Ultra Energy introduces high temperature neutron flux detector capable of operating at 800 Celsius

28 September 2022

Safe operation of next generation reactors requires leap in sensor capabilities

Ultra Energy has designed and manufactured a new neutron flux sensor capable of operating from room temperature up to 800°C with no change in its performance. The device is based on other Ultra sensors that have operated successfully at up to 550oC for many decades in most of the UK’s existing nuclear fleet.

Next Generation nuclear reactors will play a key role in delivering low carbon energy security in countries across the world. Many of these reactors operate at very high temperatures and therefore require sensors and instrumentation that can withstand these conditions, while consistently delivering safety critical functions. One such function is measuring the number of neutrons passing through the reactor core (‘neutron flux’). The number of neutrons indicates how much energy a reactor is generating.

Neutron flux sensors are precision devices that are extremely challenging to design and manufacture. Neutrons are neutral sub-atomic particles that do not interact well with matter and are therefore difficult to detect. Specialist materials are combined with gasses and electric fields to change a passing neutron into an electrical signal. The resulting signal is very small. Individual neutrons generate a signal of 1 micro amp that lasts for 150 nanoseconds. Detection of these events needs to be delivered while the sensor itself could be glowing red hot due to its location in a reactor core operating at 800°C.

All parts in Ultra Energy’s new sensor have been designed to withstand and mitigate against stresses that occur during thermal expansion over a large temperature range up to 800oC. The sensor is made predominantly from nickel-alloy with ceramic used for insulators. It can operate from reactor start-up to full power, which represents a change in neutron flux of ten orders of magnitude. This is like having a speedometer that reliably measure speeds from 0.1mph to 1,000,000,000 mph with complete accuracy

Signals created by the sensor are received by electronics located in a room temperature environment. The electrical signal is transported through cables that must tolerate the extreme temperature whilst screening a tiny signal from electrical interference in the outside world. This cable is a type of ‘coaxial cable’ like the cable used for a TV aerial but built to an extreme specification to ensure interference can’t affect the small signal. The mineral insulated cable is made from metal and ceramic and can also operate at 800°C.

Jeff Ridgway, Head of Consultancy and Compliance, Ultra Energy, lead our development of the new high temperature neutron flux sensor and will present its test results at the 4th international conference on Generation IV and small reactors being held in October 2022 in Toronto Canada.

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