mass spectrometry (HR-ICP-MS), the IDM has been applied to lanthanide nuclides.
The developed method was applied to the measurement of isotopic composition of
used BWR 9 Â 9 fuel and evaluation of the burn-up calculation code was carried
out [5].
After the accidents at Fukushima Dai-ichi Nuclear Power Plants (hereafter
referred to as 1F) of Tokyo Electric Power Company (TEPCO) in 2011, we need
a confirmed method to assay the composition of the fuel irradiated in 1F to carry out
decommissioning of the Fukushima site. For this purpose, JAEA has a further
measurement plan of not only BWR but also PWR used fuel to obtain enough
experience to measure the isotopic composition of the irradiated nuclear fuels.
This report summarizes the analytical procedure to measure the amount of
fission products isotopes developed in JAEA and the future measurement program.
6.2 Analytical Procedure
The objective fission products required for reactivity assessment are samarium,
europium and gadolinium. Cesium-133 is also required. Of the important fission
products, several metallic isotopes exist in the barely dissolved residue:
97 Mo,
99 Tc,
101 Ru,
103
Ru, and
109 Ag.
We decided to adopt the isotopic dilution method (IDM) and the calibration
curve method to measure the amounts of the stable fission products. For this
purpose, we introduced the high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS), ELEMENT2 of Thermo Fisher Scientific (Photo 6.1). This
instrument has very high sensitivity and enough precision and accuracy to measure
the isotopic ratios of objective elements belonging to the rare earth elements.
In this technical development, five samples taken from ZN2 (average burn-up is
35.6 GWd/t) and ZN3 (average burn-up is 53.5GWd/t) fuel assemblies of used fuel
of Fukushima Dai-ni Nuclear Power Plant Unit 1 (2F-1) were used for demonstrating the measurement method. Sample positions are shown in Figs. 6.1, 6.2, and 6.3.
Five fuel samples taken from ZN2 and ZN3 fuel assemblies were dissolved initially
in 3 M nitric acid solution at about 110
C, then the dissolution residue was
dissolved again in mixed solutions of nitric, hydrochloric, and sulfuric acid at
180
C.
Before the measurement of isotopic ratio, the isobar should be separated to avoid
contamination. Figure 6.4 shows a schematic of chemical separation. The dissolution solutions of spent fuels were filtrated and the filtrate solution was fed to an
anion-exchange resin of UTEVA (Eichrom, USA) to separate U, Pu, and Nd
individually. Figure 6.5 shows the yields of lanthanide in each fraction eluted
from the Ln resin column in the separation experiment using a simulated dissolution
solution of spent fuel. U and Pu in the solution were effectively separated from the
solution with more than 95 % efficiency. The eluate solution from the UTEVA resin
column was fed to the Ln resin column. Lanthanides elements were separated with
hydrochloric acid solutions in the Ln resin column.
6 Development of the Method to Assay Barely Measurable Elements in Spent. . .
49
The developed method was applied to the measurement of isotopic composition of
used BWR 9 Â 9 fuel and evaluation of the burn-up calculation code was carried
out [5].
After the accidents at Fukushima Dai-ichi Nuclear Power Plants (hereafter
referred to as 1F) of Tokyo Electric Power Company (TEPCO) in 2011, we need
a confirmed method to assay the composition of the fuel irradiated in 1F to carry out
decommissioning of the Fukushima site. For this purpose, JAEA has a further
measurement plan of not only BWR but also PWR used fuel to obtain enough
experience to measure the isotopic composition of the irradiated nuclear fuels.
This report summarizes the analytical procedure to measure the amount of
fission products isotopes developed in JAEA and the future measurement program.
6.2 Analytical Procedure
The objective fission products required for reactivity assessment are samarium,
europium and gadolinium. Cesium-133 is also required. Of the important fission
products, several metallic isotopes exist in the barely dissolved residue:
97 Mo,
99 Tc,
101 Ru,
103
Ru, and
109 Ag.
We decided to adopt the isotopic dilution method (IDM) and the calibration
curve method to measure the amounts of the stable fission products. For this
purpose, we introduced the high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS), ELEMENT2 of Thermo Fisher Scientific (Photo 6.1). This
instrument has very high sensitivity and enough precision and accuracy to measure
the isotopic ratios of objective elements belonging to the rare earth elements.
In this technical development, five samples taken from ZN2 (average burn-up is
35.6 GWd/t) and ZN3 (average burn-up is 53.5GWd/t) fuel assemblies of used fuel
of Fukushima Dai-ni Nuclear Power Plant Unit 1 (2F-1) were used for demonstrating the measurement method. Sample positions are shown in Figs. 6.1, 6.2, and 6.3.
Five fuel samples taken from ZN2 and ZN3 fuel assemblies were dissolved initially
in 3 M nitric acid solution at about 110
C, then the dissolution residue was
dissolved again in mixed solutions of nitric, hydrochloric, and sulfuric acid at
180
C.
Before the measurement of isotopic ratio, the isobar should be separated to avoid
contamination. Figure 6.4 shows a schematic of chemical separation. The dissolution solutions of spent fuels were filtrated and the filtrate solution was fed to an
anion-exchange resin of UTEVA (Eichrom, USA) to separate U, Pu, and Nd
individually. Figure 6.5 shows the yields of lanthanide in each fraction eluted
from the Ln resin column in the separation experiment using a simulated dissolution
solution of spent fuel. U and Pu in the solution were effectively separated from the
solution with more than 95 % efficiency. The eluate solution from the UTEVA resin
column was fed to the Ln resin column. Lanthanides elements were separated with
hydrochloric acid solutions in the Ln resin column.
6 Development of the Method to Assay Barely Measurable Elements in Spent. . .
49