Degradations of Thermal Shock Resistance and Fracture Toughness of Neutron Irradiated Reactor Graphite

Abstract

This paper deals with the irradiation effects on the thermal shock resistance Δ = σ_tk/Eα (σ_t : tensile strength, k: thermal conductivity, E: Young's modulus, α: thermal expansivity) and the thermal shock fracture toughness ∇=K_Ick/Eα (K_Ic : fracture toughness value of mode I) in addition to other mechanical properties such as the diametral compressive strength and fracture toughness of two kinds of near isotropic graphite neutron irradiated at 750∼1,000°C to a dose of (1.1 ∼ 1.5)10²¹ n/cm² (>29 fJ). One of the graphite specimen is an isostatically molded graphite IG-11 with fine grain petroleum coke and the other is a binderless molded graphite HCB-18 which was prepared using mesophase pitch carbon with very fine grain size. These measurements are carried out by means of disk testing method developed by us. Results show that both the thermal shock resistance and the thermal shock fracture toughness of the two kinds of graphite after irradiation decrease considerably in contrast with increasing trends of the usual mechanical strengths.

KEYWORDS:

• fracture toughness
• graphite
• irradiation
• mechanical properties
• neutron beams
• physical radiation effects
• thermal shock
• thermal shock resistance