Vermont Yankee fixes new leak, powers plant back up

first_imgAs of Tuesday afternoon, the plant is operating at 100 percent power ~615 megawatts after reconnecting to the New England power grid early Saturday morning. Plant power will vary slightly over the next several days while operators perform rod pattern adjustments to the reactor to achieve 100% steady state operation.Source: Vermont Yankee. 6.1.2010 Northstar Vermont Yankee,During plant start-up activities Friday night, plant operators at the Vermont Yankee nuclear power plant in Vernon identified a condition described as vapor and water dripping in the Advanced Off Gas excavated area. The volume was estimated to be extremely small and occurred over a period of approximately four hours. According to Yankee, this was a new leak. The leak has been stopped and there is no leak at this time. Yankee said there is no threat to public health or safety.The vapor and water dripping was identified at approximately 7:30 pm during warm up of the AOG system. No leakage was visible after warm up and shortly after the AOG system was placed in service. The leak was located on a two-inch drain line and is approximately one-eighth of an inch in diameter.The vapor and water dripping was observed coming from the end of a concrete enclosure surrounding a two inch drain line in the AOG excavation just before the pipe enters the wall of the drain tank room. Soil testing of the area was performed and tested positive for several radioisotopes in a one-foot radius from the leak source.The surface areas where water had previously been observed were sampled for surface contamination.  Samples were positive for tritium.  A sample of wood that had been exposed to the leak and soil below the leak site showed measurable levels of radio-isotopes.  Isotopes detected were chromium-51, manganese-54, cobalt-58, cobalt-60, zinc-65, zinc-69, niobium-95, rhodium-105, xenon-131, cesium-137, barium-140 and lanthanum-140.  Some of these isotopes (rhodium-105, xenon-131, barium-140 and lanthanum-140) are short lived and are evidence that the contamination was recent.Yankee said its current plans are to remediate the soil at the area of the leak and evaluate the condition of the two inch drain line. Repair options under evaluation include removing the line from service, replacing the line, or performing an on-line leak repair. The identified leak should not reoccur during normal plant operation, with the AOG system in service.The NRC and State of Vermont were notified.Vermont Yankee was reconnected to the New England electrical grid shortly after midnight Saturday.On Sunday and Monday, Vermont Yankee engineers and maintenance personnel worked to develop a repair technique to isolate the 2 inch AOG drain line, which was the source of minor leakage during plant startup on Friday night.  During development of the procedure, a test mock-up was made that simulated actual condition in the in-service pipe.  The repair process involves drilling into the pipe at two locations and injecting compounds that harden as they cure.  A different compound is then injected between these two locations that expands to become a rubber like plug.The technique was validated about midday on Monday, and repairs were then begun on the 2 inch drain line.  The repairs were completed by about 6:30 pm on Monday.  This effort successfully isolated this line within the AOG Pipe Tunnel, by installing the sealing materials, and the AOG Drain Tank Room, by closing an existing valve.   This effectively removed the portion of the system within the excavated area from service. No steam or water is currently flowing through this drain pipe. Vermont Yankee said that it should be noted that there was no leakage from this pipe since the recent leak occurred and was terminated during the evening of May 28th. Conditions for the leak in the drain line to occur only exist for a short time during plant start up.  That is the reason leakage was not detected earlier during normal operation.Following isolation of the drain pipe, workers today are in the process of removing contaminated soil from the area.  Excavation is expected to be completed on Wednesday.  Groundwater samples taken at the nearby GZ-10 well on Sunday and Monday showed no detectable levels of tritium.The leak has been entered into Vermont Yankee s corrective action process which will determine the cause of the event and how it can be prevented in the future.last_img read more