For that monitoring which is statutory, results are required to be reported to the authorising government departments at quarterly intervals, although generally samples are taken and measurements made more fre­quently than this.

Table 4.15 shows typical levels of radioactivity observed in environmental samples near CEGB sites. In most cases these levels are due only to background radioactivity.

For airborne discharges, the milk route constitutes one of the more important pathways back to man. Except for sulphur-35, there is no reason to believe that radioactivity in milk samples results from station emissions. In the case of sulphur-35 discharges from Hinkley Point, members of the public who consume local milk, do not receive radiation doses in excess of 0.1% of the ICRP recommended limit. Sulphur-35 discharges from other stations result in much lower radiation doses.

For liquid discharges, the critical pathway is usu­ally via consumption of fish or shellfish. Near most stations, the radiation doses to which members of the local population may be exposed as a consequence of liquid effluent discharges is not more than 0.2% of the ICRP limit. The exception is Trawsfynydd where the dose to a small group of trout eaters could in 1983 have been approximately 4% of the ICRP
limit. At Bradwell, the critical exposure pathway was originally considered to be through the consumption of oysters from beds in the Blackwater Estuary, with zinc-65 and silver — 110m as the critical radio­nuclides.

This pathway has now declined to such an extent that the consumption of fish is currently more signi­ficant. These exceptional pathways are summarised in Table 4.16.

In addition, film badges exposed on the site fence enable an estimate to be made of radiation doses to the public due to direct radiation from the nuclear site. Generally, the average dose measured by these film badges around any site does not exceed 5 mSv/ year and the dose to individual members of the public near the site would not be expected to be more than about 0.15 mSv/year. At Berkeley, however, dose rates are usually higher and in a normal year the average dose rate measured by its fence film badge is approximately 10 mSv/year.

This results in an estimated maximum radiation dose to certain members of the public near the site of about 2 mSv in a year.

Further details of environmental monitoring near CEGB sites are reported annually, the most recent report being Heap and Short, 1984 [8]. Additionally, DoE publish an environmental monitoring report deal­ing with each individual station for presentation to that station’s Local Liaison Committee which meets once a year. MAFF publish an annual report dealing with monitoring of the aquatic environment around UK. The most recent was published in 1984 [39].