Photon Factory Activity Report 2022 #40 (2023)

BL-27B/2020G606

Structural analyses of insoluble residue (platinum group metals) in high-level
radioactive waste
1

Koki SAKASHITA1, Haruaki MATSUURA 1, Isamu SATO 1, Haruka TADA 2
Tokyo City University, 1-28-1, Tamazutsumi, Setagaya-ku, Tokyo, 1588557, Japan2
IHI Corporation, 1, Shin-Nakahara-cho, Isogo-ku, Yokohama, 235-8501, Japan

1 Introduction
During reprocessing process of spent fuels, fineinsoluble residue including fuel cladding materials aregenerated considerably. This residue is contained the highlevel radioactive waste and is the alloy called as “platinumgroup metals”. The composition varies depending on thefuel fissile composition, irradiation history, reprocessing
conditions and so on (e.g., high burnup fuel and MOX fuel,which are being considered for reprocessing in the future).
And platinum group metals can have adversely affected
vitrification process for the high-level radioactive waste.
Therefore, it is necessary to investigate the effect ofplatinum group alloys composition change is necessary tovitrify the stable waste.
In this study, platinum group metals simulated alloys
with some compositions depending on fuel types wereanalyzed the structure to study the effect of platinum groupalloys on vitrification such as, EXAFS structure analyses
were performed to clarify the local structure of Mo, Ru in
the platinum group alloys.
2 Experiment
The composition of platinum group alloys wasdetermined by literature survey and others [1]. In thealloying process, pellets were made from the quantitative
powder mixture, alloyed by the arc melting method (Aratmosphere), and then embedded in epoxy resin andpolished. These samples were collected at the High Energy
Accelerator Research Organization (KEK) at the BL-27B
beamline. The Mo-K and Ru-K absorption edges weremeasured by EXAFS using the fluorescence method withthe SSD detector.
3 Results and Discussion
The EXAFS radial structure functions (RDF) of thealloy samples (Fig. 1) shows a peak at around 2.5 Å, whichindicates the Mo and first neighbor metal correlationreferring to epsilon phase (the hexagonal close-packingstructure) [2]. However, the intensity of the peak in thelarger percentage of Mo (Arc#3) is extremely smaller thanthe peaks in the less percentage of Mo (Arc#1 and 2),
which is thought to be due to the distortion of thehexagonal closed packing structure in the alloy. This trend
on structural variation depending on molybdenum
composition must be affected to oxidation behavior byheating, thus we will evaluate the bulk samples after
heating treatment by focusing on EXAFS of multielements.

Fig. 1: EXAFS radial structure functions of various
alloy samples. #1:Mo20Ru60Rh10Pd10,#2:Mo15Ru55Rh15Pd15,#3:Mo40,Ru45Rh7.5Pd7.5

References[1] I. Yamagishi et al, Global 2015, in proc. Paris, France,
September 20-24, 2015.
[2] H. Kleykamp, Journal of the Less Common Metals,136(1988) 271-275.
Acknowledgement
This research is a part of the results of the "FY2021 Basic
Research Project on Vitrification Technology for Volume
Reduction of Radioactive Waste (JPJ010599)" of theAgency for Natural Resources and Energy, Ministry ofEconomy, Trade, and Industry.
* g2081806@tcu.ac.jp, hmatuura@tcu.ac.jp