Form and structural response calculations for NIF neutron exposure sample case assembly design

We describe the calculations used to design an aluminum foam protection layer for a stainless steel neutron exposure sample case. The layer protects the case from impulsive loads generated by a 20 MJ NIF capsule 10 cm from the sample case assembly. Impulse only from ablating x-rays and hohlraum plasma debris is considered. One dimensional CALE foam response calculations and analytic estimates are used to show that 1 cm of aluminum 6101-T6 foam 10 % of solid density is sufficient to attenuate the incoming peak pressure without complete melting on crush-up. Two dimensional DYNA calculations show that a 304 stainless steel spherical shell sample case with an inner radius of 1 cm and a wall thickness of 2 mm encased in 1 cm of foam does not yield to the pressure that is transmitted through the foam by a 220 Pa-sec (2.2 ktap), 2 GPa (20 kbar) load due to recoil of x- ray ablation. An unprotected spherical shell case subjected to a gentler load with peak pressure reduced to 0.2 GPa (2 kbar) not only yields but its effective plastic strain exceeds the failure point of 0.4 in 304 stainless steel after 160 microseconds. Doubling the impulse for the protected case to approximately account for debris loading results in very localized yield and an effective plastic strain that does not exceed 0.014. (U)