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

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Alpha-Ray Irradiation Damage on Rubber Applied for
Glove Box for Plutonium Powder Treatment
K. Saito, Y. Nogami and H. Endo
Plutonium Fuel Development Center, NFCEL, JAEA
Currently, for economical reasons, newly improved
long-lasting glove is desired and under development at
Plutonium Fuel Development Center (Pu center), Tokai,
JAEA. For the basic step of the development, helium ion
irradiation experiments have been conducted in order to
evaluate α-ray effects against the glove rubber material. In
these experiments 1, 2) , not only dose (ion fluence) but also
temperature increase caused by ion flux was suggested as
one of the possible factors of material deterioration. The
separation of the factors is important to apply experimental
data to glove box condition. Therefore, the experiment
was conducted to confirm the effect of the temperature
increase.
Sample material is chlorosulfonated polyethylene (CSM)
glove which SANKO CHEMICAL INDUSTORY CO. Ltd.
manufactures and Pu center mainly employs. JIS K 6251-7
dumbbell-shaped pieces cut from the rubber materials were
irradiated in a vacuum with 4 He 2+ ion beam generated from
3MV tandem accelerator in TIARA. The kinetic energy of
the accelerated ion was 5 MeV close to the average energy
of α rays emitted from plutonium isotopes. To evaluate the
effect of temperature increase caused by irradiation, ion flux
was varied while fluence was kept constant. Fluence was
set at the level of 0.2 ~ 3 years by 2.9 MBq/cm 2 of
α-contamination, i.e. 0.9 ~ 14 × 1013 cm -2 . Flux, duration,
the corresponding absorbed dose and its rate were 1.3 ~ 15 ×
10 10 p/cm 2 /s, 2 ~ 180 min, 1.9 ~ 28 MGy and 9.4 ~ 111 MGy/h,
respectively. Four sample pieces were simultaneously
irradiated for one condition and the irradiated samples are
sent to visual inspection and two tensile tests: tensile
strength and elongation at break. Experiments were
divided into two parts and tensile tests were performed at
July and November. Since temperature may impact the
result of tensile tests, non-irradiated samples were tested in
each experiment.
Up to the fluence of 1.4 × 1014 cm -2 , there are no
differences observed in surface appearance for various flux
levels as shown in Fig. 1. The results of tensile tests are
shown in Table 1. Tensile strength decreases with increase
of fluence, and elongation at break slightly does. However,
there is not the obvious indication of the differences from
flux variation.
In the experiments, the direct measurement of sample
temperature was desired, but it is not easy because of the
irradiation chamber geometry and instrumentation.
Therefore, consideration about sample temperature was
given with indirect evidences, such as the decomposition
temperature of CSM and the pressure of the irradiation
chamber, on the supposition that the specific heat of the
JAEA-Review 2010-065
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rubber is constant. The consideration indicates that the
possible maximum temperature is 31 C at the minimum ion
flux irradiation in the present study. This temperature is
within the range of ordinary environmental condition in
plutonium-charged glove boxes. In conclusion,
experimental data is available only in view of fluence.
Another “cold” experiment of tensile test was performed
to strengthen the interpretation of the results described
above. The target of this test is non-irradiated samples
with surface incision whose depth has variation. Some
reduction of tensile strength and little change of elongation
at break were observed for interpolated 30 μm-depth-incised
samples. This result fairly agrees with the ones of
irradiated samples which have about 30 μm-thickness
damaged layer by ion bombardment, and bolsters the
conclusion of the irradiation experiments.
The obtained data are unexampled and quantitative ones
for α damage of glove and its material.
References
1) K. Saito et al., JAEA Takasaki Ann. Rep. 2007 (2008)
20.
2) K. Saito et al., JAEA Takasaki Ann. Rep. 2008 (2009)
28.
3.7×10 10 p/cm 2 /s 7.4×10 10 p/cm 2 /s 10×10 10 p/cm 2 /s
Fig. 1 Photographs of irradiated surface with the fluence
of 1.4 × 1014 cm -2 .
Tensile
strength
Elongation
at break
Table 1 Results of tensile tests.
Ion flux
(cm -2 s -1 )
Fluence (cm -2 )
[Relative values*]
9.1E+12 4.6E+13 1.4E+14
3.7E+10 93.8% 88.8% 80.1%
7.4 E+10 92.0% 88.2% 80.6%
1.0 E+11 92.3% 90.1% 76.6%
3.7E+10 98.7% 96.9% 97.5%
7.4 E+10 98.9% 98.7% 97.5%
1.0 E+11 99.3% 99.5% 95.8%
*Normalized to non-irradiated samples.