficients • Knowledge of lung clearance classes • Knowledge of particle size distributions • Knowledge of radionuclide characteristics

Chain (segment) Fast Moderate Slow Ratio S/F Ratio S/M 238U 5.9E-07 1.7E-06 5.7E-06 9.8 3.5 238Usec 1.2E-04 3.7E-05 3.4E-05 0.28 0.92 238Usec *) 1.2E-04 4.8E-05 6.5E-05 0.53 1.36 226Ra 4.4E-07 2.2E-06 6.9E-06 16 3.2 226Ra *) 4.4E-07 1.4E-05 3.8E-05 87 2.8 226Ra+ 2.3E-06 5.1E-06 1.4E-05 6.1 2.7 226Ra+ *) 2.3E-06 1.6E-05 4.5E-05 20 2.8 210Pb 1.1E-06 7.4E-07 4.3E-06 3.8 5.7 210Po 7.3E-07 2.2E-06 2.7E-06 3.7 1.25 *) Low Rn emanation rate Dose coefficients, 238U chain, AMAD = 5 m, GSD = 2.5 Nuclide,

SMOPIEWork Programme • To prepare a summary of information on the number of workers exposed to internal contamination and the dose levels involved (WP1) • To obtain a set of case studies on monitoring strategies for internal exposure in real work place conditions in industries (WP2)

SMOPIEWork Programme (2) • To identify and categorise the main characteristics of exposure situations based on the case studies (WP3) • To evaluate the potentials and limitations of monitoring strategies and methods in relation to optimisation of internal exposure situations (WP4) • To derive recommended monitoring strategies and methods for optimising protection against internal exposure (WP5)

SMOPIE Work Package 1 Info on exposed workers

SMOPIE WP1: Info on exposed workers Objective: • To provide information on: • the numbers of workers exposed to industrial natural sources • the associated levels of dose of these exposures

SMOPIE WP1: Info on exposed workers Sources of information: • National dose registers • European studies • EURADOS, OMINEX, BIODOS, EULEP • Surveys carried out in relation to Title VII of Directive 96/29/Euratom • Other sources of information • Additional information from UK, Ireland, France

SMOPIE WP1: Info on exposed workersRange of doses from work with NORM • This information is NOT available from national dose registries or from other current European Research projects • There are, however some data from work done in response to Title VII of the Euratom BSS, and from sources specifically commissioned for the SMOPIE project

SMOPIE WP1: Info on exposed workersRange of doses from work with NORM (2) • The information suggests potential annual exposures by inhalation ranging from below 1 mSv to above 20 mSv • But: In many cases, doses have been modelled rather than being based on actual workplace measurements. Such estimated doses would appear to be grossly pessimistic in many cases

SMOPIE WP1: Info on exposed workersRange of doses from work with NORM (3) • In some cases, there are more realistic estimates of dose: in fact, these occupy the same dose range, i.e. from below 1 to greater than 20 mSv/y • Overall, there is insufficient data to provide any more than a broad indication of the doses involved

Potential annual dose from inhalation Type of NORM industry Above 20 mSv From 6 to 20 mSv Below 6 mSv Rare earth processing (a few workers) Grinding of thoriated electrodes; Zircon milling (a few workers) All other NORM industries SMOPIE WP1: Info on exposed workersRange of doses from work with NORM (4) Summary of data on dose ranges associated with NORM work

SMOPIE WP1: Info on exposed workersEstimates of number of exposed workers • The information is NOT available from national dose registries, current European Research projects, or work done in response to Title VII of the Euratom BSS • The exceptions to this are a German study and, to a lesser extent, the on-going work in Ireland which do contain estimates of the number of exposed workers

SMOPIE WP1: Info on exposed workersEstimates of number of exposed workers (2) • The information that has been gathered from other sources specifically for the SMOPIE project does provide a better indication of the number of exposed workers • Even then, only approximate, order-of-magnitude, estimates are possible

SMOPIE WP1: Info on exposed workersEstimates of number of exposed workers (3) Order of magnitude estimates of workers potentially exposed to significant annual doses from internal contamination in NORM industries

SMOPIE WP1: Info on exposed workersEstimates of number of exposed workers (4)

SMOPIE WP1: Info on exposed workersRecommendation 1 There is a lack of published data on the actual numbers of exposed workers and the doses received Much more data based on industry surveys and workplace measurements is required to provide an accurate position of the situation in EU NORM industries

SMOPIE WP1: Info on exposed workersRecommendation 2 The implementation of Title VII of the European Directive 96/29/Euratom has so far provided very little published data of the kind referred to above It is recommended that any studies made in response to Title VII aim to include the number of workers and the actual doses received

SMOPIE WP1: Info on exposed workersRecommendation 3 By far the largest NORM work activity, in terms of number of workers, appears to be the use of thoriated welding rods. There is evidence that inhalation doses can be significant from both welding and grinding activities Despite this very little is known about the precise scale of the problem. This work activity warrants further specific study at a European level

SMOPIE Work Package 5 Recommended monitoring strategies and methods

General observations • The results provide a scientific and practical basis for monitoring programs, both for individual workers and for the workplace • It describes the way to use sampling equipment which has intrinsically be designed for industrial hygiene instead of radiation protection purposes • Samplers cannot sample the true ambient aerosol required for radiation protection purposes

General observations (2) The results show that: • Appropriate sampling efficiency correction factors should be applied, depending on the sampling device (Inhalable, Thoracic, Respirable), and dust particle size distribution characteristics (AMAD, GSD) • Without such correction factors, significant underestimation can be made in the assessment of internal exposures

General observations (3) • The results provide practical information • how to assess the radiological consequences for the workforce in a first screening campaign, and • how to get more information when the first screening warrants further research • By this approach, the most efficient use can be made of resources, • without spending unnecessary time and money where this is not justified, and • by advising about the use of the right instrumentation required to implement radiation protection controls

GRADED APPROACH From simple first screening to detailed assessment

Strategy for a first screening • For situations where it is already recognised that the nature of the processes as well as the materials can give rise to exposure of workers by inhalation • First step is to visually identify sources of dust • Measurement campaigns to assess the exposure of workers should in the first place be directed to these visible sources

First screening of workers exposure Dust characteristics • Information on radionuclide composition of dust • If not known, then analyse samples • Lung absorption type (Slow, Moderate, Fast) • Based on the chemical characteristics of the materials • Otherwise default type should conservatively be chosen on the basis of radionuclide composition • Same solubility type for various radionuclides in same matrix • Particle size distribution • Almost always unknown in first screening

First screening of workers exposure Monitoring strategy • Aims to obtain a minimum number of measurements for a first estimate of the range of exposures of workers performing different tasks at different workstations under normal variation of working conditions • Number of workers to be monitored • Define reasonably homogenous groups of workers • Define number of monitored workers in a group • Define number of samplesper worker

First screening of workers exposure Monitoring strategy (2) • Sampling duration • Collection of shift-long samples • Shorter sampling durations to assess exposures resulting from short-term tasks • Total number of samples • Indication: at least five shift-long samples per worker • If some tasks of short duration could significantly contribute to the total exposure, it should be ensured that exposures during these tasks are representatively included in the sampling

First screening of workers exposure Choice of sampling device • Preferred sampling device should be PAS that sample • Thoracic particles (for dust of lung solubility type S or M) • Inhalable particles (for dust of lung solubility type F) • However, PAS that sample inhalable particles may be used in the first screening • Slightly higher amount of material (activity) collected, as compared to thoracic samplers • More widely available in practice

First screening of workers exposure Analysis of filters • Must provide the identification of radionuclides and their activities on the filters, if such information cannot be obtained otherwise • Repeated radionuclide identification is not necessary if there is only one well-known source of airborne material • All radiometric analyses methods require considerable operational skills • Gravimetric analysis may be used when the mass of material on the filter can be directly related to the radionuclides and their activities

First screening of workers exposure Dose estimate • Determine annual intake • Choose appropriate dose coefficients • Depend strongly on lung absorption type • Choose appropriate correction factors • Depend on information about AMAD and GSD • Estimate dose

Strategy for elimination of doses well below 1 mSv/y • Choice of dose level of no further concern for internal exposure • Depends on national regulatory requirements • 300 µSv/a may be appropriate (RP 122 Part II) • Analysis of exposure data • Statistical uncertainties are likely to be significant and should be a major consideration when designing monitoring programmes • Case studies suggest that the reverse is true in practice • Further guidance is needed

Strategy for optimising the exposure assessment • Detailed exposure assessment for workers potentially exposed to levels of radiological concern • Should remove any uncertainties from assumptions in first screening where possible • May partly be based on recalculation of the dose estimates from the screening stage and partly on repeated monitoring

Strategy for optimising the exposure assessment (2) • Identification of lung absorption type • Dependency of dose coefficients is strong case for assessing the true lung absorption type of the ambient aerosol • Much information should be drawn from the characteristics of the raw materials, products and residues • Heavy mineral sands, ores like rutiles, Ra-bearing sulphates are resistant to chemical attack:Type S • Uranates: Type M • U-oxides: Type S • Ideally, simple experimental determination of lung absorption type should be conducted • More complex analyses can be time consuming and costly

Strategy for optimising the exposure assessment (3) • Particle size distribution • In principle necessary for a detailed exposure assessment • However, choice of an appropriate sampling convention and sampling efficiency correction factor is more important • This, together with an assumed default AMAD of 5 µm (GSD 2.5) will avoid excessive bias in the exposure assessment

Strategy for optimising the exposure assessment (4) • Choice of PAS – Preferred sampling convention • Type S; Type M: THORACIC • Type F: INHALABLE • Thoracic samplers • Less material deposited  lower detection limit • Existing thoracic samplers rely often on “sponges”, rather than flat filters • In practice it may be necessary to use inhalable samplers for types S and M and use the bias estimates to correct for possible underestimation

Strategy for optimising the exposure assessment (5) • Optimised exposure assessment through • Recalculation of the exposure data from the first screening • Identification of inhomogeneity of worker groups and regrouping if needed • Repeated shift monitoring of workers with PAS and appropriate sampling convention • Reassessing workers exposures

Strategies for Optimisation of Protection against Internal Exposure: SMOPIE Project

Strategies for Optimisation of Protection against Internal Exposure: SMOPIE Project

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