Virtual radiation

The Q-Track radiation worker training system combines a software program that can be used to define a virtual radiation zone with an indoor wireless tracking system that monitors trainees’ movements. When a trainee approaches a ‘virtual’ radiation source within the simulated radiation environment they will receive a realistic dose, rate and alarm from their simulated electronic dosimeter. Q-Dose also tracks the cumulative dose incurred during the training process. Software can be used to record the trainees’ responses, creating a radiation trail mapping their movements. Instructors can later replay this location, dose and rate data so that trainees can review and critique their performance.

The same technology is also used in a simulated survey meter (Q-Dose XL), which students use to survey areas of the plants such as pipes or vessels. Students hold the same meter that they use in the plant with a Q-Track XL attached to the meter face. It creates a realistic survey meter response based on the distance from a given virtual ‘hot spot.’

American Electric Power’s D.C. Cook nuclear power plant is one facility that has been using both the Q-Dose and Q-Dose XL systems to enhance its training programmes.

“We now have the ability to add the virtual radiation environment to any training setting and train on dose reduction while we are training on other routine tasks that we are expected to perform at our plant,” said Milton Paquette, lead instructor for radiation protection training at Cook.

So far the Q-Track Dosimulation system has been to train both operators and radiation protection technicians at Cook. In 2012 it will be used to train supplemental workers for the plant’s spring refuelling outage and other training groups as the year progresses.

The technology was employed at Cook for the first time in July 2011 during operator training conducted in the RP simulator building—a mock-up that is meant to mirror an area of the plant that is within an actual radiation area. The RP simulator is 50 ft by 80 ft in area and comprises four 15x15 foot bays, each containing pumps or pipes that are simulated to contain radioactive fluid.

“Operators carried out a dynamic learning activity (DLA) in our RP simulator building that involved doing a valve line-up and connecting some vent hoses to some pipe connections,” said Paquette.

“In the past, the operators would not have added the ALARA concept to this exercise, or if they did, it would have been based on instructor estimated dose rates and dose accrued,” adds Paquette. (ALARA stands for ‘as low as reasonably achievable’ exposure). Previous RP training at Cook involved the instructor verbalizing the dose rates to the student. Other plants may carry a controller that sends a signal to a student’s handheld meter based on an educated guess of the dose rate. These methods are not as realistic or as accurate as using Q-Track. Radiation protection technicians also use the Q-Dose in a DLA that involved training on radiography and locked high radiation area (LHRA) controls.

How does it work?

Q-Track’s indoor wireless tracking system uses proprietary near-field electromagnetic ranging (NFER) real-time location systems (RTLS). This system, which is similar to GPS, operates at low frequencies (typically around 1 MHz), and long wavelengths (about 300 m). The system requires three types of equipment: a location server, location receivers and tracking tags.

Trainees wear a small lightweight tracking tag, which provides real-time location information to the RTLS.

Location receivers (typically 8x8x10 inches in size) are mounted on the walls and/or ceiling of the training area. In Cook’s RP simulator building four receivers cover four 15 ft x15 ft training bays. At Vogtle—the first plant where the Q-Track technology was installed—six to eight receivers were deployed to cover the plant’s training flow loop simulator. The location receiver picks up low-frequency signals emitted by tracking tags and uses this to calculate the trainee locations. It evaluates two magnetic and one electric field component to determine the location and bearing of the tag. Location data is accurate to 30-100cm (1-3ft). The location data is sent to the Q-Track position server via a built in wireless or ethernet connection.

Displays of training dosimeters are updated to show the cumulative radiation exposure, and internal alarms sound when user-defined radiation thresholds are met. Like the tracking server, the radiation module features web services that allow users to connect to the teledosimeters and configure training sessions. This module also stores historical radiation data for each transmitter tag in the system. From an operator point of view, instructors need to be trained on setting up the system.

Feedback

The system allows instructors to place multiple virtual radiation sources in a safe environment. It also allows them to be moved around to test workers’ behaviour in changing conditions.

“The student is more apt to react to the training simulator ED and then apply that same reaction to the actual ED in the plant,” says Paquette. So far the feedback from Cook is largely positive, although Paquette said that he is working with the vendor to evaluate the need to add more receivers to more closely reflect the environment in the real nuclear power plant. “When we started to use our system in a routine frequency we noticed that the rate of change readings were not a mirror image of the rate of change we see in the plant,” said Paquette.

This disparity could be caused by two contributing factors: the accuracy of the NEFR positioning system (1-3ft), as well as constraints on the size of the virtual source.

“The source that Q-Track allows you to place is a two-foot square. Exactly mirroring what we see in the plant would require inch level accuracy, and as far as I know that technology does not currently exist at a similar price,” Paquette adds. (However, Paquette also says that he has already noticed improvements following the most recent firmware upgrade.)

From mid-2012, plants may be able to use the same software in ‘live’ mode so that operators wearing a dosimeter combined with a communication module (such as Mirion’s WRM and IPAM) can be tracked and produce real radiation maps while working inside real radiation environments in an operating plant, according to John Unden, deputy chief operating officer at Q-Track Corporation. However, putting such a system inside a nuclear plant may not be straightforward and it would need to be assessed for interference with other plant systems.

This article was published in the March 2012 issue of Nuclear Engineering International magazine.