Traditional PWR safety qualified pressure transmitters are devices that are able to supply an electronic signal that is proportional to an absolute pressure measurement or a delta pressure measurement. Nuclear versions of these devices were originally manufactured and qualified in the 1970s and 1980s, but have had various features modernized for recent advancements in electronics and materials. The most important feature of the traditional device is the qualification of that device. A class 1E safety qualification for any transmitter means that the device has been through a series of tests and longevity assessments that prove that it is operational and survivable for nuclear conditions. Specifically it means that the device can meet the radiological, temperature, pressure, and longevity requirements for a nuclear reactor environment. Specifics on the qualification requirements for class 1E equipment is contained in IEEE 323-197419, 198320 and 200321 and IEEE 344-197522, 198723, 200424 and 2013.25

The issue with the traditional transmitters is that they were designed for an environment unlike the one that will be experienced in an iPWR design. In a traditional PWR, the containment environment, where most safety classified traditional pressure transmitter electronics are mounted, is a large, airy environment with relatively low ambient temperature and pressure, and with easy access for maintenance and repair of equipment; whereas most iPWR containments are designed as capsules that closely envelop the reactor vessel. These capsules have limited access with small enclosed environments of air, vacuum, or water that may include high ambient temperature and pressure. The location and mounting of these pressure transmitters will be quite different from the traditional approach, and the limited access for maintenance or repair will need to be factored into the design. In some cases, there will be no traditional pipe mountings for the sensing elements, and the use of sensing lines may not be possible in all cases. These hurdles in instrumentation, going from the traditional PWR to the iPWR, will necessitate the redesign of traditional models and/or the development of new technology.

The quandary in which iPWR instrumentation designers find themselves is that the least risk-averse approach, from a licensing and schedule perspective, is to use the instrumentation that already has the qualification pedigree and has worked in the past with traditional PWRs. However, the many changes in iPWR mechanical and physical design mean that the traditional devices may not function correctly or even fit in this new environment and design. This dilemma forces the I&C designer to look outside the ‘traditional box’ for answers.

New technologies, discussed in other sections, offer some solutions and some problems. Some new technologies offer smaller packaging, submersible options, more reliable manufacturing, flexible-mounting options, remote electrical processing, and fewer maintenance-intensive options. It is easily seen how these features would be welcomed by the iPWR I&C designer. The major drawback is the lack of device qualification and the lack of longevity field data that substantiates the survivability of these devices in the actual environment. As with the generation II reactors that populate many countries today, the iPWR I&C systems will undoubtedly experience the same growing pains as those experienced in the 1970s, as new designs are tried and lessons are learned.

As mentioned above, digital technology is expected to expand greatly in iPWRs. The same concern for common mode and common cause failure potential with software-based digital systems will continue to be an issue for iPWRs as it is with the large PWRs. The FPGA technology (Section 6.6) and technology like it that provide the reliability of digital devices without the need for operational software, has the appeal to take the forefront of safety and NSSS system processing in iPWRs.