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Abstract

HIGH-TEMPERATURE GAS-COOLED REACTORS (HTGR) HAVE MASSIVE BLOCKS OF GRAPHITE WITH THERMAL AND NEUTRON-FLUX GRADIENTS CAUSING HIGH INTERNAL STRESSES. THERMAL STRESSES ARE TRANSIENT; HOWEVER, STRESSES GENERATED BY DIFFERENTIAL GROWTH DUE TO NEUTRON DAMAGE CONTINUE TO INCREASE WITH TIME. FORTUNATELY, GRAPHITE ALSO EXPERIENCES CREEP UNDER IRRADIATION ALLOWING RELAXATION OF STRESSES TO NOMINALLY SAFE LEVELS. BECAUSE OF COMPLEXITY OF IRRADIATION CREEP EXPERIMENTS, DATA DEMONSTRATING THIS PHENOMENON ARE GENERALLY LIMITED TO FAIRLY LOW FLUENCES COMPARED TO THE OVERALL FLUENCES EXPECTED IN MOST REACTORS. NOTABLE EXCEPTIONS HAVE BEEN EXPERIMENTS AT 300 C AND 500 C RUN AT PETTEN UNDER TENSILE AND COMPRESSIVE CREEP STRESSES TO FLUENCES GREATER THAN 4 X 10 E26 (E>50 KEV) NEUTRONS/M2. THIS PRESENT STUDY COMPLEMENTS PREVIOUS RESULTS BY EXTENDING THE IRRADIATION TEMPERATURE TO 900 C. IT IS SHOWN THAT THE EFFECT OF INCREASING THE IRRADIATION TEMPERATURE TO 900 C IS TO ACCELERATE THE BEHAVIOUR OBSERVED AT THE LOWER TEMPERATURES (300 AND 500 C). THE CREEP BEHAVIOUR AT ALL TEMPERATURES CAN BE CHARACTERIZED BY A DECREASING CREEP RATE WITH INCREASING CREEP STRAIN, FOLLOWED LATER BY AN INCREASE IN CREEP RATE. A MODEL TO DESCRIBE THE CHANGE IN RESISTANCE TO CREEP CONSIDERING THE DENSIFICATION OF THE GRAPHITE IS PRESENTED. THE AGREEMENT OF THE RESULTS WITH THE MODEL IS SHOWN TO BE EXCELLENT.

Additional information

Authors: KENNEDY C R OAK RIDGE NATIONAL LABORATORY, TENNESSEE/USA CUNDY M JRC-PETTEN KLEIST G KFA, JUELICH, D , OAK RIDGE NATIONAL LABORATORY, TENNESSEE/USA;JRC-PETTEN;KFA, JUELICH, D
Bibliographic Reference: PAPER PRESENTED: CARBON 88, NEWCASTLE-UPON-TYNE/UK, SEPT. 18-23, 1988, AVAILABILITY: CEC-LUXEMBOURG, DG XIII/A2, BP 1907, MENTIONING PAPER ORA 34100 E
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