The Nuclear Hazards of the Recovery of the Nuclear Powered Submarine Kursk

As well as the pre-prepared arrangements for response to a serious mishap to the Kursk during recovery (i.e. torpedo explosion, falling equipment, etc.), the barge and support vessel crews had to work under a strict radiological management regime. This regime was administered by a radiation adviser overseeing shifts of health physics monitors surveying and managing contamination, dose receipt and recording, sheltering and other dose mitigation countermeasures.

^{Giant 4 with the Kursk slung underneath awaits entry into the floating dock at Rosljakovo — two specially designed sinkable pontoons were deployed to raise Giant 4 for the necessary clearance into the floating dock}

The NCG cooperated with the RF over analysis of a hypothetical radioactive release from the reactor compartment at the stage when the lifting Kursk approached close to the underside of the Giant 4 barge — this was assumed to be the point at which the barge crew were most at risk of radiation exposure. The conditions assumed for this analysis were:

• expansion of the air/gas bubble drives a discharge of 150m³ of water from the reactor compartment via the 6mm diameter instrumentation hole (a known open route into the reactor compartment), taking 36 hours.

• the discharged water contains fission and activation products released from fuel corroded for 14 months by seawater, as determined by a representative test, amounting to some 3 × 10¹² Bq (Becquerel). Allowing for dilution in the sea, the total effective dose to a barge crewmember would be less than 1 μSv (at less than 0.1 μSievert/hour). Further development of this model analysis concluded that:

• a larger leak path would not significantly affect the above conclusion.

• if the same amount of fission and activation products were not discharged by the bubble expansion, but remained at the top of the reactor compartment, the 2m of seawater that will fill the space between the pressure hull and the casing would reduce the dose rate to a barge crew member to a few μSv/hour.

To mitigate these risks and those from uncontrolled criticality, discharge of radioactivity or direct radiation resulting in unacceptable levels of exposure, emergency arrangements to protect personnel, including evacuation by the RF Northern Fleet vessels and aircraft, were agreed with the RF Northern Fleet. These actions, triggered by an emergency reference level (ERL) protocol, applied to all personnel present on board M-S vessels.

^{Checking the sail for radioactivity the sail (conning tower) of the Kursk protruding up into the cavity formed in the underside of the Giant 4}

OVERVIEW

In completing its task, the Nuclear Coordinating Group adopted the following principles to ensure that the preparatory and recovery operations would not present an unacceptable nuclear or radiation risk to those involved with the recovery and, generally, to the marine environment (NCG 2001):

• Limits and Conditions: A clear set of limits and conditions had to be established for all of the operations to ensure that credible hazards would not challenge the capability of the structures, systems and components involved, both on the Kursk and or the Giant 4.

• Degradation and Recovery Operations: The limits and conditions safeguarding the structures, systems and its components would have to account for damage sustained during the sinking, the degradation over the year on the sea bed, and for forces and circumstances introduced by the Mammoet-Smit recovery operations.

• Defense in Depth: There should be a number of separate safeguards in place at all times against all of the significant hazards.

• Tried & Tested Technology: Since the deployment of novel procedures and processes introduces additional risk, preferably tried and tested technology should applied.

• ALARP: the risk should be reduced to As Low As is Reasonably Practical.

• Radiological Management Regime: Radiation doses to those personnel involved in the recovery operation should be controlled below the limits for Class B radiation workers (as defined for the UK).

• In Contingency: Contingency plans should exist in the unlikely event of a significant radiological release, particularly for mitigating the impact upon the marine environment.

Mammoet-Smit had contracted to raise the Kursk in May 2001 and in just six short months, on 23 October, the Kursk was lowered from Giant 4 onto the cradles of the floating dry dock at Rosljakovo — a quite remarkable and World-first achievement.