http://msnbc.com/news/729694.asp THE CORRODED cavity was found in the reactor vessel head at FirstEnergy’s 25-year-old Davis-Besse nuclear power station in Oak Harbor, Ohio. During a scheduled refueling outage that began Feb. 16, engineers found boric acid — used in the primary coolant bath surrounding uranium rods in the reactor core — had leaked at the base of five of the 69 control rod nozzles that penetrate the reactor vessel head. The bottom of the Davis-Besse reactor vessel head before the corrosion. At one of the nozzles, the acid had eaten all the way through the 6-inch thick vessel head — a massive 150-ton, 17-foot wide piece of carbon steel bolted down on top of the reactor. Federal inspectors said the hole was the largest ever discovered on top of a U.S. nuclear plant reactor. The corrosion was so severe that a 3/8-inch thick stainless steel liner inside the reactor was the only barrier left between the reactor core, which operates under enormous pressure, and the metal shroud surrounding the reactor vessel. A second but smaller cavity has also been discovered. BACKUP SYSTEMS Advertisement While FirstEnergy and federal Nuclear Regulatory Commission officials described the corrosion as “serious” and “not anticipated,” they point out it posed no danger to the public since the entire reactor is housed in a steel-reinforced concrete containment building. Even if the acid had penetrated the massive cap and allowed steam to escape, safety systems would have immediately cooled the reactor, said NRC spokesman Jan Strasma. The steam would contain some radioactive material, but would have been confined by the reactor containment building. Anti-nuclear activists counter that it would only take the failure of a backup system to start a chain reaction that could lead to a meltdown of the reactor core. Boiling-water reactorPressurized-water reactorPebble-bed modular reactorGas-cooled reactor BOILING-WATER REACTOR Water is used as both coolant and moderator, and it boils in the radioactive core. The steam can be used to drive a turbine and electrical generator, which produces electricity. To view the reactor, click here. (MSNBC is not responsible for content of Internet links.) PRESSURIZED WATER REACTOR Water is kept under high pressure and at a high temperature in the primary system. The heat is transferred from the core to an exchanger by the water. Steam is produced in a different circuit. This is the most widely used reactor to produce electricity. To view the reactor, click here. (MSNBC is not responsible for content of Internet links.) PEBBLE-BED MODULAR REACTOR An experimental, small-scale reactor using helium gas to turn a gas turbine. Natural radiation, convection and conduction are sources for cooling down the core. Modular construction lowers costs. To view the reactor, click here. (MSNBC is not responsible for content of Internet links.) GAS-COOLED REACTOR Widely used in Europe, this reactor uses gas both to cool the radioactive core and to run gas turbines that create electricity. To view the reactor, click here. (MSNBC is not responsible for content of Internet links.) Printable version OTHER PLANTS TOLD TO CHECK Concerns raised by Davis-Besse have spread far and wide through the industry, prompting the NRC last week to order operators of 68 other pressurized water reactors — more than half of the nation’s 104 nuclear generating units — to double check the condition of their reactor heads and report back by April 1. Boiling water reactors, the other basic design used at U.S. nuclear power plants, were exempt from the order. The NRC has been aware of tiny cracks forming around nozzles in some reactor heads for over a year and repairs have already been carried out at some plants. But none of the reactors inspected so far has shown anywhere near the damage found at the 860 megawatt Davis-Besse unit. EXPENSIVE FIXES Aside from safety concerns, the economic implications of the discovery are huge. The fear of other plants closing for repairs is pushing up energy prices as traders brace for the possibility of shrinking nuclear supplies over the next few months. Nuclear accounts for 20 percent of U.S. power generation. “The markets are behaving as if lengthy outages are a strong possibility. But it’s still too early to tell,” Sam Brothwell, utility analyst with Merrill Lynch in New York, told Reuters. At Davis-Besse, FirstEnergy estimates that in a best-case scenario, repairs to the reactor head will take three months and cost $10 million to $15 million. In a worst-case scenario, it could take two years. That’s the time it would take to manufacture a replacement head. While the company hopes judicious welding work can patch the hole, FirstEnergy officials confirmed that in February they ordered a new reactor head from Framatome ANP, Inc. in France for delivery in 2004. FirstEnergy estimates the cost of replacing the reactor head at about $20 million. And downtime at Davis-Besse, which generates 7 percent of FirstEnergy’s electricity, will force the company to spend anywhere from $10 million to $15 million a month buying replacement power for the 4.3 million customers served by its seven subsidiary utilities, they said. OTHER PLANTS The problem has focused industry attention on six other plants, all sharing the same Babcock and Wilcox design as Davis-Besse and all built about the same time. The plants in question include the Crystal River 3 nuclear power station in Florida, owned by Progress Energy, and Duke Energy’s three reactors at the Oconee plant in South Carolina. The other two units in the group are Entergy’s Arkansas 1 unit in Arkansas, and Amergen’s Three Mile Island 1 reactor in Pennsylvania. Entergy, Progress Energy and Amergen officials said reactor heads at their plants had all been inspected and repaired as needed during scheduled refueling outages last autumn. Duke Energy, the first to grapple with this problem, found small cracks and boric acid leaks at one of its three Oconee units back in November 2000. Since then, Duke has checked and repaired all three Oconee reactor heads, and ordered new heads for each unit, scheduled for delivery next year. Lawmaker: 'Black holes' in plant security EYES ON NRC REVIEW Meanwhile, the energy markets are anxiously awaiting the NRC’s review next month of the inspection and maintenance reports requested from plant operators, on which it will decide the need for further inspection outages. “This is the next big thing to watch,” said Merrill Lynch’s Brothwell. “So far, this is still a single-plant and single-company issue. However, if it spreads, it could rekindle the nuclear risk premium of yesteryear,” he added. The NRC has its own team of engineers and metallurgists at Davis-Besse and others at the headquarters working on the corrosion problem. David Lochbaum, representing the Union of Concerned Scientists, participated in an NRC meeting last week on the issue and said afterward that he was satisfied the agency is properly handling the situation. “Their answers were helpful,” he said, while adding that “there is still a lot that is unknown.” The NRC has created a special section on its Web site with background, at www.nrc.gov/reactors/operating/ops-experience/vessel-head-degradation.html.
