1 August 2002
Nuclear, fossil fuel talks ignite
By Ellen Fussell
Bill Sotos knows set points are a key element to ensure safe processes in a nuclear plant. In fact, they're a crucial layer of protection in the overall defense of the plant's design.
Sotos is leading an ISA SP67.04 subcommittee effort to revise a standard on safety-related set points and instrument uncertainties.
"We're expanding into indication uncertainties and emergency operating procedure set points," said Sotos, a senior consulting engineer at STP Nuclear Operating Co. in Wadsworth, Texas. "These include a number of areas we didn't address with the current standard, and there really isn't any other document in the industry to do that."
What's a set point?
A set point is a predetermined value for which, once a process measurement hits that particular value, an automatic action will take place, said Bill Sotos, senior consulting engineer at STP Nuclear Operating Co. in Wadsworth, Texas. "Think of it as a thermostat. When you set your air conditioner to 75°F, if it's a hot day, your house would get hot, and the thermostat would turn on the air conditioner once it got above that temperature."
"The whole design of a nuclear plant is based on layers of protection and redundancy upon redundancy," said Bob Webb, senior project manager at Power Engineers Inc. in Novato, Calif. While a set point malfunction wouldn't necessarily cause a disaster on its own, if a set point in the protection system didn't exist—and other things went wrong—it could endanger the health and safety of the public and those working in the plant, he said.
More on POWID
The Power Industry Division, or POWID, is organized within ISA's Industry and Sciences department so engineers, scientists, technicians, universities, and management can exchange information relating to electricity production.
Sotos and other standards committee members met at this year's Power Industry Division Symposium in San Diego to forge ahead with a deluge of plans for upcoming standards for nuclear power and fossil fuel power plants.
He said there's a real need to expand the scope of the standard to include areas beyond strictly set points.
The committee proposed covering a set of generic instrument uncertainties that could be applied by utilities for a certain population of instrument loops in lieu of doing their own uncertainty calculations.
Instrument uncertainty is related to accuracy of instrumentation, Sotos said. "When determining a set point, you have a value you want to protect; you don't want the pressure to exceed, say, 100 pounds. You have to account for your instrumentation loop accuracy. So you set your set point 5 pounds below the 10-pound set point to make sure you don't exceed it.
Cybersecurity was another main topic of discussion, especially in nuclear standards. The SP67 committee is looking at what kind of standard the industry needs on top of those already developed for cybersecurity in general.
And, of course, time is of the essence in developing standards about security. Yet Sotos said it's difficult to develop them faster than a few years.
"The most difficult aspect is to get committee members and to keep them involved and active for long periods, especially when depending on volunteers," he said.
Now that coal-fired power plants are having to comply with emissions regulations, they look to selective catalytic reduction (SCR) units to solve the problem. But controls for the units are still not standardized. That's why ISA's SP77 Fossil Fuel Plant standards committee plans to write new catalytic reduction standards.
"These units are expensive and need standardized controls so they're controlled safely and efficiently," said Gordon McFarland, director of power plant initiatives at Westinghouse Process Control in Eatonton, Ga., and ISA's SP77 committee chairman.
"A lot of companies have been putting these SCR units in, and there's no set definition on how to control them. So we're trying to come up with a standard to do that," he said.
"To operate the SCR, you inject ammonia into the flue gas—as it leaves the boilers and before it passes through the SCR—and this ammonia in combination with the catalyst causes a chemical reaction so the NOx converts to nitrogen and water," said Cyrus Taft, chief engineer at EPRI I&C Center in Harriman, Tenn.
The standard will reveal what kind of instrumentation control strategy and operator interface you need.
"There are no industry standards on how you should control an SCR that I know of," Taft said. "People are using them, but any time you get into something new, there are always a lot of questions about the right way to do it."
McFarland said the National Fire Protection Agency is also looking at SCR units, so it's a particularly timely issue.
"For these coal plants to keep operating and meet emissions standards, they'll have to do something," McFarland said. "So now SCR seems to be the big way to do it." IT
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