COBEM99

S25 Métodos Numéricos

Title:

A STUDY ON BRITTLE FRACTURE IN PWR VESSELS UNDER PRESSURIZED THERMAL SHOCK WITH ASYMMETRIC REFRIGERATION

Summary :

ABSTRACT. IN THIS STUDY WE DEVELOP A METHODOLOGY FOR MAPPING OPERATIONAL CURVES (PRESSURES IN THE VESSEL VERSUS COLD LEG TEMPERATURE), TO AVOID BRITTLE FRACTURES UNDER PRESSURIZED THERMAL SHOCK WITH ASYMMETRIC REFRIGERATION. THE METHODOLOGY BEGINS BY A THERMAL ANALYSIS OF SEVERAL TRANSIENTS WITH AN ASYMMETRIC REFRIGERATION OF THE BELTLINE REGION (THE FLUID TEMPERATURE OF THE VESSEL INNER WALL DEPENDS ON THETA AND THE MAXIMUM HEAT TRANSFERENCE COEFFICIENT IS TAKEN FOR ALL TEMPERATURES). THE THERMAL PROBLEM IS SOLVED BY USING A HYBRID METHOD OF FINITE ELEMENTS AND A GLOBAL BASE FOR SPATIAL DEPENDENCY. AN IMPLICIT SCHEME OF FINITE DIFFERENCES, AS THE EULER S, HAS BEEN USED FOR TEMPORAL DEPENDENCY. LATER, A STRESS ANALYSIS WAS CARRIED OUT CONSIDERING A QUASI-STATIONARY MODEL. A HYBRID METHOD IS USED, ONCE AGAIN, TO OBTAIN A THERMOMECHANICAL STRESSES PROFILE. FINALLY, THERMOMECHANICAL STRESSES ARE POST-PROCESSED TO CARRY OUT THE FRACTURE MECHANICS ANALYSIS USING THE LINEAR-ELASTIC FRACTURE MECHANICS MODEL. OPERATIONAL BOUNDING CURVES (PRESSURE VERSUS COLD LEG TEMPERATURE) ARE PRESENTED FOR A TYPICAL PWR. THESE CURVES PROVIDE THE OPERATORS WITH INFORMATION RELATED TO THE PLANT S SAFETY STATUS CONCERNING THE POSSIBILITY OF A BRITTLE FRACTURE IN THE BELTLINE REGION. KEYWORDS: BRITTLE FRACTURES, THERMAL SHOCK

Author :

Alvarez, Gustavo Benitez
Dutra do Carmo, Eduardo Gomes
Roberty, Nilson Costa

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