Low and intermediate level radioactive waste treatment

Sections

• Waste management
• Treatment of laundry wastewater
• Treatment of boron wastewater
• Treatment of UF₆ production wastewater
• Solid waste treatment

Waste management

According to the World Nuclear Association, as of June 2018 there are 450 nuclear reactors in operation worldwide, another 58 under construction and 153 more at the planning stage. Without a doubt, in the short and medium terms it is very hard to imagine an alternative to nuclear power, more difficult still if one takes into account the advantages of nuclear power in mitigating climate change as it is a form of energy that produces no greenhouse gases.

Nuclear power’s main drawback is the waste it generates, which is radioactive to a greater or lesser extent, and which must be managed in accordance with the strict procedures required by the regulatory bodies.

Nuclear waste is classified according to its radioactivity as:

• Highly radioactive waste (3% of the total volume)
• Moderately radioactive waste (7% of the total volume)
• Low radioactive waste (90% of the total volume)

The most important highly active waste is spent nuclear fuel. Low activity waste consists of the utensils, tools and work clothing used by personnel in nuclear power plants that are slightly contaminated with radioactive particles. Moderately active waste is generated from materials of equipment used as filters, metal components of the inside of the reactor and some liquid effluents from reprocessing.

While the management of highly active waste is a matter that needs to be discussed separately, the management of medium and low activity waste is based on confining it in 220-litre drums sealed with concrete and stored in controlled nuclear waste sites. This management entails very high economic costs, so optimizing it produces very significant economic benefits, as well as environmental ones.

It is in this regard that Condorchem Envitech has developed 4 solutions which, each in its own way, seek to minimize the medium and low radioactivity waste generated both in nuclear power plants and uranium enrichment plants. Below are described the processes developed by Condorchem Envitech for the nuclear industry:

NUCLEANTECH® LAUNDRY

This solution has been developed for the treatment of waste water generated in the washing of nuclear power plants and in showers for the personnel. These waters carry radioactive particles that have adhered to the protective clothing and safety gear worn by the personnel (masks, gloves, boots, etc.), especially during maintenance tasks, To obviate managing this water as a low activity nuclear waste due to its high cost, the NUCLEANTECH® LAUNDRY process approaches its treatment in an efficient, sustainable and safe way.

The NUCLEANTECH® LAUNDRY process consists of two lines of treatment, which are effective according to the waters’ level of radioactivity. If the levels of radioactivity are under the discharge limits (0.02 mSV/yr), to achieve a water quality that is acceptable for its reuse in washing, the organic material is oxidized using ozone and ultra-violet radiation. The effluent is then filtered and refined by passing it through a bed of active carbon and, finally, evaporated. The condensed vapor is recirculated to the wash unit and the concentrate is dried and managed as conventional waste.

In the event that the waters contain significant levels of radioactivity (over 0.02 mSv/yr) the radioactivity treatment line comes into operation. The first step is oxidation of the organic material using ozone and ultra-violet radiation and, at the same time, the ionization of the radioactive particles, generally metallic ions. Next, these are held using cationic and anionic columns for ionic exchange, and once the waters are free of radioactive isotopes, the concentrated waste is separated from the water and from any non-condensable gases, using an evaporator-dryer. These gases are released into the atmosphere after being held for a period of time in a decay tank, the water evaporated and subsequently condensed can be discharged to the outside and the concentrated solid waste is the only residue that must be managed as low activity nuclear waste.

The advantages of this system are many and notable:

• High efficiency in the washing process, in which the use of ozone in the washing allows the dose of detergents to be reduced and the washed materials to be hygienized.
• Reuse of the water, which in addition to achieving a saving of this resource, means the minimizing of the residual effluents generated in the process.
• A drastic reduction in the volume of the low and medium activity wastes generated, with the resulting economic savings and reduction of the environmental impact.
• Provision and control of the radioactive isotopes found in the waste water (60Co, 129I, 131I, 90Sr, 55Mn, 59Fe, 137Cs, 134Cs, 51Cr, etc.).
• Flexibility of the process in the presence of radioactivity in the effluent to be treated.
• Flexibility of the process to deal with flow fluctuations and the load to be treated.
• Strict compliance with the strictest standards.

NUCLEANTECH® H₃BO₃

The NUCLEANTECH® H3BO3 process is presented as an alternative to the management of low and medium activity nuclear waste from the effluents from the regeneration of ion exchange resins, which are used to retain the radioactive isotopes of the coolant purges of the secondary circuit of PWR reactors.

This process makes it possible to treat the effluents produced in the regeneration of ion exchange resins and, through an evaporator-dryer, the concentrated and medium level radioactive waste is separated from a decontaminated effluent that can be discharged.

The main advantage of the NUCLEANTECH® H3BO3 process is the minimization of the volume of low and medium activity waste generated, which must be treated in a way that is consistent with its nature. This minimization of the production of this nuclear waste translates into a major economic saving and an increase in the environmental sustainability of the overall process.

NUCLEANTECH® UF₆

In uranium enrichment plants, effluents are generated in the washing process of the equipment used in the synthesis and transport of UF6. These effluents contain dissolved salts and radioactive particles, which are managed as low and medium activity waste.

The NUCLEANTECH® UF6 process is a solution for the treatment of this effluent so that most of it can be reused in the washing process, with the consequent saving of water and, most importantly, minimizing the volume of nuclear waste that must be managed externally.

The process is based on the filtration of the effluent followed by a vacuum evaporation process, in which the concentrate is fed into a crystallizer to obtain a completely dry waste. This waste concentrates all the radioactive particles in the smallest possible volume, so that the cost of managing the waste generated is significantly reduced. The water separated in the evaporator, once condensed, possesses a suitable quality to be reused again in the washing operations of the process equipment.

The NUCLEANTECH® UF6 process is a sustainable solution to the generation of low and medium activity waste in washing operations in uranium enrichment plants, while at the same time minimizing the volume of waste produced, with the resulting economic savings.

NUCLEANTECH® NWDR

In uranium enrichment plants and, above all, in nuclear power plants, large volumes of waste are generated which, despite their very low radioactivity, must be managed in accordance with the standardized protocols for nuclear waste. This waste consists of all the utensils and disposable protection materials used by the workers at the facilities, such as masks, gloves, caps, glasses, protective suits, etc. Managing this huge volume of waste by confining it in 220 L drums sealed with concrete is very costly.

In some facilities, where it is permitted, this waste is incinerated; Although it is an economic alternative, it is not the most advantageous from the environmental point of view.

The NUCLEANTECH® NWDR solution (nuclear waste disposal reduction) has been conceived as an innovative alternative to reduce to a minimum the volume of this type of nuclear waste, with up to an 80% reduction in overall volume. The heart of the process is a stage of pyrolysis of the waste, in which, in the absence of oxygen, the waste is destroyed and transformed into a solid waste (5% of the initial volume), a liquid fraction and a gaseous current that is suitably treated before being released into the atmosphere. The treatment of the liquid fraction and the gaseous fraction also generates a dry residue, which may constitute 15% of the initial waste volume.

The advantages of the NUCLEANTECH® NWDR process are many and very important. Among the most relevant are the following:

• Reduction of 80% of the volume of nuclear waste of low and medium activity generated in plants that handle radioactive substances, particularly uranium enrichment plants and nuclear power plants. This means a drastic reduction of the costs of management of this waste.
• The size of the installation is relatively small, so that the waste can be treated on site without the need to be transported.
• No polluting ash or dioxins are generated in the process since no incineration occurs.
• The process is efficient, compact and safe.