Extreme Risk Management and Exceptional Engineering Enterprise

An excellent and totally absorbing presentation, robustly delivered by John Large of Large & Associates, Consulting Engineers, provided a wonderful start to the new season of events from IMechE West Cumbria. Jointly organised with the British Nuclear Engineering Society, a packed Hundith Hill audience heard John describe the reasons for the sinking of the submarine, and just how the exceptional hazards were assessed and innovative engineering solutions developed and applied to allow the successful recovery of the gigantic wreck in just seven months from placement of the contract.

The Russian Federation nuclear powered submarine Kursk sank in August 2000 with the loss of all 118 lives on board. In May 2001 the Russian Federation entered into a contract with the Dutch consortium Mammoet-Smit for the recovery of the Kursk on the condition that it had to be completed within that year. The consortium prepared for this World-first salvage of a nuclear powered and conventionally armed submarine that was very substantially damaged lying at 110m in the icy waters of the Barents Sea. Working at breathtaking pace, Mammoet-Smit prepared, lifted and transported the wreckage of the Kursk delivering her to a floating dock at Rosljakovo, about 200km south of the foundering site, in just over six months from the contract date – an astounding achievement, appreciated by many in the audience for whom nuclear programmes are measured in decades, not days..

The catastrophe and the events that occurred after the initial ‘pre-cursor’ explosion were recorded as seismic disturbances by a Norwegian seismological station. Detailed analysis of these traces indicated that the first explosion was equivalent to 100 – 200kg TNT, and was probably caused by the failure during launch of an experimental torpedo that used a lithium fluoride propulsion system. The activity levels after this explosion suggest that a fierce fire occurred which then led to the catastrophic detonation some 135 seconds later of up to 7 fully armed conventional torpedoes in the forward hold within the space of half a second. This multi-explosion was equivalent to approx 3 tonnes of TNT and ripped out a very large section of the forward pressure hull and outer casing and, at the same time, sent out a reverberating hammer blow through the compartments in the submarine towards the stern.

The statistics of Kursk are impressively daunting – an OSCAR II class submarine, built in 1995, weighing 11,500 tonnes. 154m long, 18m outer casing built from 8mm steel plates plus 11m inner pressure hull formed from 50mm high yield steel plate. The entire outer hull was clad in 80mm rubber tiles (using asbestos-based adhesive!) to deaden sound transmission outwards and to absorb incoming sonar pulses – a form of stealth technology. 24 cruise missiles plus up to 24 torpedoes were being carried, which, together with the condition of the nuclear power reactors, formed the basis for the nuclear risk assessment.

The task that faced the recovery team was considerable, the most urgent being how to assess the condition and risks that could jeopardize a successful lift. John was asked to head and form a Nuclear Co-ordinating Group that would assess the principle nuclear hazards and define the limits and conditions under which the lift and recovery would take place. A team of 15 were (reluctantly) supported by Russian technicians and key personnel from RUBIN, the State Design Agency that designed Kursk. John described how the NCG held a trump card that effectively controlled the sometimes buccaneering approach of the salvage teams – insurance cover was only granted if work was done in accordance with the terms laid down by the NCG!

Using information gathered from incredibly brave diving teams, remote cameras and sensors, the wreck and debris fields were assessed and the principal hazards identified as from the torpedoes, cruise missiles and from the nuclear reactors. In addition, the activities in raising the vessel by cutting off the severely damaged front section, drilling 26 anchor points through both hulls and attaching lift wires, also had to be considered to ensure that reasonable safeguards were in place.

The method of assessment – identifying hazards, possible faults and consequences – was distinctly different the Russian approach, which tended to passively consider one event in isolation. The NCG approach considered torpedo explosion a credible risk during operations and established the criteria for vessel and human deployment that would minimize any consequences.

There was major concern at whether the reactors had successfully closed down and ceased radio-active function, and if they had survived the massive detonation that sunk the submarine. The absence of any radio-active contamination and the lack of any thermal gradients suggested that shut-down had been fully achieved, but there was a worrying gas bubble evident within the reactor compartment which could certainly have exploded during lift due to decompression. Examination of the skeletal remains from one of the officers who would have been in the control room next to the reactors at the time of the main explosion indicated that a shock load of up to 60g had been experienced – could the reactors and the mounting systems have successfully accommodated this loading? Design data eventually obtained from the Russians suggested a design capability of up to 50g…

John showed some excellent PowerPoint animations to demonstrate the lifting methods and the heave compensation systems that were used to ensure even tensions were maintained in the huge lift wires at all times. Whilst the lifting equipment principles were tried and tested, they had never before been deployed and co-ordinated on such scale, and the cutting operation that sawed off the forward compartment was a world first – a heavy cable carrying very coarse (~25mm) abrasive was deployed and reciprocating motion supplied by two 30 tonne hydraulic rams attached by suction anchors to the sea bed. Like some gigantic cheese cutter, the wire was drawn back and forth over the hull, eventually slicing through the thick steel structure. This system is now being used to cut the car-carrying ship that sank in the Channel.

The lift went surprisingly well, with no significant suction effect of the Kursk on the sea bed. Once lifted by the massive Giant 4 lift barge, Kursk was tethered underneath into a specially made cradle to begin the long journey back to land. To get both vessels into dry dock, additional pontoons had to be devised and built to lift the pair prior to Kursk being lowered into her new home..

The recovery of Kursk was a success that derived from a tragedy, completed by a group of commercial organizations. Quite remarkable levels of ingenuity were shown to meet the politically imposed timescale. The Nuclear Co-ordinating Group had to work rapidly, crossing the divide between East and West, accounting not just for the different approaches to nuclear and engineering technologies, but also how the safety reasoning of the original design could be integrated into the salvage scheme. There was no radiological release or significant radiological hazard to any of the personnel involved, and for that a great deal of thanks must go to the work of the Group headed by the redoubtable John Large.