Abstract
Radioactive gas of Unit 1 of the Fukushima Daiichi Nuclear Power Station was released from the exhaust stack shared by Units 1 and 2 through the venting line on March 12th, 2011. In the present study, radiochemical analysis of drain water sampled at the drain pit of the exhaust stack was conducted to study radionuclides released during venting of the Unit 1. Not only volatile 129I, 134Cs and 137Cs but also 60Co, 90Sr, 125Sb and Unit 1-originated stable Mo isotopes were detected. Although Unit 1-originated stable Mo isotopes were clearly detected, their amounts were quite low compared to Cs, suggesting that the formation of Cs2MoO4 was suppressed under the accident condition. Approximately 90% of iodine existed as I− and 10% as IO3− in November 2020. Furthermore, larger amount of 129I than 137Cs was observed, suggesting major chemical form of 131I was molecular iodine rather than CsI at the accident time. The 134Cs/137Cs radioactivity ratio decay-corrected to March 11th, 2011 was 0.86, supported the results that Unit 1 originated radiocesium in environment has smaller 134Cs/137Cs radioactivity ratio than Unit 2 and 3 originated radiocesium.
Highlights
Because of the tsunami caused by The Great East Japan Earthquake, TEPCO’s Fukushima Daichi Power Station ammonium phosphomolybdate (AMP) Ammonium phosphomolybdate (Nuclear) Power Station (FDNPS) lost all electric power, followed by the severe accidents at Units 1, 2, and 3
The results indicated a rapid release kinetics for volatile (I, Cs, Te) and even for semi-volatile (Mo, Ba) fission products (FPs) during oxidizing condition and re-volatilization of iodine during air injection on the contrary to Cs
Drain water sampled at the drain pit of the exhaust stack shared by Units 1 and 2 was analyzed to obtain the information about components and chemical species of radionuclides released by vent of Unit 1
Summary
Because of the tsunami caused by The Great East Japan Earthquake, TEPCO’s Fukushima Daichi Nuclear Power Station (FDNPS) lost all electric power, followed by the severe accidents at Units 1, 2, and 3. While many source term studies have assumed Cs chemical form as CsI and CsOH, recent studies pointed out possible formation of C s2MoO45–7,14–18, CsBO219, Cs2CrO419,20, Cs2Si4O919, and C sAlSiO421 The formation of these chemical species would be related to the leakage pathways since some reports indicated the production of Cs2Si4O9 and CsAlSiO4 via chemisorption of Cs onto stainless steel and reaction with concrete[22,23]. Radiochemical analysis of samples collected inside of FDNPS buildings has been planned to improve severe accident analysis and source term. Drain water sampled at the drain pit of the exhaust stack shared by Units 1 and 2 was analyzed to obtain the information about components and chemical species of radionuclides released by vent of Unit 1. Salinity and pH of the drain water were preliminary measured using salinometer and pH test paper, and they were 0.01% and neutrality
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