Neutron Measurement

Neutron measurement in a reactor is vital for reactor control and protection because the instantaneous power of the reactor is related to the neutron population through the simultaneous release of neutrons and energy in the fission process. Instrumentation based on neutron measurement is able to determine the presence of an unwanted transient at low powers before it is able to develop into a serious problem. Such instrumentation is also fast and responds quickly to high power transients. Hence the reactor safety circuits include neutron detectors and their associated electronics.
 
A range of neutron detectors, instrumentation channels and interconnecting cabling for Advanced Gas Cooled Reactors (AGRs) detectors were originally designed in the 1960’s by UKAEA. The department responsible is now part of Ultra Electronics Ltd and is still the Design Authority for the detectors and associated cabling and has extensive knowledge of the manufacturing techniques employed in detector production.

Detector Management Services

Ultra offers the following capabilities over the lifetime of the detectors. 
  • Safety Case Justifications for use of detectors
  • Health Check testing of detectors and whole nucleonic systems before and after installation into the reactor
  • On-load testing of detectors to give early indication of any faults
  • Fault-finding and diagnosis of problems with nucleonic systems

 

Specification

Detector Types

Four types of ionisation chambers were designed to cover the wide range of reactor power from shutdown to full power.
 
The P7A detector is a high temperature in-core pulse fission chamber designed to provide signals at shutdown and at low power levels. The neutron sensitive coating is Uranium Oxide applied to the cathode.
 
The DC12A detector is a wide range gamma compensated boron ion chamber, designed for high temperature in-core operation. The gamma compensation allows the detector to work at low power levels where the gamma contribution to the signal is significant when measuring neutron flux.
 
The DC14A detector is an uncompensated uranium-oxide lined DC fission chamber, designed for high temperature in-core operation. The detector was designed to provide signals diverse from those of the DC12A at high power levels.
 
The P8A detector is a uranium-oxide lined Pulse Fission chamber, designed for high temperature in-core operation. The detector can be used in the pulse and ‘Pulse Campbell’ modes and therefore can be used from shutdown to full power.
 
Low temperature detectors designed by UKAEA were modified for use in the early UK manufactured land and sea based reactors. Current reactors use high temperature versions of these designs.