Study on thermal transient strength evaluation method using cylindrical struetural test data; Proposal of an advanced creep-fatigue damage evaluation method and comparison with a conventional one for the prototype fast reactor

Kawasaki, Nobuchika ; kasahara, Naoto

As main components of fast reactors, there are reactor vessels, pipes, heat exchangers, nozzles. In order to keep their structural integrity, the elevated temperature structural design guide evaluates primary stress, strain, and creep-fatigue damage of them. Especially in fast reactors which operate under low pressure and high temperature conditions, creep-fatigue damage is dominant, and limits a design range. For the purpose of extending a design range, author evaluated strength of cylindrical structures by an advanced proposed method based on the generalized elastic follow-up model. Furthermore we studied evaluation accuracy of a method of 'monjyu" and a proposed method, through comparison of thermal transient strength test data with damage calculated by two strength evaluation methods. Results are summarized as follows. (1)An advanced proposed method predicted lower fatigue damage (Df) than a method of 'monjyu'. (However, in structural discontinuities where an elastic follow up is large, a proposed method shows higher damage than a method of 'monjyu'.) (2)An advanced proposed method calculated lower creep damage (Dc) than a method of 'monjyu'. (About 0.7 times lower in a cylindrical structure with a structural discontinuity (STF-3). About 0.1 times lower in a cylindrical structure without a structural discontinuity (STF-10). (3)On no-crack portions in STF-3, prediction of a method of 'monjyu' is out of a limit of crack initiation, nevertheless one of an advanced proposed method is within the range. Through above results, an advanced proposed method was evaluated to be more accurate in prediction of creep-fatigue damage. We concluded from the above investigation that we calculated more rational and lower damage by proposed method, and it has the possibilities to get extension of a design range.