Table of contents

A preliminary assessment has been made of the individual doses to critical group members of the public in the environs of Berkeley, Gloucestershire, arising from fallout resulting from the Chernobyl nuclear reactor 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 200 mu Sv for an adult, and 500 mu Sv for a 1 year old child; 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.

The long-range atmospheric dispersion model MESOS has been used to provide a preliminary evaluation of the distribution over Western Europe of radioactivity released during the accident which occurred at the Chernobyl-4 reactor in the USSR in April 1986. The results of this analysis have been compared with observations during the first week or so following the accident of airborne contamination levels at a range of locations across Europe in order to obtain an estimate of the accident release source. The work presented here was performed during the 6-8 weeks following the accident and the results obtained will be subject to refinement as more detailed data become available. However, at this early stage they indicate a release source for the Chernobyl accident, expressed as a fraction of the estimated reactor core inventory, of approximately 15-20% of the iodine, tellurium and caesium isotopes, approximately 1% of the ruthenium and lesser amounts of the other fission products and actinides, together with an implied major fraction of the krypton and xenon noble gases.

A simple ionisation method for estimating tube voltage and total filtration is described. The technique is evaluated on twelve 3-phase X-ray sets in-service and is shown to produce determinations of kVp to within +or-10% (<8 kV) and total filtration to within +or-20%. HPA guidelines suggest that discrepancies of 5-10 kV between the real and set tube voltages be brought to the attention of the user and discrepancies of greater than 10 kV be referred to the manufacturer. It is also suggested that tube total filtrations be estimated to within +or-25%. Thus it is thought that this method has a place in quality assurance programs as a guideline to generator calibration.

Data on concentrations of radionuclides in the marine environment near Sellafield have been used to estimate past, present and future doses to the critical group of local fish and shellfish consumers. Doses are compared with criteria recommended by the International Commission on Radiological Protection (ICRP); it is shown that, in the past, doses are likely to have been well within the subsidiary dose limit of 5 mSv y^-1 for members of the public. Following the trend of liquid radioactive waste discharges, doses are currently reducing rapidly, and on the basis of measures already implemented at Sellafield, they will reduce to within the principal limit of 1 mSv y^-1 even if consumption occurs at the highest rates observed in the past. Further measures planned to be effective by 1992 will reduce doses to well within these levels. Any potential lifetime members of the critical group are likely to receive less than 1 mSv y^-1 on average.

In its Report 39 published in February 1985, the International Commission on Radiation Units and Measurements (ICRU) put forward four new quantities for use in radiation protection from external sources. The BCRU (British Committee on Radiation Units and Measurements) recommends that these quantities should be adopted for use in the UK, together with the conversion coefficients given in this memorandum.

The BCRU has taken note of the statement from the recent meeting of the ICRP in Paris, which recommended that the effective quality factor, Q, for neutrons should be increased by a factor of 2 as compared with the values given in ICRP Publication 21. Having considered this statement, BRCU recommends that no change should be made to the quality factor for neutrons in radiation protection practice in the UK for the time being, that the quality factors should continue to be based on information in ICRP Publication 21, and that the quality factors used should be recorded from now on.

Report of One-day Seminar, Bristol, 11th April 1986, organised by the British Institute of Radiology as part of its Annual Congress, `Radiology '86'.

Corrections to J. Soc. Radiol. Prot.6 (2) pp 63-67