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�������� %�!����&!���%�!����&!���%�!����&!���%�!����&!���2222 The Radiation processing facility was created todemonstrate the feasibility of increasing the shelf life of potatoes and onions oncommercial scale at Lasalgaon, Maharastra. The facility is having a wet sourcestorage pit, categorized under panoramic class IV type of irradiator (fig-1),designed to house of maximum of 300 kCi of 60Co. It was expected to saveonions worth Rs 50 million/annum (~ 20 % of total onion production). Radiometrywas carried out to identify plug radiation leaks, to reduce the radiation hazards topersonnel while working in vicinity of the irradiator and also to test the integrity ofradiation shielding of irradiator to rule out any defects. It was done at height of490 mm & 1240 mm and horizontally at every 50 cm of the cell. Thickness ofvarious concrete walls were 700 mm, 1000 mm & 1700 mm. A number of testpoints were decided to evaluate the effectiveness of the shielding system, for thepurpose for which it was designed. The shield source 60Co with average gammaphoton energy of 1.25 MeV was chosen considering its high penetration power in

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Fig-2 (Radiography Camera) Fig-3 (Driving Unit of Radiography Camera)photon energy of 1.25 MeV was chosen considering its high penetration power inconcrete. The source strength was estimated considering the cell wall thicknessand the minimum transmitted dose rate. 160 Ci 60Co source was chosen to get acontact dose rate of ~100 �Sv/h. This work of radiometry testing was carried outusing ���� gamma camera remotely operated IGRED (Industrial GammaRadiography Exposure Device) (fig-2) and radiation monitoring instrumentsteletector & µR survey meter were used.

�������� ��!�������$��!�������$��!�������$��!�������$2222 Radiometry testing essentially consists of placing thesource and the detector on the opposite sides of the concrete wall andmeasuring the transmitted gamma radiation through the shield. If the transmittedradiation level is more than the expected radiation level then it is an indication ofweak shield / leak at that point. The selection of test points is based onconsidering the type of items (Ducts, embedment plugs, penetration points etc) tobe checked. Any defect will be reflected in terms of increased dose rates on theother side. As the driving unit of the tech ops camera was extended up to 8m itwas easy and convenient to operate it from remote places at the desiredlocations without the operator getting exposed to radiation. By using the drivingunit (fig-3)of the radiography camera the sealed source was positioned at theexpected place. Radiation field were measured by teletector and µR surveymeter at opposite side of the source. Teletector is the preferred device forradiation measurement as it provides lot of safety because of distance from theradiation source. Strict radiological protection was observed to avoid anyuntoward event. During the radiometry process the whole area was ‘cordoned off’and caution boards like ‘No Entry’, ‘Keep Away’ were displayed at different placesto restrict the movement of persons closer to the source. In addition to the displayof caution boards, persons were standing at different locations during the processto restrict personnel movement towards the restricted area. Persons involved inthe radiometry were using TLD (Thermo Luminescence Dosimeter) and DRD(Direct Reading Dosimeter) to estimate the individual exposure�

8888���� �����!������!������!������!������������� "��&������"��&������"��&������"��&������2222 Radiometry of Shielding integrity ofPOTON irradiator unit was carried out at height of 490 mm & 1240 mm atevery 50 cm horizontally on the cell wall. No major defect was found in thestructure & thickness uniformity was also found satisfactory. Radiometry ofplug door showed radiation leakage of maximum about 45 mSv/hr (4.5 R/hr)at a few locations (shown in table-1). Subsequently after the repairsradiometry testing was again carried out and no major radiation leakagewas observed then and results indicated the structure & thicknessuniformity.

Table-1: Showing the observed unacceptable high Dose rates in (mSv/h) atthe bottom portion of the plug door.

Bottom portion of the plug doorPositi

onLeft side At the Centre Right side

35 25 45

4. Conclusions: Total of about 160 points were covered during theradiometry inspection. No major defect was observed in the structure &thickness uniformity was satisfactory. Radiometry of plug door showedradiation leakage of about 45mSv/hr (4.5 R/hr) at a few locations.Subsequent to the repair of door, radiometry testing was again carried outand then door shielding was found satisfactory. From this technique it isobserved that radiometry technique is very useful technique to find anyradiation leakage and rule out flaws in shielding at joints / crevices anddefects of the cell so that better shielding mechanism can be achieved in theshielding system.

References:[1] A. S. Tapase1, Umesh Kumar2 and Ashutosh Dash3, Controlling Sensitivity in Gamma Radiometry Testing, Proceeding: National seminar on non destructive testing NDE 2014.

Fig-1 (Sketch view of POTON Irradiator