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Radioactive Graphite Waste Management Plan for VHTR

- Large volumes of radioactive graphite waste involved:about 60,000 tons in the UK, 50,000 tons in the former Soviet Union, similar amounts in France and in the USA Totally 230,000 tons assumed- The significant quantities of the long lived isotope Carbon-14, as well as significant amounts of Tritium and other radionuclides contained within the graphite waste- Graphite is an inert stable material that maintains its good mechanical properties in adverse conditions over many years. Therefore, the safe storage concept can be usedneed not involve a high level of technological skillHowever, the location and construction of near surface or deep geological waste repositories requires political support

- Conventional Burial Option- Preparative Treatment- Incineration- Chemical Decontamination- Mobilization of Isotope by Heating & Grinding- Pyrolysis and Steam Reformation- Vitrification- Recycling and Reuse- Carbon14 Isotope Separation Technique

- The incineration of graphite has a number of advantages it disposes of the stored Wigner energy problem completely, it greatly reduces the volume of waste i.e. 1,400 m3 of graphite could be reduced to as little as 35 m3 of cemented ash product and filters.

Graphite react with oxygen in the air

1. Conventional Burningcontrolled combustion of the graphite. The graphite is first of all crushed into pieces of typical dimension 2.5 cm. then placed in a furnace where it is subjected to a blast of air at about 1000. Cooler air blasts would be needed to keep down the temperatures of the furnace walls and the graphite bed. Assuming that about 10 tons of graphite could be incinerated per day.-disadvantagesthe milling effort requiredthe production of active dust the difficulties of the incinerator design.2. Fluidized Bed Incinerationburning the graphite in a fluidized bed. ground to a powder (possibly down to 30m) to provide enough surface area for reaction with oxygen at incineration temperatures. produce dust that would have to be contained. could lead to ignition if significant stored Wigner energy and air were present. These factors alone preclude this option.the milling prior to burning produces waste itself, irradiated graphite can be very hard making milling more difficult other materials can become mixed with the ash from the carbon thereby increasing the ash volume, as can any inefficiency during burning.

3. Power Laser Driven IncinerationAn alternative method of incineration. no prior milling or crushing of the graphite is required before incineration. Thus the bricks can be loaded straight from the reactor core and the furnace design is very simple compared with earlier options.At the heart of the system is a 30 kW CO2 laser. The laser beam heats the graphite surface to about 1500 and rapid combustion takes place when O2 is supplied.The laser itself can be outside the furnace area so does not require handling within an active area.Control is completely governed by the presence of the laser beam, as high temperatures are limited to one side of a single block. energy in the block is only a few percent of the total energy release and so does not constitute a problem. The suggested combustion rates are about 150 kg/h which with a 50% load factor would consume 700 tons of graphite per year. The main disadvantage of this process is that it is not proven technology on this scale and so would require a significant research and development program to support this work.

- It is difficult to cost this system since there is little experience with radioactive plant of the required duty.- a combustion/ash immobilization unit could be constructed and approved for use at a cost less than 30 M- Estimated costs range from a maximum of 15,000/ton of graphite for numerous smaller facilities down to perhaps 500/ton plus transport for a national facility-Cost Comparison-Assessment of management modes for graphite from reactor decommissioning(1984)1 =1,80030 M=540

15,000/ton=27,000,000/ton500/ton=900,000/ton

2013-63(2013.06.27):1,193,000,000/200L =59,650,000/ton

- Major political / environmental concerns about release of 14C despite favorable comparisons with the natural production rate.- Similar concerns about CO2 release and greenhouse effect.- Technology to trap 14C capable of development but probably expensive.Effective half-life of 14C in the environment may be much shorter than the actual half life. IAEA Specialists Meeting in 1995, W. Morgan (Pacific Northwest National Laboratory, USA, personal communication) considered that the effective half-life of incineration 14C emissions was around 35 years if the dissolution into oceans followed by the formation of carbonate sediments was considered as a removal process from the habitable environment.

Conceptual Design of isotope Separation of 14C after Incineration18