Alien From The Deep (1989)

"Alien From The Deep" is an "Alien" rip-off made by Italians so, of course, it's excellent. A pair of greenies sneak into a nuclear power plant on a volcanic island (not a better place in the world the build one of those) and find themselves running and screaming from a giant radio-active yabbie. Lots of pus and goo and killer cobras and Charles Napier shooting an infected member of staff in the head because "Nothing spreads quicker than fear!"