Target irradiation systems for the production of radioisotopes

A target irradiation system comprising:

• a fission reactor having a vessel penetration and a calandria;
• a target delivery assembly mounted in the vessel penetration;
• the target delivery assembly having a target well, the target well including an outer tube and an inner tube disposed therein so that a first annulus is formed therebetween, a target being positioned in the inner tube during irradiation;
• at least one flow channel extending between a bottom end of the outer tube and a bottom end of the inner tube to allow flow of a propellant medium between an interior of the outer tube and an interior of the inner tube;
• and
• a movable elevation piston slidably disposed within the inner tube to elevate the target, the elevation piston including a one-way check valve allowing flow in a downward direction and preventing flow in an upward direction.