Design, Development and Qualification of In-Core Neutron Proportional Counters

High sensitivity in-core neutron proportional counters are developed and qualified for reactor applications. The commonly used in-core neutron detectors used in reactors have neutron sensitivities lower than 1 cps/nv. Two types of high sensitivity detectors are developed; one using 94% enriched Boron-10 coating and the other using high purity Helium-3 filled at high pressure. The small outer diameter of 18.8 mm for both the detectors enables easy loading and unloading in the in-core locations. The detectors are fabricated following stage wise manufacturing and inspection guidelines and were subjected to stringent quality assurance to ensure reliable operation at reactors. To ascertain reactor worthiness, both the detectors were subjected to functional tests, nuclear tests and climatic tests. The detector performances remained unchanged after undergoing all the qualification tests, thus ensuring the reliability of operation. The Boron-10 detector has 4 cps/nv thermal neutron sensitivity and Helium-3 filled detector has 10 cps/nv thermal neutron sensitivity. This increased sensitivity enhances counting statistics and improved accuracy of estimation of fuel pins and critical height.