The modern movement: digital I&C4 July 2018
Today’s instrumentation and control technologies are key to efficient, reliable plant operations. Clayton Scott explains how the transition to digital is helping to support the current and future fleet.
Instrumentation and control (I&C) systems are the central nervous system that monitor and control nuclear reactor operation and balance of plant systems. Initially, plants were built with analogue technology, but like much of the technology in the world, these systems are moving increasingly to digital.
Nuclear utilities adhere to strict licensing requirements and regulation, and regulators have processes in place that facilitate the upgrade and modernisation of original plant equipment. While some utilities opt to maintain their original, licence-based I&C configurations, new digital systems can allow plants to improve productivity and efficiency, cut the number of unscheduled outages and reduce surveillance, with greater plant optimisation and increased performance.
Further, new digital systems bring more flexibility. For example, equipment that would previously have been a single monolithic item can comprise smaller ‘distributed’ packages in multiple rooms. This offers greater safety, because of physical ergonomic separation considerations. Digital equipment also allows for automatic, remote diagnostic, analytical and self-testing capabilities, which mean utilities can gain time during outages and operation, while having a better understanding of the state of their control equipment.
I&C systems today are built on three main technologies.
- Analogue: This technology was used when the existing fleet of nuclear power plants was built.
- Microprocessor: This is a mainstream technology that is used in new-build projects worldwide, as well as in many modernisation and upgrade projects. Most upgrades to nuclear steam supply systems or balance of plant controls use microprocessor-based technology.
- Field-programmable gate array (FPGA): This technology is relatively new to the nuclear industry. It is similar to microprocessor technology, but is often used when there is a need for low power consumption and fast parallel processing.
The trend for I&C systems in nuclear new-build projects around the world is clearly digital. Among the first countries to use digital technology for I&C systems comprehensively were Japan (at Kashiwazaki-Kariwa 6&7, which entered commercial operations in 1996 and 1997, respectively) and France (in the 1450MW N4 series). Today, Generation III reactors are equipped with the latest technology for their digital safety and normal operation I&C systems, and many of them use microprocessor-based technology. This is the case with new-builds in China, Finland, Russia, South Korea, the United Kingdom and the USA.
The global nuclear industry is also working to realise the full potential benefits of FPGA technology. Some utilities around the world have considered FPGA to diversify the technologies they use for their I&C systems. However, so far it has been used only in Ukrainian and Japanese nuclear power plants.
A move towards digital I&C systems is also apparent in modernisation projects, and many US and Canadian utilities appear to be looking at long-term digital upgrades. In the USA, the pursuit of operating licence extensions could be a significant driver behind I&C upgrades. These upgrades face different challenges than new-build projects. The original design basis of the plant serves as the benchmark for this type of upgrade work, as well as for the accompanying licence amendments.
When embarking on an I&C upgrade, integration engineering capabilities are needed to ensure there is a clear understanding of the plant architecture and it is matched with a strong I&C solution that meets regulatory requirements. I&C engineering alone is often not sufficient to deliver a sound solution. Continual interaction with process and safety engineering is necessary to cope with the licensing requirements, safety classifications and process understanding.
Challenges that the utility and its vendor must overcome when interfacing with existing I&C systems relate to the signal runtime between interconnected systems (especially for safety and trip systems), and the need to ensure a smooth transition from analogue architecture to modern, multichannel digital architectures.
The first step should be a front-end engineering design study. This allows the utility and vendors to understand the challenges associated with the project, and provides a clear view of the technologies already in use at the plant. Mastering the licensing requirements is probably the most challenging part of this work. The focus has to be on as-built documentation, requirements for project documentation and testing, common-cause-failure robustness of the solution, cybersecurity, and verification and validation. Commercial terms, supplier capabilities and technological factors play significant roles in decision-making. Each I&C upgrade project is tailor-made, based on the existing infrastructure, and designed to keep the plant offline for the shortest amount of time.
In France and the USA, the nuclear industry is taking steps to transition to digital technology.
France is making this transition in both its 900MW and 1300MW series of PWRs.
In the USA, nuclear utilities have jointly launched a multiyear initiative to transform the industry, ensure its viability for consumers and recognise its essential role in protecting the environment. This strategy includes several opportunities to increase efficiency, and I&C systems have an important role in achieving that goal. The Nuclear Energy Institute leads the US industry’s work to modernise the regulatory infrastructure for digital upgrades, and with the Nuclear Regulatory Commission it developed an integrated action plan to align the priorities for modernising the regulations surrounding digital I&C.
Supporting the lifecycle of I&C systems
Utilities have to consider the lifecycle management of their I&C systems, whether a new-build or an upgrade and modernisation project. The approach to maintaining these systems depends on each individual plant’s operating conditions. While a reactor is at power, scheduled preventive maintenance, such as calibration, can be performed, along with emergency repair work, if necessary. Upgrades, modernisations and equipment replacements are only conducted during an outage.
The lifecycle of an I&C solution can easily span decades and, in some cases, utilities can still receive support from the original equipment manufacturer (OEM). In the best case, the vendor supports its platform for 20 years or longer. That means a utility has to exchange the I&C systems just once during the plant lifecycle, assuming 60 years of operation. This is the case for platforms like Teleperm® XS, Tricon and Foxboro.
For the analogue system SPEC 200, which was deployed initially in the 1970s, many complete SPEC 200 modules are available today.
In partnership with vendors, utilities have undertaken projects to re-engineer and even reverse-engineer modules to support continued operations. Operators decide to re-engineer analogue systems due to cost or regulatory uncertainty, including how the regulator defines digital and re-engineering in terms of common cause failure, cybersecurity and defence in depth. For non-safety systems, the ability to adopt digital modules in place of analogue can provide new opportunities for automated operation, testing and diagnostics.
Two recent examples of this in US utilities are a Framatome re-engineered off-gas control system and a re- engineered drive control unit (DCU) for a traversing in-core probe system (TIP).
The off-gas system is designed to remove hydrogen and other gases from the primary reactor coolant system (RCS), which transfers heat from the reactor to the steam turbine. Along with integrating digital and analogue control components based on the facility’s requirements, the new re-engineered system was customised to improve the way operators interpret and manipulate the controls for improved safety performance.
For the drive control unit, a joint effort between the engineers at Framatome and a cross-disciplinary team at the utility reverse-engineered the probe system controls to significantly improve reliability while retaining the existing operator-machine interface. This resulted in a product that is more reliable and easier to maintain and test, but does not require extensive operator training, procedure revisions or changes to the control room panel layout. The new digital controls look identical, but perform at a much higher level than the original analogue equipment.
Author information: Clayton Scott is Deputy of the Instrumentation and Control Business Unit at Framatome