Development of two in-core gas release devices has been completed. Both of these passive devices are sealed with low-melting-point, fusible materials and can produce controlled, predictable releases of gas. The two devices can simulate typical burst and slow gas releases from reactor fuel pin cladding breaches and will be used during acceptance testing of the Fuel Failure Monitoring System of the Fast Flux Test Facility. A series of feature tests was first performed to demonstrate the feasibility of using fusible plugs to seal gas capsules and achieve controlled, predictable releases. Development efforts continued with a gas loading demonstration and gas release characterization studies of both types of capsules. Finally, a water flow test was conducted in a full-scale prototype gas release capsule assembly to verify structural integrity of the design.