Mr Cook, surrounded by officials with Geiger counters, spent the day at Atomflot, the plant that stores and processes liquid waste from Russia's atomic icebreakers as well as the rotting submarines of its Northern Fleet.
Environmentalists say there are some 300 discarded reactor cores, or 20 per cent of the world's total, on the peninsula and warn that leaks into the sea could affect Norway andBritain.
The Foreign Secretary said Britain would give money for new storage casks to hold the waste safely until it could be reprocessed. "Britain by itself cannot solve the problem," he said. "I hope what we do in Murmansk is something of a catalyst for the release of more resources."
Norway and the European Union have already granted $100m (pounds 64.1m) but tens of billions are said to be required for a thorough clean up, which could take 40 years.
"Part of the problem," said Mr Cook, "is the lack of openness and the fact that we're getting close to what they [the Russians] see as the heart of their defence sector."
British officials said the Foreign Secretary would tactfully take up the case of Alexander Nikitin, a former Soviet naval captain now facing treason charges for having blown the whistle on pollution to a Norwegian environmental organisation.
From Murmansk, Mr Cook flew to Moscow, where he will meet the Russian Foreign Minister, Igor Ivanov. The US Secretary of State, Madeleine Albright, had a rough ride on her recent visit to Russia, when relations between Moscow and Washington were frostier than at any time since the Cold War. Britain may also feel the chill because of its involvement in the bombing of Iraq. "But we hope we can agree to differ on some things, if we and the Russians are still friends," said a British official.
On Yugoslavia, where the West and Russia also fail to see eye to eye, Mr. Cook will try to persuade Mr Ivanov that Russia should take part in any Nato-led peacekeeping operation in Kosovo.
At the end of the week, Mr. Cook will have his first meeting with Yevgeny Primakov, the Prime Minister, and the man who really runs Russia, at Sochi on the Black Sea.