In order to operate aging nuclear power plant instrumentation and control systems for up to 60 more years or longer, there must be a smooth transition from existing analog technologies to advanced digital platforms. For this to occur, electromagnetic compatibility concerns related to both qualification testing and the electromagnetic environment must be addressed to ensure safe and reliable operation of these systems within the plant’s electromagnetic and radio frequency interference environment. By understanding the regulatory requirements and sharing implementation experience, digital system upgrades can be installed successfully.
As nuclear power plants continue to operate beyond their design life, maintenance of their instrumentation and control (I&C) systems is becoming increasingly important. Most of the I&C systems that monitor and control processes in today’s nuclear power plants are based on analog technology designed in the 1950s and 1960s. As technological advances have been made over the past several decades, a shift away from analog technology toward digital technology is occurring in the I&C industry. This shift is happening for a number of reasons, some of which are:
-
Obsolescence of installed analog I&C equipment.
-
Increased performance and functionality provided by digital technology over analog technology.
-
Cost reductions presented by digital technology over analog technology.
However, several technical issues are preventing a smooth transition from analog to digital I&C. Table 1 lists examples of some of these issues along with an explanation of each. Of particular concern when addressing digital I&C upgrades is the issue of electromagnetic compatibility (EMC), which encompasses the effects of electromagnetic and radio frequency interference (EMI/RFI). Consequently, organizations such as the U.S. Nuclear Regulatory Commission (NRC), the Electric Power Research Institute (EPRI), and the Institute of Electrical and Electronics Engineers (IEEE) have developed requirements and guidelines with respect to EMC for the installation and use of digital instrumentation in nuclear power plants.
Table 1. Technical issues surrounding digital I&C upgrades. Source: Analysis and Measurement Services Corp.
Digital Upgrades and EMI/RFI in Nuclear Plants
Obsolescence of analog I&C system components and the lack of replacement parts for I&C systems that are no longer supported by the manufacturer are leading to the increased use of digital instrumentation in nuclear power plants in the form of upgrades or completely new installations. The shift toward digital technology, however, is not entirely due to factors beyond the control of the nuclear power plant such as obsolescence. Many advantages are offered by the new digital I&C systems, including these:
-
Self-checking features such as power supply monitoring, communication channel testing, and cyclic redundancy checks of memory
-
Online diagnostics
-
Improved accuracy
-
Fault tolerance
-
Improved human-machine interface
-
High data handling and storage capacities
The advantages offered by digital technology and the challenge of obsolescence issues make a digital I&C system an attractive upgrade for a nuclear power plant’s process control. Consequently, several digital I&C systems have been developed and installed in nuclear power plants over the years. Table 2 lists examples.
Table 2. Digital I&C system installations. Source: Analysis and Measurement Services Corp.
[Editor's correction 2/16/10: The Common Q plants identified in this table as being in Europe are in South Korea.]
However, the transition to digital instrumentation in a nuclear power plant is not trivial. There are numerous regulatory and technical hurdles to overcome. As mentioned previously, EMC is of particular concern. Equipment installed as part of an upgrade needs to be compatible with its environment, so EMC qualification must occur to ensure that the new equipment does not introduce EMI/RFI problems and affect plant safety and reliability. In addition, the new equipment must be protected from the emissions of currently installed equipment.
Table 3. Specific RG-1.180 regulatory positions for EMC guidance. Source: Analysis and Measurement Services Corp.
The operational behavior of equipment in the presence of EMI/RFI is defined as its immunity or susceptibility. Immunity is the ability of equipment to remain operationally "immune," or unaffected, in the presence of defined levels of EMI. Susceptibility is the degree to which the equipment’s operation is unintentionally affected when in the presence of a defined level of EMI. The immunity or susceptibility of equipment is determined by performing various EMC tests. These tests are divided into two types: emissions testing and susceptibility (or immunity) testing.
Emissions testing is used to determine the EMI/RFI profile of the equipment under test, which identifies the frequency and magnitude of any emissions from the equipment. Emissions can occur in two forms — radiated and conducted:
-
Radiated emissions are transmitted via noncontact mechanisms, such as the magnetic field that radiates from a current-carrying wire. The radiated magnetic field can couple into adjacent circuits and interfere with the operation of those circuits. The effects of radiated emissions can be reduced through shielding and filtering.
-
Conducted emissions are transmitted through contact mechanisms such as plant wiring or an instrumentation cabinet acting as a ground path. Conducted emissions are coupled directly into other circuits and can be reduced by filtering.
Email
Comments
Print
Reuse
Comments (1)