Although the reactor machinery – steam generators, pumps, valves and piping – now contains no enriched uranium, the metals in it are rendered radioactive by decades of neutron bombardment shredding their atoms. So after fuel removal, the sub is towed into dry dock where cutting tools and blowtorches are used to sever the reactor compartment, plus an emptied compartment either side of it, from the submarine's hull. Then thick steel seals are welded to either end. So the canisters are not merely receptacles: they are giant high-pressure steel segments of the nuclear submarine itself – all that remains of it, in fact, as all nonradioactive submarine sections are then recycled.

Russia also uses this technique because the West feared that its less rigorous decommissioning processes risked fissile materials getting into unfriendly hands. At Andreeva Bay, near Sayda, for instance, Russia still stores spent fuel from 90 subs from the 1960s and 1970s, for instance. So in 2002, the G8 nations started a 10-year, $20bn programme to transfer Puget Sound's decommissioning knowhow to the Russian Federation. That involved vastly improving technology and storage at their de-fuelling facility in Severodvinsk and their dismantling facility, and by building a land-based storage dock for the decommissioned reactors.

Floating menace

Safer land-based storage matters because the reactor blocks had been left afloat at Sayda Bay, as the air-filled compartments either side of the reactor compartment provide buoyancy, says Bohmer. But at Pavlovks, near Vladivostok, 54 of the canisters are still afloat and at the mercy of the weather.

Decommissioning this way is not always possible, however, says Bohmer. Some Soviet subs had liquid metal cooled reactors – using a lead-bismuth mixture to remove heat from the core – rather than the common pressurised water reactor (PWR). In a cold, defunct reactor the lead-bismuth coolant freezes, turning it into an unwieldy solid block. Bohmer says two such submarines are not yet decommissioned and have had to be moved to an extremely remote dockyard at Gremikha Bay – also on the Kola Peninsula – for safety's sake.