Band 69, Heft 5-6

In case of a radioactive emergency radioactive plumes may be expected in heights up to the tropopause. For this reason aircraft measurements are necessary as a supplement to ground-based measuring sites. The authors present an aircraft type Learjet 35A used for localizing and analyzing radioactive contaminated air masses up to 12,000 m. The aircraft is equipped with an isokinetic high-volume sampler to collect aerosols on filters outside the pressurized cabin and an onboard gamma spectrometry system with a high purity germanium detector to analyze the filters during flight as well as a dose ratemeter, a radon daughter monitor and equipment to collect gaseous iodine and noble gases. The meteorological parameters temperature, atmospheric pressure, relative humidity, wind speed and wind direction are determined as well. Resulting data are transmitted from the plane to the headquarter of the German Meteorological Service (Deutscher Wetterdienst, DWD) and used for verifying the prognosis.

The emergency response system of the German Weather Service (Deutscher Wetterdienst – DWD) will be described including the models (trajectories, LPDM), the national (IMIS, RODOS) and international (IAEA, WMO) co-operation. Examples show the performance of the models and the system.

Based on the Precautionary Radiation Protection Act, the Federal Institute of Hydrology (BfG) is the Federal Center for the monitoring of radioactivity of the German Federal Waterways. In this function, the Institute operates a Radioactivity Measuring and Sampling Network along the Federal Waterways. Priority monitoring tasks are the early warning, the determination of radionuclides in water, suspended solids and sediment (laboratory measurements) and the prediction of dispersion by means of dispersion investigations using tritium as a tracer. This report gives a survey on the present status of the concept and the methods used, as well as an outlook on their further development.

The activity concentrations of Ra-226, Ra-228, Po-210, Pb-210, U-234, U-235, U-238 and Ac-227 have been determined in approx. 400 bottled mineral waters in Germany. The median value of radiation exposure for children (age 0–1 year, 1701/y) is 0.047 mSv/a. The main part of exposure (80–90% approx.) is caused by the isotopes Ra-226 and Ra-228. The median values of concentrations are 7 mBq/l, respectively. Maximal concentrations up to 370 mBq/l were observed.

The unique physiology and the layered structure of forest ecosystems result in dynamic transport and transfer processes which greatly differ from those in agricultural ecosystems. Radionuclides are retained in the upper organic horizons of forest soil for several decades and remain highly available for uptake by fungi and green plants. Contamination levels of mushrooms and game may therefore by far exceed those of agricultural produce. The efficient cycling of nutrients and radionuclides, which is characteristic for ecosystems poor in nutrients, can largely be attributed to forest soil with its complex and multi-layered structure and fungal activity. Fungi directly affect dynamic processes, playing a key role in the mobilization, uptake and translocation of nutrients and radionuclides. Fungal fruit bodies may be highly contaminated foodstuff and fodder. They are most likely the cause of the surprising trend of increasing contamination of wild boar which has been observed in the last few years in Germany. This paper is intended to give a qualitative survey of dynamic transport processes in forests and their relevance for radiation exposure to man.

A rapid method for separating strontium (Sr) radionuclides from liquid milk has been improved and tested for the determination of Sr-90 in milk. The method is based on the specific extraction of Sr from the milk with cryptand 2.2.2 on a cation exchange resin (Dowex Marathon C). Decontamination from other radionuclides such as those of caesium and from chemically similar elements such as calcium and barium is efficient. At least 6 samples can be treated in one day by one person. Tests were carried out on series of six 1.0 and 0.10 litre milk samples representing respectively routine milk samples and samples for fast analysis i.e milk contaminated with fresh fallout, including Ba-140, and requiring barium separation. For the 1.0 litre samples Sr recoveries ranged from 75–85 % while for 0.10 liter samples the range was 65–80 %. Conditions for the use of Sr-85 as yield tracer to correct for the losses were established. The method minimizes the handling of hazardous reagents.

In the case of a nuclear emergency situation, as compared to normal operation, other requirements such as type of information, availability in time and amount must be met in order to characterise the radiological situation and provide recommendations for countermeasures. These requirements are dependent upon the different phases of the emergency. In the beginning phases (Phase 1 and Phase 2) the timely availability of information is of great importance. The focus changes more and more to the diversity of the analysed environmental media in the course of the event. The status at the plant, source term estimates, meteorological data, and weather forecasts are needed in order to calculate trajectories and assessing the prognoses of the expected external dose and contamination during Phase 1 before the release. In addition, on-line dose rate measurements and information on the radionuclide spectrum are necessary. The aim is to get an overview of the actual radiological situation and its possible development in time in order to introduce countermeasures, where necessary. In Phase 2, when the dispersion of radioactivity is finished, measurements according to § 3 of the Precautionary Radiation Protection Act (StrVG) are of primary interest, particularly the determination of contamination to human food and animal feed. During the phase following the deposition, the external dose as a function of time can be well predicted if the nuclide spectrum is known. In Phase 3, i. e. weeks following the emergency, measurements are used to observe the activity concentrations in different media over a longer period of time.

Model predictions for rapid assessment and prognosis of possible radiological consequences after an accidental release of radionuclides play an important role in nuclear emergency management. Radiological measurements (e. g., dose rate measurements, contamination measurements of foodstuffs) can be used to improve such model predictions. This paper describes a method for combining model predictions and measurements (data assimilation) in the deposition model and the food chain model of the European radiological decision support system RODOS. The data assimilation approach is based on the Ensemble Kalman Filter, a Monte Carlo variant of the Kalman filter.

Results of a nationwide measuring programme in Germany are presented where long-lived natural radionuclides of the uranium and thorium series in samples of daily total diet were analysed. Typical ranges and average values of the specific activities are given. There are neither differences between the specific activities in total diet for adults and the age group ≤1 year nor meaningful regional differences. The resulting dose due to ingestion of natural radionuclides has been deduced for all age groups and evaluated. The radionuclides 210 Pb, 210 Po, 228 Ra and 226 Ra are responsible for about 90 % of the total ingestion dose which is 0.09 mSv per year on average without 40 K contribution.

Kurzfassung Die Brennstabauslegung ist ein wesentlicher Aspekt für den sicheren und wirtschaftlichen Betrieb von Kernkraftwerken. Die langjährige Betriebserfahrung zeigt, dass der Sicherheitsstandard der Brennstäbe sehr hoch ist und die international anerkannten Schutzziele eingehalten werden. Zwischenzeitlich haben wirtschaftliche Überlegungen zu einer Erhöhung der mittleren Brennelementabbrände von 35 MWd/kgSM auf heute etwa 55 MWd/kgSM geführt. Neben der besseren Wirtschaftlichkeit wird dadurch im Sinne des Umweltschutzes der Kernbrennstoffbedarf reduziert und die Anzahl der zu entsorgenden Brennelemente verringert. Allerdings bedeutet jede weitere Abbranderhöhung auch zusätzliche Anforderungen an die Brennstäbe, insbesondere an die Hüllrohrmaterialien, wodurch sich erneut die Notwendigkeit des Nachweises der Brennstabintegrität ergibt. Im Vordergrund dieser Nachweise steht seit geraumer Zeit der Übergang von deterministischen zu statistischen Auslegungsmethoden, mit dem Ziel durch Berücksichtigung der vorhandenen Variabilität der Vorgänge im Reaktorkern zu einer wirklichkeitsnäheren Beschreibung zu gelangen. Dadurch können zuverlässigere und genauere Vorhersagen über das Verhalten der Brennstäbe gemacht werden, die die Grundlage für eine effektive Brennstabauslegung und den Nachweis der Brennstabintegrität bilden. Dieser Beitrag beschäftigt sich mit der Frage, inwiefern die bestehenden Modelle aus stochastischer Sicht die Variabilität berücksichtigen und zeigt, dass ein stochastisches Modell neue Chancen für zuverlässige Nachweise bietet. Das vorgeschlagene stochastische Modell behebt gewisse Schwächen der bisherigen Vorgehensweisen, setzt alle vorhandenen Erkenntnisse direkt um und macht die stets vorhandene Ignoranz sichtbar. Zusätzlich werden im Beitrag einige, insbesondere in der Bundesrepublik Deutschland aufgeworfene Fragen, kritisch betrachtet. Der Beitrag besteht aus zwei Teilen. Im ersten Teil werden die benötigten Grundlagen gelegt, während im zweiten Teil auf die mehr technischen Fragen eingegangen wird.