DESAGUES PLUVIALES RURALES SECTOR BARRIO EL LINCE

Radioactive waste is a waste product containing radioactive material and it is usually as a result of a nuclear process such as nuclear fission and other industries that produce it (Rafferty, 2011). According to Bonin (2010), at every stage of the nuclear fuel cycle, there is a production of waste. However, large volumes of short-lived radioactive waste are already handled by the nuclear industry in surface storage facilities, the management mode of high-

activity long-lived waste has not been decided in detail and is still under study in all nuclear countries. In South Africa, Vaalputs is the national radiological waste disposal facility for the Republic (NECSA, n.d.; Eskom, 2014; Carolissen, n.d.). It was designed as a national facility for the disposal of low and intermediate level waste only. Therefore, it is not licensed to accept any other types of radioactive waste at the moment except low and intermediate level waste from Koeberg NPP. According to Eskom (2014), NECSA’s low and intermediate level waste at present is being stored at Pelindaba, west of Pretoria, but negotiations could also lead to permission of disposing at Vaalputs in the near future. Vaalputs is situated in Namaqualand, approximately 600km north of Cape Town.

2.12.1 Nuclear Fuel Cycle

The nuclear fuel cycle (See Figure 2.25) is the chain of processes whereby nuclear fuel is produced and managed during and after its use in a reactor for generating electricity. However, to prepare Uranium for use in a nuclear reactor, it undergoes the steps of mining and milling, conversion, enrichment and fuel fabrication as detailed below (DME, 2005;IEA, 2011; MIT, 2003; Stott, 2013)

2.12.1.1 Mining and Milling

These two processes are the first in the 'front end' of the nuclear fuel cycle. Uranium is mined either by surface often called open cut mining, underground mining techniques, or using in situ leaching – a method whereby a solvent is injected underground to dissolve the uranium and is recovered from wells and pumped to the surface for further processing depending on the depth at which the ore was found. Thereafter, it is sent to a mill where the ore is physically reduced to a suitable size and chemically treated to extract and purify the uranium.

The resulting solid uranium oxides concentrate (U3O8) is called yellowcake.

2.12.1.2 Conversion

This is the process that transforms yellowcake into uranium hexafluoride (UF6) because to

enrich uranium, it must be in a gaseous state at a conversion plant in Europe, Russia or North America.

2.12.1.3 Enrichment

This is the process of increasing the amount of the U235 isotope, compared with the U238

isotope. However, enrichment involves the partial separation of uranium into its two main naturally occurring isotopes (U235 and U238). Majority of all nuclear power reactors in

operation and under construction require enriched uranium fuel in which the proportion of the

U235 isotope has been raised from the natural level of 0.7% to 3.5% or slightly more. However

PHWR uses natural uranium and does not require enrichment. With the enrichment process,

85% of U238 is removed by separating gaseous uranium hexafluoride into two streams: One

is enriched to the required level and proceeds to the next stage of the fuel cycle and the

other stream is depleted in U235 and is called tails. The composition of the tail is usually less

that 0.25% which is no further use for energy.

2.12.1.4 Fuel fabrication

The enriched uranium is then sent to a fuel fabrication plant where it is changed into uranium

dioxide (UO2) powder. The powder is pressed into small pellets, which are then put into metal

tubes, forming fuel rods. The rods are then sealed and assembled in clusters to form fuel assemblies for use in the core of the nuclear reactor. The fuel assemblies are put into the core of the nuclear reactor along with a moderator such as graphite or water. A typical boiling water reactor (BWR) contains over 730 assemblies containing about 46 000 fuel rods.

2.12.1.5 Spent fuel storage

The “back end” of the fuel cycle starts when the irradiated or “spent” fuel is unloaded from the reactor for interim storage. To maintain efficient reactor performance, about one-third of the spent fuel is removed every year or 18 months, to be replaced with fresh fuel. When the spent fuel is removed from the reactor, it is hot and very radioactive. It must be cooled and shielded from people. It is put into storage ponds at the reactor site. The water provides

cooling and radiation shielding. The heat and radioactivity decrease over time - after about 40 years they are down to about 1/1000 of what they were when taken from the reactor. Spent fuel can be stored safely in these ponds for long periods. It can also be dry stored in engineered facilities, cooled by air. However, both kinds of storage are intended only as an interim step before the spent fuel is either reprocessed or sent to final disposal. The longer it is stored, the easier it is to handle due to decay of radioactivity. There are two alternatives for spent fuel: reprocessing to recover the usable portion and vitrification. However, reprocessing steps are not undertaken in South Africa.

2.12.1.6 Reprocessing

Reprocessing is the operation by which the unused energy content of spent fuel is recovered for future re-use or where various constituents in the spent fuel are separated for waste management reasons. Spent fuel still contains approximately 96% of its original uranium, of

which the fissionable U235 content has been reduced to less than 1%. About 3% of spent fuel

comprises waste products and the remaining 1% is plutonium (Pu) produced while the fuel was in the reactor and not "burnt”. Therefore approximately 97% of spent fuel can be recycled for further use. Reprocessing separates uranium and plutonium from waste products and this is achieved commercially using a chemical process called plutonium and uranium extraction (PUREX). Recovered uranium can be returned to the conversion plant for

conversion to UF6 and subsequent re-enrichment.

2.12.1.7 Vitrification

After reprocessing, the rejected high-level fission product waste stream which also contains the minor actinides is stored for subsequent solidification in a highly leach resistant glass. The glass is then poured into stainless steel canisters. The canisters are then sealed and sent to a cooled storage facility until they are eventually sent for deep geological disposal. For allowing some relaxation of criticality constraints and safeguards requirements, it is a fact that vitrified glass canisters, no longer contains any fissionable materials after its disposal.

2.12.1.8 Final disposal

After more than 60 years of nuclear technology, there is still no universally accepted mode of disposal yet (Abbott, 2012; MIT, 2003; Pickard, 2009). However, technical solutions are emerging due to progressive scientific knowledge and there is necessity to find a final place for the final waste. According to MIT (2003), preserving the nuclear option for the future means planning for growth, as well as for a future in which nuclear energy is competitive, safer, and more secure source of power. Similarly, Macfarlane (2011) noted that, it is no longer the safe production of electricity but also the safe, secure, and sustainable lifecycle of nuclear power, from the mining of uranium ores to the disposal of spent nuclear fuel. Therefore, the deep geological underground disposal seems to be the only long-term solution

which does not require a continuous control by the society. The safety of the underground disposal relies on its capacity to confine radionuclide within an underground facility until radioactive decay has brought their radio-toxicity down to an acceptable level. The technologies exist, but their implementation requires a political decision. Contrary to a widespread view within the public, much progress has been made towards technically and socially acceptable nuclear waste repositories. Most of the experts agree, but the public and the political circles are still reluctant and in the process of building their confidence, they must be convinced faultlessly. According to Lidskog and Andersson (2001) and USNRC (2002), in many countries, public involvement seems to be a key issue for the successful implementation of radiological waste management. It is believed however that more public involvement and improved communication will lead to a greater social acceptance.