Mechanical Properties of Fast Reactor Fuel Cladding for Transient Analysis

Abstract

In order to determine mechanical behavior under various simulated reactor transient events, internally pressurized specimens of fast flux-irradiated 20 percent cold-worked Type 316 stainless steel fuel pin cladding were rapidly heated until they burst. Tests were conducted at heating rates of 10F°/s and 200°F/s with pressures of 2500 to 14 300 psi (17.2 to 98.6 MPa), resulting in failure temperatures from 1000 to 2000°F (811 to 1366 K). The specimens were taken from subassemblies irradiated in the Experimental Breeder Reactor-II at temperatures from 700 to 1300°F (644 to 978 K). Peak burnup and fluence levels ranged from 28 000 to 50 000 megawatt days per metric ton metal (MWd/MTM) and 2.5 to 4.0 × 1022 neutrons (n)/cm2 (E > 0.1 MeV), respectively. Irradiation degraded both the failure strain and failure strength, when the transient test conditions resulted in intergranular fracture; intergranular fracture occurred above 1000 to 1200°F (811 to 922 K), depending on strain rate. Below these temperatures the fracture mode is transgranular, so that the failure strength is not reduced. A correlation based on the ratio of irradiated material failure strain and failure strength was developed to describe the effects of irradiation on the mechanical properties of the cladding. The strain ratio correlation indicates that the failure strain does not further decrease beyond a fluence of 2 × 1022 n/cm2. The mechanical properties of cladding which had contained fuel during irradiation were degraded more than were the properties of unfueled material.

Fuel Pin and Assembly Design

“…As with the steady-state fuel pin performance, there is also a Fuel Adjacency Effect exhibited under transient conditions for some cladding materials [16,17]. Both the Larson-Miller parameter and the Dorn parameter, as well as other correlation approaches, have been used to describe the dependence of fast reactor irradiated 20% cold worked 316 stainless steel cladding on the irradiation and transient conditions.…”

Gas-Cooled Fast Breeder Reactor preliminary safety information document, Amendment 9. GCFR fuel cladding PC-5 (faulted) temperature limit

“…Analyses using the LIFE-3 computer code (Ref. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] indicate that, in the GCFR rod design, the pellet-to-clad diametrical gap never completely closes during steady-state lifetime operation. The presence of the relatively high primary system pressure within the rod suppresses the gaseous fission product component of fuel swelling.…”

“…(1) it reduces the oxygen available in the coolant for reaction with the stainless steel cladding, and (2) it affects the oxidation rate (Ref, [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19].…”

“…[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. The parabolic rate constant in dry air is extremely low up to '\^1370°C (2500°F).…”

Vacancy Type Defects in Oxide Dispersion Strengthened Steels

“…The knowledge about ageing-induced changes in terms of microstructure of the structural materials and in the fuel cladding [2,3] is not sufficient for the Gen IV reactors. Therefore, structural materials (included those developed for the Gen IV) have to be tested and the results of these tests need to provide microstructural interpretation.…”