Photon Factory Activity Report 2022 #40 (2023)

BL-27B/2020G606, 2022G618

Penetration behavior of cesium and iodine into epoxy coatings
Daiki FUJINO1 *, Isamu SATO1, Eriko SUZUKI2 and Haruaki MATSUURA1
1Tokyo City University, 1-28-1, Tamazutsumi, Setagaya-ku, Tokyo, 1588557, Japan
2JAEA, Shirakata, Tokai-mura, Ibaraki, Japan

1 Introduction
In the decommissioning of the Fukushima Daiichi
Nuclear Power Plant, it is necessary to treat and dispose of
the associated dismantling waste safely and rationally. The
decommissioning of the Fukushima Daiichi NuclearPower Plant requires safe and rational treatment anddisposal of the associated dismantling waste. For thispurpose, it is necessary to accurately determine theproperties and distribution of radioactive materials
attached to or immersed in various structural materials of
the reactor before and after dismantling, and to provide
appropriate treatment and disposal accordingly. In thisstudy, we focus on epoxy coatings used for concrete
structures and CsI solution as a contamination source andaim to investigate the local structure of these elements by
XAFS measurement to clarify the penetration behavior ofCs and I into epoxy resin coatings.
2 Experiment
Solidified epoxy resin E205 (Konishi Co., Ltd.) for civilengineering and construction was placed in a pressure
vessel as an immersion sample, into which 1M CsI solution
was poured, the lid was closed, and the vessel was placedin a constant-temperature oven at 110oC for 5, 10, and 40
days, respectively. After the soaking period, the epoxy
resin sample was dried, shaved down to 0.9 mm every 0.3
mm from the surface, and pellet-formed from powder form.
Among them, the third layer (0.6~0.9 mm) sample
immersed for 10 days, NaI reagent, and CuI reagent wereselected as the I-edge specimens. On the other hand, twosamples were selected for the Cs arrival: the first layer(0~0.3 mm) sample immersed for 5 days and the first layer(0~0.3 mm) sample immersed for 10 days. Cs and I were
measured simultaneously by the fluorescence method
focusing on the absorption edges L3.
3 Results and Discussion
Figure 1 shows the results of the derivation up to theradial structure function with respect to I. From theseresults, the only sample in which a prominent peak
appeared was the CuI reagent, and the peak seen around 4
Å may be the correlation between I and I. However, nosignificant peaks were observed in the NaI reagent of theother two samples and in the third layer (0.6~0.9 mm)sample immersed for 10 days. We believe that this islargely due to the fact that the EXAFS oscillations for I
were potentially weak.
On the other hand, the results for Cs up to the radial
structure function are shown in Figure 2. Unlike theprevious radial structure function for I, the result shows apronounced peak.
Therefore, we considered the peak around 4 Å as thecorrelation between Cs and I bonding, and the peak around2.5 Å as the correlation between Cs and O bonding, andperformed fitting analysis. We found that the bonding
correlations were correct, with the coordination number ofCsI decreasing and the coordination number of Cs-O
increasing with increasing immersion duration. Thissuggests that Cs itself does not permeate the epoxy resin,but that Cs that is unbound from the Cs-I bond graduallybinds to O in the CsI solution or to O on the resin surface.
On the other hand, we believe that the unbound I of CsI
will cause penetration into the epoxy resin.

Fig. 1: Radial structure functions for I (yellow: CuI, blue:NaI, green: 3rd layer after 10 days of immersion)

Fig. 2: Radial structure functions for Cs (blue: 1st layer
after 5 days of immersion, green: 1st layer after 10 daysof immersion, purple: CsOH reagent)Acknowledgement
This research is part of the results of joint research with
Tokyo City University and Japan Atomic Energy
Agency.
*g2281813@tcu.ac.jp