Abstract
Papers written by Russian researchers on matters concerned with implementing the “Zero Fuel Rod Defect Concept” are reviewed. The results from investigations of structural, technological and operational factors causing loss of fuel rod (FR) leak tightness are considered. The purpose of these studies is to find the root cause affecting the efficiency of a particular fuel assembly (FA) and to make changes for eliminating it. The results of the study aimed at establishing a correlation between the degradation of defective FRs and the fuel operating parameters are presented. The results obtained from testing the models of FRs and FAs for VVER reactors and Kvadrat type FAs for a PWR-900 reactor for fretting-induced wear under the conditions of the PWR reactor water chemistry are analyzed. It is shown that experimental physical modeling of fretting wear for FA fragments with ensuring similarity and possibility of extending the results for the standard FA is an approach based on which fretting wear can be combated. Based on reviewing the results of numerous investigations, conclusions are drawn about the need to refine data on the level of hydrodynamic loads (in particular, when resonances occur) and to refine data on the content of non-condensable gases in the coolant in the operating reactor under different operating conditions. For verifying the design and technological solutions, for substantiating the reliability and operability of new-generation FRs and FAs, for elaborating recommendations on further improvement of the designs and manufacturing technology, and for developing and certifying computer codes, the following must be carried out and used: integrated experimental investigations of the basic regularities pertaining to the dynamic interaction between the coolant flow and fuel, and the changes in the properties and characteristics of fuel for VVER-type reactors; combined application of theoretical and experimental methods for investigating an abnormal growth of the FR and FA vibration levels in order to predict the conditions of their occurrence, and to identify and prevent them. Refinement of these data will make it possible to solve strategic objectives such as increasing the fuel burnup depth, constructing repairable FAs, and substantiating the fuel efficiency in maneuvering modes and under the conditions of increased reactor power.
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