The facilities dealing with radiation technology face the brunt of Radioactive decontamination. A unique UV-Curing method is provided for decontamination of radioisotopes on the surfaces which has radiation dealing facilities. In this method acrylic UV-Curing resin was poured on a contaminated surface followed by exposure under the UV light of 365nm wavelength from a UV irradiation chamber. Upon UV irradiation, the UV-Curing resin interacted with the radioactively contaminated surface and after polymerization, the solidified resin was then stripped off, leaving behind a précised clean surface. The present study is the proof-of-concept of a novel application of acrylic resin UV-Curing methodology for Radioactive surface contamination removal to create a economical clean, effective and safe environment with minimal waste generation post processing ready for environment friendly incineration.
Research Article
A novel application of acrylic resin UV-Curing methodology for Radioactive surface Decontamination
https://doi.org/10.21203/rs.3.rs-1977957/v1
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UV-curable Resin
decontamination
surface decontamination
radioactive spill management
peeling off
stripping out
Radioactive materials have commonly been used in research activities and health care areas all over the world. During the process of managing the radionuclide, decontamination is one of the major hurdles. When handling open isotopes in a nuclear medicine laboratory, radioactive contamination of worktops or personnel occurs either as a result of the regular operation or as a result of mismanagement of precautionary measures. Deposition of radioactive material in any place such as working surface area, skin, clothes, equipment etc, where its presence is harmful is known as radioactive contamination. Radioactive contamination causes high radiation exposure to the occupational community causing serious health problems related to high radiation exposure (Natalia et al., 2014). Decontamination is the process of removing hazardous materials from situations where they are not needed. The decontamination techniques used in decommissioning activities are chemical decontamination, electrochemical, mechanical decontamination, decontamination by melting, etc. (NEA 2020). Surface decontamination is a requirement for decommissioning and dismantling, making the process easier and reducing the amount of radioactive waste generated (Liu et al;2022). Methods for decontamination includes direct and indirect method. A direct method is used for estimation of both fixed and loose contamination, reliable, quick and easy to perform in routine practices. The indirect method estimates only a loose type of contamination, used where background activity is high and the direct method is not feasible to perform.
Various methods available for decontamination include swiping, absorbents and strippable coatings (Pulpea et al; 2020; Rao et al; 2004). The conventional surface swiping methodology have limitations of high risk of spreading the contamination, multiple personnel’s involvement for cleaning of radioactive contaminations, time-consuming and have rationally high exposure to radiation workers. When strippable coatings were used for decontamination the curing time was found to be 24 hours which is the limitation of the study (Banerjee et al., 2015; Pulpea et al., 2020). Therefore, newer techniques need to be evolved which can reduce the curing time as well along with the safe and secured précised containment of radioactive spills and /or surface wet contaminations.
There are available UV-Curable masking resins which have surface treatment applications which include protection against milling, laser drilling, grit blasting, shot peening, acid stripping, plating, and thermal spray coating (Bachmann et al.; 2015).
The goal of the research discussed in this paper is to improve the shortcomings of existing radioactive cleaning technologies. Therefore, in order to minimize the probability of spreading, minimizing the volume of waste generations, minimize the time, cost, radiation exposure and ease of application for the decontamination process, ease of stripped films waste collection followed by disposal after decaying appropriately for ten half-lives, the present method for resin UV-Curing was studied.
This study contributes to the field of radioactive decontamination in numerous ways, including; the acrylic resin on which UV irradiates the surface of resin polymers breaks the bonds when absorbed in molecules, also it improves the adhesive property of coating (Loyaga et al.,2007) material used as the decontamination solution, the decontamination tests were carried out on several types of radioisotopes simultaneously, on different types of surfaces, and moreover, high decontamination factors were obtained, proving the remarkable decontamination efficiency of this new method of using UV-Curing resin for surface radioactive decontamination. Another feature of originality is the development of a new application of UV-curing resins and UV-curing technology that allows for decontamination in minutes.
For controlled contamination of the surfaces radioactivity of F-18, Tc-99m, Tc-99m labelled, I-131 and Lu-177 as experimental setup were chosen. Tc-99m is the most common radioisotope that is found after the radioactive spill. Iodine being volatile used for diagnostic and therapeutic purposes. F-18 positron emitter which has the shortest half-life and Lu-177 has the longest half-life of the aforementioned.
Various types of surfaces were chosen for decontamination Poly Vinyl Chloride (PVC), Glass, Stainless steel ( S.S), Ceramic tiles and glazing wood. These materials were chosen in this study since they are the most common to find in radiation-related facilities and areas.
2.1 Materials
UV-Resin hard, UVA light 365nm wavelength − 8 watts, Irradiation chamber, GM based contamination monitor and dose calibrator
2.2 Methods
2.2.1 Selection of UV-Curing light and determination of UV-Curing time
The appropriate UV-Light among UV-A, UV-B and UV-C for UV-Curing process trials were done with the settings as: UV A source of light (365nm, 8 watts) For 10 minutes, aimed at a spot 10 cm distant. UV B source of light (302nm, 8watts) For 30 mins, aimed at a spot 10cm distant. UV C light source (254nm, 8 watts) For 60 mins and 24hrs, aimed at a spot 10cm distant. It was concluded visually that the resin got cured in 5 minutes with UV-A light, in 30 minutes with UV-B light and in 24 hours with UV-C light. Hence from Table 1, UV-A light was selected as the UV source and the time determined for UV-Curing was kept 5 minutes all these testing was done in the irradiation chamber as shown in Fig. 1.
Table 1
Optimization with UV-A light to see UV-Curing effect and time
2.2.2 Surface contamination/decontamination procedure and measurement
A well-known radionuclide volumetric activity of F-18 FDG, Tc-99m, Tc-99m labelled, I-131, and Lu-177 radioisotopes was diluted into 0.1ml of saline. Each surface was contaminated with 50microcurie of radioactivity in the marked area. The radioactive counts were recorded as initial activity counts (Ao) using a contamination monitor as shown in Fig. 2 (a). On the contaminated area, UV-Curing resin of 0.2ml volume was poured over the marked area, exposed under the UV-Light in the UV irradiation chamber for 5 minutes for solidification as enumerated in Fig. 2 (b). The UV-Curing resin coating was stripped off from the surface and the activity of the surface was measured again, and this was recorded as final activity counts (Af)
Our study relates to a UV-Curing method for efficiently removing the radio-contaminants by using the UV-Curing resin recording the counts before and after decontamination. The decontamination factor (DF) is calculated individually for each sample with equation (1) (Gurau and Deju, 2014):
Where Ao is the initial activity counts recorded after contamination and Af is the final activity counts recorded after the decontamination peeled off process.
PVC was treated with radio isotopes and the Mean± SD decontamination factor for all the radioisotopes on PVC was recorded as 94±2.82, 85.6±2.88, 89± 1.87, 92.2±2.48, 81.6±3.04 for F-18, Tc-99m, Tc-99m labelled, I-131, Lu-177respectively, with p < 0.05 was considered to be statistically significant as visualize from Fig. 3 (a). The best result on PVC was observed by giving maximum DF with F-18 and minimum for Lu-177. As observed visually, the top layer of the PVC surface remained unchanged and there were no changes observed before and after decontamination. Further, the resin was peeled off very smoothly and easily from the surface as seen in Fig. 3 (b)
Glass when treated with different radioisotopes, reported Mean± SD for all the radioisotopes as 96±1.58, 85.4±5.12, 87.8±1.64, 97.6±0.54, 84.4±3.91 for F-18, Tc-99m, Tc-99m labelled, I-131, Lu-177respectively, with p < 0.05 considered to be statistically significant as visualized in Fig. 4 (a) I-131 showed the highest DF over the glass surface, whereas Lu-177 showed the least. It was further observed visually that the glass surface became more clear and clean after decontamination was performed, with the resin getting entirely peeled off from the surface at one time as shown in Fig. 4 (b)
Steel when treated with different radioisotopes, reported Mean± SD for all the radioisotopes as 95.8±0.83, 94.8±2.16, 89.8±2.77, 88.8±2.94, 89.6±2.07 for F-18, Tc-99m, Tc-99m labelled, I-131, Lu-177respectively, with p < 0.05 considered to be statistically significant as visualized from Fig. 5 (a). F-18 gave the maximum DF value while I-131 showed the minimum DF value. No significant change was observed on the surface but the peel was a little harder to peel off from the surface with more force as compared to glass and PVC Fig. 5 (b)
Ceramic tiles when treated with different radioisotopes, reported Mean± SD for all the radioisotopes as 86.8±1.30, 93.4±3.20, 93± 0.70, 84.4±4.03, 86.6±1.34 for F-18, Tc-99m, Tc-99m labelled, I-131, Lu-177respectively, with p < 0.05 considered to be statistically significant as visualized from Fig. 6 (a). Ceramic tiles provided the best results with Tc-99m labelling which provided the highest DF, on the other hand, the lowest results were obtained with Lu-177. On visual observation, no significant change was observed on the ceramic tiles with resin getting easily peeled off from the surface as seen in Fig. 6 (b)
With WOOD the Mean± SD for all the radioisotopes is reported to be 84.8±94, 85.4±3.84, 90.6± 0.54, 89.8±3.96, 92.2±31.64 for F-18, Tc-99m, Tc-99m labelled, I-131, Lu-177 respectively, which was statistically significant (p < 0.05) as visualized from Fig.7 (a). On the wood surface Lu-177 showed the maximum DF value while F-18 showed the minimum value. Surface was same before and after decontamination process showing no change in topmost layer when observed visually. Peeling off required little extra force than normal to peel off the resin as seen in Fig. 7 (b)
When comparing the overall efficacy of the DF obtained by performing decontamination by UV-Curing method, we observed outstanding results as compared to performing decontamination by conventional type of methods as swiping, adsorbent sheets, brushing, etc. This method overcomes the limitation of curing time for decontamination from 24hours to 5 minutes.
With F-18 the DF came 94% with PVC, 96% with glass, 95% with steel, 86% with tiles and 84% with wood. For Tc-99m DF was found to be about 85.6 % with PVC & glass, 94% with steel, 93% with tiles and 85% with wood. With Tc-99m labelled the DF value was 89% with PVC, 87% with glass, 89% with steel, 93% with tiles and 90% with wood. For I-131 the DF was 92% with PVC, 97% with glass, 88% with steel, 84% with tiles and 89% with wood. With Lu-177 the DF value was 81% with PVC, 84% with glass, 89% with steel, 86% with tiles and 92% with glazed wood. F-18 & I-131 are almost similar removable capability compare to 99mTc & Lu-177 for all the surfaces tested in this study except glazed wood
In some cases, low DF might have resulted due to nature of the surface material and resin on simulated work surfaces, polymerization interaction between resin & surface and activity concentration. Also, the results and technique can be improved by doing further formulations as sprayable form, to check for dry decontamination and application for large surface areas.
When the decontamination process by the UV-curing method with the radioisotopes F-18, Tc-99m, Tc-99m labelled, I-131 and Lu-177 from the surfaces of PVC, glass, steel, ceramic tiles and wood was performed, the best results were observed for glass surfaces with I-131(97%) and least for PVC surfaces with Lu-177(81%). The UV-Curing process gave an average DF of more than 90% across different surfaces, hereby proving the concept that UV-Curing resin has good efficacy in trapping radioactive contamination. The UV-curing process has the advantage of being a cost-effective, less time consuming and simple technique and it opens the door for the future application of this method and formulations. The present study is the proof-of-concept of a novel application of acrylic resin polymer-based UV-Curing methodology for radioactive surface contamination removal to create a clean and safe environment.
Declaration of competing interest
The author declares no competing financial interest.
Funding: All authors hereby declaring that there is no financial interests.
Acknowledgement
The author wishes to express the sincere thanks and gratitude to Dr Sumeet Suresh Malapure Associate Professor Nuclear medicine KMC Manipal for providing Kasturba hospital radioisotope laboratory facility. Authors are thankful to IRC and IEC committee for kind approval. The sincere indebtness to K & K team and Dr Manthan Janodia Technology Transfer office MAHE Manipal, for facilitating and for filing this novel, innovative proof of concept work to Indian patent registration office Chennai. Authors are very much thankful to Manipal Academy of Higher Education Manipal for constant support for the entire journey.
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No competing interests reported.