DEVELOPMENT AND FABRICATION OF EXTENDED SPARK PLUG TYPE LEAK DETECTOR (ESPLD) FOR PFBR M.R. JEYAN INSTRUMENTATION DEVELOPMENT AND SERVICES DIVISION FAST REACTOR TECHNOLOGY GROUP Introduction The main vessel (MV) of PFBR contains the reactor components, which are immersed in sodium pool. In case of sodium leak from the MV, it will be collected in the safety vessel (SV). The leaked sodium in SV is detected by Extended Spark Plug type Leak Detector (ESPLD) provided in the inter space between MV and the SV. MI type leak detector is used as a diverse method of leak detection. PFBR VIEW Fig. 2. ESPLD SENSOR PORTION (PHOTO) Fig. 1. ESPLD SENSOR PORTION (SCHEMATIC) ESPLD WITH 24 METER LONG M.I. CABLE The SS needle tube (O.D.0.9&I.D.0.6mm) will work like a conductor The active length of the sensor is around 50 mm and the overall diameter is 5 mm. M.I cable of 1.5 mm dia. 24 m long is used for electrical signal from sensor. A 4 mm dia. 24 m long S.S. capillary tube is welded with sensor to protect M.I cable. Challenges involved The assembly of this sensor consists of 5 laser weld joints with close tolerance. The SS sleeve and 24 meter long M.I cable is to be joined using laser welding. Each joint has different sizes and has different welding parameters. One of the challenging jobs is to laser weld the M.I. cable center conductor (0.59mm dia.) to the SS needle. For this weld joint, M.I. cable conductor portion has to be machined from 0.9 mm dia. to 0.59 mm dia. for a length of 30 mm long. Specially designed jigs and fixtures were used and machined the conductor successfully at IDEAS. To set the welding parameters, and for welding procedure qualification, three sets of mock up pieces are machined and welding parameters are set. The welding procedure has been qualified by visual, liquid penetrant test and macro examination. After improving the I.R. value of M.I. cable using tape heaters, the laser welding was carried out on the actual job. In each stage of welding, quality assurance was ensured and welding was qualified with visual and Liquid penetrant test. Conclusion The ESPLD with a suitable leak tight arrangement has been developed and fabricated. This sensor has been successfully qualified for PFBR. After insertion of sensor in the guide tube of PFBR, the leak tightness (nitrogen) of the sensor should be ensured. Hence a leak tight arrangement was designed, for guide tube (1), capillary tube (2) and M.I cable (3) which are shown in Fig.3. The leak tight arrangement will be welded after insertion of the sensor in the guide tube at PFBR site. 3 Nos. Of ESPLD with leak tight arrangement are ready for delivery to BHAVINI for installation in PFBR. Fig. 3. ESPLD SEALING ASSEMBLY Construction details The schematic and photographic of active sensor portion is as shown in Fig-1 and Fig.2 respectively. It consists of a center S.S. needle tube insulated from the outer SS tube by alumina. There is a ceramic to metal seal between the SS tube and the alumina insulator as well as between the insulator and the SS needle tube.