[en] Accumulation of DNA strand breaks has been studied in mammalian cells after incorporation of ³H-thymidine (³H-TdR), ¹⁴C-thymidine (¹⁴C-TdR) and ¹²⁵Iododeoxyuridine (¹²⁵IUdR). In the experiments the cells were incubated at 37 degrees C followed by DNA strand break analysis by the DNA unwinding method. ¹²⁵ IUdR was extremely efficient to induce unrepairable DNA strand break while ³H-TdR and ¹⁴C-TdR showed a much smaller effect. The relative Biological Effectiveness (RBE) for ¹²⁵I in relation to ³H was found to be 7-13. The frequency of chromatid-type aberrations in Chinese hamster cells was investigated after incorporation of ²H-TdR and ¹²⁵IUdR. RBE for ¹²⁵I in relation to H wascalculated at low doses for (i) chromatid aberrations (17+-6), (ii) the sum of isochromatid aberrations and chromatid exchanges (21+-9) and (iii) the total number of chromatid aberrations (18+-5). Our results are consistent with the assumption that chromosomal aberrations mainly originate from unrepaired DNA strand breaks. ¹²⁵I-triiodothyronine (¹²⁵I-T3) binds to a high-affinity, low-capacity nuclear receptor close to DNA and thereby induces serious DNA damage in GH1 abd Chinese hamster cells. The efficiency of inducing DNA strand breaks was as high as after incorporation of ¹²⁵IUdR implying and extremely high radiotoxicity for ¹²⁵I-T3. A method based on accumulation of DNA strand breaks was established to estimate radiotoxic effects ¹¹C-labelled compounds. As a model system ¹¹C-methionine was chosen. The number of unrepaired DNA strand breaks was examined by the DNA unwinding method after incubation of Chinese hamster cells at 37 degrees C for 60 minutes in ¹¹C methionine containing medium. RBE of ¹¹C-methionine was estimated to be slightly above 1. With 60 refs. (author)

[en] Traditionally, the concept of ALARA has been the basis for limitation and optimisation of releases of radioactive substances from nuclear power reactors in order to protect human health. In recent years, it has been discussed whether the ALARA principle can be applied also to protect the environment. For the protection of the environment, in particular for non-nuclear pollutants, the precautionary principle and the concept of Best Available Technique (BAT) have been applied. New Swedish regulations concerning the protection of human health and the environment from radioactive discharges from certain nuclear installations entered into force January 1st, 2002. The prime purpose of the regulations is to limit the radioactive releases. This limitation shall be based on the optimisation of radiation protection and shall be achieved by using BAT. In order to show compliance with the regulation and BAT, the concepts of reference values and target values have been introduced for nuclear power reactors. The reference value should be the release that is representative for optimum use and full functioning of systems of importance to the occurrence and limitation of radioactive releases from nuclear power reactors. The target value should show the level to which radioactive releases from nuclear power reactors can be reduced during a certain given period of time. Reference and target values have been determined for each nuclear power reactor in Sweden. Each year, the reactor licensees shall report to the Swedish Radiation Protection Authority (SSI) the measures that have been adopted or that are planned to be adopted to limit radioactive releases with the aim of achieving the target values. The first report has been submitted to the SSI in 2003. (Author) 8 refs

[en] The evolving integration of environmental impact assessments into the regulatory process together with Society's concern about environmental protection have emphasised the importance of developing a common international approach that demonstrates protection of the environment from ionising radiation. ICRP has expressed their wish to play a key role, both in advising and in providing the basic interpretation of existing scientific knowledge for such an approach. The European Union launched a research project three years ago, aiming at developing a methodology to be used for environmental risk assessments for ionising radiation (Framework for ASSessment of Environmental impacT). The main objective of FASSET has been to produce a system for the environmental risk assessments which links together exposures, doses and effects. This is accomplished by use of reference organisms including radioecological and dosimetric modelling. Within FASSET a database on biological effects was also set up including more than thousand references and ca 25 000 data entries. Most of the information in the database, however, originates from studies on acute exposures while the focus for non-human organisms must be on chronic exposures to long-lived radionuclides in the environment. It therefore seems necessary to perform several extrapolation tasks in order to characterize the risks. The heterogeneity of exposure conditions in the environment along with non-uniform deliverance of doses of main practical relevance must be considered. This will have great impact on the final biological effects. Applications of weighting factors may be anticipated which are already an established method in radiation protection dosimetry. A summary of the work that has been completed to date in FASSET and ICRP will be presented. Some aspects will be further given on the RBE key issues

[en] The regulations concerning non-nuclear radioactive waste in Sweden is dated 1983. We are now in the process of rewriting them since a lot has happened in the field of radiation protection according to national and international regulations, agreements and recommendations. New areas in the regulations will for example be risk assessment and quality assurance programs

[en] Nuclear operations give rise to small releases of radionuclides to the environment either under controlled conditions (immediate releases) or uncontrolled from waste repositories in the near or far future (delayed releases). The radiation doses to man from the discharges can be estimated using radioecological and dispersion modelling methods. The system for limiting exposure of individual members of the public is currently based on the recommendation by the ICRP. Their risk philosophy, which stems from the fact that the probability of cancer resulting from radiation will be linear with dose, has hitherto gained broad acceptances for setting authorised dose-limits for man. A discussion has recently emerged on the protection of the natural environment from harmful radiation effects. In this case there is concern for the viability of the population rather than the individuals. As our understanding of important mechanisms regarding the protection of the environment is limited it seems appropriate to adopt a precautionary approach. In matters where little is known about the risks the precautionary principle has a major role to play. Concomitantly, the best available technology (BAT), as stated in the precautionary principle, could be employed to minimise discharges of radionuclides. The development of a regulatory frame-work requires that an objective is set and that standards and indicators are derived in a multi-tiered approach. By applying the precautionary principle for environmental radiation protection the safety margins have to increase. However improving knowledge may in due time lead to more rational decision-making

[en] Chinese hamster cells grown in vitro were labelled with ¹⁴C-thymidine for 18 hours and after 3 hours in non-radioactive medium they were stored at 0⁰C for various periods ( 1 to 12 hours). During this treatment a number of DNA strand breaks were induced by ¹⁴C decay which were not repaired at 0⁰C. The number of DNA strand breaks was determined using the DNA unwinding technique. At 0.5-1 dpm per cell a detectable number of DNA strand breaks were found. Treatment for six hours (1 dpm per cell) reduced the percentage of double-stranded DNA from 80 to 70%, corresponding to about 750 DNA strand breaks per cell. The rejoining of DNA strand breaks was studied after treatment for 12 hours at 0⁰C followed by incubation of the cells for various periods at 37⁰C. Most of the DNA strand breaks induced by ¹⁴C decay at 0⁰C were repaired after incubation at 37⁰C for 15 minutes. Assuming an absorbed dose of 1.8 mGy per ¹⁴C decay to the cell nucleus an RBE value close to 1 was found for internal irradiation from ¹⁴C decay as compared with ⁶⁰Co-gamma irradiation. (author)

[en] A simple Gaussian plume model was used to predict the concentration distribution of releases of elemental tritium into surrounding environment from two different sources. The Monte Carlo simulation approach was used to capture the effect of uncertainties caused by the input parameters. The simulation results indicated that the releases in general caused very low doses. However the ambiguity regarding the chemical form of tritium entails the greatest uncertainties in the calculations in comparison to estimated uncertainties in the input parameters. The dose conversion coefficient for tritiated water is four orders of magnitude greater than for elemental tritium, which makes the assumption of the amount of uptake of tritiated water in the lung critical for the calculations. Consequently the maximum doses may range from nSv to μSv per year. Therefore further studies are needed to achieve more realistic assumptions and to validate the model to be able to reduce the predicted uncertainties

[en] An investigation was made of the appearance of DNA damage and survival of IUdR-labelled CHO cells irradiated with gamma (sup 137 Cs) or soft X-rays (75 kV). The absorbed dose and radiation quality were measured using an ionization chamber and thermoluminescent dosemeter. Results show that there was a dose-dependent decrease in the survival of cells after irradiation with gamma or soft X-rays. In both cases the survival of IUdR-labelled cells was less than that of control cells. They yield of strand breaks increased linearly with doses up to a maximum of 6 Gy for gamma rays and 4 Gy for X-rays. After gamma irradiation the capacity of cells to repair DNA breaks was slower in IUdR-containing cells than in control cells. The potential of photon activation for improvement of radiotherapy is discussed

[en] The radiotoxicity of ¹²⁵I incorporated into DNA is extremely high. This has been attibuted to the emission of Auger electrons, resulting in high ionizing density close to the decay. Triiodothyronine (T3) binds to a high affinity, low capacity nuclear receptor close to DNA. ¹²⁵I-T3 induces serious DNA damage in GHl cells and results in the accumulation of several DNA strand breaks per ¹²⁵I decay. The D₀ of V79 cells after ¹²⁵I-T3 treatment was found to be 750 ¹²⁵I decays per cell, corresponding to less than 375 ¹²⁵I decays per cell nucleus. (author)

[en] The Government has given the Swedish Radiation Protection Institute an assignment to review the limitation of releases of radioactive substances from nuclear power plants and, if necessary, suggest further actions including relevant alterations of the statutes. In this document contemporary legislation and regulations, sources and source terms for releases, clean-up systems and release paths for radionuclides, risk reduction philosophy, and health risks are reported. SSI judges that a survey of the existing regulations regarding releases of radioactive substances to the environment is motivated. The regulations which hitherto have been solely based on limitations of radiation doses to man should in the future also take into account other environmental effects similar to environmental legislation in general and international conventions. The cover letter to the Government is also included as a supplement