|Year : 2010 | Volume
| Issue : 4 | Page : 177-179
Radiation surveillance programme and control of personnel exposure during 2001-2007 at RPhD, RLG
NV Choughule, Pratap Singh, JA Sapkal, S Murali
Radiation Safety Systems Division, BARC, Mumbai, India
|Date of Web Publication||1-Dec-2011|
N V Choughule
Radiation Safety Systems Division, BARC, Mumbai
Source of Support: None, Conflict of Interest: None
Radioisotopes find innumerable applications in medical, industrial and agricultural applications. Radiopharmaceutical division is engaged in activities to promote peaceful uses of radioisotopes and radiation. In Radiopharmaceutical division production and processing of radio chemicals take place for low activity sealed sources for various applications such as brachytherapy, references sources for calibration, sources for industrial application. These sources are then supplied to end users through BRIT. Radiopharmaceutical division handles significant amount of beta and gamma emitting radioisotopes in solid and in solution form. Board of Isotopes and Radiation Technology (BRIT) has committed supply of these sealed sources to various hospitals and industrial institutions in India. Annually, TBq level of radioisotopes are handled in facilities such as - fume hood, shielded production plant, glove boxes, RLG, BARC. This paper brings out a detailed account on the radiological surveillance provided during the production of these radio chemicals and sources implementing As Low As Reasonably Achievable (ALARA). The decrease in collective dose per activity handled is the outcome of improved operation practices, radiation surveillance and safety compliance carried out at various stages of production.
Keywords: ALARA, radiopharmaceuticals, shielded plant box, control of personnel exposures
|How to cite this article:|
Choughule N V, Singh P, Sapkal J A, Murali S. Radiation surveillance programme and control of personnel exposure during 2001-2007 at RPhD, RLG. Radiat Prot Environ 2010;33:177-9
|How to cite this URL:|
Choughule N V, Singh P, Sapkal J A, Murali S. Radiation surveillance programme and control of personnel exposure during 2001-2007 at RPhD, RLG. Radiat Prot Environ [serial online] 2010 [cited 2021 Aug 3];33:177-9. Available from: https://www.rpe.org.in/text.asp?2010/33/4/177/90455
| 1. Introduction|| |
At Radiopharmaceutical division, RLG, BARC the facility has in all 24 laboratories, wherein various isotopes are handled. Radiopharmaceutical division handles significant amount of beta and gamma emitting radioisotopes (solid and solution form) in facilities such as - fume hood, shielded production plant, glove boxes at RLG, BARC. Due to increase in demand for sources the activity handled in the facilities has increased to two fold during the last seven years. Radiological safety surveillance provided includes a detailed study of nature of job, it's duration to complete and assessment of radiological safety status in the work area prior to the issue clearance (RHC Manual for Isotope Wing, RLG (1999)). This paper gives account on various operations such as handling of β, γ emitters, the potential exposure situations during few special operations like source loading / unloading operation, transfer of high level solid / liquid waste, filter change operations with radiation safety aspects such as dose budgeting, radiation field measurement, estimation of air activity and contamination status.
| 2. Design and Safety Features|| |
Radiopharmaceuticals Division (RPhD), BARC is engaged in the production of radiopharmaceuticals for medical use i.e. both for diagnostic and therapeutic applications. Radioisotopes involved in this laboratory mainly are 99 Mo, 131 I, 32 P etc. 99m Tc, the daughter product of 99 Mo is 'work horse' of nuclear medicine. Annually, TBq level of activity of radioisotopes 99 Mo, 131 I, 32 P is handled in this laboratory. The radiochemical processing is carried in a shielded (100mm lead) enclosure, tong-box kept at negative pressure (~1" WG). The boxes are connected to high efficiency particulate air filter (HEPA) bank located on top of the box. The exhaust from these tong boxes passes through a filter bank of HEPA prior to the release to atmosphere through a stack 76.45 m height. The lab air and the stack air (filtered through the filter bank) are continuously monitored and assessed for gross βγ counting using a calibrated GM counting set-up.
| 3. Radioisotope Handling Facilities|| |
The zoning concept and directed ventilation flow is used / followed to prevent the spread of radioactive contaminant in the working surface / ambient air. Containment systems in design features are used for facilitating the same. The Radio Pharmaceuticals Laboratory areas are provided with the handling facilities such as production plants, fume hoods, Beta-Gamma glove boxes etc. Their general descriptions are given below.
3.1 Fume hoods
Fume hood is a partially contained system. Laboratory air is exhausted through them. It is enclosed to isolate the material from the operator's environment and the opening allows accessibility to the material inside for handling. Usually mCi level of beta gamma activity is handled in process fume hoods. The typical face velocity of air in a fume hood is 100-150 linear feet/minute (30-45 m/min).
3.2 Glove boxes
Glove box is a fully contained system. The external skin of the box consists of Stainless Steel and safety glass. All the glove boxes have been designed to be air tight for the containment of activity, to protect personnel and the surroundings. These boxes have transfer ports with double doors for loading of the materials in or out of the box and have glove ports for handling operations on materials inside the boxes. Air inlet for these is through leakages from lab environment. The boxes are maintained at 1.2 to 2.5 cm WG (0.5 to 1" WG) negative pressure. Each box has it's own individual filters on the top, for preliminary filtration of the exhaust air. Glove boxes without lead shielding are mostly used for pure beta activity.
3.3 Production plants
The isotope processing cells are constructed with 100 mm thick Pb-Sb alloy (93% Pb +7% Sb) walls with dry lead glass windows for viewing in-cell objects. The inside surfaces of the cell bank contain SS / Al to provide containment of activity and to facilitate regular decontamination. The front panel is provided with gaiter rings for inserting remote handling tongs and small cut-outs closed with Perspex and lead glass for serving as viewing windows. The processing of irradiated target materials or chemical separations involving beta gamma activities in mCi to Ci levels are carried out remotely in these plants by using remote gadgets provided in the front. A production line consists of two such boxes connected to a fume hood for material transfer. The production plants are maintained at 1.2 to 2.5 cm WG (0.5 to 1" W.G) negative pressure.
| 4. Personnel Radiation Monitoring|| |
However during the handling in shielded facility, the various beta, gamma emitting isotopes pose external hazard. Individual monitoring viz. external - TLD monitoring, internal monitoring - whole body counting, bioassay at periodic intervals is carried out for the occupational workers engaged in the radiochemical operations. In addition to the TLDs, pocket dosimeters are also provided for the quick assessment of the personnel dose. The lab personnel are periodically referred to thyroid monitoring for assessment of thyroid burden, if any, due to 131 I.
| 5. Job Wise Dose Distribution|| |
In RPhD, isotopes such as 99 Mo, 131 I, 32 P and 153 Sm are mainly handled. 131 I is used in diagnosis & the therapeutic applications in thyroid disorders including thyroid function studies/scan, treatment of thyrotoxicosis, imaging of neuro endocrine tumors and ablation of thyroid remnants and treatment of thyroid carcinoma. 99m Tc, the daughter product of 99 Mo is 'work horse' of nuclear medicine studies. 32 P and 153 Sm are used in palliative treatment of bone pain due to bone metastasis, for cancer patient. Due to increase in demand for sources the activity handled in the facilities had increased around two fold during the last seven years.
The contributory factors for doses incurred by the occupational workers are:
- Loading and unloading of the sources manually, occasionally
- Radioactive waste transfer
- Decontamination of facilities
- Maintenance inside the plant
- Pre-filters replacement
Comparison of the activity of 131 I and 99 Mo handled per anum since last 7 years and the collective dose incurred for radiochemical operations are given in [Figure 1]. As an outcome of improved operation practices, radiation surveillance and safety compliance to achieve ALARA, there is a decreasing trend in collective dose consumed, in spite of the increase in activity handled.
| 6. Modification in Operating Practices|| |
6.1 Loading / unloading of radioactive sources
While transferring the bulk activity ~1.3 TBq (4 Al cans) of 131 I and ~1.3 TBq (9 Al cans) of 99 Mo from lead cask into transfer box using 2 meter long cee-vee tong, unshielded exposure measured at chest level was found as 2-3 mGy/h. Though the transfer is carried out within the couple of seconds, the cumulative personnel exposure of the staff engaged in regular production is of concern. Segregating the staff for each operation led to reduction of personnel exposure. Operations like cutting of Al cans by using can cutter, capping of vials (auto) is carried inside the plant. RHC surveillance was provided by measuring radiation field, dose budgeting and ensuring safety compliance.
6.2 Radioactive waste (liquid) disposal
The high level liquid waste generated during radiochemical operations was collected in the carbuoys below the plant and stored in the shielded storage facility allowing them to decay. Special work permit procedure was introduced for transferring the waste to minimize the personnel exposure.
| 7. Role of Health Physicist|| |
The health physicist plays an important role in limiting radiation exposure to the lab personnel. Reduction in occupational exposure is achieved by implementing good work practices and an effective monitoring programme. Implementation of man-Rem budgeting, conducting dummy runs, adhering to standard operating procedures, radiation monitoring at each stage, enforcing use of personal protective equipment etc. has effected significant reduction of personnel exposure both internal and external. Introduction of "Special Work Permit" ensures availability of utilities and resources in term of materials and man power. This in turn makes the work procedure for the operations to be safer and helps to avoid any unusual occurrence, leads to achieve ALARA.
| 8. Conclusion|| |
Better equipment performance, decontamination procedure, improvement in work practices with regular health physics surveillance have resulted in collective dose reduction from 98.7 p-mSv to 85.47 p-mSv (i.e. 13.4 %) even though activity handled increased from 26.2 TBq to 51.8 TBq for I-131 and 30.54 TBq to 43 TBq for Mo-99 (i.e. ~ two fold) during radiochemical and sealed source production at RPhD, RLG. Efforts are underway to reduce the collective exposure further irrespective of the higher amounts of activity that are handled.
| 9. Acknowledgements|| |
Authors are grateful to Dr. Meera Venkatesh., Head, RPhD and Dr. D. N. Sharma, Head, RSSD, BARC, Dr. P.C. Gupta, Head, RHCS, RSSD for their for their keen interest and continuous encouragement in carrying out these work. Authors would like to thank Dr. P. R. Sangurdekar, Shri. N. Swaminathan and ex-colleagues for their HP support.
| 10. Reference|| |
- Manual for Radiation Hazards Control activities for the Radiochemical laboratories at Isotope Wing, RLG BARC, 1999.