Why nuclear missile inventories are expensive to maintain

Is maintaining an inventory of roughly 125 nuclear intercontinental ballistic missiles expensive?

Yes; exact costs are difficult to isolate, but nuclear forces demand much higher safety and reliability assurance than an ordinary system can accept.

Maintaining a large nuclear missile inventory is expensive, although exact pricing is difficult to extract. Nuclear forces cannot be managed on the assumption that a system is merely probably safe or mostly reliable. Their maintenance burden reflects the exceptional assurance expected of both warheads and delivery systems.