T. Matsuoka et al., INTERGRANULAR CRACKING IN CLADDING TUBE OF PWR RCCA RODLETS, JSME international journal. Series A, mechanics and material engineering, 38(4), 1995, pp. 515-523
Increase in outer diameter of the rod cluster control assembly (RCCA)
rodlets in a PWR plant was observed. Visual inspections of RCCA rodlet
s with large increases in outer diameter using a fiber scope and hot c
ell examinations of some RCCA rodlets lead to the following conclusion
s. (1) The increase in outer diameter was caused by the swelling of th
e absorber (Ag-In-Cd alloy). (2) At the RCCA rodlet tip, which was exp
osed to the largest amount of neutron fluence, an axial crack in the c
ladding tube was observed. (3) From the tensile test of cladding tube
material, the uniform tensile strain was reduced to about 1.4% at 320
degrees C due to neutron irradiation. In the slow-strain-rate tensile
test, intergranular cracking was observed. (4) From the above, it is c
onsidered that the axial cracking in the cladding tubes of PWR RCCA ro
dlets was caused mainly by a decrease in elongation due to neutron irr
adiation and an increase of hoop strain due to the swelling of the abs
orber.