E. Pluche
Deputy Manager, T7 Vitrification Facility
COGEMA, La Hague

J. Jeannette
Quality Department Manager
COGEMA, La Hague

HLW fission products separated by spent fuel reprocessing at La Hahue UP2 et UP3 plants are conditioned in glass. The combined capacity of the two plants is 1,600 metric tons of uranium per year. They accommodate commercial light water reactor fuels from French utility EDF and foreign utilities world-wide. The glass production at La Hague in 1996, was 930 canisters.

The purpose of the paper here submitted is to describe how the quality management system implemented by COGEMA at La Hague, guarantees the quality of the glass product, thus completing the third stage of the acceptance programme. The quality management system is in compliance with international standard ISO 9002. It comprises a Quality Assurance Programme and a Quality Control Programme, allowing to demonstrate the quality of the glass product as well as the mastering of the conditioning process.

The spent fuel unloaded from nuclear reactor contains 96 % of uranium, 1 % of plutonium and
3 % of fission products and other actinides. Uranium and plutonium, once recovered, can be reused to make new fuels. Fission products and actinides are ultimate waste and are called High Level Waste. It is necessary to dispose these waste safely, and to ensure they will remain safe for several thousand years. This waste will be stored in underground geological repositories in France.

During reprocessing, the separated HLW arises in the form of an aqueous nitric acid solution. In this form, it can be stored safely in stainless steel tanks equipped with cooling systems. However, it is easier to carry out the interim storage in a solid form; and in any case, it is necessary to solidify the waste for final disposal.

For more than 30 years now, French scientists and nuclear experts have been dealing with vitrification in order to give a proper and comprehensive answer to this fundamental issue. Today, French vitrification process clearly appears as one of the best solution both in terms of industrial maturity and efficiency. Commercial-scale high level waste vitrification in France is on line at the La Hague reprocessing plant (R7 and T7 facilities).

These two units were commissioned, respectively in 1989 and 1992. Each unit was designed to produce around 600 glass canisters per year. At mid-1997, more than 5,100 glass canisters had been produced at both facilities. Vitrification operations at La Hague are based on the continuous process developed by the French CEA (Commissariat à l’Energie Atomique), and operated in the AVM (Atelier de Vitrification Marcoule) facility since 1976. Today, vitrification of fission products contained in one ton of spent fuel represents 0.1 m³ of glass.

To demonstrate that the glass product is suitable for final disposal, as waste acceptance process was set up with three goals:

• develop and characterize a reference glass formulation and variations there of,
• demonstrate that process variations can be detected and corrected without affecting glass quality,
• control the quality of glass by controlling process parameters in normal and abnormal situations.

The successful completion of the first two steps in the waste acceptance process resulted in the establishment of glass specifications accepted by French nuclear safety authority (DSIN). Subsequently, the R7/T7 glass specifications were also approved by the regulatory authorities of COGEMA's baseload customers in Germany, Belgium, Netherlands, Switzerland and Japan.

The quality management system implemented by COGEMA Group at La Hague, guarantees the quality of the glass product, thus completing the third stage of the acceptance programme. The quality management system is in compliance with international standard ISO 9002. It comprises a Quality Assurance Programme and a Quality Control Programme, allowing to demonstrate the quality of the glass product as well as the mastering of the conditioning process.

Long term studies performed by the CEA (French Atomic Energy Commission) resulted in the formulation of the so-called R7 and T7 glasses. Characterization studies have verified the main properties of the final products and have established the glass specifications. The vitrified waste specifications were subjected to peer review by an independent commission of nuclear specialists.

The principal criteria for the formulations were: mechanical and thermal stability, homogeneity, radiation resistance, high containment capacity, low volume, corrosion resistance, low leachability, easy fabrication (mastered technology), and flexibility with regard to the composition of waste to be conditioned.

Characterization testing was conducted in both inactive and active conditions to determine the principal properties of the reference glass composition. Inactive characterization testing focused on the physical, thermal, and mechanical properties of the glass, on its homogeneity, on the thermal stability of the glass in a temperature range of 500 to 1,200 °C, on its leach resistance, and on glass volatility, i.e. weight loss as a function of temperature.

Active characterization testing was conducted on hundreds of active glass formulations using alpha doped and beta tracer glasses to determine radiation resistance, leach rates and the thermal stability and volatility of the glass.

In addition, tests were performed to assess glass quality sensitivity to variations in process parameters and to qualify a broad range of acceptable glass/waste compositions. A total of 90 glasses were characterized in this manner.

In parallel with glass sensitivity studies, tests on inactive full-scale prototype were conducted to determine the sensitivity of the melter to variations in process parameters, such as different melting temperatures, variations in time periods between glass pours and variations in glass-to-frit ratios or frit-to-calcine ratios.

A range of acceptable glass compositions was defined on the result of the sensitivity tests, and failure modes and effects analyses were performed to identify fault conditions that would impact glass quality, including its chemical composition, homogeneity, cracking rate and propensity to crystallize.

The objective of the glass characterization programme previously mentioned was to provide a reference glass composition and a variation range around, to cater for operational constraints and for actual fuel to be reprocessed. The glass characterization program resulted in identification of an optimum glass composition for HLW from oxide fuel (LWR type reactor), along with an operating range of process parameter for the "AVM type" technology.

This was formalized in the "Specifications of Vitrified Residues produced from reprocessing at UP2 / UP3 La Hague plants". The specifications include "Guaranteed Parameters" i.e. those parameters identified as key parameters in the process to ensure the glass canister's quality.

These specifications were subject to peer review by an independent commission of scientists and nuclear experts. They were also provided to ANDRA (French National Radioactive Waste Management Agency) for comment, and then submitted to the French regulatory authority, DSIN. The French safety authority approved the vitrified residue specification in February 1986.

The so called Guaranteed Parameters include the following data which refers to the chemical composition of the glass:

The Guaranteed Parameters are key parameters. The compliance with the Guaranteed Parameters, that the reprocessor is bound to respect, allows to declare the conformity of each glass canister. COGEMA Group also specifies the canister fill rate, the welding procedure and the glass cooling procedure.

COGEMA Group has implemented a quality management (or QA/QC) system for the final products (U, Pu) as well as for residues, the glass canister being one if them. This quality management system is in accordance with international standard ISO 9002. According to this standard, COGEMA Group is able to demonstrate the quality of each residue as well as the mastery of the conditioning process.

A Quality Assurance Programme is defined for the production of glass canisters:

• an organisation of production facilities,
• a general organization of quality,
• a quality documentation,
• a quality control programme,
• a treatment of deviations,
• a customer surveillance.

The quality control programme includes three type of actions which pertain to controls of raw materials specifications compliance, controls of process functions affecting vitrified residue quality, and controls of the Quality Assurance Programme.

All raw materials are subject to QA/QC system prior to acceptance. Raw materials are controlled for their compliance with procurement specifications. A conformity file is systematically established. This concerns the quality of glass frit and chemical reagents, the glass canister procurement, the smear test swab and welding torches. In addition, COGEMA is performing audits and inspections of the raw materials suppliers.

The basic glass properties required for vitrified residue depend on containment capacity, radiation resistance, vitreous state stability and non fixed surface contamination of the canister.

Containment capacity is a function of alterability and leachability that are linked to the glass chemical composition which should comply with the specifications previously defined. « Glass chemical composition » will be controlled as an essential process function.

Radiation resistance depends on the vitreous state of the product whose quality is assessed from the viscosity and homogeneity of the glass. A good vitreous state is achieved if the melting temperature is correct and the pouring rate satisfactory. « Glass pouring » will be followed as a second process function.

Vitreous state stability will be guaranteed if the temperature conditions supported by the glass after pouring are satisfactory. The process function « glass cooling » will be controlled.

The main property affecting the safety of vitrified residue intermediate storage are the non fixed surface contamination of the canister and the canister tightness. these fourth and fifth process functions will be subjected to control.

With regard to the basic properties, the five process functions represent effective means to demonstrate the product quality on a real time basis. Process control is performed both directly, by monitoring and measuring operating parameters at various stages in the process (flow rate, temperature, density, weight, welding parameters, canister transfer to storage), and indirectly, by corroborating operating parameter through analyses or comparisons of inlet and outlet materials balances.

An independent Quality Control structure is in charge of regularly inspecting the facilities. The frequency of inspection, their contents and the inspection report format are defined in the Process Inspection Plan (PIP). This document is a technical support for the use of the Quality Control structure and ensures the methodical verification of the parameters listed in the quality control programme, and of the process equipment related to the residue quality. All these process equipment are linked to official measuring chains of international metrology standards.

The verification made allows the data subsequently transmitted by the production unit in the Canister Quality Files to be validated.

Such a Quality File is attached to each glass canister and recorded. It contains all of the pertinent data relating to its production, including analytical results on the adjusted feed solution, the glass composition calculation sheet, and a description of processing operations for the corresponding glass batch. The Quality File is certified by COGEMA Group’s QC structure prior to shipment and disposal.

In addition, all the customers have entrusted an independent agency (Bureau Véritas) with the responsibility of performing an independent survey (on a permanent basis) to evaluate COGEMA's measures of maintaining the specified quality. Bureau Véritas has to certify the conformity of each glass canister with the specification. Bureau Véritas is conducting inspections and quality audits to make sure that at any time the structure of the QA/QC set-up by COGEMA is appropriate and consistently applied.

Finally, Bureau Véritas checks all the documents pertaining to the production of each glass canister (including control parameters, COGEMA QA certification of material, ...). On this basis, Bureau Véritas will certify that the glass canister is conform to the specifications. Bureau Véritas also checks all documents pertaining to the control of the glass canister at the time of loading into the transportation flask. On this basis, Bureau Véritas will certify that the glass canister meets the whole specifications and can be shipped.

For the industrial glass producer COGEMA Group, the primary objective is the making of a final product with properties that meet the vitrified waste specifications while keeping a high throughput of the vitrification facilities to cope with the requirement of an in-line waste conditioning in the reprocessing plant. A comprehensive QA/QC system ensures that the requisite quality is consistently achieved in the final product al all stages in the vitrification process.

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