Flux effects on defect production and damage accumulation in cu and fe exposed to211 IFE-like conditions

摘要

Radiation damage production and accumulation in solids can be divided into two211u001estages. In the production stage, the impinging particle gradually gives off its 211u001ekinetic energy to lattice atoms in the form of energetic recoils. These deposit 211u001etheir energy by generating secondary and higher order recoils that result in a 211u001edisplacement collision cascade. The outcome of this stage, of the time scale of a 211u001efew to 100 picoseconds, is a population of point or clustered defects known as 211u001ethe primary state of damage. In the second stage, which can extend over seconds, 211u001edefects that survive recombination within their nascent cascade migrate over long 211u001edistances, interacting with the microstructure. These freely migrating defects 211u001e(FMD) are responsible for the changes in the macroscopic properties of metals 211u001eunder irradiation, such as void swelling, embrittlement, radiation enhanced 211u001ediffusion, etc. Such changes in mechanical properties are most often detrimental 211u001eand severely limit the flexibility in materials choice and operating temperature 211u001ewhen designing a fusion power plant. Under most conditions, such as those that 211u001ewould be present in a magnetic fusion energy plant, or when bombarding with 211u001efission or spallation neutrons, irradiation takes place at a certain dose rate 211u001eand temperature, but in a continuous manner. However, in an Inertial Fusion 211u001eEnergy (IFE) reactor, or when using a pulsed neutron source such as that recently 211u001eproposed by Perkins (1), the irradiation flux is pulsed and the interplay between 211u001etemperature, flux and pulse frequency controls the kinetics of damage 211u001eaccumulation. For sufficiently low pulse frequency, and at elevated temperature 211u001ewhere the defects migrate fast, it may be expected that annealing between pulses 211u001emay result in a significantly decreased rate of damage accumulation compared to 211u001ethat seen under steady state conditions. On the other hand, very high neutron 211u001efluxes in the pulse itself may severely limit recombination therefore leading to 211u001eextremely fast rates of damage accumulation even at elevated temperatures.