The final product is reinforcing bars which would be manufactured from radioactive carbon steel arising from the decommissioning Spanish nuclear installations. The manufactured reinforcing bars are used instead of commercial reinforcing bars (total or partially) in concrete disposal containers. Concrete containers will be manufactured using reinforcing bars of 10 mm diameter.
Quantity of Carbon Steel Required and Arisings of Suitable Material
Currently between 440 and 500 concrete containers are used per year at the El Cabril disposal site. Each concrete container has a reinforcing bars weight of around 620 kg. Thus the possible requirement for bars at the disposal site would be between 273 and 310 t per year. The estimated quantity of steel radioactive scrap arising from the nuclear Spanish installations is more than 20,000 t from 2000 onwards. This quantity is sufficient to supply material to a recycling plant for 10 years. In the case of using radioactive scrap for
Process Steps for Scenario 5
The main activities of this scenario are the following:
• Segmentation scrap for transport.
• Transport and monitoring of radioactive material.
• Reception, sorting and storage in the melting plant.
• Preparation of scrap for melting.
• Loading of furnace and melting.
• Ingots production. Storage and characterisation.
• Selection of ingots for smelt and casting preparation
• Melting and casting bars. Storage and characterisation.
• Reinforcing structure manufacturing at recycling plant.
• Reinforcing structure and secondary wastes transport to disposal site.
• Manufacturing of concrete containers at disposal site.
• Conditioning wastes in concrete containers and disposal.
It is considered that there is not enough scrap available at any one installation to justify an on site recycling installation and it has been considered that the melting and manufacturing plant will be integrated as a specific installation of an existing conventional melting/casting plant or as an independent melting, casting and manufacturing plant.
Besides the equipment and installations of a commercial melting or casting plant, some ancillary areas or systems are also considered inside the recycle plant, eg storage and handling radioactive scrap, occasional cutting equipment in order to fit the size scrap to capability of furnace, radiological protection system, special ventilation and filter systems, monitoring, radiological characterisation, etc. The scrap arriving to the plant, inside transportation containers, must be temporary stored on site in order to fit the planned melting campaign. The nominal capacity of the plant could be about of 2000-3000 t per year and the furnace would be electric induction type of 4.5 t capacity.
The general acceptance criteria for metal melting in the plant are estimated to be the following (based on current literature and discussions with plant operators) :
Radiation levels:
Radiation level per package <0.1 mSv/hr contact (1 cm)
Surface contamination or activated metal <0.1 mSv/hr average contact (unshielded) Radionuclide limits:
In general terms the average radionuclide concentration shall not exceed the 1500 Bq/g for Co-60 or gamma - beta emitters and 100 Bq/g for alpha emitters over the package or component. There will also be a list of radionuclides with the upper activity limit defined for each of them, although the details of this list are not considered here.
The dose rate calculation for this reinforcing bars scenario should be developed according to the IAEA models and on the base of a maximum of 200 Bq/g in the final product. Appendix 3 presents estimated doses to workers for the manufacturing of reinforcement bars using this model.
In this scenario the radioactive scrap must first be prepared at the decommissioning site (eg first stage decontamination, segmentation, etc) and transported in an acceptable container to the recycling plant. A distance of 600 km has been assumed from the scrap producer installation to the melting plant. From the producer installation and the melting plant to disposal site the distance of 700 km has been considered. During the melting operations a production of 3.5% of secondary waste has been considered.
Technical Details of Scenario
The objective of this study is to determine the technical viability and the necessary equipment for manufacturing bars (either corrugated bars or non-corrugated bars) for use as reinforcement in construction. These products would be obtained from steel ingots manufactured with scrap carbon steel from nuclear installations. A production of 2000 t/year is assumed.
Both smooth and corrugated bars for construction (concrete) must fulfil a series of requirements both with regard to their composition and with regard to their mechanical and geometrical characteristics. Details of these are included in Reference [21] and are not repeated here. The manufacturing technology for both smooth and corrugated bars to be used in reinforcing concrete is hot rolling. Bars with a diameter greater than 12 mm will be obtained as the final product of the hot rolling.
One aspect which must be borne in mind in the manufacturing process of these bars is that the larger the final diameter, the less hot rolling will be required and, therefore, the process will be more simple and more productive. Should bars with diameters smaller than 12 mm be required (wires) a further cold process is required after the hot rolling which may be either wire-drawing or cold rolling.
The manufacturing process consists of the following steps:
+HDWLQJ the ingots until they reach the temperature required for beginning the rolling and
keeping the ingots at this temperature.
5ROOLQJ Once the ingot leaves the furnace at the correct temperature it is subjected to the
rolling process. This consists of deforming the original material ("ingot", "billet", etc) compressing it between two cylinders which rotate in opposite directions in such a way that a reduction and modification of the original cross section elevation is achieved.
&RROLQJ Once the bars have been cut into the required lengths, it is necessary for them to be
cooled as they are still at very high temperatures. Therefore, before the bars are stacked or, in the event, packed, they are subjected to rapid cooling.
6WDFNLQJDQGSDFNDJLQJ of the bars: Once the manufacturing process has concluded and the
bars are ready, they are stacked and packaged in order to facilitate their storage, handling and transport.
The basic installations for carrying out the rolling process for bars (smooth or corrugated) are as follows:
+HDWLQJIXUQDFH (for heating the initial ingots)
7KHUROOLQJPLOO The rolling mill is composed of a series of roll stands (two-high or the-
high) with different channels through which the section is formed until the finished product is obtained. The last roll stand - the surface finisher - gives the final dimensions of the product. For the case under study, an open rolling mill is recommended, which is cheaper than a continuous rolling mill and which has been designed for large quantities of production. The installation should have a furnace with a capacity for 40 t/hr.
7KH FXWWLQJ OLQH This piece of equipment cuts the bars to the established lengths (for
example, corrugated bars may be cut to lengths of between 6 and 12 m).
7KHFRROLQJEHG Once the bars have been cut they must be subjected to rapid cooling before
they can be handled and stacked.
7KHUROOVWUDLJKWHQHU This corrects any deviations caused during the process. 7KHVWDFNLQJVWDWLRQ This stacks the bars once they have been cooled and cut.
7KH HOHFWULFDO LQVWDOODWLRQ For putting an installation of this kind into service, some
1000 kW would be required.
The estimated cost for an installation of this kind is around 150 million pesetas according to manufacturers. However, it should be pointed out that for an installation of this kind (an open rolling mill, which is not the most productive kind), which might have a production of 10 t/hr, the production of 2,000 t would require 200 hours. If the installation were to be operating for 2,000 hours per year, a production of 2,000 t/year would mean a return of 10% for an installation of this kind.
Economic Assessment of Scenario 5
In this section a comparative economic assessment is carried out between direct disposal of metallic scrap and the alternative of manufacturing rebars from the scrap.
The associated costs involved in the recycling option include :
• Cutting and packaging (20 ft ISO containers) of the arising scrap.
• Scrap transportation.
• Investment in a radiological metal recycling installation.
• Bars and secondary wastes transportation.
• Manufacturing of reinforcing and containers.
• Conditioning wastes in concrete containers and disposal.
0DQXIDFWXULQJUHEDUVFRVW
PROJECT
Engineering 25 Million pts £125,000 179 kECU
Civil Works 120 Million pts £600,000 860 kECU
Equipment 150 Million pts £750,000 1075 kECU
Tests 15 Million pts £75,000 108 kECU
Radiological Protection 40 Million pts £200,000 287 kECU
Control 20 Million pts £100,000 143 kECU
TOTAL 370 Million pts. £1,850,000 2652 kECU
6SHFLILFFRVW SWVNJ W (&8W
OPERATION
Workers 12.8 Million pts/year £64,000 / year 92 kECU/yr
Technicians 4.2 Million pts/year £21,000/ year 30 kECU/yr
TOTAL 17.0 Million pts /year £85,000/ year 122 kECU/yr
6SHFLILFFRVW SWVNJ W (&8W
ENERGY 1.200.000 kWh
6SHFLILFFRVW SWVNJ W (&8W
OVERHEAD EXPENSES
20 Mill pts/ year or £100,000 /year or 143 kECU
6SHFLILFFRVW SWVNJ W (&8W
DISMANTLING
160 Mill pts or £800,000 or 1147 k ECU
6SHFLILFFRVW SWVNJ W (&8W
OTHERS
16.0 Mill pts / year or £80,000/year or 115 kECU
6SHFLILFFRVW SWVNJ W (&8W
7RWDOUHEDUVFRVW SWVNJ W (&8W
5HEDUVFRVW
650 kg of scrap = 650 kg of bars and 1 drum of wastes Dismantling activities 430 ECU/t
Melting 860 ECU/t
Casting 774 ECU/t
Milling 430 ECU/t
Manufacturing structures 72 ECU/t
Transport 287 ECU/t
TOTAL 2852 ECU/t
Manufacture of rebars 1854 ECU Secondary wastes disposal 180 ECU
Re-evaluation of Scenario 5 with Common Cost Assumptions
The costs for each of the main stages in the scenario are summarised here using two disposal charges - one typical of a near surface disposal facility and another typical of a deep geological repository. The cost analysis below includes common assumptions relating to transport costs and scrap handling charges. The calculation of disposal costs for secondary waste and for the disposal option includes minimal volume reduction prior to disposal. Supercompaction of some wastes may be carried out but calculations have assumed a packing density of 1.2 t/m3 for secondary wastes from processing and 1.5 t/m3 for direct disposal of wastes.
5HF\FOLQJ&RVW (&8
Capital cost of plant 5,404,000
Operating costs of plant (per year) 3,318,000
Decommissioning costs of plant 3,082,000 (57% of capital cost)
Costs of containers for disposal of secondary wastes (drums) 60 Costs of containers for disposal of secondary waste (concrete) 3585 Total disposal charge for secondary waste (shallow) 926,000 Total disposal charge for secondary waste (deep) 25,210,000 Costs for handling of wastes/scrap and transport (717 ECU/t) 2,222,000 TOTAL (shallow) 14,951,000
TOTAL (deep) 39,235,000
'LVSRVDO&RVW (&8
Cost of buying final product (each) 315 ECU/t Costs of containers for disposal of wastes (drums) 60
Cost of containers for disposal of wastes (concrete) 3,585 Costs for handling of wastes/scrap and transport (575 ECU/t) 1,777,000 TOTAL (shallow) 6,852,000
TOTAL (deep) 114,263,000
Cost of recycling - disposal (shallow disposal) 8,099,000 Cost of recycling - disposal (deep disposal) -57,028,000 Scenario 5 - Conclusions
The economic analysis using Spanish data has shown that the recycling of steel for production of reinforcing bars which could be used in the manufacture of concrete disposal containers is around half the cost of disposing of the metallic waste. A re-evaluation of this scenario with a common set of assumptions relating to scrap handling charges and transport requirements to enable scenarios indicates that a slight rise in disposal charges for a near surface disposal facility may be required in order to make the scenario economically attractive.