In BWRs the reactor core shroud is a large cylinder of stainless steel which serves to direct flow around the core. Recent examinations of core shrouds have revealed the presence of circumferential cracks at the core shroud welds. If the 360deg. cracks went all the way through the weld thickness, the free floating shroud could disrupt the coolant flow, and cause damage to the reactor internals.
 
 

One of the issues that has recently come to the fore in radiation damage is the influence of displacement mechanisms other than fast neutron collisions (e.g.(n,a) and (n,[gamma]) reactions) on the degradation of materials. This is because it has become clear that the fraction of defects that actually survives the first picoseconds after creation is much higher in [gamma] irradiation than fast neutron irradiation, which could compensate for the lower displacement rate from [gamma]'s compared to neutrons.

At Penn State we are conducting collaborative research with Dr.Haghighat's research group to determine the extent of gamma damage in the cracked regions. This research couples detailed transport calculations of the gamma and neutron flux with the development of displacement cross sections for displacement damage from the Compton effect. Preliminary results indicate that Compton displacements originated from [gamma]s could be a factor. Calculations are also being conducted on the He production in the welds.
 
 

Researchers: J.Kwon, A.T.Motta, B.Petrovic, A.Haghighat.

 Funding: FERMI Project