DETERMINATION OF NEUTRON AND PHOTON DOSE-EQUIVALENT AT WORKPLACES IN NUCLEAR-FACILITIES IN SWEDEN - A JOINT SSI-EURADOS COMPARISON EXERCISE

The accuracy of the dosimetry (personal and area monitoring) has been investigated inside the containment buildings of two pressurised water reactors and in the environment of a transport cask with spent fuel e lements. The dosimetric quantities of main interest were ambient dose equivalent and personal dose equivalent, as operational quantities, an d effective dose equivalent, as limit quantity. They were either direc tly determined by means of instruments and dosemeters or calculated fr om the experimentally determined directional spectral neutron fluence. Several groups employing different techniques carried out the investi gations. The comprehensive comparison exercise has shown that a well s pecified Bonner sphere spectrometer and a set of proton recoil detecto rs are well-suited to determine the neutron field for reference purpos es. The neutron fields were rather soft with up to 70% of the neutron dose equivalent contributed by neutrons of energies less than 100 keV. On account of their energy dependence, rem counters overestimate, and TEPC systems underestimate, the neutron dose equivalent, even if cali brated in the field of a D2O-moderated Cf-252 source. Only a recently developed active dosemeter, based on superheated drop detectors (only used outside the containment), measured the ambient dose equivalent in good agreement with the results obtained with Bonner spheres). Measur ements with several personal dosemeters irradiated on a phantom were u sed to estimate the directional properties of the neutron field. This is required for the calculation of personal and effective dose equival ent values. Some personal dosemeters gave dose equivalent results in s atisfactory agreement (+/-20%) with the reference values. In any case the measured dose equivalent values were conservative estimates of the corresponding effective dose equivalent values. The application of th e new recommendations of the International Commission on Radiological Protection (ICRP) will result in about 50% higher values of neutron am bient dose equivalent. In the determination of the photon ambient dose equivalent, which amounts to about 30% of the total dose equivalent, differences up to 50% were observed between the readings of GM counter s and TEPC's, chiefly caused by high energy photons present in the con tainment building.