Atomic Energy of Canada Ltd. (AECL) is playing down the danger caused by a so-called "near-miss" at its nuclear reactor in Chalk River, Ont., but says it's still being taken seriously.
An operator mistakenly shut off a pumping system that supplies coolant to the reactor's core, officials of the Crown corporation told the Canadian Nuclear Safety Commission on Wednesday.
But the Feb. 27 incident created no danger, the corporation's boss told the panel, according to the Ottawa Citizen.
“We have and we will continue to the operate the NRU [national research universal] reactor safely,” Randy Lesco, AECL's vice-president of operations and chief nuclear officer said. “This event had no safety consequences to workers, the public or the environment. Cooling to the reactor was maintained at all times.”
Although no one was reportedly in danger, Lesco said AECL was not sloughing off the operator's mistake.
“When we have a human performance event that deals with a reactor operation, we need to take this event very seriously and we’ve done so,” said Lesco.
Unless there's a release of radiation, the public rarely hears about accidents at nuclear facilities, so AECL's session before the commission provided a rare glimpse into what can happen.
The Chalk River site, about a two-hour drive northwest of Ottawa, is Canada's foremost nuclear research facility. It's also the oldest, first established during the Second World War as part of the atomic bomb program. After the war it transitioned into research on the peaceful uses of nuclear energy and production of isotopes used in medicine.
The facility was the scene of two nuclear accidents in the 1950s, the first in 1952, severely damaging a reactor and creating 4,500 tons of radioactive water that was dumped in ditches near the Ottawa River. A 1958 incident involving the NRU reactor contaminated the reactor building and surrounding area.
The NRU reactor, which went online in 1957, was temporarily shut down in 2007 to deal with safety issues, raising concern about a worldwide shortage of medical isotopes during the year-long closure. It also suffered a radioactive water leak in 2008. The reactor was shut down again in 2009 for more than a year after the water leak recurred.
The latest incident seems trivial by comparison but could have had serious consequences.
In their appearance before the safety commission, AECL officials said control room operators were shutting down the NRU reactor for a routine overhaul, the Citizen reported. One operator was to close the valves to the reactor's secondary cooling system.
Instead, he pushed several buttons on the control panel that began closing the valves for the main heavy water pumps, the Citizen said.
Coincidentally, a senior AECL official was taking a visiting official from the World Association of Nuclear Operators through the control room for a peer review. He spotted the mistake and reversed the valves before the closed completely, but not before a "low-flow" alarm sounded, the Citizen said.
David Cox, senior director of NRU operations, told the panel the reactor was running at minimal power levels at the time.
“There would have been no consequences to the fuel if this event had progressed to full-valve closure for many hours,” assuming no corrective action was taken, he said, according to the Citizen.
It's not known why the operator pushed the wrong buttons but the AECL's own investigation ruled out operator fatigue, fitness-for-duty issues or sabotage, Cox said.
Despite the minimal danger, the mistake required a strong response from AECL, commission executive Peter Elder said.
That’s a very unusual type of error to see," he said. "So whenever you see a very unusual error in a nuclear reactor control room you have to treat this very seriously regardless of ... what the causes would be.
“Nothing actually happened, but there was certainly potential for something more serious to happen and therefore it needs to be thoroughly investigated.”
According to a 2011 article in the Guardian newspaper, there have been 33 serious incidents and accidents at nuclear power plants since the first Chalk River meltdown in 1952. That one was rated a Level 5 incident on an ascending scale of 1 to 7.
Level 1 is classed as an "anomaly," the Guardian said, while Level 7 is Chernobyl, the only accident of its kind that's ever been publicly acknowledged.
A 2011 post on the website of the environmental Bellona Foundation warned of an alarming number of emergency shutdowns, or scrams, and unscheduled repairs at Russian nuclear power stations.