Safety and control philosophy of radiation loaded vessel components

In the current preparation of WWER-440 and WWER-1000 reactor inspections increased care is devoted to nondestructive and destructive testing of surveillance specimens. The program is based in the assumption that a pressure vessel may be divided in two regions. Region I is a part adjacent to the reactor core with neutron irradiation where no zone of stress concentration practically exists so that the increase in the number of defects due to cyclic load is negligible. What is of importance are material properties. For this region mainly surveillance specimen destructive testing is applicable. Region II consists of the remainino. part of the pressure vessel where radiation effects are not operative while zones of stress concentration are frequent, ie., an increased number of defects occur due to cyclic or other loads. Changes in the properties of material due to aging, however, cannot be excluded. For this region, mainly nondestructive compact testing is of importance. In designing and implementing in-service inspections both regions of a pressure vessel should considered with regard to the corresponding type of testing. (O.K.)