Integrity Assessment of HANARO Irradiation Capsule for Long-Term Irradiation Testing

The capsule technology was basically developed for irradiation testing under a commercial reactor operation environment. Most irradiation testing using capsules has been performed at around 300 .deg. C within four reactor operation cycles (about 100 days equivalent to 1.5 dpa (displacement for atom)) at HANARO. Based on the accumulated experience as well as the sophisticated requirements of users, HANARO has recently been required to support national R and D projects requiring much higher neutron fluence. To scope the user requirements for higher neutron irradiation fluence, several efforts using an instrumented capsule have been applied at HANARO. In this paper, the applied stresses on the capsule are estimated because the capsule was suspected to be susceptible to fatigue failure during irradiation testing. In addition, the on-going design improvements of the irradiation capsule for higher neutron irradiation fluence at HANARO are described. The applied stresses on the rod tip were analyzed using the ANSYS program. The applied stresses on the rod tip can be classified into stresses by the designed bottom spring, by the upward flowing coolant, by the capsule vibration, and by the welding residual stress. The maximal stresses due to the first three factors were estimated as 5.4 MPa, 132.9 MPa, and 161 MPa, respectively. These stresses do not exceed the known fatigue strength of stainless steels (∼300 MPa). Residual stress by welding is another possible stress and it is known to occur at up to about 300 MPa.