J. Deckers, P. Luycx, R. Vanbrabant
BELGOPROCESS

M. Detilleux, Ph. Beguin
BELGATOM

CILVA is a centralized treatment facility for b and g low-level and a -suspect waste produced in Belgium, based on a 2000 ton supercompaction installation and an incineration plant for solid and liquid radioactive waste, with a capacity of about 100 kg waste per hour.

After a short description of the CILVA facility, a project developed by BELGATOM for ONDRAF/NIRAS, the Belgian nuclear waste management agency, this paper describes the feedback experience after almost four years of operation of this facility operated by BELGOPROCESS.

The following aspects are coveted in the paper.

• organization of the project for the design and construction of the CILVA plant
• general functional description, lay-out of the plant ,and main design parameters
• overview of the operational experience for each of the functional units: reception/storage and distribution, precompaction, supercompaction, conditioning, incineration and waste traceability unit
• problems solved and lessons learned.

BELGATOM is a nuclear and consulting engineering company, providing a wide spectrum of nuclear services, among other in radwaste management, in Belgium and abroad.

BELGOPROCESS, a company set up in 1984 at Dessel (Belgium) where a number of nuclear facilities were already installed, is specialized in the processing of radioactive waste. It is a subsidiary company of ONDRAF/NIRAS According to its mission statement, the activities of BELGOPROCESS focus on three areas:

• treatment, conditioning and interim storage of radioactive waste,
• decommissioning of shut-down nuclear facilities and cleaning of contaminated buildings and land,
• operating of storage sites for conditioned radioactive waste.

At the end of the eighties, the low level waste treatment facilities located on the BELGOPROCESS site were rather old and could not be adapted or refurbished to provide for a modern management of radioactive waste. Therefore, in 1989, ONDRAF/NIRAS decided to build, on the same site, a new centralized facility, the CILVA facility, using supercompaction, and incineration for primary waste treatment.

BELGATOM performed the conceptual study of the facility in 1989-1990. Then, BELGATOM acted as Architect Engineer for the detailed design, construction and commissioning of the CILVA plant. These tasks mainly covered the preparation of the invitation to tender, the selection of the various contractors for the different functional units (see further) as well as for the civil works, the building ventilation systems and the utilities. These tasks also covered the overall project management, including management of the supply contracts, follow-up of fabrication, co-ordination and supervision of the on-site activities, performing of tests and commissioning activities for the whole facility.

BELGOPROCESS started the plant operation in June 1994 (first radioactive waste supercompaction) and May 1995 (first radioactive waste incineration). The general schedule of completion of the project is shown in Figure 1. The investment in the supply of the different packages listed above was about 1.2 10⁹ BEF (year 1990).

The low level nuclear waste to be processed in the CILVA facility is solid b and g waste with a radio nuclide concentration in the collected waste packages generally less than 5 GBq/m³ (1).

The waste annual design quantities considered are the following:

• combustible waste: 1200 m³ (including 30 m³ of ion exchange resins and 600 m³ of waste precompacted to about 300. kg/m³ at the power plats);
• compressible solid waste: 1150 m³;
• various waste: 80 m³;
• liquid waste: 60 m³.

The waste producers prepare the solid waste in primary packings generally placed in 2201 drums (compressible waste) or in 1 m³ stainless steel containers (combustible waste).

The liquid waste is spent oil, .delivered to the facility in special transport containers, and organic and aqueous solutions delivered in 281 polyethylene bottles.

The transport package contact dose rate generally is lower than the authorized limit of 2 mSv/h (200 mrem/h).

The facility is represented in a simplified scheme (figure 2). Its main installations include the following:

• a reception, storage and distribution unit;
• a waste preconditioning unit;
• a supercompaction unit
• an incineration unit;
• a conditioning unit.

These traits are briefly described below.

This unit comprises a road transport reception hall, a waste package reception hall and a large storage hall. After administrative formalities, the transport packages are unloaded and presented at reception where controls are performed: dose rate measurement, surface contamination and weight.

After the conformity of the declaration sheet issued by the producer is checked, all transport packages are marked with a bar code to ensure they can be followed up and traced during treatment in the facility.

The transport packages containing solid waste are placed in the storage hall. The liquid waste bottles are stored in separate rooms with specific protection against explosion and fire.

The spent oil transport containers are stored in a separate area. Their content is transferred to a storage tank. When necessary, the waste packages are transferred to the treatment units described hereafter.

The facility includes a routing and sorting installation as well as a pretreatment installation.

• In the routing and sorting installation, transport packages with combustible waste are emptied and the primary packages are controlled (dose rate measurement, weight, absence of metallic parts) before being transferred into bins to the incineration unit. If the acceptance criteria are not fulfilled, the primary package can be opened inside a glove-box and the waste resorted and repackaged according to the treatment further required.
• The pretreatment installation is mainly devoted to the preparation of specific waste, e.g. ventilation filters (prefilters, HEPA and charcoal filters) that cannot directly be introduced in a drum for supercompaction. A 140 t precompactor (with two movements) is therefore used. This equipment is also used to reduce the volume of 28 litre metallic cans to be supercompacted later.
• The waste that is neither compressible nor combustible is drummed before being embedded in concrete.
• The preconditioning unit includes also a dismantling cell and a steam decontamination station.

1. The maximum authorized radioactivity concentrations are the following:

• solid waste to be incinerated:, b ,g £ 4 E10 Bq/m³ and a £ 4 E7 Bq/m³
• liquid waste to be incinerated:, b ,g £ 4 E7 Bq/l and a £ E5 Bq/l
• waste for supercompaction:, b ,g £ 4 E10 Bq/m³ and a £ E10 Bq/m³

In this unit, 200 litre drams are compacted by means of a 2000 t hydraulic press. The obtained pellets are then stacked into 400 litre overpack drums where they will later on be immobilized with mortar in the conditioning unit.

The fully automated installation is designed to treat about 6000 drums per year at a rate of 8 drums per hour. The use of an eight-position turntable for accumulation of the produced pellets, coupled with a computer management system, optimizes the filling of the overpacks.

With an upstream storage area for the 200 litre drums to be supercompacted and for the empty 400 litre overpacks as well as with a downstream storage area for the filled overpacks (both areas equipped with roller conveyers), it is possible to organize separate supercompacting campaigns.

To size the incineration unit, a yearly capacity of about 280 t of solid combustible waste and 50 t of liquid waste was considered, to be incinerated in maximum 4000 operation hours.

The primary combustion chamber operates in a partial pyrolisis mode, at a temperature between 800°C and 950°C. The secondary chamber, an after-burning and flue gas retention chamber, provide complete burn-out of combustible products while retaining the gases for minimum 2 seconds at a temperature of about 1050°C.

The automatic furnace feeder takes care of the internal bins in which the solid waste packages have been inserted. Biological waste (animal carcasses, etc.) is frozen and stored in refrigerators prior to being manually loaded in the incinerator.

Liquid waste is pumped into the incinerator, either directly from the transport package, or from a tank. The off-gas system ensures the dry cooldown of the combustion gases in a boiler, their filtration and purification through baghouse filters, HEPA f'ilters, a quencher and a scrubber. The purified gases are released after dilution with the release of the building ventilation extraction air.

Ashes at the bottom of the combustion chamber are slowly moved by two screws. Ashes and dust from the boiler and the baghouse filters are collected in 200 litre drums for further supercompaction.

This unit includes an installation for immobilization and embedding and another one for control and inspection of the conditioned waste.

• Immobilization and embedding installation:
  This installation includes all equipment needed to prepare a cement matrix and for its filling into 400 litre drums where supercompacted pellets or special incombustible and incompressible waste are to be immobilized. This installation also includes an active mixer for embedding of wet waste like ion exchange resins, sludge, etc. should the need arise.
• Control and inspection installation:
  After solidification, the hardness of the cement matrix is checked. A metallic lid is then crimped on the conditioned waste dram. All the prepared drums are finally inspected by an automatic system, checking the absence of surface contamination, determining the main radiological characteristics, weighing the drums and transferring these data to the computer management system.

The drums, ready for final disposal, are transported to an intermediate storage building on the same site.

In the Cilva facility, waste traceability is assured by a centralized waste management system that collects information from the different management systems in the treatment units described before. This management is handled by personal computers. Each drum or package is provided with a bar code. Bar code manners, installed at every stage of the treatment operation, identify each package.

With the help of this management system, the operator has a complete overview, at any time, of the progress of the waste packages inside the facility and of their main characteristics.

The operator considers that the global performance of the CILVA facility is very satisfactory. The operator's overview of the operational experience for each of the functional units, including problems solved and lessons learned, is given hereafter.

The following main results were obtained:

From operational experience, and as far as radiological protection is concerned, it appears that:

• the only improvement that can be done is the automation of the storage of 2001 and 1 m³ containers in the storage hall to prevent exposing the operators to too high dose rates. Today the operator is in close contact with the 2001 drums and 1 m³ containers he has to store. For the year 1996, 19 % of the total yearly exposure of operators of the CILVA installation (21 men.mSv) is allocated to the reception, storage and distribution of the different waste packages. An improvement could consist of an automatic storage system as initially foreseen in the conceptual study, but not installed for cost reasons.
• a positive result is that no contamination spreading was found in the different working areas, which means that the specifications for the incoming waste are satisfactory and that the layout of the different areas is well designed.

The precompactor was at the beginning licensed only for preparing special b and g -waste (b , g < 4 El0 Bq/m³), which cannot be directly introduced in a drum for supercompaction.

Special care was taken to prevent contamination during the operation of the 140 T precompactor in the cell. Operators wear no special protection clothes or mask, and each special waste item (281-cans, ventilation- and active coal filters) is controlled with respect to surface contamination.

From operational experience it appears that:

• the specifications concerning each type of special waste are not always followed by the producers. This means that, for some packages, the operator has found:
• a surface contamination higher than allowed limits, i.e. b g > 0.4 Bq/cm²;
• damage to the protective plastic bag around filters;
• 281 cans containing liquids.

• precompaction of active charcoal filters produced some dust in the working area. This was duo to an insufficient tightness and an insufficient underpressure at the filling device of the precompactor. After modification the problem was solved.

The following main results were obtained:

The installation is operated during one shift with two operators.

Since no contamination was found around the precompactor or in the working area, BELGOPROCESS decided to use the same infrastructure for treating the a -bearing filters up to an alpha content of 2 E9 Bq/m³. In 1997, the corresponding license was obtained.

As a conclusion we can say that the initially intended performances have been achieved and that the various problems initially experienced during active precompaction were solved in such a way that even a -bearing waste can be treated without the operator having to wear any special protective clothing.

During the first supercompaction campaign in 1994, only waste with an a content of maximum 4 E7 Bq/m³ was processed. As no contamination spreading took place outside the installation and the contamination of the supercompactor with its turntable was very low, the originally foreseen operational limit for activity was applied. This means that from the beginning of 1995 not only b ,g waste but also a waste, up to 1 El0 Bq/m³, was processed without special measures being taken.

Only after each campaign of a -waste are the supercompactor and its turntable cleaned to prevent a -contamination of the b ,g waste.

From an operational point of view the following problems were encountered:

• three times the mould of the supercompactor dropped, and the pressing plate was damaged. This problem was solved by adding extra hydraulic valves in the hydraulic system;
• when supercompacting ash drums or drums with active charcoal, quite a lot of dust was produced in the confining area of the compactor and sometimes also in the area surrounding the supercompactor. This problem was solved by reducing the speed of compaction and by not using the drum piercing system for air evacuation. During such a campaign the filters of the cells have to be changed, and after the campaign the supercompactor is cleaned;
• the specifications are not always followed by the producers. Some drums containing paint, sludge and liquids were found. The consequence was that the whole installation needed to be cleaned up.

Table III displays some of the characteristics achieved during the different supercompaction campaigns.

The installation is operated in one shift with two operators. The effective throughput was 6.6 drum/hour in 1995, 7.1 drum/hour in 1996 and 7.6 drum/hour in 1997, which are consistent with the design throughput.

As a conclusion, the supercompaction unit has proved that drums with b ,g - waste and with "a - waste" (a content £ 1 El0 Bq/m³) could be treated in a safe way and that the special confinement, connected to the ventilation system of the building, is efficient for collecting aerosols and dust produced during the compaction campaign. The technical performances (Volume Reduction Factor, throughput and intervention time) are satisfying, the VRF has been further optimized by selecting the incoming 2001 drums according to their weight.

The conditioning unit is composed of two installations: one for immobilization of the supercompacted pellets and one for homogeneous embedding of various waste (like sludges, etc.) in a cement matrix. As the latter has not yet been operated due to lack of waste, only the immobilization unit will be discussed.

With the immobilization unit, the following main results were recorded:

From an operational point of view, some availability of the system was lost, at the beginning, because the process was fully automated and did not allow for easy manual intervention in case of failure. This problem was solved by introduction of manual sequences in the system.

As a conclusion, the process gives a good qualified product (mechanical compressive strength of grout min. 30 N/mm²) consistent with the ONDRAF/NIRAS specifications for conditioned waste packages ready for final disposal. The daily production capacity has exceeded contractual requirements.

From the active start-up in May 1995 to the end of 1997 the incineration plant has been operated during some 5440 hours and treated 341 ton of solid waste, 65 ton of organic liquid waste and 121 ton of aqueous waste. In particular, during the first year the operation was plagued by various problems.

The main problems were ash screw damage due to erosion and. presence of metallic pieces within the waste, high pressure drop across the bag filters, underpressure control malfunction and failure of the emergency programmable logic controller (PLC). On the other hand we had positive figures for flue gas purification: since the initial start-up, chemical emissions (table V) were much lower than the reference limits and radioactive emissions of typical isotopes such as Co-60 and Cs-137 were below normal detection limits. In 1996, some 140 t of solid waste, 20 t of organic liquids, 53 t of aqueous liquids and 14 t of spent oil were burnt in 1700 hours, leading to an average incineration throughput of 133 kg/h. The radioactivity releases at the stack were only 1.02 E5 Bq in b ,g and 3.7 E3 Bq in a .

In 1997, 133 ton of solid waste, 23 ton of organic liquids, 59 ton of aqueous liquids and 1 ton of spent oil were burnt in 1738 hours, leading to an average incineration throughput of 127 kg/h.

Capacity figures (table VI) from the beginning to the end of the first operational period illustrate the throughput improvements.

After the problems were solved it was possible to improve the capacity of the incinerator as follows: for solid waste from 59 kg/h to 79 kg/h and for liquid waste from 35 kg/h to 61 kg/h.

The increase in the capacity of solid waste treatment is mainly achieved through improvements to the fabric filter bags by forming a chalk precoat on the bag fabric and adjusting chalk dosage, while for liquid waste it resulted from a modification of the way the liquid wastes are fed to the combustion chambers.

As we have solved the main problems, we can now focus on improving the bum-out and further increasing the solid waste capacity. However, the present waste quantities to be processed have been significantly reduced following the .waste producers' policy of waste minimization.

While in normal circumstances augers are helpful automatic devices to mix and to transfer the ash to the ash drum, they still remain a delicate component in an hostile environment, they have to be adequately sized and they requite effective precautions to avoid presence of metallic pieces within the waste.

To control the process, a well programmed main PLC coupled with a conventional relay cabinet equipped with indication lamps and switches in the control room is sufficient.

The waste traceability system is operating very satisfactorily for the reception/storage/distribution, the supercompaction and the conditioning units. For the precompactor and incineration units, process signals are also used for traceability purposes, but cause undue interlocking of the waste feed systems of those installations. This problem will be solved by implementing some computer programme adjustment.

Taking into account the improvements backfitted in recent years, the CILVA plant has reached a state-of-the-art facility status with a high safety standard and a good reliability. Also, it has obtained the ISO 9001 certification. In practice the following were achieved:

• The specific safety features are sufficient to prevent spreading of contamination, and make it possible to treat b ,g or a -waste in a safe manner.
• For most of the CILVA installations no important technical problems remain to be solved.
• The operational performance is consistent with the design specifications, with some restrictions concerning incinerator solid waste capacity.
• Some installations can be used to treat types of waste which were not initially considered.
• In comparison with the former LLW processing systems which the CILVA installations now replaces, the operators' global exposure to radiation has been further reduced. In 1996, the collective exposure of the operators was 21 man.mSv, of which 19 % were received at the reception and storage unit, 25 % at the supercompaction and cementation units (routing out), 26 % at the incineration (sorting), 1% from radioprotection activities and 29 % from repair work.
• Extensive automation in the Cilva facilities reduces manual contact with the waste, but the drawback is that skilled technicians are necessary to maintain the different hardware and software and to solve the problems in case of failure.

Valuable experience and capabilities have been gained performing this project.

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