Design and development of a neutron detection based novel criticality accident alarm system (CAAS) using liquid activation technique

Criticality Accident Alarm System (CAAS) is a mandatory system for prompt alarm and immediate evacuation of personnel during the unusual event of a criticality accident in all nuclear facilities using fissile materials. False criticality alarms are not desirable as they create a panic environment for radiation workers of the plant and the public. We have studied the use of different materials for such alarms and effective monitoring during such events. The present paper describes the design and development of a neutron detection based novel CAAS using the unique method of liquid activation technique of vanadyl sulphate solution, which can prevent false alarms. The neutronic properties of vanadium has been utilised for fast response. The performance evaluation of CAAS such as: testing, efficiency evaluation, threshold setting and various response studies using laboratory neutron sources including 252Cf fission neutron source, standard thermal neutron facility and reactor neutrons has been carried out by following the international recommendations and ensured the compliance. The results are also validated using Monte -Carlo FLUKA simulation. The concentration of vanadyl sulphate solution for liquid activation is optimized as 0.0082 g. cm -3 and the alarm threshold setting is evaluated as: 3881 CPS and 3.61 MBq of induced activity based on the current study. It is also worth mentioning that this liquid based system can be deployed in any reactor and fuel re -processing plants easily.