Tritium Surveillance around Nuclear Facilities in Japan
In order to measure tritium levels in the environmental water around nuclear facilities in Japan, and consequently to assess the public health significance of tritium, a tritium surveillance program began from 1967 locally at Tsuruga and Mihama districts. It had been expanded to twelve commercial nuclear power stations and five nuclear facilities until 1980. The data from 1967 to 1976 were reported in "Radioactivity Survey Data in Japan, NIRS-RSD-44 (1978)", and those from 1977 to 1980 were in "Radioactivity Survey Data in Japan, NIRS-RSD-56 (1981)".
Though the frequency of sampling was limited once or twice a year in most cases, the times and points were managed to fix at each station in order to record/observe annual variation of tritium levels, taking account of seasonal variation. Water samples were selected basically according to following categories:
a) land water such as streams, rivers, reservoirs or ponds and wells around a nuclear station,
which are utilized as the source of the primary cooling water or the tap water in the station.
b) sea water at an inlet or an outlet of secondary cooling water.
c) tap water around a nuclear station.
d) land, sea and tap water being remote from the station whose data serve as the baseline level to compare with those belong to categories of a), b) to c).
For samples whose tritium concentrations are expected less than 3.7 Bq/l they were electrolytically enriched. Radioactivities were counted with the low background type liquid scintillation counters, Aloka LSC-LB 600 with 20ml vials or Aloka LSC-LB 1 with 100ml vials. The typical counting efficiency of tritium and the background count rate of Aloka LB1 were 12% and 4.5 cpm, respectively for a sample prepared by mixing 45 ml of water with 55 ml of emulsion scintillator in a 100 ml Teflon® vial.
General trends were obvious from the data: Tritium from the effluents was not reflected in all the land water and tap water around the nuclear facilities.
The tritium concentration in rivers, streams, and reservoirs decreased exponentially from about 9-15 Bq/l in 1971 to about 2-4 Bq/l in 1980 with a half-life of about 5 years at Fukushima and Ibaraki Pref., in north-eastern Japan. In Fukui, Shimane, Saga Pref., in south-western Japan, it decreased exponentially from about 7-11 Bq/l in 1971 to about 2-5 Bq/l in 1979 with a half-life of about 5 years.
The sea waters sampled at the inlet of the station or on the seashore far from the outlet were regarded not to often be influenced by the effluent from the nuclear reactors or facilities. Tritium concentration in these coastal waters decreased from 1-4 Bq/l in 1971 to 0.4-2 Bq/l in 1979 with a half-life of about 6 years.
Tritium concentrations of tap water around the nuclear power stations were lower or same with those of the rivers.
For quality control of measurement NIRS occasionally participated in IAEA's inter-comparison programs for low level tritium analysis.
You are free to access to and use the data in this Website of National Institute of Radiological Sciences (NIRS), but with acknowledgment in your paper. You may use the data only for non-profit purposes.
1) Radioactivity Survey Data in Japan, NIRS-RSD-44 (1978)
2) Radioactivity Survey Data in Japan, NIRS-RSD-56, ISSN 0441-2516 (1981)
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