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CAThyMARA: Child and Adult Thyroid Monitoring After Reactor Accident (OPERRA Project number 604984)
DESCRIPTION This report presents the result of the work carried out by the Work Package 6 of the CAThyMARA project. This work focused on the direct assessment of the thyroid dose or committed effective dose from measurements. As a result dose per content functions are derived for different ages (new born, 1,5,10,15-years old children and adult) and for five radio-iodine isotopes (131-135 I) and 132 Te. Thyroid dose to the foetus is also obtained from measurement of the mother. If short-lived radioiodine isotopes cannot be measured correction factors to 131 I measurement are given. The interpretation of measurements in case of stable iodine prophylaxis is also addressed. This report also discusses the parameters influencing thyroid dose assessment. Finally a review of existing software for internal dose assessment is given and a demonstration software for dose assessment in case of nuclear emergency is presented. Approval WP5 leader Lara Struelens: 30/05/2017 OPERRA coordinator Jean-René Jourdain: 31/05/2017 2 1. PREFACE This report presents the methods and the results regarding the direct dose assessment from measurement of radio-iodine isotopes in the thyroid. Several cases are considered: from the newborn to the adult, the foetus and public members of the public who took stable iodine. This report also discusses the sources of uncertainties related to dose assessment, presents a review of existing software for dose estimation in case of emergency and finally presents a demonstration software dedicated to both professionals and citizens carrying out their own measurements. It is necessary, prior to any other text, to mention that materials presented here are based on some assumptions and a priori set boundaries. The considered scenarios cover serious accidents on light water nuclear reactors (PWR/BWR) in which population is subject of single acute intake. Dose assessment is performed during early phase after the accident, thus no intake by (chronical) ingestion is covered. Intake by ingestion was not covered in this project for two reasons: firstly because of the time limitation to carry-out the work, secondly because it can be reasonably assumed that food ban will be correctly implemented and followed after a reactor accident, at least for a vast majority of the population. One have to keep in mind, that the main purpose of the dose assessment system described in the CAThyMARA guidelines and here is the classification of subjects to those who need medical attention or follow-up and to those who not. Dose reconstruction for epidemiology is not considered as a primary goal, since is usually done when more accurate data are available. Thus robustness and easy use of the dose evaluation method, particularly in situations without detail information, was prioritised over high precision assessment. The system stands on old, however well-established, models related to ICRP 60 general recommendation, i.e. it does not consider dosimetric models and feature from newer ICRP documents (e.g. ICRP 103, 100, 130). The main reason for such an approach is that the updated ICRP dosimetric models were not yet fully available and implemented at the time of this project. However the use of the older system does not necessarily limit applicability since it is in general conservative. Moreover introduced systems may be easily adopted to the new one when needed. Simplistic approaches, such as one dose per measurement function for rather large spectrum of intake parameters, is used when inaccuracy due to aggregation is smaller than uncertainty of the input parameters. Other arguments for this simple approach is that it is less prone to evaluation error (mismatching) and may be used by a less skilled personnel. While guidelines is written in prescriptive form, this report is more of scientific nature. It shows particular issues in detailed way and tries to indicate limitation of the used approach in order to explain the methodology used in the guidelines. It may be read independently however it is recommended to read the guidelines prior to this report.
DESCRIPTION This report gives technical guidelines for radio-iodine monitoring following a nuclear incident. Monitoring aspects addressed include the choice of detectors, the calibration and measurement process, factors affecting measurements, measurement uncertainties, the preparation of equipment and measurement locations, the measurement time, the measurement of very young children, management of results and measurements performed by members of the public. This latter point is addressed by making recommendations to professionals to enable them to train and inform citizens. Interpretation of measurements is addressed by providing data on doses per unit measurement, enabling the direct conversion of a measurement into thyroid doses and committed effective doses. The information provided can be used to calculate doses for different age groups, for the embryo or foetus, and for different radio-iodine isotopes. Interpretation of measurements following iodine prophylaxis is also addressed, as well as the case of doses from intakes of short-lived radio-iodine isotopes that cannot usually be measured in the thyroid.