Non-combustible waste vitrification with plasma torch melter

Our plain-English summary of Non-combustible waste vitrification with plasma torch melter, by J.K. Park, Y.P. Moon, B.C. Park, et al (Journal of Environmental Science and Health. Part A, Toxic/hazardous Substances & Environmental Engineering, 2001).

The study

• Authors: J.K. Park, Y.P. Moon, B.C. Park, M.J. Song, K.S. Ko, J.M. Cho
• Journal: Journal of Environmental Science and Health. Part A, Toxic/hazardous Substances & Environmental Engineering
• Published: 2001;36(5):861-71
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Non-combustible radioactive wastes generated from Nuclear Power Plants (NPPs) are composed of concrete, glass, asbestos, metal, sand, soil, spent filters, etc. The melting tests for concrete, glass, sand, and spent filters were carried out using a 60 kW plasma torch system. The surrogate wastes were prepared for the tests. Non-radioactive Co and Cs were added to the surrogates in order to simulate the radioactive waste. Several kinds of surrogate prepared by their own mixture or by single waste were melted with the plasma torch system to produce glassy waste forms. The characteristics of glassy waste forms were examined for the volume reduction factor (VRF) and the leach rate. The VRFs were estimated through the density measurement of the surrogates and the glassy waste forms, and were turned out to be 1.2-2.4. The EPA (Environmental Protection Agency) Toxicity Characteristic Leaching Procedure (TCLP) was used to determine the leach resistance for As, Ba, Hg, Pb, Cd, Cr, Se, Co, and Cs. The leaching index was calculated using the total content of each element in both the waste forms and the leachant. The TCLP tests resulted in that the leach rates for all elements except Co and Cs were lower than those of the Universal Treatment Standard (UTS) limits. There were no UTS limits for Co and Cs, and their leach rate & index from the experiments were resulted in around 10 times higher than those of other elements.

In plain English

This was a laboratory engineering experiment, not a health study. Authors from Korea tested whether a 60 kW plasma torch melter could turn simulated non-combustible nuclear power plant waste into glassy waste forms. The article lists asbestos as one kind of such waste, but asbestos was not among the materials melted. Ten surrogate wastes (PT1 to PT10) were prepared: five mixed two of concrete, sand and glass, four used a single material, and one combined all four materials. Non-radioactive cobalt and cesium were added to stand in for radioactive material. The authors reported volume reduction factors (how much smaller the waste became) of 1.2 to 2.4; a second measure on ground samples reached 7.364 for simulated filters. In a standard US EPA leaching test, all the glassy forms met EPA treatment limits for every element tested except cobalt and cesium, which have no such limits. About 10 times more cobalt and cesium leached out than the other elements. Considering volume reduction together with cobalt and cesium leaching, the authors concluded the best waste form came from 25% concrete with 75% glass.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory melting (vitrification) experiment on simulated waste; engineering study, not a health study
• Who was studied: No people studied. Ten prepared surrogate wastes, PT1 to PT10, each weighing 500 g except PT10, which weighed 600 g. PT1 to PT5 mixed two of concrete, sand and glass in a 3:1 ratio. PT6 to PT9 each used a single material (concrete, glass, sand, or simulated filters). PT10 combined four materials in equal weight. The work was done at the Nuclear Environment Technology Institute, KEPCO, Korea, with Kumho Engineering.
• Exposure: No human exposure was studied. Asbestos is named only as one component of non-combustible nuclear power plant waste. The surrogate samples were made from concrete, sand, glass, and simulated filters (stainless steel, galvanized steel, glass fiber and polypropylene). Non-radioactive cesium (as Cs2CO3) and cobalt powder were added at 5 g per kg of waste.
• Main results:
  • In the EPA leaching test (TCLP), all glassy waste forms met EPA Universal Treatment Standard limits for all elements except cesium and cobalt, for which no limits exist.
  • Leached cobalt (2.4 to 67.19 mg/l) was around 2 to 5 times more than leached cesium (0.5 to 28.84 mg/l). Both were about 10 times more than the other elements.
  • Mercury was examined but was not detected in the leaching test.
  • The share of added cesium retained in the waste forms was 30 to 80 wt.%; for cobalt it was 2 to 25 wt.%.
  • The authors summarized the volume reduction factors as 1.2 to 2.4. In Table 2, superficial factors (measured on the solid waste forms) ranged from 1.190 to 2.400 where reported. Intrinsic factors (measured on ground powder) ranged from 1.510 to 7.364.
  • The largest volume reduction factor was for PT9 (simulated filters): an intrinsic factor of 7.364, with no superficial factor reported. The authors attributed this to its polypropylene content.
  • Wastes with a basicity (CaO/SiO2 ratio) of about 0.06 or less picked up extra alumina in the waste forms. The authors thought the source was the melter's alumina lining.
• The authors' conclusion: The authors concluded that, considering volume reduction and cobalt and cesium leaching, the best waste form came from 25% concrete and 75% glass. They also concluded that waste basicity should be 0.07 or more to prevent corrosion of the alumina lining.
• Limitations the authors state:
  • Because there are no treatment-standard limits for cesium and cobalt, the authors stated they could not interpret those leaching results.
  • Most waste forms contained bulky cavities, which the authors considered undesirable for volume reduction and waste form quality.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Power plants and utilities.

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