Evaluation of individual dosimetry in mixed neutron and photon radiation fields (EVIDOS). Part I: scope and methods of the project

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7Swedish Radiation Protection Authority, SE-171-16 Stockholm, SwedenThe paper presents the main conclusions and recommendations derived from the EVIDOS project, which is supported by the European Commission within the 5th Framework Programme. EVIDOS aims at evaluating state of the art neutron dosimetry techniques in representative workplaces of the nuclear industry with complex mixed neutron-photon radiation fields. This analysis complements a series of individual papers which present detailed results and it summarises the main findings from a practical point of view. Conclusions and recommendations are given concerning characterisation of radiation fields, methods to derive radiation protection quantities and dosemeter results.

Section: Introductionmentioning

confidence: 99%

Evaluation of individual dosimetry in mixed neutron and photon radiation fields (EVIDOS). Part II: conclusions and recommendations

Schuhmacher¹,

Bartlett²,

Bolognese-Milsztajn³

et al. 2006

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“…More detailed information on the measurement positions is presented elsewhere (4,8) . The distributions were strongly-directed forwards for the simulated workplace fields CANEL and SIGMA (see Figure 1, note the logarithmic scale) and for the 'Cask midline' positions (see Figure 2), and directed less strongly forwards for the positions 'Krü mmel Cask side', 'Ringhals Pos N Cask end' (see Figure 2), 'Krü mmel Reactor top' and 'Ringhals Pos.…”

Section: Measurements In Workplace Fieldsmentioning

confidence: 99%

Direction distributions of neutrons and reference values of the personal dose equivalent in workplace fields

Luszik-Bhadra

Bolognese-Milsztajn

Boschung

et al. 2006

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6Swedish Radiation Protection Authority, Sweden 7 Radiation Protection Division, Health Protection Agency, Chilton, Didcot OX11 0RQ, UK Within the EC project EVIDOS, double-differential (energy and direction) fluence spectra were determined by means of novel direction spectrometers. By folding the spectra with fluence-to-dose equivalent conversion coefficients, contributions to H Ã (10) for 14 directions, and values of the personal dose equivalent H p (10) and the effective dose E for 6 directions of a person's orientation in the field were determined. The results of the measurements and calculations obtained within the EVIDOS project in workplace fields in nuclear installations in Europe, i.e., at Krümmel (boiling water reactor and transport cask), at Mol (Venus research reactor and fuel facility Belgonucléaire) and at Ringhals (pressurised reactor and transport cask) are presented.

“…The following combinations of wall materials and boron-covers of the chamber with a high-neutron response to fast neutrons were used: PE with 4% LiNO 3 . PE with 4% LiNO 3 and 1 mm B 4 C.…”

Section: Dosemeter Design and Dose Determinationmentioning

confidence: 99%

“…With the ratio H p (10) DS /H Ã (10) DS of personal to ambient neutron dose equivalent, determined with a novel directional spectrometry system (5) , a value for the personal neutron dose equivalent H p (10) DS can be calculated. For the irradiations, the dosemeters were mounted on a Perspex-slab-phantom of size 30 Â 30 Â 15 cm 3 . The surface of the slab-phantom, on which the dosemeters PE 4% LiNO 3 (bare and with 1 mm B 4 C) were mounted, was oriented to a direction specified to be 0 (front).…”

Section: Field Measurementsmentioning

confidence: 99%

Performance of a personal neutron dosemeter based on direct ion storage at workplace fields in the nuclear industry

Boschung¹,

Fiechtner²,

Wernli³

2006

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In the framework of the EVIDOS project, funded by the EC, measurements were carried out using dosemeters, based on ionisation chambers with direct ion storage (DIS-N), at several workplace fields, namely, at a fuel processing plant, a boiling and a pressurised water reactor, and near transport and storage casks. The measurements and results obtained with the DIS-N in these workplaces, which are representative for the nuclear industry, are described in this study. Different dosemeter configurations of converter and shielding materials were considered. The results are compared with values for personal dose equivalent which were assessed within the EVIDOS project by other partners. The advantages and limitations of the DIS-N dosemeter are discussed. DOSEMETER DESIGN AND DOSE DETERMINATIONThe personal neutron dosemeter DIS-N, developed by RADOS, is based on ionisation chambers with direct ion storage and a double-chamber system which allows for differential readings to separate the neutron from the photon dose equivalent (1) . However, ionisation chambers are sensitive to both neutrons and photons. Therefore, application of the double-chamber principle requires that the photon energy sensitivities of the two chambers are almost equal and the neutron energy sensitivities of the two chambers are significantly different.Four different types of dosemeter were investigated within the EVIDOS project. The chamber with a high sensitivity for fast neutrons is build with tissue-equivalent wall material (A-150) or polyethylene (PE) for the detection of recoil protons. The response to thermal neutrons can be modified by adding boron nitride (BN) to A-150 or LiNO 3 to PE and by surrounding the dosemeter with additional 'boron-covers' (containing 40% B 4 C). Thermal neutrons can then be detected by the secondary charged particles of the (n,a) reaction with 10 B and 6 Li, respectively, while the boron-covers will reduce the thermal neutron flux.The chamber with a low sensitivity to neutrons was in all cases made up of Teflon (polytetraflouroethylene) containing 60% graphite. Owing to a 1-mm-thick tin shielding around the chambers, photon energies <100 keV may be neglected.The following combinations of wall materials and boron-covers of the chamber with a high-neutron response to fast neutrons were used: PE with 4% LiNO 3 . PE with 4% LiNO 3 and 1 mm B 4 C.A-150 with 1.25% BN. A-150 with 1.25% BN and 2 mm B 4 C.The measured quantities N 1 and N 2 (arbitrary units, a.u.) in both chambers 1 (high-neutron sensitivity) and 2 (low-neutron sensitivity) in a mixed neutron/ photon field are due to the sum of neutron-induced and photon-induced effects and can be written as follows:where H n and H g are the neutron and photon dose equivalent; S 1n and S 2n are the neutron sensitivities of chambers 1 and 2; and S 1g and S 2g are the photon sensitivities of chambers 1 and 2. The sensitivities S i are average sensitivities dependent on the angular and energy distribution of the neutron and photon fields. The neutron dose equivalent can then be ...