By andy Marso
WASHINGTON – Calvert Cliffs Nuclear Power Plant General Manager Thomas Trepanier warned his employees about a pattern of “tolerating degraded roof conditions” at the 35-year-old facility last year after water damage shorted out backup power systems, leading to a weeklong shutdown.
“The station had developed a reactive culture rather than a preventive strategy on dealing with roof leaks, thereby eliminating an increased sensitivity,” Trepanier wrote in an internal PowerPoint presentation about the incident.
Trepanier titled the presentation “Calvert Cliffs: A Case for Change.” It includes pictures from the leaky section of roof and, after a slide titled “So What?,” has pictures of the interior of the Three Mile Island plant that leaked radiation in Pennsylvania in 1979.
“We must use these events as a burning platform to identify all issues and understand the extent of condition to arrest this decline and improve plant performance,” Trepanier wrote near the end of the presentation.
He then complimented the employees saying, “Good human performance, fundamental behaviors and training prevented the situation from deteriorating.”
Trepanier also warned his staff that “Events are lagging indicators of the direction of the plant.”
According to Nuclear Regulatory Commission inspection records, a roof leak at the Calvert Cliffs plant shorted out one of the Unit 1 reactor’s two electrical distribution buses on the morning of Feb. 18, 2010. This caused the emergency diesel generators to kick in automatically, but a failure of an electrical relay caused one of the five generators to stop working.
Massive generator failures led to the current crisis at the Fukushima nuclear plant in Japan.
“The emergency diesel generators — as came into play in Japan — are a backup source of power,” said Dave Lochbaum, the director of the Nuclear Safety Project for the Union of Concerned Scientists. “So if they don’t work when you need them to, there’s a safety significance.”
NRC inspector Glenn Dentel said the Calvert Cliffs roof leak may have been caused by excessive snowmelt after blizzards hit the area. He and his team found that the plant’s operators had not adequately prioritized roof repairs to protect the most sensitive equipment first.
“The leak that ended up impacting dripped down in the cabin that had electrical equipment,” Dentel said. “Obviously electricity and water ended up in a short. That’s not where you want it to be leaking.”
After evaluating the incident, the NRC issued a rare “white” finding — the third-most severe rating in its “green, white, yellow, red” system. According to NRC data, there were 819 green findings, 9 white findings, 2 yellow findings and 0 red findings at the nation’s 104 nuclear reactors last year.
Mark Sullivan, communications director for the Constellation Energy Nuclear Group, which operates the plant, said via e-mail that Trepanier’s PowerPoint was “an internal document for an employee meeting that was presented at an industry human performance working group.”
The presentation was available online on the Department of Energy’s “Operating Experience” Wiki page. It was removed a few hours after Capital News Service called Sullivan for comment.
Sullivan also said the company had learned from the incident and worked to fix the problems.
“As soon as we found out we had roof leaks, we put an employee team together, we jumped on it and we came up with solutions to the problem so it doesn’t happen again.” Sullivan said in a phone interview. “I don’t know what else to tell you. Every business has issues that you deal with and that’s exactly what we did in this case.”
But NRC’s latest inspections show that Calvert Cliffs had more problems with water buildup as recently as December. The facility had three “green” findings in an integrated inspection report dated Jan. 28, 2011, including one for “submerged safety related (SR) cables including the 1A diesel generator (DG) cables.” The inspection report warned that “repeated submergence of medium voltage cables can cause excessive aging and degradation in the exposed sections of the cables, which could significantly shorten its qualified life and cause unexpected failures.”
“We determined that their actions were not effective for addressing that, and that’s why we ended up giving the green finding,” Dentel said. “The reason it wasn’t any more significant is that, actually, though the cables had water, they … still performed their designed function.”
Dentel also said that the submerged cables should not necessarily be connected to the leak that caused the Feb. 18 incident, because they were in a different area of the plant.
But the NRC is clear on the fact that water and electrical cables — even insulated ones — don’t mix. The agency issued a generic letter in 2007 titled “Inaccessible or underground power cable failures that disable accident mitigation systems or cause plant transients,” in which it warned that water damage was leading to electrical failures, especially in cables more than 10 years old.
“At each nuclear station, there may be only a dozen or so power cables installed in locations susceptible to moisture-induced damage,” the letter stated. “The low number of cables notwithstanding, the staff identified 23 licensee event reports and 2 morning reports since 1988 regarding failures of buried medium-voltage, alternating current (AC) and direct current (DC) low voltage cables from insulation failure. The staff has knowledge of several other cable failures that were not required to be reported and therefore, these reported events are only a fraction of all failures.”
At Fukushima plant, a tsunami overwhelmed backup generators and cut off-site power on March 11, leading to a failure of cooling systems and the release of dangerous levels of radiation.
At Calvert Cliffs last year the water damage was much less dramatic and much more easily contained. Workers tied in an alternate power source and “Reactor Coolant System temperature increased slightly,” but “there were no actual nuclear safety consequences,” according to NRC. The agency sent a team of inspectors and the plant was shut down voluntarily until Feb. 26.
In e-mails, Sullivan said all of Constellation’s nuclear plants had multiple backup safety features and that the company had spent $26 million in safety and security enhancements at Calvert Cliffs.
Mohammad Modarres, a professor in the nuclear engineering department at the University of Maryland said in an e-mail that while the Feb. 18, 2010, shutdown was “an important event” it was not very serious “since the plant had not lost all its normal power and had emergency cooling capability.”
He said it also illustrated the effectiveness of the backup power systems at Calvert Cliffs, which sits in Lusby, Md., about 50 miles from downtown Washington, D.C.
“It shows that the general designs of nuclear plants are robust due to its defense-in-depth design philosophy (availability of multiple ways and barriers to prevent or mitigate events),” Modarres wrote.
The NRC did a follow-up inspection of the systems that failed in the “white” incident last week and Dentel said the agency will release its findings in about a month.
