Monitoring of Low-Level Radioactive Liquid Effluent in Tokai Reprocessing Plant

Abstract

The Tokai reprocessing plant (TRP), the first reprocessing plant in Japan, has discharged low-level liquid wastes to the Pacific Ocean since the start of its operation in 1977. We have performed liquid effluent monitoring to realize an appropriate radioactive discharge control. Comparing simple and rapid analytical methods with labor-intensive radiochemical analyses demonstrated that the gross-alpha and gross-beta activities agreed well with the total activities of plutonium isotopes (238 Pu and 239þ240 Pu) and major beta emitters (e.g., 90 Sr and 137 Cs), respectively. The records of the radioactive liquid discharge from the TRP showed that the normalized discharges of all nuclides, except for 3 H, were three or four orders of magnitude lower than those from the Sellafield and La Hague reprocessing plants. This was probably due to the installation of multistage evaporators in the liquid waste treatment process in 1980. The annual public doses for a hypothetical person were estimated to be less than 0.2 mSv y À1 from the aquatic pathway. Plutonium radioactivity ratios (238 Pu/ 239þ240 Pu) of liquid effluents were determined to be 1.3-3.7, while those of the seabed sediment samples collected around the discharge point were 0.003-0.059, indicating no remarkable accumulation of plutonium in the regional aquatic environment. Thus, we concluded that there were no significant radiological effects on the public and the aquatic environment during the past 30-year operation of the TRP. KEYWORDS: monitoring, liquid effluent, discharge control, Tokai reprocessing plant (TRP), Plutonium radioactivity ratio (238 Pu/ 239þ240 Pu), gross alpha, gross beta, tritium (3 H), gamma emitters, strontium-89 and strontium-90 (89 Sr, 90 Sr)

Cesium, iodine and tritium in NW Pacific waters – a comparison of the Fukushima impact with global fallout

“…The surface 137 Cs concentrations in the western and eastern belt decreased exponentially during the period 1970-2000 (except a small peak observed in 1986 due to the Chernobyl accident), with effective half-lives of 16.5 ± 0.9 yr and 10.6 ± 0.5 yr, respectively. Higher 137 Cs concentrations in surface water occurred in the 1980s, probably due to liquid radioactive discharges from the nuclear fuel reprocessing plant at Tokai, which were, however, by several orders of magnitude lower than releases from the European reprocessing plants (Mizutani et al, 2009). By combining all 137 Cs data, the mean effective half-life of 137 Cs in North Pacific surface waters was estimated to be 13 ± 1 yr (Povinec et al, 2005a).…”

Tritium Concentration and Diffusion in Seawater Discharged from Tokai Reprocessing Plant

“…Another was obtained in seawater collected at 0.35 km around the outlet after the discharge. At that time, 3 H concentration in the effluent was lower than those in the other effluents. Moreover, 3 H concentration in the seawater was a little higher than in the other seawaters.…”

“…At that time, 3 H concentration in the effluent was lower than those in the other effluents. Moreover, 3 H concentration in the seawater was a little higher than in the other seawaters. Therefore, it would not be considered as a direct influence from the discharge, but it was regarded as the influence by the previous discharges before collected these samples or by discharged effluents from the other facilities.…”

“…Empirical equation estimating 3 H concentration was used in diffusion calculation as shown in Eq.(1). The equation was utilized in the safety assessment of the TRP to evaluate the 3 H concentration in seawater from the outlet to the stream direction.…”

“…Figure 1 shows the actual discharge of 3 H to sea from the TRP. The maximum annual 3 H amount was about 0.5 PBq in 1994, which was less than one fourth of the maximum authorised discharge of 3 H activity. The TRP discharged 4.5 PBq of 3 H to the sea during the operation in all.…”