What next for the Kursk?

29 September 2000

Two reactors lie at the bottom of the Barents Sea as a result of the Kursk tragedy. What options are available to prevent radioactive pollution of the Barents Sea?

On 12th August 2000, the Russian submarine Kursk sank outside Rybatschi Peninsula in the Barents Sea, northeast of Murmansk. This is one of the most important fishing areas for both Russia and Western Europe. Just tens of kilometres west of the resting place of the Kursk is the famous fishing ground Kildinbanken. Despite all the rescue attempts, the crew died, and the Kursk is now a 14,000 ton coffin. The problem now is to ensure that the two reactors do not have a detrimental effect on the environment.

The Kursk, 154m long and weighing 14,000 tons, is at a depth of 108m. The submarine was lost following two explosions in the front of the vessel. The cause of these explosions, like so much surrounding this incident, is not known for certain. Siesmic stations in Norway and Finland detected two seismic events at the time of the accident. A small event was followed by a larger event registering 3.5 on the Richter scale. The second event is comparable to an underwater explosion corresponding to 1-2 tons of TNT. This is confirmed by the damage inflicted on the submarine, which left the boat damaged from the bows as far back as the conning tower. Investigations have shown that the boat has filled with seawater, with consequent implications for the two reactors.

The Norwegian Radiation Protection Agency (NRPA) and the Murmansk Meterological Institute (MMI) have been monitoring radiation levels in the vicinity of the Kursk. So far, there have been no signs of short-lived isotopes in the surrounding water. The background level of radiation for the area is 10-20µRoentgen/hour; the MMI measurements indicated a radiation level of 16µRoentgen/hour. Furthermore, the evidence of previous nuclear submarine accidents (see box) is that radiation leaks tend to be very localised in the region of the submarine.

There is little information available on the radioactive inventory for the two reactors. So far, all that is known for certain is that the Kursk started its mission on 10 August. Information from the Kurchatov Institute on the reactor on the submarine Komsomolets, lost in the Norwegian Sea in 1989, had an inventory of 2.8x1015Bq of Sr-90 and 3.1x1015Bq of Cs-137 in the reactor, and two nuclear torpedoes with mixed uranium/plutonium warheads contain about 1.6x1013Bq of weapons-grade plutonium. The reactor on board Komsomolets is similar to the two reactors on the Kursk, and thus initial estimates of the Kursk's radioactive inventory should be 5.6x1013Bq for Sr-90 and 6.2x1013Bq for Cs-137. The Kursk may carry two nuclear torpedoes similar to those on the Komsomolets. However, official Russian information has stated that there are no nuclear weapons on the Kursk.

Surveys on the Komsomolets indicated that minor releases of radioactive material have taken place through a reactor ventilation tube. However, the likelihood of large-scale releases is small. As the containment barriers in the submarine are breached by corrosion, further gradual releases may occur and these will increasingly comprise long-lived fission products from the reactor. If there are nuclear weapons on board, uranium will gradually be mobilised as the structural integrity of the torpedo and warhead casings is breached. Since uranium is relatively soluble, the environmental contribution will be insignificant in the context of the surrounding environment. Plutonium has limited solubility and a high affinity for particles. Accordingly, most of the plutonium released from warheads would probably be retained in sedimnents in the immediate vicinity of the wreck.

Two major assessments of the radiological threat posed by the Komsomolets have been carried out. The first was carried out in 1995 by Norwegian experts under the auspices of a NATO sub-committee, and the second in 1996 by the Russian Navy. As a result of these assessments, it has been found that the hull and several barriers inside the reactor are expected to prevent corrosion of the reactor fuel for about 2000 years. By that time, only plutonium and americinium isotopes will be present in the reactor in significant amounts. In the intervening period, the main pathway for release of radioactive substances from the reactor will be through the reactor compartment ventilation tube. Warheads would not be protected from sea water to the same degree, and would be open to corrosion much earlier than the reactor fuel.

Condition of the reactors

The Kursk was powered by two VM5 PWRs, each with a thermal output of 380MW, and each driving a GT3A turbine with an electrical output of 72MW.

Current information indicates that there is serious damage to the bow of the Kursk, and that all sections of the submarine are flooded. This probably means that the reactor section is also flooded. Both reactors are equipped with an automatic shutdown system, which operated effectively, and convection cooling has transfered heat from the reactors.

What next?

The key question now with regard to the Kursk is what should be done with the two reactors? There are several possible courses of action: raising the submarine; cutting out the reactor compartment and raising that to the surface; leaving the Kursk on the seabed; and leaving the Kursk on the seabed and sealing the reactor compartments to minimise the risk of leakages. Russian Navy officials are also considering partially lifting the Kursk and towing it to shallower waters.

The main problem with lifting the 14,000t Kursk is the condition of the wreck. The bows of the Kursk were devastated in the double explosion, and the submarine is at an inconvenient angle. In addition, Russia does has neither experience nor equipment in this field. Any operation will require international assistance.

The lifting operation will be risky. If the Kursk breaks up during the lift, then radioactive material could be spread over a larger area via the atmosphere and sea currents.

Should research show that it is safe to lift the submarine, then it will probably be carried out by floating cranes, or air balloons, or a combination of these methods.

If it is too risky to raise the Kursk, the reactor compartment may be cut out and raised to the surface. Large-scale cutting of submarine hull steel at 108m in Arctic waters has never been carried out before, and it would require special equipment, not available in Russia.

If the reactors were successfully lifted, the cores would have to be safely stored. At present, all Russia's storage for spent submarine fuel are full.

The alternative to lifting the Kursk is to seal the reactor compartments to minimise the risk of leakages. Russia claims to have developed a special plastic to seal off naval reactor sections, used at the submarine reactors dumped in the Kara Sea. Russia claims that this material will seal reactor compartments for 500 years.

Some of the openings in the hull of the Komsomolets – at 1685m depth in the Norwegian Sea – were partly sealed with metal lids to stop water penetration and plutonium washout.

The most probable solution if this option is adopted is for a combination of these two sealing methods.

The final option is to build a sarcophogus around the submarine, as at Chernobyl. The sarcophogus would probably be of concrete, although other materials might be used.

This option is probably the least satisfactory, as experience from Chernobyl indicated there were leaks after just 10 years, and this option would make any future lifting operations much harder and more expensive.

No hurry

At present, there has been no detectable leakage from the Kursk. As a result, the issue, while important, is not currently time critical. What is critical is that discussion of the next steps is transparent, especially in the light of the way Russian officials handled the rescue operation, presenting misleading information and keeping information secret.

Other submarine losses

USS Thresher, 10 April 1963. Position: 160km south of Cape Cod. Depth: 2600m. Studies show low levels of radioactivity in the sediment (12Bq per kg of cobalt-60) K-129, 11 April 1968. Position: Northwest of Hawaii. Depth: 5000m. USS Scorpion, 22 May 1963. Position: 650km southwest of the Azores. Depth: 3600m. Measurements show very low levels of radioactivity in the sediments. K-8, 8 April 1970. Position: Bay of Biscay. Depth: 4680m. K-219, 6 October 1986. Position: North of Bermuda. Depth: 5000m. K-278, Komsomolets, 7 April 1989. Position: Norwegian Sea, south of Bear Island. Depth: 1685m.

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