The Fracture Toughness of Nuclear Graphites Grades

Abstract

New measurements of graphite mode I critical stress intensity factor, K Ic (commonly referred to as the fracture toughness) and the mode II critical shear stress intensity, K IIc , are reported and compared with prior data for K Ic and K IIc. The new data are for graphite grades PCEA, IG-110 and 2114. Variations of K Ic and acoustic emission (AE) data with graphite texture are reported and discussed. The Codes and Standards applications of fracture toughness, K Ic , data are also discussed. A specified minimum value for nuclear graphite K Ic is recommended.

Fundamental Graphite Irradiation Behavior Research at ORNL for FY23

“…OG-1 was irradiated in position C-3 in the ORR for cycles 113-115 (3200 full-power hours), at temperatures of 600°C to 1400°C and neutron fluences of 1.6-3.7x10 21 n/cm 2 [E>0. 18 MeV]. Some samples were previously irradiated in GEH-13-422 capsules at PNNL with General Atomics, while some OG-1 samples were included in OG-2 for additional fluence accumulation.…”

“…In this report the authors changed the fluence units from fast fluence in the water moderated ORR [n/cm 2 E>0. 18 MeV] ORR to fluence values that are expected for a gas-cooled reactor [n/cm 2 E>0.18 MeV] HTGR . The conversion used is: Fluence [n/cm 2 E>0.…”

“…The conversion used is: Fluence [n/cm 2 E>0. 18 MeV] HTGR = 0.894 × Fluence [n/cm 2 E>0.18 MeV] ORR .…”

Status Report on ASME Code Development for Nonmetallic Core Components in 2020

“…[9]. However, compared with fine-grain graphite such as IG-110 and NG-CT-10, previously identified [10,11], the code approach is ultra-conservative on its calculations when only grain size is used to define the process zone volume (V m ) size.…”

“…More detail and background on the validity of the proposed change as it relates to graphite properties, component geometry, and stress gradients is provided in ref. [11]. Table 2 shows the implication or suggested changes of the rule for different graphite grades.…”