Managing the Use of Wireless Devices in Nuclear Power Plants

Wireless technology is experiencing explosive growth. More than just devices of the same kind, there is a proliferation of applications that take advantage of wireless connectivity, using it in new and novel ways. Wireless technology itself is developing and radio access technologies are becoming increasingly complex and sophisticated. The result is that today’s electromagnetic environment is changing. This means that old test methods and limits are no longer adequate to insure systems have adequate electromagnetic immunity.

Further, there is a movement to bring wireless into nuclear plants and make it part of plant design. Existing plants have examined the use of wireless, but formal integration is slow. Next generation, advanced plants, some plants presently under construct specify significant use of wireless technologies. There is a wide variety of beneficial applications, including mobile connectivity with personnel, sensing, and wireless data networks. Expanding applications make managing the use of wireless technology in nuclear power plants (NPPs) an emerging requirement.

This article discusses the need to go beyond traditional requirements for EMC interference protection to managing wireless and the use of spectrum so that interference is avoided and wireless services can coexist and operate at the high levels of reliability required by nuclear plants.

The first time a nuclear reactor generated electricity was on December 20, 1951, at the EBR-I experimental station near Arco, Idaho.[1] In 1956, when the first commercial nuclear power station was built, portable wireless devices were not in common use. Portable radio transceivers were first developed in 1940 by the Galvin Manufacturing Company (predecessor to Motorola) who coined the name “Walkie-Talkie”. The first Walkie-Talkie was a backpacked unit. Motorola produced the first hand-held amplitude modulation (AM) radio during World War II for military use and called it the “Handie-Talkie”. Both devices used vacuum tubes and high-voltage dry-cell batteries. The “Handie-Talkie” became a registered trademark of Motorola in 1951. After the war, Walkie-Talkies were adopted by public safety departments, followed by commercial entities and jobsites. Industrial plants and power plants also adopted them at this time.

The use of wireless devices that transmit and receive radio power in a nuclear power plant (NPP) has been a concern since the first wireless device (i.e., the simple hand-held portable radio transceiver, or Walkie-Talkie) was used in a power plant. Fossil and hydro power plants were the initial users of Walkie-Talkies. When the first NPP went on line in the late 1950s, instrumentation and control (I&C) engineers were surprised to find that Walkie-Talkies were able to cause malfunctions and upsets of analog I&C equipment. EMI problems with I&C equipment caused by portable radios were obviously among the first type of EMI-related I&C problems to be reported.

Similar to the historical path that Walkie-Talkies took, the concept of a radio telephone stemmed from the invention of the radiophone. This was followed by shore-to-ship demonstrations of radio telephony through World War II, when the US military used radio telephony links. Civil service personnel used radio telephony in the 1950s. In June 1946, the first mobile telephone call was made from St. Louis, Missouri using the Bell System’s Mobile Telephone Service. The first automatic mobile phone system (Mobile System A), using vacuum tubes and relays designed for an automobile, was launched in Sweden in 1956. A more modern version (Mobile System B), which used transistors to reduce its weight and improve call capacity and operational reliability, was introduced in 1962. This was followed by the development of Mobile System D, which provided a pathway for different brands of equipment and stimulated the successful use of this technology in commercial markets. In a race against Bell Labs to develop the first practical mobile phone for non-vehicle use, Motorola was credited with its invention in 1973 (the same year that EPRI was founded). As the development of wireless technologies continued to expand, other wireless devices such as cellular telephones (cell phones) began to take shape.

Since that time, efforts to protect against EMI-related events occurring in NPPs have been an ongoing part of risk mitigation. The potential for EMI events from natural and man-made sources has been known for many years. Over time, risk mitigation efforts have seen ongoing development as understanding of the physics of EMI events improves and as changing technology require continual development to keep protection appropriate to the current environment.

The Growth of Wireless Technologies

As the use of wireless technology grows dramatically, not only are the number of devices that use wireless transmission increasing, but the number of bands, modulations and protocols being used are also increasing. The rate of growth in number, as well as the increasing the variety of applications and diversity of potential interference sources, makes a complete listing almost impossible. Furthermore, the result would be of little use, being a long list of devices using virtually every available area of the spectrum for an ever increasing variety of applications. Such a list would provide little to help industries make decisions on how to deal with all the potential sources of interference. Even worse, the list would soon be out-of-date.

A prominent set of examples is the growth of the frequency bands used for industrial, scientific, and medical (ISM) equipment. The ISM bands were established by international agreement to be unlicensed bands, available for a wide range of uses. The ISM bands have been extremely popular, as demonstrated by the dramatic increase of US Federal Communications Commission (FCC) equipment grants for these bands. Figure 1 shows the continued heavy and increasing use of the ISM bands. The 900 MHz, 2.4 and 5.8 GHz bands support the most equipment by far, though recent growth of the 2.4 GHz band is extraordinary. The 900-MHz band seems to have stabilized at a level of approximately 500 new products introduced into it every year. While the 5.8-GHz band is experiencing heavy growth, is it not as notable as the 2.4 GHz band.

Figure 1 through Figure 4 report trends in equipment grants. Each unique model of wireless transmitter must have a FCC equipment grant to be legally marketed in the US. However, the existence of a grant does not indicate whether only a few devices or many millions of them are sold every year. The most popular, high volume product and the very specialized, custom product, each will have one equipment grant. To fully comprehend how widely a set of devices is used requires more information about sales volume, market trends, and whether old models are withdrawn as new ones are introduced. However, equipment grant data is easily quantified and provides an objective basis for demonstrating growth trends. It is important information, but does not provide all the information we want.

Figure 1: FCC equipment grants for the ISM bands, 1990-2010

Figure 2: FCC equipment grants, by category, for the 900 MHz ISM band, 1990 to 2010

Figure 3: FCC equipment grants, by category, for the 2.4 GHz ISM band, 1990 to 2010

Figure 4: FCC equipment grants, by category, for the 5.8 GHz ISM band, 1990 to 2010

Figure 2 through Figure 4 show the most popular equipment categories in each band. As can be seen immediately, a variety of equipment types use each of the ISM bands. Under FCC rules, any device may use the ISM bands so long as it complies with the service rules for that specific band. At one time the FCC tried to designate specific uses for each band, but generally has moved away from that practice for bands such as the ISM. These are now treated as general use bands, applying a minimum of restrictions and allowing a wide variety of equipment operating access to these spectrums.

Not only is the use of wireless growing dramatically, but the resulting spectrum crowding is requiring a bold, fresh look at how spectrum is regulated. There is an increasing trend toward more flexible spectrum regulations, allowing devices to dynamically share frequency bands. It is now common for devices to be capable of communicating on multiple frequency bands using multiple radio-frequency (RF) protocols. With software-defined radio, a device’s capabilities may be changed by a remote software update. The result is that a single device may, from an RF interference viewpoint, be many devices, as it uses different frequency bands and protocols at different times. A single device may be capable of operating on the cellular networks using CDMA, GSM, UMTS or LTE protocols, on local area networks using any of several ISM frequency bands and 802.11 protocols, or by using Bluetooth, DECT, ANT or a number of other protocols and bands. Having access to multiple radio access technologies is a great benefit. However, this benefit presents a real challenge for EMC management.

What is needed for those with a role to play in managing spectrum or protecting against interference is a taxonomy that can bring order to the vast array of potential sources of interference, many of which are known to have caused interference in NPPs. A method is needed by which those with responsibility for interference avoidance or spectrum management can address classes of products that are of most concern, as well as monitor trends and market changes in many other classes of devices. Nuanced solutions are needed if overly conservative requirements, which are either wasteful of spectrum or unnecessarily burdensome on product designs, are to be avoided.

A taxonomy can be conceived that is designed to identify those types of device that have a significant potential for producing RF interference with I&C systems. To produce such a taxonomy, one must understand the characteristics that make a class of equipment sensitive to RF transmission. Using audio interference as an example, audio RF interference requires that the following two conditions exist:

1. The receptor device must be exposed to an RF field with sufficient intensity to overcome its RF immunity.

2. The modulation of the RF field must contain substantial baseband audio components.

Reduction of the RF power or the content of the audio band modulation will reduce the amount of interference created.

Further, for a particular source of audio RF interference to become common, the following two criteria must also be met:

3. The combination of RF field intensity and modulation must be common enough to have an unacceptable probability of causing an interference problem.

4. There must not be readily available and easily applied remedies available to the user. If interference is easily recognized as being caused by RF and its consequences are neither serious or to rapid for human action to adequately address, then it is entirely possible that some mitigation taken by the operator will be entirely acceptable. An example might be a noise coming from a speaker that is eliminated by moving a walkie-talkie off the console and further away from the speaker.

Relatively few RF devices have these four characteristics. So, serious concerns about RF interference can be focused on those wireless devices that, considered as a class, do have these characteristics and present a serious threat for producing EMI-related malfunctions and failures.
Similar analysis can be developed for I&C systems used in NPPs. The characteristics of a system’s susceptibility must be understood in the context of the transmission parameters of potential interferes.

A well developed taxonomy extends from its focal point along multiple dimensions. It will seek to quantify modulation characteristics that impact interference. A constant wattage (CW) signal can introduce a direct current (DC) bias resulting in audio distortion or gain change, but generally these are not observed to be real field problems. At much lower power levels, modulated signals with strong content in the audio band result in disruptive audio interference in devices that produce sound, such as speakers or telephones. Similarly, pulsed modulations may interfere with digital circuits, like those used in digital I&C equipment, in a variety of ways.

Other dimensions may be explored. Some sources of severe interference are not widely distributed in the general population. However, NPPs may commonly find them introduced. Some kinds of transmitters are intended to be installed in fixed locations and remain stationary, while others are designed to be portable. The significance of these sources of interference must be evaluated based on their impact to NPPs.

An additional factor is that the methods used to provide RF immunity to the most common sources of RF interference tend to provide wideband immunity. The result is that I&C systems that are immune to mobile phones will also have good RF immunity to a number of other types of potential interference sources and electronic devices, even though they may operate in different frequency bands. This statement, like most generalities, will have exceptions and must be reexamined as new types of RF interferes are evaluated.

The purpose of this taxonomy is to assure that an adequate level of RF immunity is designed into I&C systems used in NPPs. To achieve this result, the taxonomy must identify the frequency range, power levels and modulation types that systems are likely to respond to. However, the taxonomy must equally identify the severity of the threat so that an inordinate level of RF immunity will not be required, with its attending cost and complexity resulting in overly burdensome specifications for I&C systems.

Human Behavior

Can humans enable cell phone-related electromagnetic interference problems to occur in nuclear power plants? Perhaps the more significant question to consider is whether humans are in control of the wireless devices they carry. The answer increasingly is NO! Wireless devices are becoming progressively more sophisticated and consistently redesigned to provide new generations of services. At one time, a radio only operated when its user activated it. That is not true today. Many services now provided require that the device be continually in contact with the network and that the network sends information to the device as it becomes available. Consider the simple example of your text messages that appear on your device as soon as they are available. You don’t call in to get your messages, they automatically come to you. That means that your device was in touch with the network, and conducted a communications session to receive the message without your ever being aware of it. If a sensitive piece of equipment like some part of an I&C system had been close at hand, an RF interference event could have occurred.

It is common for humans to assume their normal behavior cannot have negative consequences. Too many of us assume our normal eating and exercise habits do no harm, but our slowly increasing waistline foretells negative health issues in our future. Similarly, many people unconsciously assume their various wireless devices cannot cause problems because they haven’t in the past. Perhaps more accurately, the devices caused problems that were easily solved. Most people have heard interference on their computer or television speaker caused by their cell phones, but solved the problem by moving the cell phone or accepted the interference noise while they were on the phone. They experienced interference but its consequences were either easily dealt with or had little impact. However, in this case the past is not the future (is it ever?). Under the right set of circumstances, RF interference can lead to consequences which have much more impact and, once initiated, are much harder to mitigate or reverse, as in the case of interrupting the operation of a critical piece of I&C equipment in a NPP. Sometimes, once the damage is done, little can be put right and the damage is very bad indeed.
The challenge then is either to train people about the circumstances under which more care must be taken or, alternately, to manage the situation so that those circumstances cannot occur. Either approach works, but historically, if a lot of people (e.g., nuclear plant personnel and subcontractors) are involved, getting consistent, reliable behavior is the more difficult approach. It is often easier and more reliable to manage devices rather than people.

EMI Problems: Can They Really Still Occur?

The fact that wireless devices can cause interference is well documented and easily demonstrated in the laboratory. Even manufacturers of cell phones and other wireless devices know this. The fact that there are RF immunity standards, mandatory for CE Marking and many other requirements, and that many products initially fail these tests demonstrates that susceptibility to RF interference is a real issue. Few would argue that RF interference is impossible. However, it is more common to hear the defensive response, “My product passed the XYZ immunity standard. How can my product have a problem!!??”

What is not understood when such statements are made is that all RF immunity standards have a scope and are part of a two-part solution. RF immunity standards are meant to work with RF emission standards to provide a desired level of protection. Standards only work in the context they were written to address, and then only provide the degree of protection they were intended to provide. The commonly used IEC 61000 series of EMC immunity standards were written to provide a basic level of protection to commonly encountered RF environments. The writers of these standards well understand that there are more sever environments and that some kinds of products require a higher degree of protection. Their purpose was to provide general requirements that provide an acceptable level of protection for most equipment. However, as the following examples will make clear, this level of protection is not adequate for all situations or for more sensitive applications.

Medical Device Interference
Cell phone interference with pacemakers was raised as a problem in the 1990s and received considerable attention at the time. However, the issue of RF interference to medical devices is much broader. In a 1998 paper published by the IEEE Engineering in Medicine and Biology Magazine,[2] Howard Bassen of the FDA states:

Hundreds of incidents of RFI induced medical device failure have been reported, studied, and summarized. The most likely source of those failures has been RFI from mobile radio transmitters. The consequences have ranged from inconvenience to serious injuries and death. However, many more incidents may occur that are not reported because most users of medical devices are unaware that RF fields are present when problems are recognized and because of the intermittent nature of the failures that could cause them to be unobserved.

In the mid-1980s, the US Food and Drug Administration (FDA) had become aware that approximately 60 infants died in the United States while being monitored for breathing cessation by one model of apnea monitor. Subsequent tests have shown that this particular monitor is extremely susceptible to low level RF fields, including those from mobile communication base stations several hundred meters away and FM radio broadcast stations more than one kilometer away. Other apnea monitors have been shown to be similarly susceptible to malfunction. This has resulted in voluntary recall of more than 16,000 apnea monitors.

Another device that has demonstrated RFI susceptibility is the electrically powered wheelchair. Unintended motion has been initiated by RFI from transceivers in nearby emergency vehicles, causing persons to be ejected from their wheelchairs or propelled into traffic. New draft performance standards for wheelchairs are being developed by the Rehabilitation and Assistive Technology Society of North America (RESNA) to address these problems; many manufacturers are developing products that conform to these standards.

An additional problem area involves implanted cardiac pacemakers and defibrillators. Teams of engineers and cardiologists in several countries have independently studied these devices, either in patients or tissue simulating models, demonstrating that nearby digital cellular phones sometimes induce undesirable effects. The dominant effect observed has been loss of pacemaker adaptive control, causing the device to deliver stimuli either irregularly or at a preprogrammed fixed rate. This is not usually detected by the patient and, when the cellular phones are moved away, the pacemaker resumes its normal operation. Interference with pacemakers has not been observed when the phones are held at the ear. A panel of researchers has concluded that phone/pacemaker interference should not be considered a major public health concern and has offered specific recommendations for pacemaker wearers. Cellular phones have also been shown to cause unintended firings of implantable cardiac defibrillators.

Recently, handheld digital cellular telephones, that use pulse modulated time division multiple access (TDMA), have been found to disrupt the proper operation of in-the-ear hearing aids. TDMA phones include international Global System for Mobile (GSM) communications and North American Digital Cellular (NADC) pulse modulation formats, which utilize schemes that produce 100% amplitude modulated pulses of the RF carrier at frequencies within the audible hearing range. Subjective perception of interference varies from barely perceptible to annoying and loud, starting when the phones are within one meter of the hearing aids and becoming louder when the phones are several centimeters away. This type of interference also occurs in behind-the-ear hearing aids, making it impossible for wearers of this device to be able to use this type of phone.

Recently, warnings have been published concerning the use of wireless communications equipment in the clinical environment. Hospitals worldwide have recommended that cellular phones and two way radios not be used in intensive care units, operating theaters, and patient rooms, where critical care medical equipment is in use. Measurements that have been made inside an ambulance, where electronic patient monitoring equipment is used, have yielded field strengths of up to 22 V/m in the region of 800 MHz. Recommendations have also been made that patients using medical equipment at home be educated about possible hazards from the simultaneous use of portable telecommunication devices. Extensive measurements have been made to determine the field strengths produced by common RF sources in actual or simulated non-clinical environments, many that are greater than 3 V/m.

This history of medical device interference demonstrates a significant parallel to experiences in NPPs, where the need for constant vigilance of EMI-related interference is well justified. This vigilance is particularly justified by the increasing variety of devices that use wireless connectivity. Today, a powerful transmitter used to connect to the cellular network may not only be a cell phone, but also a laptop computer, electronic book reader, medical device, or even a light pole with a wireless emergency call box. A wireless transmitter may even be in a medical implant located inside an employee’s body.

An example to consider is a Medical Micropower Network (MMN) system, which is an exciting new medical technology currently in clinical trials. In an MMN network, a control unit uses RF communications to receive or send data to implants in a person’s body.[3] Improved treatment for a wide variety of conditions is potentially possible with such devices. As can quickly be seen, if an employee has an MMN network prescribed by his or her doctor, it will be extraordinarily hard to keep the MMN network away from the equipment that the employee works with. Reassigning the employee may be illegal, as the American’s with Disabilities Act (ADA) requires that employers make reasonable accommodations for employees with disabilities. Having digital I&C systems with adequate levels of RF immunity might be considered a reasonable accommodation.

Figure 5: A Medical Micropower Network using RF communication with implants to treat a variety of medical conditions.

The primary point to be made is that, in the future, wireless devices will be operating inside NPPs. Some even will be part of the I&C systems, such as wireless sensors used to report readings from locations where wired connectivity is not possible. As illustrated by MMNs, wireless transmitters may even be implanted in an employee’s body to provide significant health benefits. Labeling wireless devices as “will not cause EMI” and further delaying the development of a wireless device use policy in NPPs is no longer an option. It must be managed intelligently.

Hearing Aid Interference
Early in 1996, the FCC called a Summit between the hearing industry, the wireless industry and consumers to resolve the compatibility issue between hearing aids and cellular phones. Cellular phones using digital technology were then just being introduced in the US. An interference problem with hearing aids had been discovered, and a group of concerned consumer groups petitioned the FCC. The new digital telephones caused many hearing aids to “buzz” due to their RF transmission. In their petition, the consumer groups asked the FCC to deal with the problem and assure that people with hearing aids would have the same ability to use these new technologies as everyone else.

As a result of the discussions held at the Hearing Aid Summit, it was decided that a technical standard was needed which would identify a solution to the EMI problem and develop tests to show that a hearing aid and cellular phone were compatible. In the spring of 1996, the American National Standards Institute (ANSI) Accredited Standards Committee (ASC) C63, which is focused on EMC, formed a task group to develop a measurement standard (C63.19) for hearing aid compatibility with wireless communications devices. The goal was to develop a set of parameters and tests that would evaluate and predict the compatibility of hearing aids with cellular phones. The committee recently released the fourth revision of its standard. Each revision has addressed the changing technologies in phones and hearing aids and improved the testing methodology needed to insure RF immunity.

The challenges presented to the task group were formidable. In order to accomplish this task, several significant technical issues had to be faced. The effort required to complete this project ultimately came to include five research projects and over 90 engineers from 50 different companies and organizations including, the FCC and the US Food and Drug Administration (FDA), working together.

The essence of the problem is that the RF energy transmitted by a cellular phone is received by the circuitry in hearing aids. Once the energy is in the hearing aid it may be audio rectified across some non-linear junction, resulting in a “buzz” of different audible noise levels depending on the modulation used by the cellular phone. Significant effort has been invested in understanding and addressing this issue. This mechanism of interference is well known. The challenge in this case is that hearing aid wearers want to be able to use cellular phones. This means that the hearing aid must be located well into the near-field region of the transmitting antenna. Accordingly, an evaluation of the immunity of the hearing aid must be for immunity in the near-field environment, not the usual far-field test used for immunity testing. These near fields can be an order of magnitude or larger than the “standard” immunity test field.

A second challenge is that, in the near-field, the fields from a wireless device are highly variable in intensity and field impedance. Quantification of the environment in which a hearing aid must operate presents a significant challenge. Movements of only a centimeter can produce significant changes in the field magnitude or impedance.

A third challenge is introduced by the hearing aid wearer. The human tissue in the head and hand has a very significant influence on the field generated by the cellular phone. The question of how to properly account for this field deformation when evaluating a hearing aid’s immunity presents special challenges.

A fourth challenge is that many hearing aids are equipped with a magnetic coupling mode, called the TeleCoil (t-coil) mode, in addition to the primary audio coupling mode. Testing for compatibility in this mode has its own set of challenges. For example, there is the possibility of RF interference and electronic noise in the kHz region which adds a second, independent source of interference with the desired reception.

A fifth problem is that the actual annoying effect produced by the use of a cellular phone is highly dependent on the hearing impairment of the user regarding what is really “heard”.

The measurement techniques developed for ANSI C63.19 allow the accurate evaluation of system performance for a hearing aid used with the new generation of cellular phones or other wireless communications devices. The resulting tests present new methodology for near-field evaluation of system immunity. This experience illustrates several important points. The first is that new RF immunity standards for specialized standards are necessary. The IEC 61000 series of standards on EMC existed when the ANSI C63.19 effort began, but were not adequate for this specialized issue. ANSI C63.19 also illustrates the need to simultaneously manage both emissions and immunity. In the case of ANSI C63.19, both are managed in the same standard. This is somewhat unusual. The more normal arrangement is that emissions are managed by one standard and often by one regulatory agency, while immunity is dealt with in a different standard and often enforced by a different regulator.

Current Practices in Managing the Use of Wireless Devices in NPPs

With the exploding development and use of wireless devices, utilities continue to receive requests for allowing wireless devices in areas of the plant where I&C equipment is installed. Most of these requests result from internal staff, subcontractors and utility personnel not part of the plant staff who must visit the plant as part of job responsibilities. Moreover, security personnel who move through all areas internal to the plant and areas external to the plant on the site must be free to use their wireless devices at any time and without limitations. With no formal industry-wide policy for controlling the approval or use of wireless devices in NPPs, utilities set out to develop their own internal policies or guidelines, realizing that they would continue to mature as more emphasis was placed on this problem. Some examples are listed below:

1. One NPP has restricted the use of cell phones inside their control room. This decision is based on concerns which stemmed from other plants that cell phones can indeed cause EMI problems with I&C equipment.
2. One utility that operates several plants uses a distributed antenna system in each plant for portable radios operating on the VHF band, cell phones from a specific cell phone manufacturer and approved cordless phones. This utility restricts the use of any other cell phones to office and warehouse areas in NPPs. The utility tried to get another cell phone manufacturer to certify the manufacturer’s cell phones to a manufacturing specification, but the manufacturer would not meet their request. As a result, the utility has to test each cell phone model from this manufacturer before allowing the use of that specific cell phone in the plant. Other cell phones have very limited coverage inside these plants.
3. Another utility who operates several NPPs allows intentional transmitters in various areas of the power-block portion of its plants. The utility has some restricted areas that contain sensitive electronic equipment, such as control rooms where only certain intentional transmitters of low power are allowed after they have been evaluated at the plant. The evaluation includes either testing or review of the test report from the FCC submittal of the wireless device, as well as in-situ testing with a setup of electronic equipment that has been shown to be sensitive to radiated emissions from the device. This utility installed a system of slotted coaxial cable in the general areas in most plants for use of portable radios. It also approved some wireless access points and phones to interface with these points. The cables are distributed in limited areas of the plants, including the control rooms. This utility evaluated these wireless systems as follows. It noticed that some modulation and other transmitting schemes had very high peaks of radiated power (many times the stated effective radiated power (ERP)) that do not show up on typical test reports. The peaks do show up on in-situ testing and other evaluations. The utility has requested other specific technical information from cell phone manufacturers, but responses to these requests have been limited. This utility also specifies an “exclusion distance” from electronic equipment that is potentially sensitive to EMI for various approved transmitting devices. The distance is generally three feet for most portable radios and other wireless devices over a few hundred milliwatts. For wireless devices with power levels below 100 milliwatts, this distance is generally one foot.
4. Another utility operating some NPPs states that their control rooms are located inside concrete buildings. The thickness of the concrete prevents wireless power needed to operate pagers and some cellular phones from entering the control rooms. Authorized wireless devices such as wireless telephones used by plant maintenance technicians are allowed to be used in controls rooms.
5. Another utility that owns and operates a number of NPPs does not allow personal cell phones inside its plants. The policy requires that cell phones must be turned off when using electronic dosimeters and at all times in the following areas: power blocks in all buildings, control rooms, cable spreading rooms and relay houses. This utility allows for the use of personal cell phones in the operations and maintenance buildings and in supporting buildings, as well as outdoor areas of the protected and owner-controlled areas. The policies listed above also apply to the line of intelligent interactive cell phones. The use of these policies for these phones stemmed from earlier model cell phones that caused more EMI-related problems in the NPP industry. This utility developed a more mature policy that restricted the use of all cell phones unless an evaluation of the cell phone is done. Usage of a cell phone was allowed because plant workers who came into the plant from the protected area came through the turbine building. This utility has no limitations on the use of older cell phone systems and voice-over-Internet protocol (VoIP) system phones. The utility is aiming to learn how to control wireless devices as they convert their wireless access points to handle data traffic. It also maintains a list of frequencies used by wireless devices inside the plant in an effort to minimize interference problems.

Developing a Wireless Management Plan for Nuclear Power Plants

A complete electromagnetic management plan for an NPP should address the following elements:

1. First, the tradition RF immunity requirements of I&C systems should be updated and kept current with changing technology and EM operating environments. As wireless devices are used inside NPPs, these systems must be tested for and immune to wireless transmitters that may operate in very close physical proximity to them. Having a transmitter operate close to a cable or equipment cabinet not only increases the field strength placed on the I&C system, but introduces near-field effects. The electric and magnetic fields will no longer have a fixed relationship, as they do in the far-field. These field components must be considered separately to adequately evaluate the RF immunity of a system.
2. The electromagnetic management plan assumes that wireless devices are part of plant operations, requires that they be tested for co-existence with other systems, and provides adequate levels of reliability even when the spectrum becomes crowded by the growing use of such devices.
3. The electromagnetic management plan should consider low-frequency, high-impact events. Examples are the terroristic and intentional use of electromagnetic interference, direct lightening strikes, and dramatic increases in the use of wireless brought about by the need for emergency personnel responding to a disaster.
4. Finally, the electromagnetic management plan should be alert to the potential for spectrum crowding, looking for bands that may be used by too many devices. Some systems may intentionally be designed to use difference frequency bands so as to separate them from other wireless transmitters. Alternately, RF power management (such as using femtocell base stations) may be part of the plan, allowing transmitters to operate but at much reduced RF power levels.

Together, these components of the electromagnetic management plan, implemented with insight and expertise, will insure that NPPs are prepared to function in their EM environment, benefit from the use of wireless connectivity, but have adequate protection against interference and band crowding issues that otherwise could prove problematic.

Present EPRI Guidance on the Use of Cell Phones in Nuclear Power Plants: What’s Working and What’s Not

As a result of EPRI’s research on EMC and EMI/RFI issues, it published a first cut at developing guidance for the use of cellular phones in NPPs in 1994. In January 1997, EPRI TR-102323-R1 Guidelines for Electromagnetic Interference Testing of Power Plant Equipment was published. In it, portable transceivers, commercial radios and cell phones were the wireless broadcast devices identified as a continuous, high-frequency radiated source of EMI [see Section 2.1.1 (Sources), Section 2.1.2 (Coupling Mechanisms), Table 4-1 and Table B-1 in TR-102323-R1]. Related susceptibility standards (and guides) MIL-STD-462C: Test RS03, MIL-STD-462D: Test RS-103, IEC 801-3 or IEEE ANSI C63.12 (guide) were also identified as tests that could be applied to I&C equipment to identify susceptibility issues and demonstrate that systems had adequate RF immunity. No further guidance is included in TR-102323-R1 on how to manage the special challenges presented by portable wireless devices. At that time, cell phones were growing in popularity but most were still first generation devices using analog RF protocols. However, by the mid-1990s a second generation of cell phones was being introduced that used digital RF protocols. These devices further accelerated the growth of cell phone use and also introduced a much increased potential for interference. Although the RF power levels of cell phones were the same, the new digital modulation protocols brought a dramatic increase in the potential for EMI problems.

EPRI TR-102323-R2 published in November 2000 and EPRI TR-102323-R3 published in November 2004 provide no further guidance on the use of wireless devices, including cell phones. Further research to determine the propensity of these devices to cause EMI problems with I&C equipment used in NPPs was left for the future.

However, in another EPRI report (Product ID# 1011960, Requirements for the Application of Wireless Technology in the Power Industry published in 2005), one of the Equipment Attributes listed in Section 5.3 (Human Asset Requirements for Wireless Sensor Networks) in a table under Section 5.3.1 (Ability to determine what equipment needs to be, and can be, monitored), the following statement is made under ‘Sensitivity to EMI/RFI’ – “Some equipment itself may be sensitive to electro-magnetic or radio frequency interference. When selecting plant equipment to be monitored, take into account current practices regarding limitations on operation of radios near equipment or control panels.” While it is vital to continue warning plant operators and plant I&C engineers on the propensity for wireless devices (in this case, radios) to cause potential EMI problems in power plants, no specific recommendations for determining which wireless devices (or radio) will likely cause EMI problems is made nor is guidance provided on how to mitigate that risk.

Future Research

EPRI research focused on EMC for NPPs is planned into at least 2013. Through this focus, EPRI engineers are presently utilizing new approaches and methods developed in the EMC industry to solve today’s complex EMI/RFI problems and apply them to solving similar problems in the NPP industry. This focused effort is addressing new test methods, developing new standards to integrate new EMI/RFI mitigation technologies into digital I&C equipment while reducing the schedules and costs of digital I&C upgrade projects, understanding what needs to be done to present and future I&C designs to avoid the use of exclusion zones, developing dynamic interactive training materials and modules, further developing electromagnetic management plans and frequency-spectral management plans, and supporting other activities aimed at reducing the risk of EMI/RFI events occurring in NPPs. In addition, EPRI has designed a programmable in-situ test system that can be used to determine if specific transmitting wireless devices will interfere with digital I&C equipment.

Conclusion

Wireless technology has developed and proliferated to the point where excluding it from NPPs and where utilizing a blanket-approval approach to allow the use of all wireless devices in NPPs are not practical solutions. Today, wireless connectivity is being planned into many I&C systems, such as reporting critical data from 1,000’s of sensors in locations not accessible to plant personnel. What is needed is an RF protection plan complimented by a spectrum management plan which together insure that the risk of interference is adequately mitigated, but further, that the intentional use of wireless transmissions can co-exist and operate at very high levels of reliability.

Taken together, these risk mitigation measures will insure that I&C systems have adequate RF immunity to insure their protection from interference from wireless devices, even interference from low-frequency, high-impact electromagnetic events. Further, wireless connectivity intentionally used in NPPs should be tested for co-existence with other wireless transmission. The ultimate goal is that all systems used in NPPs, wired and wireless, are testing and designed to provide exceedingly high levels of reliability.

References

• Berger, S., Prasad, R., Pawelczak, P., Hoffmeyer, J., “Cognitive Functionality in Next Generation Wireless Networks: Standardization Efforts”, IEEE Communications Magazine, April 2008.
• Berger, S., “Conformity Assessment of Policy-Based Adaptive Radio Systems”, Conformity Magazine, Jan. 2007.
• Berger, S., “Conformity Assessment of Policy-Based Adaptive Radio Systems”, International Symposium on Advance Radio Technologies (ISART), March 2006.
• Berger, S., Drozd, A., Heirman, D., “A New Challenge for EMC-Policy Defined Radio!”, IEEE EMC Society Newsletter, Jan. 2005.
• Berger, S., “ANSI C63.19 – Hearing Aid / Cellular Telephone Compatibility”, IEEE EMC Society Newsletter, Issue 189, Spring, 2001.
• Berger, S., “Understanding Wireless Compliance”, IEEE International Symposium on Electromagnetic Compatibility, Montreal, Canada, August, 2001.
• Berger, S., “Wireless Handsets and Hearing Aids”, EU Ministerial Conference on the Knowledge and Information Society, Lisbon, Portugal, April 10-11, 2000.
• Guidelines for Electromagnetic Interference Testing in Power Plants, EPRI, Palo Alto, CA: 1997.
• Guidelines for Electromagnetic Interference Testing in Power Plants, EPRI TR-102323, Rev 1, Electric Power Research Institute, Palo Alto, CA, 1996.
• Guidelines for Electromagnetic Interference Testing in Power Plants, Revision 2 to EPRI TR-102323, TR-1000603, Electric Power Research Institute, Palo Alto, CA, 2000.
• Guidelines for Electromagnetic Interference Testing in Power Plants, Revision 3 to EPRI TR-102323, TR-1003697, Electric Power Research Institute, Palo Alto, CA, 2004.
• Keebler, Philip F. “Eliminating the Need for Exclusion Zones in Nuclear Power Plants: Part 1,” IN Compliance, June 2011.
• Keebler, Philip F. “Eliminating the Need for Exclusion Zones in Nuclear Power Plants: Part 2,” IN Compliance, July 2011.
• Silberberg, J.L., “Performance Degradation of Electronic Medical Devices Due to Electromagnetic Interference”, Compliance Eng 10(5):25-39, 1993.
• Silberberg, J.L., “Medical device electromagnetic interference issues, problem reports, standards, and recommendations”, Proc Health Canada Medical Devices Bureau Round-Table Discussion on Electromagnetic Compatibility in Health Care, Ottawa, Canada, pp. 11-20, 1994.
• Joyner, K., Anderson, V., Wood, M., “Interference and Energy Deposition Rates from Digital Mobile Phones”, Abstracts Annual Meeting of the Bioelectromagnetics Society 16:67-68, 1994.
• Segal, B., Skulic, B., Liu-Hinz, C., Retfalvi, S., Lorange, M., Pavlasek, T., “Preliminary Study of Critical-care Medical Device Susceptibility to Portable Radiofrequency Sources”, Proc Annual Meeting and Exposition of the Association for the Advancement of Medical Instrumentation 13:83, 1995.
• Tan, K.S., Hinberg, I., “Malfunction in Medical Devices Due to RFI from Wireless Telecommunication Devices”, Proc Annual Meeting and Exposition of the Association for the Advancement of Medical Instrumentation 13:96, 1995.
• Ruggera, P., O’Bryan, E., “Studies of Apnea Monitor Radiofrequency Electromagnetic Interference,” Proc Annual International Conference IEEE Engineering in Medicine and Biology Society 13:1641-1643, 1991.
• Use of Portable Radio Transmitters in Nuclear Power Plants, U.S. NRC Information Notice IN 83-83. 1983.
• Witters, D., Ruggera, P., “Electromagnetic Compatibility (EMC) of Powered Wheelchairs and Scooters”, Proc Annual International Conference IEEE Engineering in Medicine and Biology Society 16:894-895, 1994.

Notes

1. Source: Wikipedia: http://en.wikipedia.org/wiki/Nuclear_power
2. Howard Basen, Radiofrequency Interference With Medical Devices, IEEE Engineering in Medicine and Biology Magazine 17(3):111-114 (1998). Article available at: http://ewh.ieee.org/soc/embs/comar/interfer.htm
3. Guidelines for Electromagnetic Interference Testing in Power Plants, EPRI, Palo Alto, CA: 1994.

Philip Keebler is a Senior Research Engineer in the Power Delivery & Utilization Sector at EPRI with one focal area on electromagnetic compatibility (EMC). Philip received his M.S. and B.S. in Electrical Engineering from the University of Tennessee. Philip is active in many professional organizations, including but not limited to IEEE, Illuminating Engineering Society of North America (IESNA), and the Association for the Advancement of Medical Instrumentation (AAMI), and is Chair of the TC-4: EMI Control within the IEEE EMC Society. Mr. Keebler is also currently working on new EMC standards for the nuclear power plant industry.

H. Stephen Berger Mr. Berger is president of TEM Consulting, an engineering services and consulting firm dealing in regulatory compliance, wireless, voting equipment and EMC.Stephen was the convener and founding chair of IEEE SCC 41, Dynamic Spectrum Access Networks and immediate past chair of the IEEE EMC Society Standards Development Committee. He is a past president of the International Association of Radio and Telecommunications Engineers (iNARTE), a professional certification agency. Currently he works with ANSI ACLASS as a lab assessor and on issues of conformity assessment. Before forming TEM Consulting Mr. Berger was a project manager at Siemens Information and Communication Mobile, in Austin, TX, where he is responsible for standards and regulatory management. He has provided leadership in the development of engineering standards for 30 years, including 5 which have been adopted and incorporated into federal regulations by the FCC. More recently he has been active in the areas of dynamic spectrum access and policy defined radio.