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The Rod Position Indication System in an important system in a nuclear power plant to monitor and display all control rod position information in the reactor core. 

Mitsubishi provides a highly reliable Digital Rode Position Indication (DRPI) System which measures and monitors the position of rod assemblies, displays rod positions, provides alarms to plant operators for a dropped control rod, and sends rod position data to the plant computer. Compared to analog RPI System, the DRPI System improves the precision of rod position detection and display. the Mitsubishi DRPI is implemented with the digital nuclear Instrumentation and Control (I&C) platform MELTAC®. ​

Mitsubishi provides all equipment needed to configure the RPI system including detectors, measuring circuitry and Human System Interface (HSI).

System Configuration​

The Mitsubishi DRPI System is composed of the rod position detectors, prefabricated cables, the rod position ​​monitoring cabinet, and electrical-optical converter cabinet.

  • Rod position detector: Utilizes a stack of coil sensors to detect control rod positions. Transmits the rod position signals to the Data cabinet.
  • Prefabricated Cables: Transmits signals to the rod position monitoring cabinet.
  • Rod Position Data Cabinet: Receives discrete rod position signals from the detector and converts them to the digital signals. Then, transmits the rod position information to the E/O Convertor cabinet.
  • E/O Converter Cabinet: Receives rod electrical position signals from the data cabinet, and converts them into optical signals before sending to the Reactor Control System.

System Features

The Mitsubishi DRPI System is designed to minimize the effects of varying ambient temperature and magnetic permeability of the rod drive shafts. 

  • The measurement is accurate within less than 6 steps
  • Compared to analog RPI, DRPI is less susceptible to temperature changes, can operate at higher temperature, and in generally more stable.
  • High reliability is achieved through application of redundant​ rod position detectors and interface circuitry
  • Rod position indication is displayed on the Visual Display Unit (VDU), which enhances information visibility.

Legacy Equipment

In addition to the latest digital equipment, MELCO can supply legacy equipment such as analog indicators, LED type indicators , and analog RPI Systems to respond to the customer needs.