Effect of enhanced ionizing radiation on the cloud electricity after the Fukushima nuclear accident

Abstract

The vertical downward component of the DC atmospheric electric field, or potential gradient (PG), at Kakioka 150 km southwest of the Fukushima Dai-ichi Nuclear Power Plant (FNPP1) was analyzed before and after the FNPP1 accident to examine possible influence of floating radioactive particles on the PG under the highly electrified clouds. Using 1-min PG data from March 13 to April 30 (late April 2011 corresponding to the time when floating radioactive materials decreased significantly) from 2006 to 2015, time profiles to/from the PG peaks (<− 100 or >+ 100 V/m) for 2011 are compared with other years. The PG developed toward and decays from its negative peaks faster in the first 50 days after the FNPP1 accident than for the same period in other years, making the 10-min averaged PG values for the same negative PG peak higher (smaller in terms of absolute value) during the first 50 days after the FNPP1 accident than those in other years in the study period, while the distribution of peak PG values is similar between 2011 and the other years. The observed shortening of the timescale is symmetric between the rise and decay and is the most clear when the negative PG peak is about − 200 to − 400 V/m. For positive peaks, the change of the baseline resulting from the radioactive contamination on the ground in 2011 caused superficial difference on such time profiles. Otherwise, there are no significant difference between 2011 and the other years. Possible explanations based on increased ionizing radiation from floating radioactive particles, which are found to be concentrated at low altitudes (< 500 m according to radiosonde in-situ observations of gamma rays) where negative cloud charges normally exceed positive charges, are discussed. The scenarios discussed include enhanced electrostatic shielding and electric conductivity-led decay rate of cloud charges. The result opens up a new possibility of using PG as an independent monitor of radioactivity at some altitudes in case of nuclear accidents.

Nature of Relationships Between Atmospheric Electricity Parameters at Ground Surface and Air Ionization on the Basis of Nuclear Accidents in Power Plants and Weapons Tests

“…During nuclear explosions, nuclear lightning can occur on the electric charge distribution in a strong electric field (Holzer, 1972;Williams et al, 1988). There may be a negative charge at the top of the thundercloud (Holzer, 1972), unlike the proposed model of Yamauchi et al (2018).…”

“…If the air-Earth current measurements were carried out, one would expect bipolar pulses related to the time change in space charge radioactive cloud. The model of the radioactive cloud or aerosol with polarized electric charges (positive at the top, negative at the bottom) was proposed by Yamauchi et al (2018) to analyze spikes in the course of an electric field during the Fukushima accident. During nuclear explosions, nuclear lightning can occur on the electric charge distribution in a strong electric field (Holzer, 1972;Williams et al, 1988).…”

Historical data of atmospheric electric field observations in Japan

“…For example, it has been reported that the PG at KAK and MMB decreased due to radioactive materials released by nuclear test explosions in the 1950s and 1960s (Kondo, 1959, 1963) (Figure 2). Moreover, it has been found that the PG at KAK was affected by radioactive materials released by the Fukushima Daiichi nuclear power plant accident in 2011 (Takeda et al, 2011; Yamauchi et al, 2018).…”