Study On The Mechanism Of Aluminum Irradiation Damage

Aluminum and its alloy have been widely applied in many reactors. It is the generally material of choice for construction of many components in Chinese research reactors. To ensure our reactors safety, we require the mechanical properties of aluminum under irradiation of high accumulative neutron fluence rate. Now, SPRR-300(Swimming Pool Research Reactor-300) is out of commission, so we can gain and research the aluminum material under neutron irradiation.The process of irradiation damage is extremely complex. We can’t research it just through experiment, and computer simulation can explain the process clearly. According to the neutron spectrum of SPRR-300, we have first calculated PKA(Primary Knock-on Atom) spectrum of core boarding, and the PKA with 10keV has been chosen as the most important investigative object. Then, classical MD(Molecular Dynamics) with the embedded atom method potential has been used to simulate collision cascades caused by PKA and investigate the production of point defects and their clusters. We have also investigated the effects of different PKA’s energy and temperature on the defects formed in collision cascades of Al. When the temperature keeps steady, the number of point defects increases quickly as PKA’s energy grows. When the PKA’s energy remains unchanged, the number of interstitials and vacancies decrease as temperature grows. At last, density, volumetric heat capacity and edge dislocation of aluminum under irradiation have been simulated. Results show that density and volumetric heat capacity have changed a little bit after cascades, but edge dislocation of aluminum has changed obviously. This change may cause the tensile strength of aluminum to increase and the tenacity to decrease.Aluminum material in SPRR-300 under long-term irradiation during the whole lifetime of the reactor has deeply changed in properties. We must calculate the accumulative neutron fluence rate of aluminum to research the change. Firstly, all reactor core loadings have been incorporated into four groups. Then, neutron fluence rate of four typical reactor cores have been calculated with MCNP5 program respectively. Consequently, the neutron fluence rate during the lifetime of the reactor in core boarding location is obtained. According to the data, three test zone have been chosen and their accumulative neutron fluence rate are 2.33 X 1020n/cm2,1.02×1021cm2 and 2.15×1021n/cm2 respectively. Finally, three test zone have been machined and tested. Test results show that as accumulative neutron fluence rate rises, the hardness of aluminum alloy LT21 increases only a little and the extensibility decreases slightly, at the same time, the tensile strength of aluminum alloy LT21 increases obviously. For example, sample 3#’s accumulative neutron fluence rate is about 10 times higher than sample 1#, and the tensile strength of sample 3# is 17.7% stronger than sample 1#.