A Nazi submarine described as an ‘underwater Chernobyl’ is being sunk into sand to stop deadly chemicals leaking into the sea and the surrounding bed.
The wreckage of the German U-boat was left with 1,800 canisters of toxic mercury seeping into the sea off Bergen in Norway.
U-864 was torpedoed by a British submarine in early 1945 as it headed for Japan carrying jet parts.
The vessel left Kiel in Germany on December 5, 1944, but the hull was damaged in an attack and the captain headed for Norway to carry out repairs.
U-864 was torpedoed by a British submarine in early 1945 as it headed for Japan to take around 65 tonnes of mercury and jet parts
After being struck by a torpedo the U-boat split in to two parts. Around 8lb (4kg) a year of deadly mercury has seeped into the water of the Norwegian Sea around the wreck causing boating and fishing to be banned
Since the battle the U-boat has stayed 500ft below the surface, split into two parts, around two miles from Fedje, an island of 600 people, leaking dangerous mercury into the sea from the rusted containers.
Around 8lb (4kg) a year has oozed into the water of the Norwegian Sea causing boating and fishing in the area to be banned due to the toxicity coming from the wreck.
The leak caused high levels of contamination in of cod, torsk and edible crab around the 2,400-tonne wreck.
As a result the Norwegian government is to seal off around 11 acres of the seabed under up to 40ft of rubble to stem the leakage from the cargo on board.
A specially-built rig was made by Dutch contractors to dig around the boat and without damaging the hull any further and contaminating the sediment in the seabed.
The burial operation, expected to cost up to £25 million, will start next year and finish in 2020.
Scientists want to bury the wreck in rubble to stop the toxic chemicals leaking from the rusted canisters. The sloping seabed where the front of the U-boat sits has caused problems for the rescue team
The shipwreck was first discovered by a Royal Norwegian Navy minesweeper and will be sunk by Dutch contractors Van Oord after 100,000 tonnes of sand was used to secure the vessel
U-864 was intercepted by HMS Venturer in the North Sea and after it left Kiel in Germany. The vessel then headed to Norway but sunk two miles off Fedje before repairs could be carried out
Environmentalists say efforts to seal off the submarine do not go far enough as even low amounts of mercury still pose a danger through contaminated fish
Stephen Hayes, senior specialist with Norwegian Geotechnical Institute’s (NGI) Section for Instrumentation and Monitoring, said: ‘We developed and built a specialised rig and used a ROV (Remotely Operated Vehicle) to install pressure probes at six different places on the seabed which will be covered by the counter-fill.
‘The purpose of the probes is to measure the stabilisation rate of the sediment during the filling process.’
Due to the sloping seabed where the front of the wreck is now sitting being so potentially unstable, the first step for scientists was to install a large ‘counter fill’ to secure the front of the boat during the work.
The seven-metre tall counter-fill will also protect the fragile vessel from movements in the ground and even earthquakes.
The large counter fill was successfully dug in June last year at the foot of the unstable slope and saw 100,000 tonnes of sand and rock used to keep the front half of the vessel in place.
According to a monitoring system set up, both environmental and geotechnical sensors reportedly showed that no further spreading of contaminated sediment took place during the construction of the counter fill.
A similar process of entombing the U-boat has been successfully used around 30 times in the past to contain mercury-contaminated sites over the last 20 years, researchers say.
But despite these measures it is feared more than 60 tonnes of mercury could still leak out from the vessel for decades to come and could become an ‘underwater Chernobyl’.
The large ‘counter fill’ put in place to stop contaminated areas of the seabed sliding away when work begins to sink the U-boat
Norwegian scientists plan to bury the rusted vessel in a plan expected to cost up to £25 million, which includes 100,000 tonnes of sand and rock being piled at the foot of the U-boat
Environmentalists say measures to seal off submarine do not go far enough as even low amounts of mercury still pose a danger to anyone who eats contaminated fish.
Campaigners wanted the submarine to be brought ashore but the authorities say that would be too risky as the bottles could break up as they were being moved.
The shipwreck was first discovered in March 2003 by a Royal Norwegian Navy minesweeper after being alerted by local fisherman.
U-864’s mission was to be the head of Operation Caesar, which was a secret mission carried out by Germany to supply Germany’s faltering ally, Japan.
The mission to sink the doomed toxic Nazi wreck will start next year and finish in around 2020
Since the U-boat was discovered in 2003, scientists have been trying to work out how to stop the deadly chemical leaking from the damaged mercury canisters. Sand and rock was dropped at the foot of the vessel by Dutch contractors
The Nazi vessel was carrying around 65 tonnes of mercury as well as parts and engineering drawings for German jet fighters.
But the plan was discovered by code-breakers at Bletchley Park in Buckinghamshire, who unearthed communications relating to the mission and HMS Venturer was sent to intercept the German U-boat.
After a chase of around several hours and the German’s taking zig-zag manoeuvres, the British boat fired four torpedoes, with the last one hitting its target and sinking their German counterpart.
All 73 crew members on board U-864 died in the attack.
The attack was said to have been the first time a submarine sunk an enemy rival while both were under water at the same time.