|Year : 2010 | Volume
| Issue : 3 | Page : 128-130
Health physics experiences in ued during handling of depleted uranium
MS Belhe1, M Shailesh1, Malti1, K Somanathan1, SK Satpati2
1 Radiation Safety System Division, BARC, Mumbai, India
2 Uranium Extraction Division, BARC, Mumbai, India
|Date of Web Publication||22-Oct-2011|
Radiation Safety System Division, BARC, Mumbai
Source of Support: None, Conflict of Interest: None
This paper describes Health Physics experience during processing of Deeply Depleted Uranium (from PREFRE) at Uranium Metal Plant. It was observed that there is a significant difference in radiological status due to the handling of DDU oxide from Tarapur reprocessing plant. Radiation background during DDU handling was significantly higher as compared to natural uranium processing. Due to 232 U, thoron daughter's concentration in working atmosphere was also observed which was found with in the apportionment provided for DDU handling.
Keywords: UMP, DDU handling, Thoron working level
|How to cite this article:|
Belhe M S, Shailesh M, Malti, Somanathan K, Satpati S K. Health physics experiences in ued during handling of depleted uranium. Radiat Prot Environ 2010;33:128-30
|How to cite this URL:|
Belhe M S, Shailesh M, Malti, Somanathan K, Satpati S K. Health physics experiences in ued during handling of depleted uranium. Radiat Prot Environ [serial online] 2010 [cited 2022 May 20];33:128-30. Available from: https://www.rpe.org.in/text.asp?2010/33/3/128/86279
| 1. Introduction|| |
Uranium Extraction Division (UED) has been producing nuclear grade uranium metal from ammonium diuranate received from IRE to meet the fuel requirement of Cirus and Dhruva reactors at Uranium Metal Plant in Trombay. However during the period October 2006, June/July 2007 and April 2008, depleted uranium metal was produced from uranium oxide (reprocessed uranium) received from PREFRE Tarapur.
| 2. Uranium Processing in UED|| |
In Uranium Metal Plant, uranium oxide powder (U 3 O 8 and UO 3 ) is first reduced to uranium dioxide in reduction furnace and is converted to uranium tetra fluoride in hydro fluorination furnace. After removing moisture and acid vapour in expulsion area, reduction of uranium tetra fluoride is carried out with magnesium in magnesio-thermic reduction furnace, pure uranium metal ingot with magnesium slag is produced. Finally natural uranium ingot is separated from slag in ingot discharging area.
Natural uranium is a low specific activity material (25MBq/kg) and it's immediate daughters are not prominent gamma emitters. Hence external radiation hazards are not dominant during processing of natural uranium at uranium metal plant. However, due to handling of large quantity of uranium compounds, internal contamination hazards are significant.
| 3. Depleted Uranium and It's Radiological Hazards|| |
In October 2006, UMP processed depleted uranium brought from PREFRE, Tarapur. Depleted uranium from reprocessing of spent fuel of research reactor has about 0.6% of U-235. The spectrometric analysis of DDU obtained from reprocessing plant (reprocessed spent fuel of power reactor), Tarapur showed ≈0.3% of 235 U. Typical analysis of this uranium oxide powder indicates the presence of 232 U in addition to Pu, Cs-137, Sr-90 and Ru-106. As a result of unavoidable presence of 232 U in the oxide powder, there will be build up of 228 Th and it's daughter products with time (Anil Kumar et al., 2008). Processing of depleted uranium of PREFRE was again carried out in June-July 2007 and April 2008.
During handling of DDU, radiological hazards due to thoron/thoron daughters should also be considered. Experience of handling DDU oxide powder at PREFRE, Tarapur also indicated the presence of 228 Th daughters in working atmosphere (Deshpande et al., 1994).
AERB has provided following apportionment for different radiological hazards in [Table 1] (Sunderarajan, 2001) during handling of depleted uranium from power reactor fuel (Srivastav et al., 2005).
| 4. Health Physics Experience|| |
Bulk processing of DDU (PREFRE) at UED, was carried out by dry route starting from reduction, hydro fluorination and magnesio-thermic reduction to produce depleted uranium metal ingot.
4.1 Air activity level
To estimate air activity level in the working area, air samples were taken regularly from different locations using portable pump. The long-lived air activity levels were determined and results are shown in [Table 2]. Inhalation of thoron daughters (from 232 U decay), mainly 212 Pb (t 1/2 =10.64h) and 212 Bi (t 1/2 =60.55m), contribute to internal dose. So thoron daughters' concentration in working atmosphere was determined by two different methods.
|Table 2: Long lived alpha air borne activity and thoron WL during DDU operation|
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a) Measuring concentration of 212 Pb and 212 Bi on filter paper by gamma spectrometry (6). Once the concentration of 212 Pb (Q B ) and 212 Bi (Q C ) are known, the WL can be calculated as:
WL = (Q B +Q C ) 7.8/1.3×10 5
Where, WL is the working level of thoron progeny in working atmosphere, Q B and Q C are the concentration of 212 Pb and 212 Bi in atoms/liters respectively.
b) Measuring Thoron activity (X Bq/m 3 ) directly by Alpha Guard ion chamber, WL can be calculated as:
WL = ((X Bq/m 3 )/275 Bq/m 3 )×0.03
Where 275 Bq/m 3 is the thoron concentration which in equilibrium with it's progeny corresponds to a potential alpha energy concentration of one working level and 0.03 is the Equilibrium factor for indoor measurement [Table 2].
4.2 Area monitoring
Daughter products of 232 U(T 1/2 =68.9 years) present in DDU, mainly 208 Tl /212 Bi give high gamma energy (IAEA-TECDOC). So, handling of DDU requires monitoring of external radiation levels also. External radiation levels during different operations of natural uranium and DDU are presented in [Table 3].
|Table 3: Radiation field variation at different areas during Natural uranium and DDU operation|
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Similarly, radiation field on contact with DDU metal is about 3-5 times higher than that of natural uranium metal. Radiation field on uranium oxide, uranium tetrafluoride and slag is presented in [Table 4] and [Figure 1]. Direct reading dosimeters (DRD) were provided to workers handling DDU during manual operation.
|Table 4: Contact radiation field at different stages of Natural uranium & DDU processing|
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|Figure 1: Gamma dose variation on different compounds of DDU and natural uranium|
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| 5. Conclusion|| |
It was observed that radiation background increased thrice, and in some areas five fold during DDU processing. This resulted in increased annual collective dose for the facility for the year 2006. Proper storage of uranium oxide drums and display of caution boards indicating background radiation field in each area has helped in reducing the collective dose for the year 2007. Air activity levels during different operations were found below the stipulated values. Comparatively, higher value of thoron concentration during ingot discharging showed the inadequacy of ventilation during the operation. Build-up of thoron daughters' concentration has to be reduced by implementing improved ventilation system in the plant to control the exposures to the workers.
| 6. References|| |
- Anil Kumar et al., (2008), Preliminary studies on 232 U and 228 Th radioactivity levels in reprocessed uranium samples, IRPA 12, Proceedings.
- Deshpande M.D., Krishnamani S. and Pendharkar K.A. (1994), Air borne activity due to Thoron daughters and associated problems in fuel reprocessing plant, Bull. Rad. Prot., Vol. 17, (1).
- IAEA TECDOC, Measurement of reprocessed uranium-current status and future prospects, IAEA-TECDOC-1529.
- Narayani, Sawant P.B., Pushparaja and Iyer M.R. (1993), Thoron working level estimation by gamma spectrometry, Bull. Rad. Prot., Vol. 16, (1-2).
- Srivastav G. K. et al. (2005), Health Physics Experiences in NFC, during handling of natural and depleted uranium, Rad. Prot. Env., Vol. 28, (1-4).
- Sunderarajan A. R. (2001), Official communication AERB/RSD/2.6/2001/9574 dt. 07-12-2001.
[Table 1], [Table 2], [Table 3], [Table 4]