Annals of engineering:Why was a radiation detector on the fritz?

nuclear reactor inside fence with warning sign
False alarms are never a good thing, but particularly bad when they happen at a nuclear power plant. An engineer investigates. (Credit: narvikk/istock/Getty Images Plus)

Before the 1996 establishment of EMC Directives in Europe, engineers had a lot more trouble with sensors in noisy operating environments than they do today.

Up until the mid-1990s, the primary goal of regulations was to protect nearby radio and TV receivers.

What no one was thinking about was the mayhem that incoming radio and TV transmissions could cause electronics equipment. That was until the EU EMC Directive made immunity to RF, ESD, and power disturbances a mandatory requirement.

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As a consultant specializing in EMC, I often was called in when engineers could not figure out why their sensors were going haywire. At one point I received an urgent call from the operators of a nuclear power plant.

If there is one place you absolutely, positively do not want sensors to be misbehaving, it would be a nuclear power plant.

And if there is one place you absolutely, positively do not want sensors misbehaving and get called in as an EMC consultant to investigate, it would be a nuclear power plant.

The particular problem they were having was that every month or so a sensor on a cooling tower would trigger an alarm, indicating a radiation leak. The alarm would subsequently turn out to be false.

False alarms are never a good thing, but in the case of a nuclear power plant there are serious consequences—as so should there be.

When the sensor tripped the alarm, operations were immediately shut down. Personnel then had precisely 30 minutes to confirm whether or not it was a false alarm. If they were unable to do so in the time allotted, they were then required to take the entire reactor offline, likely for months, until an exhaustive investigation could take place.

In the event a false alarm was confirmed, plant officials had to prepare extensive documentation to convince the Nuclear Regulatory Commission of that fact.

Drowning in paperwork, management decided to call me in to get to the bottom of the issue. Needless to say, I wasn’t looking forward to my visit. There is something unnerving about seeing armed guards in the vicinity of a power plant that produces even small amounts of radioactive gasses and liquids.

From past experience I suspected that a handheld radio was implicated. If I could prove that was a plausible theory, my plan of attack was to force a false alarm, which would require coordination with the control center.  

Radios weren't operating in the vicinity of the cooler tower. But then I had a thought: Could by chance the night guard carry a handheld radio when making his rounds? “Yes,” was the answer. Said radio was quickly produced for me to conduct my little experiment.

I then asked the engineers to show me the location of the sensor. High up on a cooling tower, it was only accessible by catwalk. It sure looked like a good place for a watchman to have a smoke and maybe check in by radio.

I scrambled up the catwalk, radio in hand. At the precise time I had alerted the operations team to watch for the radiation alert to go off, I flicked the radio switch on and off a couple of times.

Back at the control room, operators confirmed the alarm had triggered at exactly the time I keyed the radio.

For all the trouble the sensor glitch was causing, it was an easy fix. Back in the day, I always carried along some cheap ferrite beads that could be wrapped along cables to filter out the RFI.

Also a big believer in the belt-and-suspenders method, I had a huge sign drawn up and posted that read: “Do not use a radio within 20 feet of this area.”

Presumably that did the trick as much to my relief, I was not called upon to make a return visit.

Do you have a memorable experience troubleshooting sensors? We've love to hear share your story here on FierceElectronics. Email Karen Field [email protected]

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