Open Access
Issue
BIO Web Conf.
Volume 14, 2019
The 12th International Conference on the Health Effects of Incorporated Radionuclides (HEIR 2018)
Article Number 03006
Number of page(s) 2
Section Dosimetry and Dose Assessment: Oral presentations
DOI https://doi.org/10.1051/bioconf/20191403006
Published online 07 May 2019

CIEMAT Internal Dosimetry Service started in 2014 an individual monitoring program of in vitro bioassay measurements of low enriched uranium in urine by radiochemical procedure and alpha spectrometry, for workers involved in the fabrication of nuclear fuel elements for Spanish Nuclear Power Plants.

A total of 198 workers at risk of internal exposures in the Juzbado facility of ENUSA in Salamanca (Spain) have been included in routine, task-related or confirmatory monitoring programs, providing 24h urine samples for the determination of the daily excreted activity of 234U, 238U and 235U, with a Minimum Detectable Amount (MDA) of 0.5 mBq/d for each isotope. A “blank” urine sample of the new employees at the ENUSA workplace is obtained prior to start working in areas at risk of internal exposure for background subtraction. A study of the dietary contribution of natural uranium in the area is in process.

The monitoring data of 72 workers obtained in 2014 suggested a scenario of chronic intakes through inhalation of low enriched uranium at Juzbado facility. Currently workers identified at risk of internal exposure in the plant are monitored in routine at CIEMAT Bioassay laboratory in Madrid, 250 km from Juzbado. Excreta samples preserved in nitric acid are transported from Salamanca to Madrid. A creatinine test for the validation of 24h excretion is performed and correction of daily activity rate is carried out accordingly. Taking into account the available equipment and human resources of CIEMAT internal dosimetry service for measurements and dose assessments, frequency of monitoring was established according to first results of Committed Effective Dose E(50) obtained in 2014, being annual monitoring in case of E(50)< 5 mSv and semi-annual monitoring when E(50)>5 mSv.

CIEMAT established a methodology for dose evaluation based on IDEAS Guidelines [1] and ISO 16638-Part 1 [2], using IMBA software (v 4.1.60). Chronic inhalation of low enriched uranium since the beginning of internal exposure of each worker at the Juzbado fabric was assumed. The intake scenario consists in Uranium oxides, type S of solubility and a particle size of 5 μm of AMAD (default value recommended by ICRP). Dose assessment was carried out in an ICRP78/ICRP119 frame for occupational exposures.

Interpretation of monitoring data takes account of type A and type B uncertainties by calculating the corresponding Scattering Factor [1] of each measurement result, for intake estimation. The Chi squares test is used for confirming the goodness of fit of the monitoring data with the prediction of the excretion model for the assessed intake and permits to corroborate the conditions and assumptions of the internal exposure at the workplace.

Intake and dose E(50) are obtained separately for 234U and 238U when activity concentration (Bq/d) is above MDA. Total Intake of enriched uranium is estimated using isotopic composition of low enriched uranium by ISO 16638 Part 1[2] (82% alpha activity corresponds to 234U) for calculating the intakes of uranium isotopes whose data are below MDA. Dose contributions of annual chronic intakes were assessed for 106 workers with results > MDA. Results of E(50) > 1 mSv/year are reported to workers. In case of partial annual exposures, doses of E(50) > 0.2 mSv are also reported.

This publication focuses on the group of 37 workers chronically exposed to the inhalation of enriched uranium during 30 years. Bioassay monitoring data obtained in the period 2014-2018 resulted in daily excreted activities in the range of 1-15 mBq/d of 234U in urine for this long term exposed staff. Isotopic composition of excreta samples confirmed the intakes of low enriched uranium, with an average 234U/238U ratio of 4.4 of urine activity rate. Annual chronic intakes with doses E(50) above 1 mSv/year were detected in 50% of the cases (see Figure 1). Maximum annual intake corresponds to one worker exposed since 1985, with E(50) = 5 mSv/year.

Highest intakes correspond to workers developing same specific tasks in the process of the fabrication of nuclear fuel elements for nuclear power plants with enriched uranium. Dosimetry information is contributing to improve the radiation protection conditions of the nuclear workforce in Juzbado.

References

  • C.M. Castellani, J.W. Marsh, C. Hurtgen, E. Blanchardon, P. Berard, A. Giussani, M.A. Lopez, IDEAS Guidelines (Version 2) for the Estimation of Committed Doses from Incorporation Monitoring Data. EURADOS Report 2013-01.Braunschweig (2013). [Google Scholar]
  • International Organization for Standardization. ISO 16638-Part 1 Radiation Protection: Monitoring and internal dosimetry for specific materials. Part 1: Uranium. ISO: Geneva (2015). [Google Scholar]

© The Authors, published by EDP Sciences, 2019

Licence Creative Commons
This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

All Figures

thumbnail Figure 1

- Dose distribution of long term (30 years) exposed workers to chronic inhalation of low enriched uranium

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