Analysis of a Nuclear Accident: Fission and Activation Product Releases from the Fukushima Daiichi Nuclear Facility as Remote Indicators of Source Identification, Extent of Release, and State of Damaged Spent Nuclear Fuel

Abstract

This document was printed on recycled paper.

135Cs/137Cs Isotopic Ratio as a New Tracer of Radiocesium Released from the Fukushima Nuclear Accident

“…The 135 Cs/ 137 Cs isotopic ratios of forest litter samples (S1−S3 and S5) and the lichen sample (S4) collected in the 20−50 km zone in the northwest direction from the plant site and a soil sample (S6) collected in J-Village south of the plant site ( Figure 1) were analyzed in this study; the 240 Pu/ 239 Pu isotopic ratios in litter samples S2 and S3 and soil sample S6 were reported previously. 26 We found that 135 Cs/ 137 Cs isotopic ratios in the litter and lichen samples collected northwest from the FDNPP site had very similar values, ranging from 0.333 to 0.343 (reference to March, 11,2011). No significant variation in the 135 Cs/ 137 Cs isotopic ratio could be observed, although the activities of 137 Cs were extremely different, ranging from 0.12 to 4.65 MBq/kg, in these litter and lichen samples, indicating that radioactive Cs isotopes deposited on the surface of litter and lichen were mostly released from the same source in the FDNPP.…”

Radiocesium transfer from hillslopes to the Pacific Ocean after the Fukushima Nuclear Power Plant accident: A review

“…However, these shortlived isotopes disappeared quickly and were primarily below detection limits by late April 2011 . 239 Pu (T 1/2 ¼ 24,100 y), 240 Pu (T 1/2 ¼ 6560 y)) were also detected (Table 1), although only in trace levels Schneider et al, 2013;Schwantes et al, 2012). Steinhauser (2014) comprehensively reviewed radionuclides that may have been released by the FDNPP accident which have received less attention.…”

Radioiodine in the atmosphere after the Fukushima Dai-ichi nuclear accident

“…The decay-corrected 131 I-to-137 Cs ratios in the sumps and trench water in the reactor buildings, from Akihide and Ishikawa's (2014) estimates, were about 4.2 for unit 1, 17 for unit 2, and 14 for unit 3. A 1:1 ratio between 134 Cs and 137 Cs was consistently observed among the emissions from the Fukushima accident (Ohnishi, 2012;Butler, 2011;Chino et al, 2011;Kobayashi et al, 2013;Schwantes et al, 2012), and given this, the 131 I/( 134 Cs þ 137 Cs) ratio in the accumulated water would likely have been about 2, 9, and 7 for the three units. Akihide and Ishikawa's estimates were all based on sump water activity concentration measurements taken by TEPCO between March 26, 2011, and April 22, 2011(Akihide and Ishikawa, 2014.…”

“…The remainder of the accident at the TEPCO-owned plant has been well documented (Ohnishi, 2012;Butler, 2011;Chino et al, 2011;Kobayashi et al, 2013;Schwantes et al, 2012). Hydrogen explosions occurred in the reactor buildings of unit 1 (March 12 at 15:36), unit 3 (March 14 at 11:01), and unit 4 (March 16 at 05:45), destroying large parts of the outer superstructures.…”

“…This information will then be used to make some conclusions about conditions inside the Fukushima Dai-ichi plant. Schwantes et al (2012), for example, have already concluded from soil samples around the Fukushima site that the reactor units 1 and 3 were the primary source of radionuclide emissions, and that all coolant had likely boiled off from the damaged reactors prior to the releases. They made these conclusions based on observed isotopic ratios, and how they compared with ORIGEN ARP fission product inventory calculations and knowledge of fuel thermochemistry.…”