Cement Based Encapsulation Trials for Low-Level Radioactive Effluent Containing Nitrate Salts
- PDF / 929,915 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 19 Downloads / 127 Views
Cement Based Encapsulation Trials for Low-Level Radioactive Effluent Containing Nitrate Salts Atsushi Sugaya, Kenichi Horiguchi, Kenji Tanaka and Kentaro Kobayashi Tokai Reprocessing Research and Development Centre, Japan Atomic Energy Agency (JAEA) 4-33 Muramatsu, Tokai-Mura, Naka-Gun, Ibaraki, 319-1194 Japan ABSTRACT The operation of nuclear fuel reprocessing plants generates a radioactive effluent containing nitrate salts as the major constituent. This waste must be disposed of safely and economically, and to achieve this aim the Japan Atomic Energy Agency (JAEA) is developing a cement based encapsulation method to immobilise this waste. Non-radioactive development work has been performed at both small and large-scale (up to 200 litres) to investigate the optimum cement formulation. The results from these studies demonstrate that nitrate waste that has been concentrated by evaporation of the water to a predetermined level can be successfully encapsulated up to a waste loading corresponding to 50 wt% sodium nitrate. It has been identified that high concentrations of bicarbonate ions in the effluent can have a detrimental effect on the strength of the cement encapsulated waste; however, provided this concentration is controlled, successful encapsulation of the effluent is still achieved. 1. INTRODUCTION Nuclear fuel reprocessing plants generate a large volume of low-level radioactive effluent waste. It is necessary that this waste effluent is disposed of both safely and economically. In Japan this waste must be disposed of on land, and not at sea, by appropriate pre-treatment and burial underground. JAEA treats this low-level radioactive effluent waste by passing it through a nuclide separation process that produces two types of effluent waste: • A nitrate effluent (~90% original effluent volume) with a comparatively low radioactivity level that can be disposed of by shallow burial at a lower cost; • A slurry effluent (~10% original effluent volume) including several kinds of salts and with a relatively high radioactivity level that will require disposal deep underground. The typical composition of the nitrate and slurry effluent is shown in Table I. Separation into two effluents reduces the cost of disposal because it allows the larger volume of waste to be disposed of by shallow burial at a much lower cost than deep underground burial. The latter is required for the smaller volume of slurry effluent or would have been needed for the untreated effluent. Table I: Typical salt composition of a nitrate and a slurry effluent Waste NaNO3 NaNO2 NaHCO3 Na2SO4 Fe(OH)3 Nitrate effluent (wt%) 98 2 Slurry effluent (wt%) 75.5 10 12 1 0.5 Following separation into two types of waste effluent, water is evaporated from both types of waste to minimise their volume (the total salt content of the two effluents after
evaporation is about 70 wt%). So that the effluents can be disposed of safely it has been proposed that they are encapsulated in a cement matrix. This approach produces a solid material that is easier to handle and tr
Data Loading...
