Neutron Irradiation Damage to a Reactor Pressure Vessel Wall.
Neutron irradiation alters the material properties of metals. Of concern to the fission power community is the embrittlement and loss of toughness of the steel used to fabricate the reactor pressure vessel and core components. Because these changes are undesirable, they are called radiation damage. Radiation damage is caused by microstructural change that is somehow induced or enhanced by the neutron -lattice interactions. An essentially instantaneous set of events follows the collision of a neutron with a lattice atom, and therefore the damage process is partitioned into an instantaneous and evolutionary regime. The events of the instantaneous regime are those which derive their energy from the incident neutron and are the subject of this dissertation. They are the neutron-nucleus interaction, the displacement cascade, and spontaneous recombination. If present, thermal vibrations in the lattice cause the evolutionary phenomena of short - and long-term annealing to occur, and they in turn, enhance the process of micro-structural evolution. The new computer programs called DCS and ANNEAL were written to simulate displacement cascades and spontaneous recombination, respectively. For cascades in BCC iron, initiated by primary knock-on atoms with energies from 1 to 100 keV, the displacement efficiency (beta ) was found to be 0.897. The fraction of initial defects surviving recombination (gamma) was found to be 0.383. Exposure units based on these results are the first to compare acceptably with the irradiation damage measured by electrical resistivity change at 4.6 ^circ K, without the use of ad hoc, unphysical, simulation parameters. To study the behavior of different exposure units in a PV wall, very detailed neutron spectra for a power reactor were calculated. The spectrum calculations were facilitated by two new utilities for the DOT program: VMESH and VSOURCE. These utilities manage the complexity of using a "problem optimized" mesh to represent the complex geometry of a power reactor more accurately than has been previously practical.
- Pub Date:
- Engineering: Nuclear; Physics: Radiation