Nondestructive evaluation of high-temperature elastic modulus of nuclear graphite using an impulse excitation method
Eung-Seon Kim, Min-Hwan Kim And Yong-Wan Kim
The high-temperature elastic modulus of selected nuclear graphite was measured in an argon environment using an impulse excitation method, and the fundamental porosity parameters such as the pore size and distribution, pore volume, and surface area of nuclear graphites were determined using a mercury porosimeter and compared with one another. A pyrolytic graphite and six grades of nuclear graphite were used. The elastic modulus was measured at 20 to 1200°C in an Ar gas environment using a commercial impulse excitation apparatus (RFDA HTVP 1600, IMCE). The elastic modulus of nuclear graphite increased with an increase in temperature regardless of the grade, and changes in the elastic modulus during the heating and cooling processes were also observed. The higher positive temperature dependence and larger hysteresis of the modulus in high density and medium-grained graphite is attributed to their higher closed porosity. The pore size distribution became relatively broader with an increasing coke particle size, and the pore surface area decreased inversely with the bulk density and the closed porosity.