Abstract

Starting in 2002, Belgoprocess will proceed with the treatment and conditioning of some 200 m3 of widely varying high- and medium-level wastes from earlier research and development work, to meet standard acceptance criteria for later disposal. The gross volume of primary and secondary packages amounts to 2,600 m3. The wastes have been kept in decay storage for up to 30 years. The project was started in 1998. Operation of the various processing facilities will take 7–8 years. The overall volume of conditioned waste will be of the order of 800 m3. All conditioned waste will be stored in appropriate storage facilities onsite.

At present (August, 2000), the construction of a new processing facility is in progress and the call for venders for the equipment has been sent out. Several cells of the Pamela vitrification facility onsite will be adapted for the treatment of high-level and highly α-contaminated wastes; low-level β/γ wastes will be treated in the existing facility for supercompaction and conditioning by embedding into cement (CILVA).

The bulk of these wastes, of which 95% are solids, the remainder consisting of mainly solidified liquids, have been produced between 1967 and 1988. They originate from various research programmes and reactor operation at the Belgian nuclear energy research centre SCK•CEN, isotope production, decontamination and dismantling operations.

The wastes are stored in 4800 primary packages, of which 700 contain 120 g (5.1012 Bq) radium. Half the radium inventory is present in 25 containers. The presence of radium in waste packages, resulting in the emission of radon gas, requires particular measurements and the welding of packages for storage, in order to allow a correct interpretation of alpha measurements onsite.

The total activity at the moment of production amounted to 18,811 TBq β/γ and 34.4 TBq α, with individual packages emitting up to 555 TBq β/γ and 2.2 TBq α. According to calculations, the β/γ activity has decreased to some 2,000 TBq, with individual packages up to 112 TBq.

The extreme diversity of the wastes is not only expressed in their radiological characteristics, but also in their chemical composition, physical state, the nature and condition of the packages. Radioactivity ranges between 0.01 mCi to 1,000 Ci per package. Some packages contain resins, Na, NaK and Al containing wastes, poison rods, residues of fuel elements. Although most of the liquid wastes are solidified, a small fraction — both aqueous and organic — still remains liquid. Primary packages may be plastic bags, metal boxes, wire gauze, La Calène boxes; secondary packages may be steel drums and concrete containers. Solid wastes may be sources, counters, control and poison rods, nuclear fuel residues, filters, synthetic materials, metals, resins, granulates, rock, sludges, cables, glass …

Some 1000 primary packages are stored in a dry storage vault comprising 20 concrete cells, while 3800 primary packages are stored in some 2,000 concrete containers, on a concrete floor, surrounded by an earth bank to the height of the waste stacking and covered by a metal construction.

At present, the annual production of similar wastes amounts to 2 m3 divided over some 30 containers.

Generally, the primary waste packages will be loaded in 80 l drums (an average of 2 packages per drum), and compacted in a 150 t hydraulic press. The pellets will be collected in 100 l drums (an average of 3 pellets per drum). Low-level β/γ waste is transferred to the CILVA facility for further treatment, while the other 100 l drums are filled up with sand and, in the case of radium-contaminated wastes, tight-welded. Subsequently, the 100 l drums are loaded into 400 l drums and embedded into cement. Certain packages, for example solidified radium-contaminated liquids in welded metal containers, are conditioned as such in overpacks. Specific procedures will be established for the various non-standard wastes, such as sources, control and poison rods, resins and filters, fuel residues.

The new processing facility is being built partly over the dry storage vaults, in the immediate vicinity of the already covered storage area. It comprises 1) feeder locks for the introduction of the various waste packages; 2) a dispatching cell in which the primary packages are loaded into 80 l drums; 3) the processing cell in which the 80 l drums are compacted and the pellets loaded into 100 l drums; and either sent to the CILVA facility (low-level β/γ wastes), or the Pamela facility (highly active and/or heavily α-contaminated), or further treated in 4) the transport area, in which radium and medium-level waste containing drums are conditioned into cement; 5) the measurement and characterisation cell, in which the conditioned waste is characterized by gamma spectrometry, and checked for compliance with maximum allowed surface contamination and dose rate in view of interim storage in the appropriate facilities onsite.

Ideally, gamma spectrometry measurements are carried out on the primary packages, but due to the extreme diversity of these packages, ranging from plastic bags containing cardboard to highly active steel valves, preference was given to measurements on the conditioned wastes, or at least on already pre-compacted wastes in the case of treatment in the 2,000 t press of the CILVA facility. Thus tremendous problems of calibration can be largely avoided.

All operations are remotely controlled. Transfers between buildings are carried out within appropriately shielded containers and secondary wastes will be treated in existing facilities onsite.

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