Cogema's strategy for decommissioning28 July 2004
All industrial nuclear facilities have a limited lifespan before the lengthy task of their decommissioning must begin. When its facilities reached the end of theirs, Cogema opted to start work almost immediately. By G Decobert
Because spent fuel reprocessing facilities handle long-lived radioactive elements such as caesium and plutonium the decommissioning benefits derived from radioactive decay are not significant, when compared to the cost of long-term care and maintenance. Therefore, Cogema’s strategy is immediate dismantling of the facility with the objective of converting the facilities, either for conventional use or to environmentally-regulated facility status.
The advantage of immediate dismantling is that some of the operating staff continue to be employed and that their knowledge and skills can be used during the dismantling phase. Moreover, the infrastructure needed for decommissioning is still available.
When compared to power reactors, spent fuel reprocessing facilities have a number of important and unique features that have to be considered during the decontamination and dismantling programme.
• The construction of a reprocessing plant is based on the assembly of elementary process functions in distinct modules that can be isolated. That means the modules can be separated and decommissioned as individual work sites. The modules include: spent fuel unloading; decladding or shearing units; dissolution; extraction and purification; plutonium oxide precipitation and calcination; fission products concentration and vitrification; medium and low active effluent treatment and solid waste conditioning.
• A greater variety of radiological hazards – beta, gamma and alpha – will be likely as a result of the processes carried out in the various cells.
• A greater variety of risks must be managed during decommissioning because of the intrinsic diversity of the reprocessing operations (mechanical and chemical) and the variety of material which has been processed.
During the last three decades, Cogema has performed extensive maintenance and upgrades in its facilities and process modules, which represent hundreds of thousands of man-hours of experience. Safety plans, procedures and techniques were developed that are now available for use in ongoing and future decommissioning projects. All the feedback from these and similar interventions can be implemented.
The reagents commonly used during operation of the installation, such as nitric acid and caustic soda, will be preferably used during the preliminary rinsing phase after shutdown of the process circuitry. This will be followed by specific reagents such as potassium permanganate, oxalic acid and hydrofluoric acid or cerium (IV).
During the mechanical dismantling phase, off the shelf techniques are preferred (such as saws, grinders and shears). In severe environments, remote operating techniques such as carriers, dexterous arms and telescoping masts will be used.
Concerning the general waste management plan, the key idea is to use all the site support facilities and carefully manage the waste flow.
All the liquid effluent streams are neutralised, acidified and monitored. Most of it is concentrated by evaporation and transferred to the vitrification facility, where it will be calcified and vitrified to give a final product in the form of a glass canister.
The remaining liquid waste not compatible with vitrification will be processed in the liquid waste treatment facility by evaporation and coprecipitation, the result of which will be a sludge to be encapsulated in bitumen.
All the solid waste from the dismantling operations will be conditioned in the existing support facilities, such as decontamination, compaction, melting, incineration and cementation units.
A wide variety of decontamination and dismantling operations have been performed at the La Hague site during routine equipment replacement. In addition, the complete dismantling of the AT1 pilot breeder fuel reprocessing plant, owned by the French Atomic Energy Agency (CEA) and located at the La Hague site, has been successfully achieved.
The AT1 pilot facility was built to reprocess spent fuel elements from the fast breeder reactors Rapsodie and Phénix. The facility operated for ten years between 1969 and 1979, and produced around 1t of uranium and plutonium at a nominal rate of 1kg per day. As the operator of the plant, Cogema was responsible for the decommissioning of the facility.
AT1 was completely decontaminated by the end of 2001 and may now be entered without special precautions. The AT1 project provided Cogema and CEA with experience in dismantling a set of cells where a wide range of exposure risks from high activity and alpha activity were present. The high level irradiation cells were dismantled using the Atena machine, an 11m telescopic polyarticulated arm equipped with telemanipulators and cutting tools. Among the different processes applied, one interesting procedure was the overall decontamination of the building walls, which was completed by concrete abrasion using robots and tools mounted on a remote controlled Brokk carrier.
The experience gained during decommissioning of the first reprocessing plant, UP1, will be of great help for the next planned project, the final shutdown of UP2 400. UP1 and UP2 400 belong to the same generation and they have many similarities.
UP2 400, on the La Hague site, was commissioned in 1966 and processed GCR fuels until 1986, when all GCR fuel reprocessing was transferred to UP1. In the 1970s, UP2 400 was equipped with a new head-end facility known as the highly active oxide (HAO) workshop in order to process fuels from LWR plants. In its new form it began operation with a design capacity of 400t per year.
By 1994, two new facilities – R1 (shearing and dissolution) and R2 (extraction and purification) – had been commissioned to replace the HAO and the highly active extraction and decontamination facility (Hade) of UP2 400. This doubled the capacity of UP2 400 to 800t/year. In 2002, UP2 400’s original plutonium purification facility (MAPu) was closed and replaced by a completely new one, R4. With R1, R2 and R4 in operation and the advent of the new generation UP3 and UP2 800 reprocessing plants built in the 1980s and 1990s the old facilities are no longer required for production. It will soon enter a decommissioning programme planned to last several decades.
The facility reprocessed 4900t of GCR, 10t of FBR and a total of 9500t of LWR spent fuels.
AN ONGOING PROJECT: UP1
The UP1 decommissioning programme is among the biggest industrial operations of this kind in France in terms of size, duration and cost.
Commissioned in 1958, the UP1 reprocessing plant is located on the Marcoule site in southern France alongside the Rhône river. It reprocessed spent fuels from plutonium production reactors for the Ministry of Defence and later, spent fuels from commercial GCR gas-cooled graphite reactors for the CEA, EdF and other Cogema clients such as Hifrensa – a total of about 18,600t. Production was officially stopped by the end of 1997 and followed immediately by a major decommissioning project which is now underway. The decommissioning operations cover two major programmes:
• The final shutdown and dismantling of the old production facilities (the decladding and reprocessing buildings) and, in a second step, the support facilities such as the effluent treatment station and the solid waste conditioning facility.
• The retrieval and repackaging of historical on-site waste.
A reference scenario for the decontamination and dismantling operations, and retrieval and conditioning of historical on-site waste, has been put together and will last in excess of 40 years.
The final shutdown of the production facilities is the dominant feature of the early years It will be followed by a dismantling phase that lasts until 2020. The final shutdown and dismantling of the support facilities will take place after this date. The waste retrieval and conditioning programme is now beginning with a few limited operations and should increase over the next decade to last until the end of the project.
In 1996, to carry out this huge programme, the French ministers of defence and industry asked the three industrial nuclear companies (EdF, Cogema and CEA) to set up a structure called Codem to manage decommissioning operations after the end of production at UP1.
Codem, as the client, is the decision-making, financing and supervising entity for the decommissioning operations. Implementation of the programme is assigned to Cogema as the nuclear operator and industrial contractor. Cogema set up the appropriate organisational structure needed for the decommissioning task force by dedicating a decommissioning team.
The forecast total cost of the decommissioning project is r5.6 billion: 53% for the final shutdown and dismantling operations and 47% for waste retrieval and conditioning.
The final shutdown operations consist of rinsing process circuitry with conventional and specific reagents. If necessary also using mechanical processes and evacuating the equipment. The main objectives of this phase are to reduce the residual activity level in order to limit the collective dose during the dismantling phase, to optimise waste management, and to reduce surveillance requirements and the costs associated with placing the installations in a safe condition.
The following key figures describe the project status in mid-2003:
• 20kg of plutonium (1500TBq) removed.
• 2000t of equipment removed.
• 11,000m3 of effluents removed.
• 5400m3 of waste removed (90%LLW and 5% VLLW to Andra surface disposals, 5% ILW).
• 335,000 working hours undertaken.
The dismantling programme will include decontamination and evacuation operations for all the facilities that will reduce residual activity to a level compatible with the elimination of radiologically restricted access zones. Adequate surveillance will be maintained. The second major programme involves the retrieval, sorting, treatment and conditioning of historical waste.
In addition to the waste produced during the final shutdown and dismantling operations, UP1 processed numerous types of fuel and generated a large variety of waste from 1958 to 1997, most of which is still temporarily stored on-site. This waste can be classified as follows:
• 60,000 bitumen drums.
• 500m3 of process waste stored underwater (resins, diatoms, zeolites, powdered graphite and sludge).
• 2900t of structural waste in dry interim storage (magnesium, graphite core and metallic structural material).
• 26t of technological alpha waste (resins and ashes).
These waste products are stored in several areas and configurations. Activity levels and degrees of knowledge are very variable and characterisation is the preliminary step before conditioning or dispatch to the right outlet. This programme is planned to last at least 20 years.
As a priority, the pits of the northwest zone, where 6000 bitumen drums produced between 1966 and 1978 are temporally stored, have been selected and the operation is underway and planned to finish in 2007.
Another important retrieval operation that should start in 2004 is the transfer of process waste (a mixture of 120m3 of graphite, zeolites and sludge) from pits of the old decladding facility to safer pits.
CEA’s G1 reactor at Marcoule was the first reactor to produce electricity from nuclear energy in France, in 1956, although its main purpose was plutonium production. It was shut down in 1968. In the middle of July 2003, G1’s 100m, 2200t chimney-stack reached the end of its planned lifetime of 47 years and was toppled. This dismantling operation followed a detailed and meticulous protocol based on an innovative concept consisting in sawing one base foot, toppling the stack around a hinge, dynamiting the two remaining feet and landing the stack on an earth mattress. Cogema was responsible for the security and safety of the operation and assisted the owner in preparing for the operation.
Final shutdown work in the production facilities has been in progress since the beginning of 1998 and the experience gained over five years has allowed us to draw up some guidelines:
• Dismantling studies must start as early as possible to allow a smooth transition between operation and dismantling phases. This approach also aids waste management.
• Careful planning is necessary to use human and technical resources efficiently.
• The initial radiological and physical inventory is of key importance.
• The required final state must be defined carefully.
Beyond the technical challenges, Cogema’s Marcoule personnel have a human challenge: going from an operating culture to a project management culture; cultures such as operations, heath and physics project management and clean-up must co-exist within the project with the common target of controlling costs and maintaining a high level of safety.
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