A British-led team of engineers is overseeing this weekend’s hazardous operation to raise the wreckage of the 11,500-tonne Russian nuclear submarine Kursk, which sank with its entire crew last year.
John Large, a consulting engineer with more than 30 years’ experience in the nuclear industry, is leading the team of nuclear submarine specialists advising the Russian Federation and the joint venture of Dutch contractors, Mammoet-Smit, that will lift the Kursk from the seabed.
Large’s Nuclear Co-ordinating Group has more than an advisory role, however, as its approval for all phases of the operation is a condition of the commercial insurance that covers the vessels and crew of the salvage operation. The Russian government is covering the environmental risk.
‘That gives us ‘hold control’ on the operation,’ said Large. As late as 25 September, there were still 15 points on which the NCG required further assurance, although Large said there were only four still outstanding by 2 October.
It is hard to overestimate the danger of the operation. The Oscar-class Kursk was powered by two 220MW pressurised water reactors. Each is far bigger than the single 150MW units that power Britain’s Trident submarines. These have the potential to cause widespread radioactive contamination.
The assumption is that both reactors automatically shut down after the explosion that sunk the vessel. Ensuring their continued nuclear inactivity during an operation to break such a heavy hull free from the seabed is a challenging task in 110m of water in the hostile seas 160km north of Murmansk.
‘The worst case is the submarine reactors going re-critical,’ said Large. ‘It’s a foreseeable risk, but one we consider to be sufficiently remote.’
That risk is compounded by the presence of enough high explosive in and around the wreck to destroy every single vessel involved in the recovery operation.
Seventeen of the submarine’s 24 torpedoes cannot be accounted for. The 200kg warheads in the other seven caused the explosion that destroyed the front end of the boat.
If any of the missing torpedo rounds are lying under the hull, the disturbance when it is lifted off the bottom could set them off.
The NCG has calculated that the hull – and its reactor compartments – could withstand up to two such detonations, but any more would jeopardise their integrity and pose a severe risk to personnel on the vessels above. ‘If the torpedoes are close to the reactor compartments, we are sailing very close to the wind,’ conceded Large.
The missing torpedoes, however, seem relatively insignificant compared to the threat posed by the other munitions on the Kursk – 23 cruise missiles in silos along both sides of the hull, each tipped with a 700kg warhead. ‘One of these alone was designed to take out a US navy aircraft carrier,’ said Large. He added that if one of them was to explode during the operation, the containment of the reactor compartments would be ‘severely challenged’ and the nearby recovery vessels lost.
The missiles have ‘non-aligned’ warheads, which means they have some form of mechanical shield between their detonators and explosive charges that has to be withdrawn in the five-phase ‘arming’ procedure.
There is a risk that the massive shock and vibration caused during the vessel’s sinking could have at least partially armed some of the weapons. Much of the NCG’s analysis has consequently concentrated on the risk of this happening and strategies to eliminate them – or at least minimise to the status of ‘incredible events’.
This has not been easy, given the proposed means of recovering the Kursk. The damaged front section having been cut off, Mammoet’s 8,000-tonne Giant 4 barge, which is now in position, will haul the rest of the submarine up from the bottom on cables, attached to 26 jacks on the deck of the barge. The other ends of the cables are attached to grippers inserted inside the outer hull of the Kursk.
Once lifted from the seabed, the submarine will be anchored inside a cavity underneath the barge. This is where it will stay, still partially submerged, for the journey back to a floating dock in Murmansk.
But there are several risks of an explosion during the lifting and transportation phases of the operation.
During the lifting stage the danger will increase if a hawser connected to two tugs on either side of the sunken vessel, has to be run underneath the hull to release it from the bottom suction. This would clearly carry a substantial risk of triggering the warhead of a torpedo lodged there.
Then in the transport phase, heavy seas could pull the Kursk free of the barge.’Then there’s a risk that the sub starts slapping against the underside of the barge,’ said Large. ‘Pounding these weapons like that is not a good idea.’
While the problem can be addressed by lowering the hull back down to the seabed on the jacks, there are points on the route back to Murmansk where the water depths will make this impossible.
There is also a risk that one or both reactors could destabilise during the operation without any assistance from the munitions. While the control rods – which kill the nuclear fission process —are clearly inserted at present, there is no certainty that the locking mechanism that holds them in place is secure.
The single reactor compartment housing both reactors will contain air pockets, which will expand as the hull is raised with a subsequent loss of the radiation shielding provided by the water cover. This would put the manned deck of the lifting barge at risk of increased radiation exposure. The air pockets could even eject the control rods if they are not locked into position; there is also the remote risk of ‘recriticality’ if the control rods have not, as has been assumed, fully latched into the reactor cores.
Radiation monitors and a sophisticated signal processing systems will provide real-time information throughout the lifting process to give immediate warning of any such radiological disturbances.
The cost of the mission to recover the Kursk is estimated at around US$130m – half of which is the value of the Mammoet-Smit contract. Everybody involved is hoping that the operation does not end up costing a great deal more than that.
At last: Russia admits prototype torpedo caused Kursk tragedy
The Russians have been forced to reveal that an experimental torpedo was probably responsible for the sinking of the Kursk in August 2000.
The information was revealed to UK engineers who are auditing the operation for insurance purposes.
Up to now, Russia has prided itself on its military prowess and guarded the secrets that enabled it to maintain superpower status for more than four decades.
But, given the commitment by President Putin to raise the submarine, it had little choice. Not having the salvage expertise to retrieve the vessel itself, it had to engage western contractors who came with insurance requirements – one of which was that a nuclear co-ordinating group of four UK consultants approved all phases of the operation. To make qualified judgments on the risks of the undertaking, the NCG had to know what happened.
‘Apart from a somewhat bumpy start, we’ve had a remarkable degree of co-operation from the Russians,’ said John Large, NCG team leader. ‘They’ve had to divulge their foremost military secrets.’
Contrary to much of the wild speculation at the time of the disaster, no other vessel was involved in the accident. The Kursk was attempting to fire an experimental torpedo – with a dummy warhead – that was notionally capable of travelling over 30km at 160kph, considerably faster than conventional torpedoes. It relies on a gas-generating mechanism that sends a stream of bubbles down the outer casing to reduce friction. But this system jammed in the tube, overheated and set fire to the weapon’s main propellant.
The ignited propellant then either melted the door to the tube or blew it off, sending a giant flame back into the compartment behind, which contained the torpedo racks and a further 23 weapons. Exactly 135 seconds later seven of these exploded within one fifth of a second – analysis of the seismic shock- waves determined the separate detonations – blowing the front end of the submarine apart.
The Kursk would not have been far off the seabed at the time of the second explosion, as it would have been in ‘negative buoyancy’ during the firing routine and been floating downwards from the time of the initial incident.
Curiously, however, most of the debris lies on the starboard side of the vessel, whereas the explosion was concentrated on the port side, suggesting the vessel may have been pivoted around by the force of the blast – hence the concern that she may have settled over one or more of her own torpedoes.