Research on calculation and verification of hazardous area for radioactive sewage entering into the ocean

Abstract

To improve the emergency disposal capacity of radioactive sewage entering into the ocean, concentration distribution and hazardous area were observed and calculated. Haiyang nuclear power station and its surrounding coastal waters were selected as the research object. Based on Euler method, calculation model of concentration distribution and hazardous area with radioactive sewage entering into the ocean was established with a resolution of 1′ × 1'. Radionuclide concentration distribution and hazardous area were calculated under an assumed nuclear leakage accident and an assumed radioactive sewage discharge event with a plan. The study show that, under the given conditions of an assumed nuclear leakage accident, radionuclides of 137Cs are mainly distributed within about 81 km east, 39 km south and 33 km west of the nuclear power station after fourteen days. While under the given conditions of an assumed radioactive sewage discharge event with a plan, radionuclides of 3H are mainly distributed within about 58 km east, 14 km south and 23 km west of the nuclear power station after fourteen days. Compared with the total amount of source term, the high concentration is reduced by about 8 orders of magnitude. Area with radioactivity lower than 100 Bq/L is considered to be safe area, that more than 100 Bq/L（105Bq/m3）to be hazardous area, then the hazardous area account for about 50% of the main radionuclide distribution area. The hydrodynamic result was verified, and the maximum error between calculation and measurement velocities in flow field was less than 10%. The radioactive result was verified, and changes of radionuclide concentration in this research basically agreed with the monitoring data from the Fukushima Daiichi nuclear accident. So the model is considered to be reasonable and credible.