Band 77, Heft 3

In order to make the communication on radiation and radiation levels more tangible and clear to the general public, measured results from actual living environments are needed. The paper demonstrates by means of measured results of the ambient dose rates (ODL) that the ambient dose rates in the centre of German cities locally exceed levels typical for the respective geogenic environment significantly. The highest dose rates which have been measured up to now reach 680nSv/h. The role of these results from the radiation protection point of view is discussed and a level of 300nSv/h is suggested as an upper level of the normal ambient dose rate in the urban environment. Still higher dose rates have been found in areas with radioactively contaminated soil. The need for remediation of such contaminated sites is indicated.

Annually since 1989, biannually since 1994 the sites of the Swiss nuclear facilities (4 power plant sites, a nuclear research institute and a waste storage facility) are surveyed flying the same survey lines by airborne gamma ray spectrometry. The equipment and the data processing software used for those surveys was built and developed at the Institute of Geophysics, ETH Zurich. For mapping the ground radiation around the nuclear facilities a pixel representation and a modified Spectrum Dose Index (SDI) method is used. In the search for long-term trends the local dose-rates are calculated first and in turn the net dose rates over the time span 1992–2010. So far no significant change in the radiation levels was detected over the last 18 years outside of the fenced sites of the nuclear facilities, except for the operation of an industrial radiation facility in 1995.

In the context of two reactor decommissioning projects, radioactive slurry from concrete cutting was collected in the retention pond (RHB) at the Paul Scherrer Institute, along with radioactive drain outlets. Additionally, there are active residues from former operations. The task was to determine the nuclide vector of the radioactive slurry before final disposal. Due to the slurry from neutron-activated concrete, activation products, like 55 Fe, 60 Co, 63 Ni, 133 Ba, 152 Eu, 154 Eu and 155 Eu can be expected. Accumulated drain outlets from laboratories, where work with radioactive substances is being done, were expected to contain 22 Na, 60 Co, 134 Cs, 137 Cs, 133 Ba, 152 Eu, 154 Eu, 155 Eu, 241 Am, 239/240 Pu, 241 Pu, 244 Cm, 234 U, 235 U, 238 U, 230 Th, 232 Th and 90 Sr. For further clarification, 3 H and 14 C in the water and in the organic phase had to be measured as well. This work gives an overview about the slurry dissolution techniques, the radiochemical separation methods and activity concentrations of the nuclide vector. Further processing of the slurry is also discussed.

In most working environments it is fairly easy to minimize radiation doses of workers as postulated by radiation protection basics: Increasing the distance to the radiation source, reducing the exposure time, and the use of protective clothing or shielding. With air crews however, being the largest group of exposed persons and receiving the highest collective doses, classical protective measures are difficult or even impossible to enforce. Without neglecting the economical situation, effective measures could nevertheless be realized. Planning flights at slightly lower altitudes and further away from the geomagnetic poles can significantly reduce the radiation exposure for both crew and passengers. Furthermore, affordable high-quality dosimeters with the size of mobile phones have reached marketability. If installed on board, they could measure and display the actually received radiation during normal operation and additionally warn the flight crew in case of an abnormally high dose rate during solar particle events. Pilots could react to such warnings according to procedures that are yet to be installed.

As a first part of the long-term project “European Atlas of Natural Radiation”, a European map of indoor radon concentrations is currently under development. By mid-2011, 21 countries participate in the project, yielding a more or less complete coverage of the European territory. In this article we shortly present the current status before concentrating on questions of quality assurance. Such questions inevitably emerge in a project which attempts to integrate and harmonize large amounts of data of methodically different origin; aggregating them into a common map raises by itself questions of statistical significance.

In Germany radon exposure at certain workplaces has been regulated by the Radiation Protection Ordinance since 2001. However in Bavaria studies have been conducted since 1996. The radon exposure of all staff concerned was estimated and thereby several companies were identified where the exposure exceeded 6 mSv per year. Since then the exposure of the staff has been continuously monitored in these companies. Remediation measures specifically adjusted to local conditions led to a reduction of the exposure in many of these companies. Therefore only in 11 of the original 81 companies exposures of more than 6 mSv/a persist until today. As the Bavarian Environment Agency (LfU) oversaw the measurements and remediation measures there exists profound knowledge within the LfU of the local conditions mainly in water supply facilities as well as of the various remediation measures and their success. Furthermore, a few investigations concerning radon are carried out at workplaces not regulated by the Radiation Protection Ordinance. As an example we present a town hall where the measured radon concentrations led to a heated public dispute. Here the LfU successfully communicated factual information and the evaluation of the radon situation with regard to international recommendations.

In areas featuring air-filled mine workings the convective radon transport through the disturbed bedrock is a frequent cause of high radon concentrations in dwellings. The vertical transport distance of the radon propagation can be more than one hundred meters. The application of tracer gases that can be detected by gas chromatography at extreme low concentrations allows the clear detection of mine-originated radon in dwellings and provides knowledge on the complex processes of radon transport. The successful application of the method is demonstrated on the basis of investigations of the impact of former uranium mine sites on the radon situation in dwellings.

Radiation transport simulations had to be done in preparation of operation of the X-ray tube ISOVOLT 320 kV/13mA in a special laboratory. At first simulation was done without shielding the roof of the laboratory, showing a dose rate maximum of more than 100 mSv/h. This dose rate results in a skyshine dose rate of at most 2 μSv/h in the surrounding of the building without shielding the roof. For similar geometries the skyshine is negligible for dose rates at the unshielded roof of less than 3 mSv/h (exclusion area).

Within the framework of the Global Atmosphere Watch (GAW) Programme of the World Meteorological Organization (WMO), the Deutscher Wetterdienst (DWD) is taking measurements of naturally occurring radionuclides at both the environmental research platform Schneefernerhaus (2650 m a.s.l.) and the summit of Germany's highest mountain Zugspitze (2962 m a.s.l). The radionuclides measured there include 7 Be, 210 Pb, 212 Pb, 214 Pb, 214 Bi, and 222 Rn. This paper especially presents the direct measurement of gaseous 222 Rn with a limit of detection of < 0.05 Bq/m 3 . When combined with meteorological data, these measurements provide a valuable database for characterising air masses and a useful supplementary tool evaluating air transport models and identifying global atmospheric conditions.

The radiation exposure after a short-term release of radioactive substances is often calculated assuming equilibrium conditions. An example is that of the German Incident Calculation Bases for nuclear power plants with pressurized water reactors. Here, the contamination of human milk is calculated using transfer factors. Applying this equilibrium model to incident situations raises the question whether baby's radiation exposure is adequately assessed. This contribution shows that compliance with the relevant dose limits of paragraph 49 of the German Radiation Protection Ordinance is ensured for design basis accidents on the assumption that the hypothetical breastfeeding period starts at the beginning of the activity release. Comparative analyses were performed against the biokinetic models applied by ICRP for radiation protection purposes, taking the reference nuclides 137 Cs, 90 Sr, 131 I, 241 Am and long-lived plutonium isotopes as examples.