XA9952393 IAEA-SM-360/19P DEVELOPMENT AND TESTING OF RADIATION DETECTORS AT RESEARCH REACTORS K.R.Prasad, P.M.Dighe, Mary Alex, V.Balagi, S.P.Chaganty and S.K.Kataria Electronics Division, Bhabha Atomic Research Centre, 400 085

Indigenous development of radiation detectors and associated electronic instrumentation is being carried out in Electronics Division of the Bhabha Atomic Research Centre. In this programme, neutron-sensitive detectors of various types as well as ion chambers for gamma monitoring and tritium monitoring applications have been developed. Most of these devices are meant for reactor instrumentation in the research and power reactors in India. The irradiation facilities at the research reactors Apsarafc CIRUS, Dhruva and FBTR have played an important role in the testing and calibration of neutron detectors and instrumentation. In these facilities, some of the devices developed in-house for power reactor applications have also been tested. Thermal neutron flux levels of the order of 10 nv and 10 nv are available at Apsara Thermal Column and core location respectively. The ease with which the detectors can be installed and the flexibility in reactor operation have helped in carrying out the tests. Ion chambers coated with enriched boron-10 have been developed for Dhruva, Kamini, Apsara and the FBTR. Current sensitivities ranging from lOfA/nv to 25fA/nv have been achieved. By using explosion welded SS-Al clad material for the fabrication of the end plates, it has been possible to weld ceramic-metal insulators to the aluminium outer housing of these devices. In some cases, integral MI cable assembly has also been provided. Boron-10 lined proportional counters with 3.5cps/nv and 17cps/nv have also been developed on similar lines for start up instrumentation in FBTR and PFBR respectively. The greater susceptibility of the high sensitivity counter to gamma background has led to the development of multi-tube proportional counter with an expected sensitivity of about 30cps/nv. ' Fission counters with U-233 coating have been .developed as an alternative to standard fission counters. These devices could be tested extensively at Apsara reactor in the pulse, DC as well as Campbell modes. Subsequently some counters were tested in the E5 pit at the FBTR. The results have established that pulse counters with a sensitivity of 0.09cps/nv can be developed and used for start up instrumentation without encountering significant problems due to alpha pile-up. A number of tests have been carried out at Apsara reactor on LPRM detectors developed for the power reactor at Tarapur. A comparison of the results in DC and Campbell mode have established that the operational life of these detectors can be increased from 2 to 6 years in Campbell operation. Self-powered detectors with rhodium, vanadium, cobalt and platinum emitters have been developed and tested in Apsara core location and CIRUS J rod annulus. Cobalt detectors have beery used for in-core flux measurement and noise analysis in Dhruva reactor. Platinum detectors respond to neutrons as well as gamma rays. To estimate individual current contributions, its performance has been compared to that of a bismuth SPD. The latter can be used as a pure in-core gamma detector. Both detectors were tested at Apsara core position. The gamma field at 300kW in Apsara core has been estimated as

138 2.56MR/h. Calculations have shown that about 48% of the signal from the platinum detector is due to gamma rays. Gamma ion chambers have been developed for monitoring the coolant activity at Dhruva. By arranging 36 chambers in a special matrix of 4 groups, it has been possible to detect and locate fuel failure in 144 channels. The chambers are filled with argon at 45psi pressure and have a gamma sensitivity of 0.25nA/R/h. Tritium poses a health hazard to workers in moderated reactors. Flow-type ion chambers with 40Itr. and 21tr. sensitive volume have been developed for continuous tritium-in-air monitor and portable monitor units respectively at Dhruva reactor. These detectors have current sensitivity of 0.4pA/(MPC)a and 0.02pA/(MPC)a of tritium respectively.

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