Investigation of Natural Radioactivity and Dose Assessment over Steel Making Region ()
1. Introduction
The steel industries are highly successful in Sudan that leads to take it as one of the economic backbones, although steel made involving in the several activity according to United Nation Conference on Trade and Development (UNCTD) report [1]. In addition, there are different environmental impact risks according to steel-making as shown in the previous studies as one of the enhanced sources of Naturally Occurring Radioactive Material (NORM) [2], furthermore, some studies shown that the blast furnace slag contained a low level of long-lived radionuclides from the uranium and thorium series. The 210Po and 210Pb levels in dust collected from the blast furnace off-gases are generally lower than those from the sinter plant [3]. Although the regional agency for the environmental protection of Veneto was studied concerning NORM in integrated steel workers in coke production residue blast furnace dust and sinter dust in an enhanced level of 210Pb and 210Po in dust and residue sample, it was more than 40 Bq/g [4]. Also the investigation of the presence of the natural isotopes such as 40K, 226Ra, 232Th, and 238U as well as artificial isotopes such as 60Co, 137Cs, and 192Ir in the Steel Mills of CMC-Croatia was carried out [5].
In the similar case we found that the International Commission on Radiological Protection (ICRP) recommended that dose limits as an effective dose of about 20 mSv in a year averaged over 5 years, with no more than 50 mSv in each one year of occupational. Exceeding the limit of 1 mSv and exceptionally higher effective dose could be allowed in a year provided that the average over 5 years does not exceed 1 mSv in a year. Also, the reference level effective dose should be controlled by action on exposure pathway to reducing doses, and it will be taken as a reference level for radiological emergency when it ranged between 20 - 100 mSv [6]. Some cases refer to the low dose level of iron or steel NORM activity generally when it compared to 226Ra level in gold mining concentrations which is up to 1.7 Bq/g also the annually dose was recorded in range about 0.04 mSv in same field [7].
In particular, NORM contaminated dusts may be generated during handling or processing of the steel and breathed into the body, slag steel and other non-ferrous components can become contaminated with low specific activity scale (LSA) [8].
Although, the radionuclide present in NORM in slag waste giving of ionizing radiation which can interact with human cell and the hazard that may cause for human and environment depend on radionuclide type, activity, the radiation wich emit, how that radiation interacts [9]. Also Scrap metal industry such as tubing, valves and heat exchangers from various process industries may contain scales with enhanced levels of natural radionuclides, the particular radionuclide and their concentrations would depend on the origin of the scrap, since objects from nuclear industries and the uncontrolled releases of radioactive sources may be added to this material, which may be recycled, the scrap metal industry is a source of variable and heterogeneous releases of radionuclides into the environment emission, the natural radionuclides present in the raw materials or wastes of the steel industries are those of the 238U and 232Th [10].
Natural occurring Radioactive Material is one of the radiation sources released from processed materials, and affected workers, the public and the environment mainly require radiation control and regulation [11].
In this study, authors investigated the presence of the NORM over steel-making region, and measured worker radiation dose limits during the steel melting.
2. Materials and Methods
2.1. Measurements Tools
The existence of NORM in steel-making waste was measured by using different recent calibrated Techniques, for instance, X-ray diffractometer (XRD-7000) devices (Shimadzu, Japan), polimaster and backpack technique device model 1014 controller 1021 detector design BdKn-05 to Neutron, BdKG-11m to Gamma and polimaster (model pm 1703 m-01 serial 74088 GNM). The devices are also utilized in Sudanese Nuclear and Radiological Regulatory Authority (SNRA), High Purity Germanium (HPGE) spectrometer with the lead shield from (BSI) Baltic Scientific Instruments.
2.2. Experimental
Two methods of evaluating external exposures from naturally occurring radionuclides have been used. polimaster and backpack devices to a simply summarize directly measured external gamma dose rates due to steel production.
All the measurement were taken 1m above the ground and steel melting oven, also, the slag steel and soil sample were collected from selective steel factory area, sample pulverized and packed in 1 kg by mass in the cylindrical plastic containers of radius 3 inch and height 3.5 inch, which sits on the (3 inch × 3 inches) high purity germanium (HPGe) detector with geometry the containers are sealed for one week to ensure radioactive equilibrium between the parent radionuclides and their gaseous daughter decay products in the uranium and thorium series, although the small amount of sample directed measured in XRD device to detected the clay isotopes amount [12].
3. Results
3.1. Backpack Result
Table 1 shown the Backpack Result over 6 slag steel waste position in order to record the waste background radiation over the waste and the average of NORM background in Khartoum steel waste about 0.48micro Sivert/hour.
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Table 1. Backpack result over the slag steel waste in different position.
3.2. XRD Result
Figure 1 shown the XRD slag steel Homogenies sample result after used Match3! Analysis program [13] the result shown that the slag steel included the elite isotopes clay form and magnesio-ferrite.
3.3. The Hyper Pure Germanium Detector Results
Table 2 & Table 3 shown the radioactive concentration of the slag steel waste and soil sample the Result shown the existence of the K-40 and Ra-226, Th-232 and their activity.
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Figure 1. XRD analysis of the homogeneous 6 slag steel sample from Giad industrial area.
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Table 2. HPG slag steel sample result.
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Table 3. HPG soil sample around steel factories area result.
3.4. Polimaster Result
Table 4 shown the polimaster detector reading of the radiation dose in different directions over the oven during melting the scrap and the average of the dose is (2.45 mR) during the steel-making which is worked 12 hours per day approximately twice in a week in below calculation can measure the dose during the factory operation.
4. Calculation
The equivalent dose (H) is calculated by multiplying the absorbed dose (D) by the occupation time (T).
[14] (1)
The Polimaster dosimeter gives dose rate readings in Dose Rate micro-Ream per hour (μR/h). The Ream radiation dose unit (R) can be converted to Sievert radiation dose unit (Sv) according to the following equation [15]:
[15] (2)
Based on Table 4 the average of the radiation dose during steel making poling is about 2.45 mR. According to this we can calculate the following:
1) The average dose per day when the factory operated 12 hour is
(3)
2) The average dose per week is
(4)
3) The average Dose per Month is
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Table 4. Polimaster result during steel melting in Aljerif steel making factory.
(5)
4) The annual calculated dose is
(6)
5. Discussion
This study was curried out in three different positions (Giad industrial area in coordinate 15,019'12.4"N 3249'59.7"E, Aljerif East in Khartoum incoordinate 15,034'21.4"N 32,033'10.9"E, Jelly industries area in coordinate 1600.7'21.2"N 32,039'29.5"E).
The radiation dose in this case up to recommended dose given in UNSCEAR publication as shown in Equation (6), this unusual activity related to existence of NORM in slag steel waste because they were using the slag steel waste with scrap materials and raw material during steel making process, Figure 1 and Table 2, Table 3 show the existence of this NORM as form of clay elite and Th and U series.
Table 1 show that the measurement reading over slag steel waste and scrap in different area position the result within the normal range when comparing it with previous survey in Khartoum survey reading
6. Conclusion
This result indicates evidence for radiological significant existence of NORM over the steel making factories and this existence increases the worker dose level 6.448 mSv over the IAEA recommended dose level. The dose recording and reporting practices are governed by regulations and may differ for various categories of workers depending on the anticipated level of exposure in the IAEA documents [16] [17]. There are also guidelines for dose recording which may vary among countries so this may significantly affect the reported values of collective dose and these factors are technique use dosimeter, all the radiation hazard indices estimated in this study are higher than the acceptable limits, it can therefore be concluded that steel making waste is not safe for use as materials for building and rood construction until applied radiation safety requirement.
Acknowledgements
I acknowledge professor Siddig Tawer Kafi whose encouraged to completed this work special thanks to my friend Elxander F.I. Osman who read and provided useful advice on earlier draft of this articles, extended thank to my friend Mohaid Ali who support me to finished this work, and I would like to thanks my parent and my wife for them patient.