MECHANICAL PROPERTY EVALUATION OF REACTOR MATERIALSBY ION BOMBARDMENT SIMULATION
M.Shimada
Nuclear Engineering Laboratory, TOSHIBA Corporation'Abstract
To induce radiation damage in the materials, it has been
widely known to use ion bombardment simulation technique especially in the regime of void swelling. A few MeV metallic ions, suchas Ni+ 1) or few tens of MeV of c++ 2) or Ni6+ 3) are the examples.
As those ions penetrate, at most, a few micrometers beneath thetarget surface, the electron microscopic observation is the major
possible postirradiation evaluation method.
In this work, two experiences will be presented, where byusing higher accelerating energies and lighter ion species, thebombarding ion can penetrate through the target materials, leaving
only radiation damage within the materials.
1.

Creep under irradiation

The creep in-reactor may differ from the thermal creep behavior because of the co-occurance of damage production and plastic
deformation. There is, in reality, an observation that the creep
rate under irradiation is several times faster than the thermal
creep rate4).
There are, however, some difficulties in c.arrying out irradiation creep in-reactor under well controlled experimental conditions from the point of facility capability as well as economicalallowability. For these reasons, the ion irradiation simulation
technique has been applied to irradiation creep.
3.5 MeV protons were irradiated to zirconium alloy (Zircaloy2) at a rate of 6xlo-7 dpa/s at 325°C and the correlation between
stress and creep rate was studied. The elongation during irradiation was measured by LVDT 9Linear Variable Differentioal Transformer) of which sensitivity is 5xlo-6 em.
As a result, it was shown that the creep rate is proportional to the applied stress and that even under no stress, theelongation (irradiation growth) was observed.
2.

Ductility loss in iodine environmentS)

To study mechanical property of irradiated materials, 52 MeValpha particles were irradiated to dumbbell shaped specimens at
340°C up to 4xlol8 a/cm2 by Harwell VEC cyclotron. The overall
dimension is 33mm long by 0.4mm thick; the reduced gauge sectionis 18mm long by 2.5mm wide. Prior to the irradiation, three different kinds of heat treatment were given to the specimens. In somecases, 100 MPa of stress was applied during irradiation. Postirradiation tensile test was performed at a strain rate of 6.4x
l0-4/min in argon gas or 4 Torr. of iodine gas environment at atemperature of 350°C.
In both test environment, the ductility loss began to appear-289-

from the 4xlol7~/cm2 dosage. And the ductility loss appeared more
prominent in iodine environme nt indicating the occurrenc e ofstress corrosion cracking. The ductility loss was also affectedby preirradia tion heat treatment , where 580°C annealed specimen
showed the most resistant character . The stress applied during
irradiatio n enhanced the ductility loss and lowered the on-set
dosage of ductility loss compared to the stress free irradiatio n.
As shown by the above examples, the ion bombardme nt has many
usefull advantage s in oerformin g irradiatio n experimen t in elaborate condition s in a short duration. Besides radio-act ivity induced by ion bombardme nt is very much lower than by reactor irradiations.
Reference s1)2)
3)
4)
5)

W.G.Johns ton, J.H.Rosolo wski and A.M.Turka lo,
J. Nucl. Mater., 47 (1973) 155.
J.A.Hudso n, D.J.Mazey and R.S.Nelso n,
Proc Reading Con£., "Voids Formed by Irradiatio n of Reactor
Materials ", BNES, 1971, p213.
J.A.Hudso n, S.Francis , D.J.Mazey and R.S.Nelso n,
ASTM STP 529, "Effects of Radiation on Substruct ure andmechanica l Propertie s of Metals and Alloys", 1973, p326.
E.R.Gilbe rt,Reactor Technolog y, 14 (1971) 258.
M.Shimada , M.Terasaw~ S.Yamamot o and K.Koizumi ,to be published in Proc. Symp. on the "Effect of Radiation
on Materials" ,ASTM, Savannah, Gergia, USA, 1980.

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