Materials irradiation tests have been carried in Japan Materials
Testing Reactor (JMTR) with a large-scale loop that simulates
the LWR's in-core high-temperature environment. The large-scale
loop, however, had disadvantages of high cost in operation and
maintenance and of low irradiation volume in the reactor. JAERI
has successfully developed a new type water loop called as "saturation
temperature capsule" shown in Fig. 8-1. The new capsule does not need the large water
loop but has a function of water loop inside the capsule. It replaced
the large one by reducing the irradiation cost and by making all
holes available for irradiation tests. A difference between the
specimen surface temperature and the saturation temperature of
water slightly increases with increasing heat flux produced by
the gamma heating in the region of boiling curve from nucleating
boiling to burn-out. The ideas of this capsule are to control
the saturation temperature by changing the water pressure injected
into the capsule. Consequently the specimen surface temperature
is kept nearly at saturation temperature as shown in Fig. 8-2.
For instance, when the water pressure is 87 atm, the irradiation
temperature of specimen will become about 300 degrees.
Figure 8-3 shows the performance of this capsule. Corrosion rate
for the LWR's fuel cladding materials (zircaloy-4) was measured:
the corrosion rate under irradiation agrees with predicted lines
well. As reference data the corrosion rate measured in unirradiated
test was also shown in the figure. The effect of irradiation environment
on the cladding materials is to increase the corrosion rate. |
