Four times since mid-June, monitors have recorded “spurious spikes” in radiation levels inside the Vermont Yankee plant.
The “false positives” for high radiation levels were a result of faulty equipment that produced inaccurate results and did not indicate there were actual increases in radiation in the building that contains the spent fuel pool, according to Rob Williams, a spokesman for the plant.
Entergy notified the Nuclear Regulatory Commission of the equipment malfunction last week.
On July 26, the Vermont Department of Public Service sent a letter to NRC asking for a “full accounting” of the incidents.
In addition, Darren Springer, deputy commissioner of the department, insisted the NRC require Entergy to report serious equipment “failures” immediately. The first spike occurred on June 14; the state was notified of the incidents on July 25.
Under NRC rules, Entergy has 60 days to file a report.
Chris Recchia, commissioner of the department, said the false positives are alarming because the radiation monitors are the fundamental warning system for the plant. The monitors, he said, must be perfectly calibrated so that the readings are accurate.
“What happens if there was actually a radiation leak and the equipment didn't register anything or didn't register the proper amount?” he said.
Springer expressed this sentiment in the official letter to the NRC, to which the agency is obliged to respond.
“Failure of the radiation monitoring equipment is a serious issue, and could have under other circumstances led to significant harm if the failed equipment had not detected a radiation release at the plant,” he wrote.
Recchia is concerned about the integrity of the aging nuclear power plant, which was built more than 40 years ago. He says he doesn't know to what extent the NRC tested safety systems before it relicensed the plant in March 2012 for 20 more years of operation.
Springer has asked for “any information on the age and functionality of the failed radiation monitors” that was part of the NRC's relicensure decision.
“It feels like these systems need to perform accurately, as intended, and we feel like all the systems are aging,” Recchia said.
In mid-June, Entergy officials blamed a loose electrical connection for the “spurious spikes” in radiation, but were unable to locate the source of the electrical problem.
When the monitors showed elevated levels of radiation again on July 11, July 23, and July 24, the readings triggered the standby ventilation and isolation safety systems at the plant.
Entergy determined the radiation monitors were faulty and will replace four of the devices. Williams says the monitors “did not fail.” “They remained in service and fully able to perform their safety function,” he said. “We made the prudent decision to replace them.”
“We traced the problem back to the monitors themselves,” Williams said. “It was a false signal.”
Williams said the manufacturer had experienced problems with that particular “lot” of monitor devices. He declined to give the name of the manufacturer.
The radiation incidents are now part of the plant's corrective action program, according to Neil Sheehan, the spokesman for NRC's Region 1.
“Replacing the detector and electrical equipment should resolve the issue,” Sheehan said.
The equipment failures did not pose an imminent threat to human health, Sheehan said, because there are other checks and balances in place to protect the safety of workers and the public.
Recchia says he doesn't understand why the monitor failure is “such a low-level incident in NRC's minds.”
The Vermont Department of Public Service takes a less sanguine view of the incidents. “Common sense would dictate that radiation monitoring equipment be functioning properly 100 percent of the time, and that such equipment failures would be immediately reported to regulators and corrected,” Springer wrote.
Arnie Gundersen, a nuclear analyst and critic of Entergy's operation of Vermont Yankee, compared the radiation monitoring failures to a faulty check-engine light.
In this case, it was the light on control panel detecting high radiation near the spent fuel pool, he said.
“It's another age-related problem,” Gundersen said.
Vermont Yankee has had operational and physical plant problems over the past decade, including a water tower collapse, a transformer fire, tritium leaks, missing fuel rods, and condenser issues.