Keep your finger on the Pulse

THE NUCLEAR INSTRUMENTATION & CONTROL (I&C) business of Rolls-Royce and Analysis and Measurement Services Corporation (AMS), have established an international partnership to provide enhanced I&C system testing and support to the global nuclear fleet.

The combined offering under the “Pulse” product line developed by Rolls-Royce combines technology and test methodologies to address many of the performance monitoring needs of nuclear power plant I&C systems, including temperature sensors, pressure, level, and flow transmitters, neutron detectors, as well as cables and connectors for systems such as rod control and neutron instrumentation.

The partnership comes at a time when utilities around the world are struggling to find balance between providing clean and environmentally friendly power to their consumers while doing so in a cost-effective manner. Nuclear operation and maintenance costs have risen steadily over the years, causing many utilities to re-evaluate their nuclear portfolios.

In addition to the rising cost of operating nuclear power plants, the global nuclear fleet has another very real obstacle to overcome: age. For example, in the USA, with the average age of nuclear power plants at around 37 years, utilities are applying for licence extensions to 60 or 80 years. To do that, most plants are required to increase their maintenance and oversight of critical plant components and systems, including I&C systems.

Pulse offers support for cables, pressure transmitters, temperature probes, neutron detectors, electromagnetic interference monitoring, and thermography.

Cable testing: Cable health and performance is one of the biggest concerns within the ageing fleet of nuclear power plants. Each nuclear reactor has miles of cables, much of which is underground or inaccessible. Millions of dollars of research and development (R&D) has been spent to identify and validate in-situ test methodologies for verifying the health and performance of critical cables. The cable characterisation system developed by AMS employs a suite of test methodologies to verify the health and integrity of a cable’s insulation by performing a series of non-destructive electrical tests that can be administered from the measurement end of the cable in the control room area. This allows testing of most cable circuits and end devices while saving test personnel exposure to potentially harsh environments. The data collection is managed by user- friendly proprietary software that automatically trends recent measurements with historical baseline data, while flagging discrepancies and outliers. This is also useful in troubleshooting conductors and connectors.

Pressure transmitters: Proprietary hardware and software allows for in-situ response-time testing of pressure, level and flow transmitters using noise analysis. This is based on monitoring the natural fluctuations at the output of transmitters while the plant is operating. The noise is extracted from the sensor output by removing the DC component of the signal and amplifying the AC component. The data are then analysed in the frequency or time domain to provide the response time of the sensor.

An advantage of the noise analysis technique is that it also provides the response time of the sensing lines that bring the pressure information from the process to the sensor. A blockage, void, or leak in the sensing line manifests itself as an increase in the measured response time.

Noise analysis is performed remotely from the control room area where the field leads from the sensors reach the process instrumentation cabinets. Performing these tests in-situ provides the actual in-service response time of the sensor, accounting for all installation and process condition effects on response time.

Temperature probes: AMS has been measuring the in- service response time of process sensors in nuclear power plants since 1977, in most PWRs in the USA and many in Europe and Asia.

The loop current step response method and self- heating index measurements are used for in-situ testing of response time of nuclear plant temperature sensors. The former method is based on heating the temperature probe’s sensing element with a small electric current. This current causes a temperature transient in the sensor that is analysed determine the temperature probe’s response time. The method has been formally approved by the US Nuclear Regulatory Commission (NRC) for measurement of “in-service response times” of safety-system temperature probes in PWRs.

In-situ performance verification of temperature probes eliminates the need to remove the sensor each outage to perform laboratory verification, as well as any faults or errors associated with poor fit when reinstalling the sensor in its thermowell in the plant.

EMI monitoring of neutron detectors: Rolls-Royce developed a set of three tools – Wave – for diagnostic of the EMI activity. There are three tools:

• Wave-B monitors external EMI activity that could affect the system and then checks the ability of the installation to mitigate environment electromagnetic disturbances, from the detector to the cabinet.
• Wave-S verifies EMI robustness of the source range channel by measuring and quantifying their immunity.
• Wave-IP verifies EMI robustness of the Intermediate and power range channels by measuring and quantifying their immunity.

The Wave series of tools allows plants to avoid spurious shutdowns caused by EMC problems related to poor line quality, guarantees the operability of the line and can anticipate maintenance by comparative analysis of recorded data.

Thermography: In order to monitor the health and ageing status of nuclear safety classed systems and their components, Rolls-Royce uses a specific methodology based on infrared thermography. This can detect faulty components, crimping or clamping problems and identify components that lose their initial characteristics, leading to overheating. The comparison of infrared thermography pictures over time also makes it possible to establish trends and anticipate problems on components.

Neutron detectors: Neutron detectors are critical for safety and availability but are complex and operate under extreme conditions. A detector issue may trigger an emergency shutdown so, neutron detectors’ ageing condition must be carefully monitored. Rolls-Royce uses a combination of custom data acquisition, an extensive database providing condition monitoring information for the life of each detector and a team of specialists to provide analysis and recommendations for maintenance and planning. This methodology will allow for planned replacements and will reduce the risk of unscheduled shutdowns.

Author information: Romain Desgeorge, Rolls-Royce Civil Nuclear SAS; H.M. Hashemian, Analysis and Measurement Services Corporation