WASTE MANAGEMENT: TOWARDS A STANDARDIZATION OF BACK-END FUEL CYCLE PACKAGES

Ph. PRADEL
Deputy Director, Reprocessing Branch
COGEMA
2 et 4 rue Paul Dautier
78140 - Velisy Villacoublay
Phone: 0139 26 30 00

ABSTRACT

Since a few years, COGEMA has developed a policy of waste management optimization in the back-end fuel cycle which takes benefit from the La Hague plants' experience. First of all, the choice of Reprocessing-Conditioning-Recycling Strategy instead of direct disposal of spent fuel minimizes the final radiotoxicity of ultimate residues.

Furthermore, the cost optimization of final disposal facilities requires the development of advanced technology achieving reduced volumes and standardized packages characteristics.

This policy, as implemented by COGEMA, is an important milestone in the set up of the advanced waste management that will be applied at La Hague by the 2000. From then on, the total volume of long lived residues from reprocessing will be less than 0.5m³/t of U, corresponding to an approximate volume reduction ratio of more than 4 comparing to the direct disposal present estimations (about 2m³/t).

The standardization of packages will be achieved by the Universal Canister Strategy (UCS) which applies to all type of wastes (technological wastes, vitrified fission products and compacted hulls and end-pieces).

Vitrified residues currently fabricated at La Hague plants are placed in a specified stainless steel container, the so-called «glass canister». Specifications for vitrified residues have been approved by international Safety Authorities (Japan, Germany, Belgium, Netherlands, Switzerland and France) promoting this canister to an universal standard. The Universal Canister Strategy will be based on this well established standard.

By the 2000, a new facility currently under construction will provide a compacting process for hulls and end-pieces as well as for technological wastes. Hulls and end-pieces will be mixed with technological wastes for compaction. Rounds of compacted wastes will be placed without immobilization matrix in the Universal Canister in order to standardize handling and future disposal.

External dimensions of the Universal Canister are those of the canister for vitrified residues (diameter = 430 mm, total height = 1335 mm). Material and internal fittings may vary according to the type of residues contained. The little dimensions of the package as well as a limited weight are attractive features for handling and transport.

So, the Universal Canister will package all types of residues and will facilitate handling, transport as well as final disposal. For example, the design of the repository will be simplified with boreholes or galleries of the same dimensions, and the device to handle the containers in the storage will be reduced to one pliers system.

By an adapted management of interim storage of high activity packages, less constraining thermal characteristics could also be obtained and could allow to reduce the repository size.

INTRODUCTION

Since many years, France has chosen the reprocessing-recycling strategy for its nuclear energy program. The closure of the fuel cycle gives France a real energetics independence and a strong position in the worldwide nuclear community. More accurately, thanks to this coherent industrial plan, France is now the world leader of nuclear reprocessing-recycling service. The COGEMA La Hague plant, in Normandy, has reprocessed more than 1,500 tons in 1995 and is scheduled to reprocess 1,600 tons in 1996.

The whole plant has reached a high degree of industrial performance together with outstanding quality, safety, flexibility and environmental protection results. One should bear in mind that waste management is performed with the same unshaken commitment to mastery. COGEMA has set up a unique gathering of technologies in order to minimize and manage waste arising from reprocessing-recycling activity as cleverly as possible.

The first step is waste treatment. Current reprocessing processes give a real meaning to waste purification notion. This is implemented by various techniques. Second, the cornerstone of the waste management concept lies in the global packaging philosophy. It means that HLW as well as long lived waste, regardless of its form, its activity and its final destination, will be fitted with the same type of package: this is the Universal Canister Strategy.

This paper presents the current achievements in terms of waste treatment activity, and gives an outlook of the Universal Canister Strategy whose near-term implementation will open a new era in the waste management field.

WASTE TREATMENT: A DAY-TO-DAY REALITY

Three main materials result from spent fuel reprocessing industrial operation: uranium, plutonium and waste. Plutonium is widely labeled as the most important material of these last three. As a matter of fact, recycling of plutonium under the MOX form allows benefitting from the huge energetics content of plutonium.

But, separate plutonium from waste significantly contributes to environmental protection and conservation of natural resources by reducing waste radiotoxicity. Spent fuel and waste radiotoxicity essentially comes from plutonium.

On the contrary, radiotoxicity of plutonium-free waste decrease quite quickly. In-depth studies has shown that efficient plutonium extraction lessen the radiotoxicity of final waste by a factor 20 to 30.

In this regard, COGEMA has made recovery of plutonium a high-listed priority. This objective has been translated into an industrial technique knows as the PUREX process. The extraction process separates uranium and plutonium from fission products and actinides. The solvent used is TBP (30% in volume diluted in duodecane).

The extraction is realized in pulsed columns. Through this process, a 99,88% recovery rate has been achieved for recyclable materials. The reminder (0,12%) is vitrified along with the fission products.

Results are really conclusive: activity of waste is comparable to the natural uranium activity after 7,000 years. Regarding the direct disposal option, the same figure would be reach only after 200,000 years.

As previously underlined, French fuel management strategy is forcefully tied to the plutonium recovery principle. COGEMA has set up a cogent industrial strategy aimed at recover this plutonium. This concept lies on peculiar tools and workshops: among them, one can quote the two UP2-800-based workshops:

• URP workshop for redissolution of PuO2 powders and UO2-PuO2 powders commissioned in 1995. This workshop is also in charge of the americium-removing from plutonium activity.
• UCD workshop for plutonium recovery in waste.

This industrial consistency naturally led to the Universal Canister Strategy which gives the final touch to the whole French reprocessing-recycling example.

WASTE MANAGEMENT: THE UNIVERSAL CANISTER STRATEGY

In order to improve the way waste are treated and to benefit from the excellent overall result of the reprocessing operations, COGEMA has developed a new advanced waste management concept whose beginning is planned around the year 2000. The Universal Canister Strategy is the more visible part of this new management.

This policy's rationale is focused on decreasing the overall volume of high activity waste stored in underground repositories to approximately 0.5 m³/t compare to the 1980 design estimations which reached more than 3 m³/t. This target will be reached by the extension of the glass canister concept to waste other than fission products.

This strategy is based on an advanced technology mixing vitrification features and new tools. But, one must first distinguish between the different type of waste arising from the reprocessing activity, fission products, hulls and end-pieces, and technological waste.

• Today, fission products and minor actinides are vitrified and placed in dedicated, steel containers, known as glass canisters. The vitrification technology was developed in France. It was implemented in the AVM facility at Marcoule. It is based on a two-step process, which separates the calcination and glass melting operations.
• final product, vitrified residues, are today the only high level waste form licensed by the French and foreign regulatory bodies (Japan, Germany, Belgium, Netherlands, and Switzerland).
• confinement is based on a 15 years qualification program performed at CEA (the French public research institution for atomic energy), and on active quality control and quality assurance programs set forth by the operators of the vitrification facilities. At mid-1996, more than 4,300 glass canisters have been at R7 and T7 workshops.
• Hulls and end-pieces separated from the irradiated fuel in the head-end of the reprocessing plant were conditioned by cementation, a process which was licensed by the French regulators.
• Technological waste originates not from the fuel itself but from the reprocessing operations. All the technological waste were conditioned in a single type of fiber-concrete canister.

A drastic minimization has already been obtained by comparison to the design waste volume, by relying on the high equipment reliability and improved sorting, performed at the entrance of the solid waste processing facility (AD2). The sorting makes it possible to send more than 80% of the technological waste to surface disposal.

These gradual improvements have given COGEMA the possibility to set up another stage in the waste management strategy. In fact, the Universal Canister Strategy is really a new step in nuclear waste management. From now on, waste management is focused on both waste treatment and on final forms at the same time.

The originality of the COGEMA's new waste management strategy lies in the use of the existing glass canister to integrate compacted waste. The same stainless steel canister will independently serve for fission products, hulls and end-pieces, and technological waste.

That is why this canister features the same characteristics than the canister for vitrified residues. For sure, its composition materials and internal fittings may vary according to the type of residues contained and their activity.

The main characteristics of the stainless steel container are as follows:

Thousands of stainless canisters have been produced at La Hague. The manufacturing of the empty steel container and of its lid are under control by the COGEMA Quality Assurance and Quality Control System. Each container and each lid receive a certificate of conformity.

In addition, the worldwide known Bureau Veritas conducts independent inspections and quality audits to make sure that at any time the structure of the Quality Assurance/Quality Control set-up by COGEMA is appropriate and consistently applied.

The Universal Canister Strategy quick implementation requires the construction of a new facility for compaction. This workshop, known as the ACC, will compact high activity materials (hulls, end-pieces, and technological waste) in the shape of rounds. Each canister contains between 5 and 7 rounds depending on their thickness. According to COGEMA schedule, 2,400 canisters will be produced per year at the ACC facility. That represents more than 12,000 boxes of compacted waste rounds.

THE UNIVERSAL CANISTER STRATEGY:A CLIENT-ORIENTED IMPROVEMENT

Standardization of high-activity packages gives COGEMA clients, a new flexibility for their back-end management. The Universal Canister Strategy features numerous advantages.

First of all, Universal Canister Strategy - containing hulls, end-pieces and technological waste - handling conditions are easy. Previous return of canisters from France, to Japan and Germany shown that handling of canisters pose neither technical nor industrial problems.

Second, the canister facilitates transport operations. Its limited size and weight offer the possibility to increase the number of canisters transported, and then to limit the number of transports from the La Hague reprocessing site to the interim and final storage sites. The Universal Canister Strategy makes multiplication of dedicated transport means useless. Third, Universal Canister gives COGEMA's customers the ability to rationalize their waste repositories policies :

• The selection and construction of a sole site will be necessary to receive the canisters, whether they are glass canisters or Universal Canister-type.
• The repository design will be simplified with same-sized boreholes or galleries.
• The same can be said about the handling-device system: one type of pliers will be sufficient.
• By an adapted management of high activity packages interim storage, less constraining thermal characteristics could also be obtained and could allow a repository size reduction.

Fourth, further regulatory and licensing procedures for the Universal Canister will not represent an overburden. The canister have already been accepted by worldwide regulatory authorities for the fission products which is a far more complicated operation.

CONCLUSION

COGEMA has developed sophisticated technologies over the past 30 years to treat the large quantities of fuels, whatever their origin, national (i.e. the EDF 54 NPP program) or foreign (clients from Europe and Japan).

La Hague reprocessing plant has been constantly and continuously improved in order to match fuels changing features (current fuels average burn-ups reach 45,000 MWd/t compare with former levels of 33,000 MWd/t). That means real differences in terms of fuel treatment due to different isotopic compositions and taking into account growing international environmental concerns such as reducing the volume and the toxicity of the final residues.

Waste treatment and management at COGEMA are based on this second-to-none industrial pattern. The Universal Canister strategy gives a realistic answer to overall waste volume reduction by improving the way waste are conditioned and, then disposed. Due to current procedures, radiotoxicity of waste have been hugely reduced of. Tomorrow, their packaging will follow the same way.