1. Encapsulation and Quality Evaluation of 57 Co source for radiometric assay of nuclear fuel rods J. Udhayakumar, Manoj Kumar and Ashutosh Dash * Radiopharmaceuticals Division, Bhabha Atomic Research Centre, Trombay, Mumbai-85 * Corresponding author Email: adash@barc.gov.in ABSTRACT 1. P.R. Vaidya, IANCAS Bulletin, II, (3), 211 (2003). (available at http://iancas.org/bulletins.htm) 2. AERB Safety standard no: AERB/SS/3 (Rev.1), Class. of sealed sources, Published by AERB, Department of Atomic Energy, Mumbai, India (2001). REFERENCES  1xxx grade high purity Al rods with test certificate were bought from M/s Hindalco India, Mumbai, India and capsules made from these Al rods in our Divisional work shop facility.  The capsules were soldered using a digital control soldering station with 85Zn/15Al alloy.  Radioactive point source preparation procedure is developed for 57 Co sources based on electrochemical technique.  The circular sources of dimension of 4 mm (  ) made of copper substrate coated with 57 Co is illustrated in Fig-1. EXPERIMENTAL Figure 3.Loading of source in the capsule We have developed a simple and efficient method to encapsulate 57 Co- source cores in aluminum capsules of special design. The sealed sources were intact and complied with the specifications laid down by AERB. CONCLUSIONS INTRODUCTION Cylindrical Al capsule is used for source encapsulation. Capsule consists of cap and body. The body had a flat end of closed side and an open end. Open end had interior thread (female thread) for fitting the cap. Rounded screw cap having an exterior thread (male thread) was used to enclose the capsule. Schematic diagram of the source capsule is shown in Fig.2. Loading the source core in the capsule is illustrated in the Fig.3. Encapsulation involves positioning of the 57 Co source core inside the aluminum capsule sealed end in such a way that the active layer touches bottom end to avoid contamination. 57 Co source was placed with the help of tweezers to fit inside the capsule with its radioactive end facing down towards the close end. The capsule was closed by driving the screwed cap in the tightening direction. Hermetic sealing was achieved by soldering the cap (lid) with the capsule body using 85Zn/Al family) alloy. 2.1 Quality control tests for sealed sources Swipe test: The sealed sources were tested for surface contamination or presence of any transferable activity by swiping the source using alcohol immersed cotton wool and checking for radioactive content on the cotton wool, by counting in a NaI (Tl) scintillation counter. An encapsulation method for the confinement of 57 Co source cores in an aluminum capsule has been developed and demonstrated. The design of the capsule, method of encapsulation and the quality assurance practice followed were described. Circular source core of 57 Co containing ~370 MBq (10mCi) deposited on a copper foil of 4 mm dia could be safely encapsulated. Quality assurance tests of the sealed sources were performed to ensure safety during their use and application. 57 Co source is used in the ‘active assay' of nuclear fuel rods [1]. Sources are encapsulated in capsules to prevent mobilizing. Source capsules are designed for leak proof, rigid and safe use. Capsule designing depend upon mechanical strength ambient conditions of use and carefully evaluated. RPhD/BARC developed a technology to produce circular 57 Co sources core of 3.5mm active dia containing~ 370MBq (10 mCi). This paper reports encapsulation and source quality evaluation technique of circular 57 Co sealed source for such applications. Bubble test: Sealed source placed in boiling water in a glass beaker for about 2 minutes and no bubbles observed from the sealed part of capsule ensures perfect sealing otherwise the sources were discarded. Immersion test: Sealed sources immersed in 20 mL water beaker at 363°- 368°K (90°-95°C) for 4 hours. After the source removal the volume was concentrated to1mL and the total activity was assayed using NaI (Tl) counter and detected as <185 Bq and such sources are called leak free. RESULTS AND DISCUSSION Aim of this work was to establish and implement the method of encap- sulation of 57 Co sources prepared by electro-deposition method. Number of inspections at every stages of encapsulation to comply with regulatory specifications in both fabrication, quality control and safe supply with necessary documentations. Fabrication of capsule requires selection of capsule materials, testing with respect to dimensional tolerance and functionality. Al material is chosen as it is available in high purity, economical, has radiation stability, good corrosion resistance, high thermal conductivity and mechanical strength. Selected Al grade is for easy solder ability and the wall thickness gives the least radiation attenuation. The confinement of source procedures consists of safe transfer of source side into the capsule base, threadened cap closing and due to small wall thickness and oxidizing nature of Al, it is finally sealed by soldering to give utmost safe handling. Soldering involve low temperature operation causing minimal distortion of the capsule, compared to welding or other fusion processes. Ensures hermetic seal without air activity release during sealing. No detectable surface contamination was observed from thus sealed sources and the radioactivity leach was very much less than 185 Bq level of AERB compliance regulations. These encapsulated sources were subjected to quality assurance test and the results obtained is depicted in following table.1. Immersion test Bq (nCi) Bubble test Swipe test Bq (nCi) Source strength MBq (mCi) Source no. 130(3.5)No bubble70(1.9)307 (8.3)1 152(4.1)No bubble75(2.0)334 (9.0)2 126(3.4)No bubble73(1.9)375(10.1)3 131(3.5)No bubble66(1.8)348 (9.4)4 160(4.3)No bubble61(1.6)341 (9.2)5 Fig. 2 Schematic diagram of the source capsule (a) Capsule body, (b) Capsule cap Table.1. Test results of encapsulated 57 Co sources