Question

   How void swelling differs from irradiation growth?

Answer 1

Solution:

Void swelling is one of the irradiation effects that potentially have a significant impact on the service performance of core internals. Excess void swelling not only leads to dimensional instability, but also can cause severe embrittlement of internal materials at elevated temperatures. Austenitic stainless steels (SSs) used in LWR core internals are known to be prone to void swelling at certain temperatures and neutron flux ranges. Nanometer-scale cavities, which are three-dimensional aggregations of vacancies, can develop in materials exposed to fast neutron bombardments.12 A direct consequence of void formation is volumetric dilation of irradiated materials. Under select irradiation conditions, volumetric swelling of more than a few percent can readily be established in SSs with moderate neutron exposure. An example is volume increase of a Type 316 SS fuel cladding tube used in fast breeder reactors was visible to the unaided eye. This type of instability is obviously a significant safety concern and engineering challenge.

Irradiation growth is defined as irradiation induced changes in dimensions in the absence of an applied stress, is of concern both for fuel cladding and nuclear reactor structural components such as pressure tubes and calandria tubes. While void swelling is defined an increase in the external dimension of solid materials after irradiation.