JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構

Radiation-induced H2 Production and Reactions of OH
Radical in Aqueous Solutions Containing Ceramic Oxides
Y. Kumagai, R. Yamada and R. Nagaishi
Division of Environment and Radiation Sciences, NSED, JAEA
Influence of coexistent solid ceramic oxide on
radiation-induced reactions and their final products in
aqueous solutions has been reported especially on the
molecular hydrogen (H2) production 1) . The mechanism of
influence in the heterogeneous system, however, is still to be
investigated in order to understand the radiation effect on
water in contact with solid oxides. In the present studies,
the dose rate dependence of the H2 production and the
reaction of OH radical in reduction process of dichromate
2
ion (Cr2O7 ) in the presence of ceramic oxides were
conducted.
The samples were aqueous solutions containing ceramic
oxides. Irradiation experiments were carried out at
JAEA-Takasaki using 60 Co -ray source. The absorbed
dose was measured by the CTA-film dosimeter or the
dichromate chemical dosimeter.
Dose rate dependence of H2 production
The sample for the H2 production measurement is
aqueous 0.4 mol·dm -3 (≡ M) sulfuric acid (H2SO4) solution
containing 33 wt.% of alumina particles. After irradiation,
produced gas was analyzed by gas chromatography. As
references H2 from aqueous solution only and pure water
were also measured.
In the presence of alumina particles, the yield of H2 depended clearly on the dose rate in the range of our
experiment (0.08 – 20 kGy/h). The results are shown in
Fig. 1. The yield became higher with increasing the dose
rate. For the reference samples, no significant change in
the yield was observed.
The peculiar dose rate dependence and the high yield of
H2 in the presence of alumina particles suggest that H2 is
produced through a reaction pathway induced by the
H2 Production Yield: G Value / mol J -1
4-28
0.25
0.2
0.15
0.1
0.05
0
○ 0.4M+Al2O3
0.4M+Al2O3 □ 0.4M 0.4M
◇ Pure Water
Pure Water
16hrs irradiation
1hr irradiation
0.1 1 10
Dose Rate of irradiation (kGy/hr)
Fig. 1 Dose rate dependence of H 2 production yield in
0.4 M H 2SO 4 solution containing 33 wt.% of alumina
(○), 0.4 M H 2SO 4 solution (□), and pure water (◇).
JAEA-Review 2010-065
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addition of alumina particles besides the intra-spur reactions
of water radiolysis. In the intra-spur reactions, the yield of
H2 is 0.047 mol·J -1 and should have no dose rate
dependence in this dose rate range of -irradiation.
2
OH radical reaction in Cr2O7 reduction process
The sample for the reaction of OH radical is aqueous
0.1 M perchloric acid (HClO4) solution of 1 mM potassium
dichromate (K2Cr2O7) containing 9.1 wt.% of silica gel
saturated by nitrogen. Silver perchlorate (AgClO4) was
added to the samples as an OH radical scavenger. After
2
irradiation the concentration of Cr2O7 in supernatant
separated from the samples was measured by UV-Vis
spectroscopy.
The observed reduction yields in the presence and
absence of silica gel are shown in Fig. 2. The difference
between the yields of these two series also shown in Fig. 2
indicates the addition effect of silica gel. The difference
decreased with increasing concentration of Ag + and then
seemed to reach a plateau.
The effect of silica gel increasing the reduction yield of
2
Cr2O7 was partially inhibited by the addition of silver ion
(Ag + ). This suggests that, because scavenging of OH
radical in this concentration range of Ag + occurs from 0.1 to
1 s after the energy deposition, coexistence of silica gel has
influences on both the chemical and earlier physicochemical
stages of radiation-induced reactions, which divided at
around 0.1 s after the energy deposition by radiation.
Reference
1) R. Yamada et al., Int. J. Hydrogen Ener. 33 (2008) 929.
Fig. 2 Observed yield of Cr2O 7 2 reduction in the presence
(●) and absence (○) of 9.1 wt.% of silica gel in 0.1 M
HClO 4 solution as a function of concentration of Ag + .
Decrease of the deference of these two (■) indicates
that Ag + inhibited the addition effect of silica gel.