A tamper which surrounds a fissile core works to reflect neutrons and to add inertia to the compression of the Pu-239 charge.

They compress the fissile core, or pit, of the warhead until it reaches critical mass.

The smaller stores (known as "Hutches") were constructed to hold the fissile core of the weapons.

In total, there were 55 hutches giving enough capacity to store 64 fissile cores.

The latter is known as core-and-blanket, because a fissile core produces the heat and neutrons while a separate blanket does all the breeding.

That can be used for reactor fuel, or - if further enriched - the fissile core of a weapon.

The levitated pit design made it practical to allow in-flight insertion of pits to the bombs, separating the fissile core from the explosives around it.

Wrapping the weapon's fissile core in a neutron reflector (which is standard on all nuclear explosives) can dramatically reduce the critical mass.

Those pellets simultaneously explode to initiate a high-explosive hemisphere that crushes the fissile core, triggering the chain reaction.

Use of a tamper In a bomb, a dense shell of material surrounding the fissile core will contain, via inertia, the expanding fissioning material.