[en] A method is described for assessing the annual dose to the most exposed individual from routine releases of tritium and ¹⁴C to the atmosphere during normal reactor operations. A detailed assessment has been made of the resulting equilibrium contamination levels in a range of foodstuffs typical of an average UK diet and of the annual doses resulting from a chronic intake of tritium and ¹⁴C via inhalation, ingestion and, additionally, in the case of tritium, via skin absorption. Equilibrium annual doses from the global circulation of tritium and ¹⁴C have also been calculated. Upper limits to the effective annual dose-equivalents to the most exposed individual were found to be 0.6 rem.yr^-1 and 100 rem.yr^-1 per Ci.yr^-1 release of tritium and ¹⁴C respectively, with the ingestion pathway contributing significantly to the overall exposure. The most exposed individual was found to be a Reference 10 year old child. The methods outlined for calculating the ingestion dose from tritium and ¹⁴C releases hav been incorporated into the more generally applicable code FOODDOSE. The code may be used to make more realistic dose calculations to the individuals based on site-specific surveys of variables such as local meteorology, local diet and local land use for agriculture, which may lead to doses smaller than the upper limit values quoted by factors of 20 and 200 for tritium and ¹⁴C respectively. (author)

[en] Various methods are described which have been incorporated in the FOODWEB module of the CEGB's NECTAR environmental code and are currently being used within CEGB to assess ingestion doses from consumption of terrestrial foods following an atmospheric radioactive release. Four foodchain models which have been developed within CEGB are fully described and results of typical calculations presented. Also given are the results of a validation of the dynamic model against measured ⁹⁰Sr and ¹³⁷Cs levels in milk in the U.K. resulting from weapons fallout. Methods are also described for calculating individual and population doses from ingestion using the results of the model calculations. The population dose calculations utilise a data base describing the spatial distribution of production of a wide range of agricultural products. The development of such a data base for Great Britain is described, based on the 1972 land use and livestock census, and maps are presented for each agricultural product. (U.K.)

[en] An analysis has been carried out of ingestion doses from a range of postulated Magnox reactor releases to atmosphere. Calculations were made of the dose to the adult, ten year old child and one year old child, which showed the one year old child to receive the highest dose. Detailed studies were made of the significance of the ingestion dose to the one year old child in relation to other exposure routes. The ingestion dose was also analysed in terms of the contributing critical organs, foods and nuclides. Approximate calculations were also made of the dependence of the ingestion dose on the time of year when the release occurs. The results of the analysis were used to derive a set of release-specific Emergency Action Guidance Levels (EAGLs) of critical nuclide concentrations in the critical foods, which comply with NRPB's ingestion ERL recommendations. The EAGLs were supplemented with a corresponding set of EAGLs for grass, for use in situations where crop samples were not readily available. (author)

[en] The results of calculations of Magnox fuel inventories using the point source code RICE and associated Magnox reactor data set have been compared with experimental measurements for the actinide isotopes ²³⁴, ²³⁵, ²³⁶, ²³⁸U, ²³⁸, ²³⁹, ²⁴⁰, ²⁴¹, ²⁴²Pu, ²⁴¹, ²⁴³Am and ²⁴², ²⁴⁴Cm and the fission product isotopes ¹⁴², ¹⁴³, ¹⁴⁴, ¹⁴⁵, ¹⁴⁶, ¹⁵⁰Nd, ⁹⁵Zr, ¹³⁴, ¹³⁷Cs, ¹⁴⁴Ce and daughter ¹⁴⁴Pr produced in four samples of spent Magnox fuel spanning the burnup range 3000 to 9000 MWd/Te. The neutron emissions from a further two samples were also measured and compared with RICE predictions. The results of the comparison were such as to justify the use of the code RICE for providing source terms for environmental impact studies, for the isotopes considered in the present work. (author)

[en] This note describes the NECTAR-RICE module of the CEGB's NECTAR environmental code, which can be used to calculate the actinide and/or fission product inventories of irradiated nuclear fuel used as input to the calculation of the release source term to atmosphere for accidental releases. The range of actinide and fission product nuclides considered is large enough to permit studies to be made for virtually any irradiation history consisting of ad hoc combinations of irradiation and cooling periods. The actinide and fission product inventories are calculated for burnup periods using numerical methods best suited to this problem, while analytical solutions are used for cooling periods. The code can be used to perform a coupled actinide-fission product calculation, a solely actinide calculation or a solely fission product calculation. Output consists of inventories, activities, and γ spectra, among others. A brief description is also given of previous work in this field. (author)

[en] A methodology has been described which can be used to assess the relative radiological toxicities of activation products over geological timescales. A computer code, STRUMP, was written to assist in this assessment. The methodology was applied to an evaluation of the radiological implications of the waste disposal problem for decommissioned fixed steel components in Magnox reactors. The study concluded that the radiotoxicity of the activated steels was dominated, to a varying extent, by the isotopes ⁶³Ni and ⁵⁹Ni for timescales up to 400,000 years. An attempt was made to estimate toxicity levels corresponding to the activity limit of 10^-11Ci gm^-1 below which radioisotopes may be considered stable. The study indicated that steels activated in conditions typical of those encountered by large mass components in the core mid-plane of the core restraint structure became safe for unrestricted disposal only at about a million years. (author)

[en] The computer code RICE, which can be used to calculate the actinide and/or fission product inventories of irradiated nuclear fuel, is described. The range of actinide and fission product isotopes considered is large enough to permit studies to be made of the effect of decades-long irradiations and of geological cooling times. The actinide and fission product inventories are calculated for burnup periods using numerical methods best suited to each problem while analytical solutions are used for cooling periods. The code can be used to perform a coupled actinide-fission product calculation, a solely actinide calculation or a solely fission product calculation. Output consists of inventories, activities, biological hazards, decay heating, γ spectra and macroscopic cross-sections, among others. A brief description is also given of previous work in this field. (author)

[en] Sweden received a particularly high level of fallout from the reactor accident at Chernobyl in April 1986. An environmental monitoring programme was initiated jointly by the CEGB and Studsvik to study the behaviour of the deposited radionuclides in the rural and urban environment of Gaevle where the highest depositions were recorded. This report is concerned with the analysis of the rural data collected over the period from August 1987 to August 1988. The aim has been to develop an improved model to predict the migration of radionuclides through pasture soil. Two alternative models were developed; the first a compartment model and the second a diffusion-advection model modified to account for fixation. The predictions of the two models were tested against the results of the monitoring programme. Least squares analyses were used to establish the better of the two models and to obtain estimates of the model parameters. In all but one case, the diffusion model was found to provide the better description of the behaviour of radionuclides; the effect of advection was found to be negligible. It is intended that this model will be incorporated into an improved model to predict the uptake of activity into animal products. (author)

[en] A preliminary assessment has been made of the individual doses to critical group members of the public in the environs of Berkeley arising from fallout resulting from the Chernobyl accident. The assessment was based on measurements of airborne radionuclide concentrations, ground deposition and nuclide concentrations in rainwater, tapwater, grass, milk and green vegetables. The committed effective dose-equivalent was found to be as follows:- Adult - 200 μSv, 1 year old child - 500 μSv, the 10 year old child receiving a dose intermediate between these two values. The estimate accounts only for the nuclides measured and the specific exposure routes considered namely ingestion of milk and vegetables, inhalation and external exposure. However, it is believed that the inclusion of a range of other nuclides of potential significance, which may have been present but not measured, and potential intakes from additional routes is unlikely to increase the above estimates by more than a factor of 2. (author)

[en] A complete description is given of the input data requirements for the reactor inventory code RICE. Facilities for modifying temporarily the library and input data are described. Three sample cases are also included, both input and output, to facilitate programme testing. The three cases correspond to the three fundamentally different ways of running the programme, namely, to calculate actinide inventories only, to calculate fission product inventories only, or to calculate composite actinide-fission product inventories. RICE is written in Fortran IV (level H) and is compiled under release 20.6, OPT = 2 on the IBM 370/165 computer. (author)