GENERAL FACTORS IN DECOMMISSIONING

Decommissioning and waste management form part of the deeper problems that nuclear power has to face in today’s society. It is argued in Wilkie (1996) that the issues are neither technical nor just financial. Although technical issues remain, much progress has been made, and the remaining problems may be solved with sufficient financial support. This may be costly from a financial perspective, since many of the nuclear facilities that require to be decommissioned were not designed to take this into account. Nevertheless, this is not the whole problem. The problem is that the liabilities of decommissioning, e. g. spent fuel and other radioactive wastes remain hazardous over very long time scales, for hundreds of years. To deal with this problem requires stable national frameworks to sustain an appropriate nuclear industry with the required technical skills for a similar period.

The nuclear electricity generating industry involves the availability of various facilities. Facilities involved in a thermal reactor fuel cycle of the type required to support the UK reactor programme are described in Gordelier (1997). For such a cycle, the stages involve the mining of uranium ore, followed by an appropriate chemical treatment plant to produce the required uranium fuel. Following this, fuel is fabricated in a fabrication plant ready for loading into the reactor. If the fuel is to be recycled, it would be sent to a reprocessing factory where the uranium would be recovered for future use. Recovered plutonium might be for the production of MOX fuel or for utilisation in a fast reactor fuel cycle, perhaps in the future. Residual radioactive material from the fuel would be sent for appropriate storage, treatment and waste disposal. If the fuel is not reprocessed, then it would be treated as waste and sent for high-level waste storage. There are therefore many and diverse facilities associated with the fuel cycle that at some stage will come forward for decommissioning.

Different facilities pose different problems. For example, chemical treatment and fabrication plants that handle first pass fuel are relatively easy to decommission since they only handle low radioactivity materials. On the other hand, facilities that handle recycled uranium and particularly plutonium, e. g. reprocessing plants, pose a much greater challenge. The decommissioning of the power reactors themselves is also a major challenge.

There are various issues that need to be considered in the decommissioning of nuclear facilities. Many of these relate to the timing of decommissioning and dismantling and the factors that determine strategy. Some general principles are set out later, see for example Twidale (1999).

Clearly the safety of radioactive and other hazardous materials is of paramount importance. The safety of the facility will have been assured by its safety case for operation. Operations for its decommissioning phase will need to be covered in an on­going safety case consistent with the relevant national government legislation. In the UK, the policy for decommissioning is to systematically reduce the hazards until the site can be freed from licensing constraints. This is set down in the UK Government’s waste management policy (Bolton, 1996).

After shut-down, defuelling and all other clean-up operations need to be managed to minimise any risk to the general public, the workforce and the environment. The defuelling process removes a high percentage ~ 99.9% of the radioactive inventory.

In general, decommissioning should commence as soon after cessation of operations as is reasonably practicable. In particular, post-operations clean-out (POCO) should be carried out early in the decommissioning process to reduce any radioactive contamination within the plant.

The management of waste must be consistent with long-term disposal plans and no action should be taken that might prevent these plans being carried out. The quantities of waste should be minimised, e. g. waste and fuel handing operations should avoid double­handling operations if possible.

The timing of the above operations will be dependent on the existence of facilities to retrieve waste, and waste disposal routes need to become available. This could impact on the timescale for dismantling the plant, consistent with the maintenance of safety. Processing plants need to be in place together with the long-term storage facilities.

Добавить комментарий

Ваш e-mail не будет опубликован. Обязательные поля помечены *