Regulatory Requirements and Guidelines for EMC Qualification
The design of safety-related I&C equipment is required to conform to the standards set forth by Part 50 of Title 10 of the Code of Federal Regulations (10 CFR 50). This includes defining the operating characteristics of the system and performing testing on the system to verify that it meets the requirements. The goal of the testing is to be reasonably sure that the system will not adversely affect any other safety-related equipment in the plant and that the system itself will not be adversely affected by other equipment already present at the installation location in the plant.
Any new safety-related I&C systems, along with any modifications to existing systems, must be evaluated before they are placed in the nuclear power plant environment. Part of this evaluation involves measuring electromagnetic emissions and susceptibility. The systems discussed here include digital, advanced analog, and hybrid analog-digital I&C systems. The guidance provided is meant to be a compilation of approved practices for the EMC qualification of safety-related I&C equipment. The purpose of this guidance is to accelerate the approval process of permits and licenses, and of proposed plant modifications, by the NRC.
The NRC has established guidelines for addressing the effects of EMI/RFI on safety-related I&C systems in nuclear power plants. Regulatory Guide 1.180 (RG-1.180), Guidelines for Evaluating Electromagnetic and Radio-Frequency Interference in Safety-Related Instrumentation and Control Systems, was written to provide operating nuclear power plants and license applicants with a set of guidelines to use for EMC testing of safety-related equipment. This regulatory guide recommends that its information be only one part of a total package of tools combined with other good engineering practices. The guide recommends that, whenever it is feasible, the EMC practices applied to nonsafety-related I&C systems should be held to the same high standards as those applied to safety-related I&C systems.
The IEEE developed a standard, IEEE Std. 1050-1996, that describes theoretical and practical methods of grounding practices for I&C equipment and its associated circuits. IEEE Std. 1050-1996 details guidelines for controlling upsets and malfunctions in safety-related I&C equipment exposed to EMI/RFI and power surges. The standard has been endorsed by RG-1.180 with only one exception related to radiation coupling field strength, as noted in Regulatory Position 2 of the guide. The regulatory positions of RG-1.180 and the associated standards are shown in Table 3.
Until the NRC first released RG-1.180 in January 2000, the only EMC guidance for the nuclear industry was a safety evaluation report recommending the Electric Power Research Institute topical report EPRI TR-102323R1 as a method of addressing EMC concerns about safety-related I&C systems. For the testing of EMI/RFI emissions and susceptibility, RG-1.180 endorses the applicable testing methods of the Military Standard MIL-STD-461E. Applicable testing methods in the International Electrotechnical Commission (IEC) standard IEC 61000 have also been endorsed. In addition, the methods of the topical report EPRI TR-102323R1 retain their endorsement from the NRC.
EPRI TR-102323R1 defines limits for EMI/RFI emissions and susceptibility testing levels for use in establishing EMC guidelines for the nuclear power industry. The limits in the report were developed based on both existing standards and empirical data collected from several operating nuclear power plants. The result is a set of generic EMI/RFI emissions and susceptibility levels, along with the identification of emissions sources in nuclear power plants. MIL-STD-461E contains methods for EMI/RFI emissions and susceptibility testing for a variety of frequencies and environments. IEC 61000 also has parts that define generic envelopes and limits for EMI/RFI emissions and susceptibility testing. IEC 61000 Part 6 defines methods dealing with conducted and radiated emissions testing. Part 4 contains testing information pertaining to conducted and radiated EMI/RFI susceptibility.
The types of EMI/RFI tests and their applicable testing methods are shown in Table 4. The descriptions are the same as those given in RG-1.180; therefore, the frequency limits given are the endorsed limits and not necessarily the limits of the standard listed. The standards are grouped by whether they are for conducted or radiated tests, emission or susceptibility tests, and (for conducted susceptibility) power or signal line tests. An illustration of the frequency ranges as they appear in the table for the different standards is shown in Figure 1.
Table 4. EMI/RFI tests, applicable methods, and method descriptions. Source: Analysis and Measurement Services Corp.
1. EMC testing standards endorsed by Regulatory Guide 1.180 and their associated frequency ranges. Source: Analysis and Measurement Services Corp.
Depending on the needs and characteristics of the I&C system under consideration, a suite of EMC tests is determined that will be required to satisfy the NRC requirements. Although there are several different sources for the testing standards, it should be noted that the testing methods are mutually exclusive and cannot be mixed and matched. Methods from multiple standards sources cannot be mixed to provide full testing coverage; one standard must be applied in its entirety. RG-1.180 also provides the option of applying alternative test suites from the most recent versions of the MIL-STD and IEC guidelines.
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Several of the worst plant upsets in process plant have been ship or tugboat radars effects on transmitters. In one case the transmitter EMC filtering had been damaged by lighting without noticeably changing the 4-20 mA signal.