Plutonium Recycling And The Melox Fabrication Plant

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XA9744107

W. FOURNIER MELOX, Bagnols-sur-Ceze, France

Abstract

The French decision to turn to industrial plutonium recycling through MOX fuel was taken relatively recently, by (he mid-1980s, when recycling of valuable materials emerged as a satisfactory back-end solution for the fuel cycle. The French strategy currently relies on an industrial structure comprising the COGEMA reprocessing plants at La Hague with a total capacity of over 1600 tHM, the existing MOX fabrication facilities at Dessel (BELGONUCLEAERE PO Plant) and Cadarache (COGEMA Cadarache Plant) with a capacity reaching 65 tHM. In order to implement the French program of recycling plutonium through MOX fuel in 20 to 28 PWR reactors, and to serve foreign utilities as well, it was decided to create the Melox Company (50% Cogema, 50% Framatome), the goal of which is the construction and the operation of the Melox plant. This paper describes the main features of Melox design and presents current status of starting-up activities.

An innovative plant based on well-tried techniques

Several requirements are to be dealt with in order to cope with:

fuel designer requirements related with in-core behaviour. These include homogeneity of the mixed powders and of their isotopic content, pellet density mastering and stringent dimensional tolerances reprocessor requirements concerning pellet solubility.

Moreover, as a result of final customer requirements with regard to new trends in fuel management and flexibility of MOX fuel use, Melox will be able to handle a wide range of basic nuclear materials; aged plutonium and/or coming from high burnup fuel, high plutonium MOX fuel content and uranium being either depleted or coming from reprocessing.

The reference process for the Melox plant is the well mastered MIMAS process which resulted from several steps of process improvements at the Dessel plant since 1984. In this process, the Pu02 powder is first micronized with a part of the U02 powder to form a primary blend of 30% plutonium content. This primary blend is then mechanically diluted by mixing with free flowing U02 powder to obtain the specified content of the MOX fuel. These two steps significantly reduce the plutonium-rich spots in the U02 matrix.

While coping with the above requirements, special design efforts have been made to reduce foreseeable occupational exposure to a tenth of the current regulatory limit. This implies almost total automation of production and requires extensive optimization studies tailored to each workstation.

Meanwhile, waste minimization has been another major design objective: compared to the factories of the previous generation, a significant decrease of residual plutonium in the waste should be achieved, mainly due to the operation of a large on-site TRU waste incinerator.

A step-by-step commissioning programme

Inactive testing started in early 1993 and provided gradually increasing confidence concerning satisfactory operation of the whole production line, as well as of all its parts. At the end of inactive tests, special overall tests were performed in order to verify global behaviour in case of general defaults such as lack of auxiliary fluids or power supply.

Active tests were aimed at providing the customers with complete demonstration that fabricated products are of quality and reliably cope with the above described requirements. Before normal operation is reached, the commissioning procedure included functional testing with U02 paramesial tests, qualification and validation of processes and generic demonstration programmes with real products.

For cladding, rod inspection and assembly units, commissioning started from the back-end of the production line. This enabled the production of assemblies, using rods coming from the Cogema Cadarache plant, very soon after a general active operation approval by the Regulatory Authorities in August 1994.

The first Pu02 powder box was opened in mid-March, which started the entire powder and pellet units operation according to the normal process pathway.

Conclusion

The Melox plant can be seen as an outstanding achievement, taking full benefit from previous experience, while introducing several innovative features in terms of radiation protection as well as environmental concerns. It is a major input in the national energy policy, as an important link of the plutonium recycling strategy.

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