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Dismantling of nuclear-powered ships

Mise à jour  : 28/06/2010

Dismantling of a nuclear-powered ship is an unavoidable stage of its life span. The project management of this operation, led in optimum nuclear safety conditions, has been given to the DGA (French armament procurement agency). It is currentlyaimed at maintaining the six reactors of the Le Redoutable-class SSBN before completing their dismantling. This wide programme is set for the long term since the first nuclear attack submarine should be withdrawn from active service in the second part of the decade.

Since May 2002, the first French nuclear powered submarine, SSBN Le Redoutable, is open to the public at the Cité de la mer (Maritime Museum) in Cherbourg. This accomplishment is the result of a series of operations undertaken under optimal nuclear safety conditions. The hull of the former SSBN Le Redoutable has been specifically considered to be part of public national heritage. The other SNLE will follow the usual cycle which will lead to their full elimination.

It is worth pointing out that there are two completely independent processes: the dismantling referring to the operations linked to nuclear safety, and the deconstruction which deals with the hull after removal of the nuclear reactor. The DGA (French Armament Procurement Agency) is the project contractor for dismantling and DCNS is the project manager. The deconstruction of the hull will be carried out under a responsibility to be defined.

Dismantling is a sensitive operation as to nuclear safety, technically difficult to implement but well controlled with special respect to radioprotection and waste management. However, the management of the reactor-free hull, once checked, no longer raises any nuclear safety issues. The submarine, without its nuclear installation, is put back to water and towed to a quay waiting to be "deconstructed". All these dismantling operations take place on the DGA's facilities at the military harbour of Cherbourg.

The final shutdown

This several months-long operation involves discharging the heart of the nuclear reactor and disembarking the various energies. The nuclear waste and spent fuel are stocked in Homet's storage bay waiting to be collected by the French Atomic Energy Commission (CEA) for storage or recycling. The submarine is then safeguarded to avoid any risks of sinking or pollution.

Dismantling level I

Materials of the reactor are disembarked, additional surveillance equipments are put in place.

Dismantling level II

The confined part is reduced to the minimum, waterproofing and biological protection are reinforced. A thorough decontamination is operated, all fluids are drained and the primary circuit is reduced to large capacities and dried out. The walls are soldered with metallic tapes and the waterproofing of the compartment is verified. This operation lasts between ten to twelve months depending on the radiological state of the submarine. This phase ends with the separation of the reactor, which is perfectly confined.

Having no more links with the remaining equipments of the submarine, the reactor can be set apart thanks to the water immersed support, where the ship is lifted to the ground. Cutting out the 700 tons nuclear section from the remaining of the ship lasts three months. This section is eventually carried away on a rolling platform to its storage location.

The front and the aft of the submarine are then repositioned with ‘walkers' (computer-controlled) and soldered together. The whole entity is then put back to water and the hull is kept along a quay.

Long term storage

The reactor is stored under control at Homet on a sismo resistant slab. It is protected against weather conditions with a specific structure. A venting system allows annual access to verify material changes in time and to guarantee appropriate ambient conditions.

That storage is today built to last for tens of years. The decreasing radioactivity of the reactor's activated or contaminated metallic materials allows level III operations in the best radioprotection and economic conditions. The first reactor (from SSBN Le Redoutable) has been stored for sixteen years.

Dismantling level III

All nuclear materials and equipments are removed; the installation is completely cut up and conditioned into waste barrels for ANDRA (French National Agency for Radioactive Waste Management). These operations are to be carried out on site within a new facility dedicated to the complete dismantling of the reactor.

The CEA is in charge of the feasibility studies of this phase. A first result was the characterization of possible decommissioning conditions and choice criteria for the operations to be carried out in order to proceed from the dismantling level II to the evel III.

The continuation of these studies are aimed at validating the duration of the reactor storage, as well as the compatibility with the transport requirements and with the acceptance criteria of the ANDRA for the final waste storage.

Deconstruction of the hull

After approval from the safety authorities the hull is recycled out of nuclear domain. Deconstruction is currently studied regarding dangerous waste disposal and its environmental impact. This technically heavy operation requires specific tools and large work surfaces. Each hull is more than 100m long and 10m wide and makes a very heavy package of 7000 tons!

Long term vision

The dismantling level II of the former Le Redoutable-class SSBNs will be achieved in the next ten years. The first Rubis-class SSN will sail back to Cherbourg in the second part of the current decade to undergo the same operations. In a comprehensive perspective including the upcoming Barracuda-class SSNs, this programme is far from being over.

The first two levels of the SSBN dismantling have been carried out with safety conditions guaranteeing no risk for the public. This success lies on recycling and waste management principles adopted when the nuclear powered submarines were conceived and made. The success also lies on the know-how of the teams in charge of these operations.

The continuation of this initiative confirms France's willingness to complete the disposal of all unused defence-related nuclear facilities in accordance with environmental protection rules. This programme is only at its beginning. The successive operations will make the stakeholder's know-how sustainable. The rigour with which nuclear safety rules are followed and the feedback process will guarantee our safety.

(1) as defined by the IAEA