The Effect of Changes in the Separation Process for the Performance of Recycled Cement Powder: A Comparison with a Previous Study for Radioactive Waste Immobilization

Abstract

Separation of hydrated cement paste from aggregate is a key technology to reduce the amount of radioactive concrete waste during the decommissioning process. If separated cement-paste portions can be recycled as a solidifying agent for other radioactive waste, the amount of radioactive concrete waste could be close to “zero”. A study was conducted to achieve circular economy in the area of concrete decommissioning and found it to be successfully used as a solidifying agent for immobilization of liquid radioactive waste. However, previous work used a process that requires large amounts of energy (heat treatment was applied to most of the concrete fraction) because the objective was to completely remove hydrated cement powder from the aggregate. In this work, the separation system was modified to increase energy efficiency (heat treatment was applied to separated powder only), but such a change decreased the surface area of the recycled cement powder due to a higher inclusion of aggregate powder. A relatively lower solution to binder ratio could have been achieved for the preparation of wasteform specimens, and as a result, a 28 day compressive strength of wasteform could have become higher, but the final leachability indices were lower than the results observed from previous work. The results from 28 day compressive strength, thermal cycling and 90 day leaching experiments met the acceptance criteria for wasteform, indicating that this modified system can also be used for immobilization of liquid radioactive waste to meet the “zero” production of concrete waste during the decommissioning of a nuclear power plant. It should be noted that accurate monitoring of aggregate content in recycled cement powder during production is important to maintain proper reactivity of recycled cement powder.

Valorisation of baryte tailings for radiation shielding in plastics and nuclear waste disposal

“…Other aspects for using the generated composites as binder material for radioactive ash were also promising. Typical waste acceptance criteria are mechanical strength and low leachability as well as the resistance against thermal impacts [ 27 , 28 ]. The above noted chemical inertness and high-level mechanical strength encourage further testing of the generated waste products.…”

Solidification of Radioactive Wastes Using Recycled Cement Originating from Decommissioned Nuclear-Energy Facilities

“…Aggregate and cement powder can be separated from CW using thermal and mechanical treatments, and the aggregate is generally fractionated into recycled coarse and fine aggregates based on the size of 5 mm [13]. During the crushing, grinding, and separation processes of CW, powder is generated, which consists of constituents originating from the cement paste as well as fine aggregate [14]. This powder contains many inorganic substances, such as calcium silicate hydrate (CSH), calcium hydroxide (CH), and SiO 2 , which are effective materials for waste treatment.…”

Evaluation of the Solidification of Radioactive Wastes Using Blast Furnace Slag as a Solidifying Agent

“…The proportion of CW that is radioactive is less than 5% and more than 95% of CW is considered as ultralow-level radioactive [9]. At present, the cost of the disposal of this ultralow-level radioactive CW is cut down through the use of landfills, incineration, and recycling [10][11][12]. Technologies to minimize the amount of nuclear decommissioning wastes and to recycle them have been actively developed in advanced countries such as France, Japan, Belgium, Germany, Spain, the UK, and the USA.…”