Measurement and evaluation of the irradiation test parameters for a specimen in a HANARO material irradiation capsule
A material capsule system has been developed for irradiation tests of nuclear materials in the core region of the High-flux Advanced Neutron Application Reactor (HANARO) and has been actively utilized for the various material irradiation tests requested by numerous users. For an irradiation test in the reactor, nuclear characteristics and irradiation temperature of the capsule parts are basically necessary for the safety analysis of the capsule and capsule detail design. The irradiation temperature and neutron fluence of the specimens are key parameters required by a user to analyze any neutron irradiation damage effects. Based on a basic design of a capsule, the reactivity effect, neutron flux/fluence, and gamma heating of specimens are calculated by the MCNP code. To compare the calculated neutron fluence of the specimens, thermal and fast fluence monitors (F/Ms) are installed in a capsule. After an irradiation, the F/Ms are dismantled and analyzed to obtain a neutron spectrum. The obtained fast neutrons (E>1.0MeV) by using the SANDII code are located within about a 20% error range of the theoretical values calculated by the MCNP code. The irradiation temperature of the specimens is analyzed preliminary by using the GENGTC or ANSYS codes based on the basic design of a capsule and gamma heating. During an irradiation test, the temperatures of the specimens in a capsule are measured and monitored by thermocouples. The DPA (Displacement Per Atom) and activation of the irradiated specimens are also evaluated by using the SPECTOR and ORIGEN2 codes, respectively, at HANARO.
Design of a New Capsule Controlling Neutron Flux and Fluence and Temperature of Test Specimen
A new capsule that has a unique structure in which the test environments including neutron flux and fluence, and irradiation temperature can be controlled precisely during irradiation, was conceptually designed. The capsule structure and instrumentation were successfully designed according to the JMTR's standard procedures of capsule design. Based on the target irradiation, the details of the irradiation such as neutron fluence and irradiation temperature ore calculated and the related capsule safety was evaluated. In addition, the effects of design parameters including the changes in inner-capsule configuration, heater capacity, and Helium gas pressure on the specimen temperature were analyzed with a computer program. Through these thermal and strength evaluations, this capsule was proved to be safe during the irradiation in the JMTR.
The need for improved temperature control during reactor irradiation
Abstract The irradiation conditions of materials irradiated in fission reactors are nearly always insufficiently described in the literature. A carful inspection of temperature-reactor power histories reveals a deficiency in the conventional control of irradiation temperatures. In particular, a short transient irradiation at a lower temperature commonly occurs during the startup of the reactor. A large difference in the final defect structure is expected to be caused by this transient irradiation from the mechanism of the defect structure development. An electron irradiation with a similar transient irradiation leads to a remarkably different defect microstructure. The defect structures introduced by a fission neutron irradiation with this transient was compared with those produced by a fusion neutron irradiation with perfect temperatrue control without transient. The difference in structures was found to be much greater than what is normally expected between fission and fusion neutron irradiations. An essential improvement in the control of reactor irradiations is proposed.