Until recently the only equipment for spotting a suitcase bomb was an unwieldy machine the size of a refrigerator, using liquid nitrogen to cool crystal detectors down to 300 degrees below zero and taking hours to produce a reading.

FORBES: Stopping Porta-Nukes

Until recently the only equipment for spotting a suitcase bomb was an unwieldy machine the size of a refrigerator that used liquid nitrogen to cool crystal detectors down to 184 degrees Celsius below zero and took hours to produce a reading.

FORBES: Stopping porta-nukes

There are a number of different reactors in use, most commonly water-cooled pressurised or boiling water reactors - though other reactor types are kept cool with the help of liquid metal, gas or molten salt.

BBC: Will Japanese crisis curb the rise of nuclear power?