Radioactive waste discharged

Sekimoto H, Nakamura H, Takagi N. 1996. Toxicity of radioactive wastes discharged from nuclear energy center in the future equilibrium state. Ann Nucl Energy 23(8) 663-668. 

The Environment Report (reference 15.6) also demonstrates that liquid, gaseous, and solid radioactive waste discharges have been minimised in accordance with the ALARP principle. 

The principal sources of radioactive waste discharges, containing artificial radionuclides, to the Irish Sea and all UK coastal waters, are mostly related to power generation and the nuclear fuel cycle. The locations of these sources are shown in Figure 1. 

The regulation of transport of discharges of low-level radioactive waste... 

Reduction of cnviromncntal pollution requires lower energy use and new technology to decrease emission of gases such as sulfur dioxide and carbon dioxide, and to prevent toxic fluoride, heavy metal, and radioactive wastes from discharging into the environment. 

Nuclear power plants use fuel rods with a life span of about three years. Each year, roughly one-third of spent fuel rods are removed and stored in cooling basins, either at the reactor site or elsewhere. Typical modern nuclear power plants discharge about 30 tons of the spent fuel per reactor per year. Comparatively little of Lite radioactive wastes, as is currently reliably known worldwide, has been processed for return to the fuel cycle. Actually, fuel reprocessing causes a net increase in the volume of radioactive wastes, but, as in the ease of military wastes, they are less hazardous in the long term. Nevertheless, the wastes from reprocessing also must be disposed of with great care. 

In order to protect personnel from a potentially serious radiation hazard, the water from the jacket, is used on a once-through basis and then discharged to a tank used for collecting radioactive waste solutions. This practice is followed even though the water is not contaminated under normal operating conditions ... 

Radioactive xenon was also expected and in fact observed in measurements of the spontaneous fission of " Pu in subsurface soils. In this case, the origin of " Pu in the subsurface was due to Pu entrained in waste discharged into the soil from the United States weapons program. In this case, the amount of " Pu in the subsurface soil was estimated to be 10 to 10 Ci/g of soil (approximately 0.05 to 0.5 g " Pu/m soil). This amount created relatively large concentrations of Xe and Xe in equilibrium. ... 

To provide reassurance that the radiological impact of authorised discharges of radioactive waste and other transfers of radioactivity into the environment is acceptable - incorporating monitoring related to less significant exposure pathways. 

It is very important to consider the pathways of radionuclides in the environment for design of the environmental monitoring program. Radionuclides enter the receiving environment via direct emissions to atmosphere, direct discharges to water bodies or releases from land burials of radioactive wastes. 

Reverse osmosis has been employed in full scale in many nuclear centers around the world. Permeate after reverse osmosis can be directly discharged to the environment or recycled as service water within nuclear power plant. There are a number of industrial RO applications and facilities in the stage of pilot plants operating for radioactive waste processing. Some examples of installations are presented in Table 30.1. 

The RO process was implemented at the Institute of Atomic Energy, Swierk. The wastes collected there, from all users of nuclear materials in Poland, have to be processed before safe disposal. Until 1990 the wastes were treated by chemical methods that sometimes did not ensure sufficient decontamination. To reach the discharge standards the system of radioactive waste treatment was modernized. A new evaporator integrated with membrane installation replaced old technology based on chemical precipitation with sorption on inorganic sorbents. Two installations, EV and 3RO, can operate simultaneously or separately. The membrane plant is applied for initial concentration of the waste before the evaporator. It may be also used for final cleaning of the distillate, depending on actual needs. The need for additional distillate purification is necessitated due to entrainment of radionuclides with droplets or with the volatile radioactive compounds, which are carried over. 

Liquid radioactive waste was directed from the waste storage tank to the 8 m feed reservoir. After pretreatment with PP depth filters and injection of antisealant, the wastes were directed to the first stage of RO. The retentate from this stage was concentrated in the third RO unit. The concentrated solution could be directly solidified if the concentration of the total solute was appropriate (<250 g/dm ). The salt concentration is limited by the conditions of concrete solidification. If the concentration was not sufficient, the further concentration took place in the evaporator. Permeate from the first and third stages was directed to the permeate reservoir before the second RO unit. The product from the membrane installation (permeate from the second stage) was of required radiochemical purity and after the control of specific activity and salinity was discharged to the communal sewage. 

The characteristics of permeate and retentate streams in terms of upper limits at the exit of RO plant were presented in Table 30.2. The concentration of salt in permeate is lower than 0.1 g/dm. The concentration of some specific elements as heavy metals has to be in conformity with the limits of impurities for wastes discharged to the inland waters. Total specific activity for (3 and y emitters is lower than 10 kBq/m, while for a emitters it is lower than 1 kBq/m (the limits for liquid waste). The total salt concentration in retentate is limited by ability of binding the solution with the concrete, the specific radioactivity by nuclear... 

The results of radioactive waste sample C treatment with 3RO are shown in Figure 30.5. The feed radioactivity is 2,200 Bq/dm. After processing permeate has radioactivity below discharge limits (3.9 Bq/dm ) and can be discharged the concentrate of radioactivity 16,000 Bq/dm can undergo further processing. The average decontamination factor for entire plant is 564. 

Apart from radioactive compounds the radioactive wastes may contain non-active but chemically toxic substances. The national standards and regulations describe the discharge limits for these substances, too. Heavy metals are toxic compounds, most often present in liquid radioactive wastes. The experiments showed that most of these metals are removed by UF/complexation method. The method is inefficient for removal of monovalent ions, bivalent cations and anions are retained in 25%-50%, but high retention of the metals like Mn, Fe, Co, Cu, Pb, Cr was observed. The retention factors for those metals in two-stage experiment described above, were as follows ... 

---