The Incore instrumentation System (ICIS) measures neutron flux distribution in the reactor core. The ICIS routes the movable incore neutron detectors into the selected core locations (thimbles) to receive the current signals proportional to the neutron flux. The ICIS cabinets display and record these signals to provide input to the core management computer. The neutron flux information obtained from the ICIS is used to construct accurate core power distribution. The ICIS cabinet is implemented with a digital nuclear instrumentation and Control (I&C) platform MELTAC®.
The Mitsubishi ICIS is composed of mechanical components and ICIS cabinets.
- Detector: Measures the neutron flux in the reactor core. Detector is inserted and withdrawn into the core through thimbles by using a motor driven wheel that meshes with the detector driven cable.
- Thimble: Serves as a guide tube through which the detector is routed into the selected core location
- Drive unit: Inserts and retrieves/extracts the detector from the selected core location.
- Path Transfer device: Selects the core location (thimble path).
- ICIS cabinet: Controls and monitors mechanical components and receives detector signals, displays detector status, performs manual operations for insertion-extraction of the detector and system alerts.
The Mitsubishi ICIS uses the following components to ensure high reliability and maintainability.
- A brushless resolver is used to indicate the detector location with exceptional accuracy.
- The path transfer device, used for detector path selection, uses a roller-gear cam mechanism to ensure high reliability and maintainability.
- An inverter-controlled induction motor is used to drive the detector to ensure high reliability, maintainability and long service life of the motor brake.
- The ICIS cabinet uses the detector to automatically measure and record the neutron flux distribution in a predetermined (configurable) sequence. Data is stored in external media (e.g. DVD) for use in the core management program.