Radioactive waste that was produced in the past and waste still being produced by facilities in operation, are managed onsite.
Decommissioning involves the dismantling and decontamination of disused plant and facilities. Waste management includes all processes required for collecting, quantifying, packaging, compacting (where necessary), transporting, storing and finally disposing of the radioactive waste at a suitable site.
Waste material is generated by the following facilities and operations:
Closed down plants & buildings
Sludge in pans
Waste and effluent produced by operational facilities
Spent sources and spent fuel
Medical and industrial waste
Closed down plants & buildings
A total of 56 facilities have been identified for decommissioning. This needs to be done in order to minimise the state’s liabilities with regard to potential safety hazards that the facilities constitute to personnel, the public and the environment. The majority of these sites formed part of the former AEC’s nuclear fuel activities and have all been shut down permanently.
Decommissioning work is ongoing and is funded by government through annual budget appropriations as well as special allocations from the Department of Minerals and Energy.
Approach to decommissioning:
Decommissioning activities are classified as phase 1, 2 and 3 decommissioning.
- Phase 1: Plant shutdown followed by removal of process material inventory. Disused plant made safe and prepared for care and maintenance.
- Phase 2: Process plant dismantling, component size reduction and decontamination.
- Phase 3: Process building decontamination for de-regulation.
Decommissioning work to date:
The following facilities have been partially/fully decommissioned at Pelindaba:
Enrichment plants: Z-plant (Areas 14, 26) and Y-plant (Buildings C, D and E)
Auxiliary facilities: J-building, XB building.
DECOMMISSIONING OF Z-PLANT
Equipment on the Z-Plant was used for the production of enriched uranium. Decommissioning was carried out during 1996 -1999.
This plant was housed on the following six levels in Area 14 (a 260 in by 70 in building):
- Cable Attic This area originally housed 168 instrumentation marshalling panels to serve the control systems of the 56 enrichment stages on the main process floor, as well as the electrical back up systems for instrumentation (batteries and chargers).
- Control Corridor The control corridor is 250 m long and 15 m wide and contained a control panel for each of the 56 modules. The whole process was controlled from a central control room, using a process computer, which was situated in an adjacent area.
- Pipe Bridge This was an intermediate level in the main process hall, which housed.
- 63 Profan compressors (used for product pressure control);
- 56 in-line filters (each I m x I m);
- 600 mm and 300 mm diameter header pipes with a total length of 5 630 m (the 600 mm pipes contained partitions to accommodate 5 separate gas streams);
- - Specially designed 300 and 600 mm four-way valves to enable the independent switching of any of the 56 stages into, or out of the operation.
- - 6 instrumentation transducer racks per stage to accommodate control instruments for the compressors and the valves;
- Cold traps to remove product from a module if it had to be emptied for maintenance.
- Process Floor The 56 modules (enrichment stages) were installed in two parallel rows on this floor. Each module measured 12 m x 4 m diameter, and housed:
- 2 locally designed axial flow compressors, code-named 11 Mamba 11 and Cheetah,
- Approximately 280 000 gas separating elements, mounted in 360 to 400 cassettes (each measuring 640 x 520 x 150 mm);
- 20 sets of heat exchanger tubes
- A complex arrangement of partitioned gas flow channels.
The Mamba and Cheetah motors, 4 and 2,5 MW respectively, were mounted on either side of the module. Two instrumentation racks, for the compressor labyrinth seal control, were also situated next to each module. Each module weighed approximately 130 t when fully assembled, and was moved by means of an aerocastor transport system from the process floor to the maintenance area and back. This method required smooth and perfectly level floors in the process and maintenance areas.
- Cable Basement The cable basement housed all the electrical cables (approximately 200 km total length), and cooling water and compressor lubricating oil pipes also passed through this area. Pipe sizes were 300, 250 and 150 mm diameter and in total approximately 19 km were installed.
- Oil Basement This area is below ground level and contained the cooling water and lubricating oil systems.
There were 15 oil systems, each consisting of:
- I x 50 in' storage tank;
- 2 x vertical multistage oil pumps;
- 2 x heat exchangers;
- 2 x oil filters; and 2 x temperature control systems.
Apart from these, there were also three oil storage tanks for new and used oil. The approximately I 000 in' oil inventory had been contaminated and its decontamination and recovery is included in the project. Primary and secondary cooling water systems were used, with the following main components in the basement.
- 112 x pumps, driven by 45 kW motors and
- 56 x-plate heat exchangers.
Scrap and recovered equipment
|Copper & brass
|Electric & instrument cable
|Other (mostly plastic)
Sludge in pans
Use Evaporation Pans Discontinued
The evaporation pans with a total evaporation area of ±75000 m2 were constructed during the late 1970’s and early 1980’s, for evaporation of effluent generated at Pelindaba. The effluent contained chemical salts in excess of the allowable limit for disposal to the Crocodile River.
One of the pans was set aside for the evaporation of uranium-contaminated effluent from the uranium conversion plant.
The pans were operated under a permit granted by the Department of Water Affairs and Forestry as well as a licence by the National Nuclear Regulator, at the time.
The use of the pans for the evaporation of effluent is being phased out and decommissioning and rehabilitation of the area are now being investigated.
With the implementation of an effluent minimisation plan during the late 1990’s as well as the closure of most of the uranium process plants, the use of evaporation pans for effluent disposal is no longer required.
A number of different options for the decommissioning and treatment/disposal are being investigated. Once a decision has been made on the appropriate option, the process of acquiring the necessary approvals from the authorities and the public will commence.
Pre-treatment consists of the following steps:
- Collection (Pelindaba site).
- Segregation (decommissioning & materials classification).
- Chemical adjustment (limited application).
- Decontamination (chemical & metallurgical – smelter)
- Temporary storage
4. Decontamination services
The Decontamination process
The purpose of the Decontamination Services is to decontaminate components, material and oil originating from dismantled uranium processing plants, which have been contaminated by “ uraniferous compounds “.
The decontamination facility includes the following operational sections:
- Dry Decontamination Facility:
- This facility removes large quantities of contaminants by mainly scraping and “steam” cleaning them.
- This facility is “geometrically safe” to allow for the decontamination of components and material contaminated with highly enriched uranium compounds.
- Wet Decontamination Facility:
- This facility consists of two decontamination lines and the processes are similar to conventional chemical cleaning operations. Uraniferous contamination is removed by dipping batches of components into a series of chemical cleaning tanks according to procedures developed for specific material types and categories.
- Oil Purification Facility:
- Contaminated oil on the Pelindaba site is decontaminated in a uniquely designed facility, and the removal of uranium from the oil is based on liquid/liquid extraction technology.
5. Temporary storage
This includes the storage of:
- Partially cleaned materials, soil, sludges, sediments, building rubble, drummed waste, Thabana, spent fuel, spent sources, oil, effluent, etc Sediments.
SEGMENTED DRUM SCANNER FACILITY
The Segmented Drum Scanner Facility is the first and only licensed facility in South Africa to test drummed nuclear waste non-destructively. The Segment Drum Scanner (SDS) has the ability to quantify all the relevant nuclides in nuclear waste. Nuclides in the waste are measured or inferred by the SDS. The facility is managed by Nuclear Waste Management Services.
PURPOSE OF THE FACILITY
The purpose of the Segmented Drum Scanner (SDS) is to perform non-destructive tests on drums of nuclear waste. The test results are used to determine whether the drum content meet the acceptance criteria for further processing, disposal or transfer to an interim storage.
BRIEF DESCRIPTION OF THE FACILITY
The SDS is an automated facility for testing/assaying drums of nuclear waste. Each waste drum presented for testing is identified by a unique barcode number, which is recorded in a database. The database contains historical data pertaining to the origin, geometry and contents of the drum.
The SDS measures gamma vision emission from the drum over a wide energy spectrum and then computes the drum inventory from the measurement and other inferred characteristics, which are determined by prior characterisation of the waste stream.
The result is used to classify the contents of the drum in accordance with the waste classification scheme. After the classification, the drums are marked with coloured rings around the circumference, to assist operators in handling the drums. The classification is also recorded in the database, which serves as the primary record of the drum inventory and history.
LAYOUT OF THE FACILITY
The SDS facility consists of the following:
- A drum reception area with a gravity conveyor. Drums are delivered by road to the reception area in the facility. No drum is accepted unless it is accompanied by the necessary documentation. On acceptance the drums are off-loaded for further processing. Rejected drums are returned to the dispatching facility. Drums may be either be loaded directly on the conveyor or temporarily stored in the receiving area.
- A driven conveyor system for moving the drums to the SDS.The drums are moved manually along the gravity conveyor system until the reach the driven conveyor that feeds the SDS. The driven conveyor is controlled by the sequencing PLC that controls the identification and orderly progress of the drums through the scanning system. An optical sensor is used to sense the presence of the drums on the conveyor and prevent overloading.
A bar code reader, which identifies the waste drum.
- The Segmented Drum Scanner (SDS)
When the scanner is ready to accept a drum, the operator initiates the process by actuating a switch. The conveyor feeds the drum to the weighing system, the drum is weighed and the result is stored in the PLC for subsequent use. The system then moves the drum onto the scanner turntable. The operator manually initiates the measuring process from the control computer and selects the applicable waste stream as indicated on the batch list.
- The system reads the barcode and scans the drum by lifting and rotating the drum to through a scanning sequence, which allows the detectors to acquire typically 12 segments of the drums. The average duration of the sequence is about 300 seconds. Upon completion of the sequence the turntable is halted, the drum is unloaded and the spectral data are analysed. The results are interpreted in accordance with the approved interpretation model for the specific waste stream and waste type.
- A driven conveyor system, which moves assayed drums from the SDS to a colour-coding booth.
- A colour coding booth where a set of coloured rings, which identified the waste class into which the drum has been sorted, are sprayed onto the drum.
Drums, which satisfy the appropriate criteria, are marked in the spray booth. The marking consists of coloured rings sprayed onto the circumference of the drum. Drums, which do not meet the criteria, are rejected. Drums which have been rejected, pass through the system without been marked and are set aside for investigation and correction of the problem.
- A driven conveyor, which moves the marked drums from the colour-coding booth.
- A gravity conveyor for moving the drums to the dispatch area.Marked drums are removed from the conveyor for dispatch to the appropriate destination undercover of a computer generated drum transfer certificate.
- A programmable electronic system, which reads the bar code on the drum and controls the SDS and conveyor system to ensure the orderly flow of drums through the process, and transmits the assay result to a central database.
- Volume reduction (drying, incineration, compaction, melting).
- Radionuclide separation/removal (evaporation, filtration, ion exchange, melting).
- Change of composition (precipitation, flocculation).
- Immobilisation (solidification, vitrification)
- Containerisation & packaging (suitable containers for long-term storage or disposal)
- Interim storage
In 1978, a programme was launched to select a suitable site for the disposal of nuclear waste, entailing the examination of a variety of socio-economic and geology related parameters over large parts of South Africa.
Initial investigations indicated that the North West Cape was the most likely candidate area. Further detailed studies showed that a locality some 100km south east of Springbok (600 km north of Cape Town) was ideally suited for the disposal of low- and intermediate-level wastes.
The initial stage of investigations culminated in 1983 when three farms, which now constitute the Vaalputs Radioactive Waste Disposal Facility, were acquired by the State on behalf of the NECSA, which will be responsible for its management. The first low- and intermediate-level waste was scheduled for delivery in October 1986.
Vaalputs covers an area of about 10 000 ha, measuring 16,5 km from east to west and 6,5 km from north to south at its narrowest point. Approximately 500 - 1 000 ha is occupied by sites for low- and intermediate-level waste, an interim spent fuel storage facility, housing, roads, power lines and the airstrip.
Vaalputs straddles the escarpment between Namaqualand in the west and Bushmanland in the east and has a mean elevation above sea level of about 1 000 m. Namaqualand is characterised by a rugged granitic terrain with a well-developed drainage system towards the west. Bushmanland on the other hand, is extremely flat lying, often with ill-defined drainage systems and characterised by gently undulating consolidated sand dunes.
Broadly speaking, Namaqualand falls within the winter rainfall area, which has a characteristic succulent type of vegetation, while Bushmanland falls within the summer rainfall area, with its own distinct flora of woody shrubs and grass. Vaalputs therefore falls within the transition zone between winter and summer rainfall and exhibits characteristics of both regimes.
The climate is harsh and in summer temperatures often exceed 40 C, while in winter freezing conditions and winds with a high chill factor are often experienced. Rainfall is bimodal, with an annual average of about 74 mm, mainly in the form of thunderstorms. Mist is prevalent in the winter months. Years may go by without good rains falling.
Sheep farming is the only agricultural activity of any significance in the area. The carrying capacity is extremely low and one sheep per 9 ha is the generally accepted norm. The population density within a radius of 50 km around the site is extremely low and is most certainly less than one person per square kilometre.
Telephone: 27 712-2882
CLEARED WATER AND MINERALS
Unconditional clearance: Free release of materials for unrestructed use.
Conditional clearance: The release of materials subject to further regulatory control
Radioactive material for recycling/reuse
Rework and recycling of contaminated materials for further use as radioactive materials: Examples at Necsa:
- Sale of uranium enrichment plant tails for re-enrichment.
- Sale of contaminated fuel fabrication plant components
Nuclear liabilities are costs that the organisation is expected to have to meet in future as a consequence of its current and past nuclear operations. (Nuclear Energy Agency of the Organisation for Economical Co-operation and Development, 1994)
The nuclear liabilities of Necsa are assessed on an annual basis in order to:
- Monitor the discharge of liabilities during decommissioning and waste management operations, and to
- Provide information that assists in the budget and funding planning of future decommissioning operations.
Assessments are carried out according to the following steps, within a framework of policy, assumptions, definitions and costing principles:
- Inventory: A comprehensive inventory of all facilities, areas, equipment and materials that constitute nuclear liabilities is compiled by means of detailed surveys.
- Processing strategies: Materials are categorised and processes defined according to what degree each material category could be processed until the liability associated with it is fully discharged. For example, in the case of contaminated steel such processes could entail the decontamination of the steel to clearance levels as well as the treatment, conditioning and disposal of the waste generated during decontamination.
- Process capacities and costs: The capacities and cost of each of the processes are determined. In order for the assessment to be accurate, the processes modelled in this way must accurately represent actual processes currently used, or be realistic representations of processes that will be established in future.
- Long-term plan: A long-term plan is established according to when decommissioning and waste management will take place.
- Assessment calculations: The UKAEA software package, Strategic Planning System (SPS), which was developed specifically for the assessment of nuclear liabilities, is used for storing the relevant data and calculating an optimised total site liability.