Vibration Worries Delay Vermont Yankee Nuclear Power Review

WASHINGTON, DC, October 18, 2004 (ENS) - Entergy Nuclear has applied for a license to increase the power output from its Vermont Yankee Nuclear Power Station, but the application is being held up until the Nuclear Regulatory Commission is satisfied that a reactor part known as the steam dryer will not break apart under the increased vibration, as occurred twice at an Illinois plant.

The 510 megawatt boiling water reactor (BWR) is located five miles south of Battleboro, Vermont. It is the nation's oldest nuclear plant to try for a license to increase the amount of power it generates.

The Nuclear Regulatory Commission (NRC), which licenses nuclear plant power increases, called uprates, says Entergy has not provided enough information about the Vermont Yankee's steam dryer.

As a result, the assessment of Entergy's application for a 20 percent uprate will be delayed past its original January 31, 2005, completion date, the commission said.

Vermont Yankee Nuclear Power Station on the Connecticut River near Brattleboro, Vermont (Photo courtesy RadJournal)

Emergency room doctor Ira Helfand from Northampton said, "My emergency room cannot deal with the casualties that would be produced by an accident at this plant. Nor can the emergency rooms at Greenfield, or Keene, or Brattleboro. This plant should not be uprated. It should be shut down."

The steam dryer problem was explained in a January 9, 2004 document by William Beckner, who serves as chief of the Reactor Operations Branch in NRC's Division of Inspection Program Management, Office of Nuclear Reactor Regulation.

"When operating above the original licensed thermal power level," Beckner wrote, "BWR plants can experience a significant increase in the velocity of the steam generated from feedwater in the reactor core and directed through piping to the plant turbine generator."

"This increased steam velocity could damage plant components through flow-induced vibration," Beckner wrote.

The NRC is concerned that the increased vibration will cause parts of the the steam dryer to break off and fly around, damaging other parts of the reactor, the way it did after an uprate was allowed at the Quad Cities Nuclear Power Station Unit 2 near Moline, Illinois.

In June 2002, after the NRC allowed an uprate of 17.8 percent at the Quad Cities 2, a cover plate on the outside of the steam dryer "broke loose," the NRC's report on the incident states, "and caused pieces of the dryer to be swept down the main steamline."

Quad Cities Nuclear Power Station on the Mississippi River (Photo courtesy NRC)

The steam dryer the final stage of the steam separation system that removes water from steam in a boiling water reactor. This is done to ensure that the steam hitting the turbine blades that turn to generate power causes minimal erosion. The blades are large and steam laden with water can cause severe erosion and wear of the blades, the NRC explains.

The steam dryer is not classified as a safety-related part so it "has received less attention by the licensee and the NRC during preparation for nuclear power plant operation above the OLTP [original licensed thermal power] level, the commission explained in its reason for extending the date for completion of Entergy's application review.

"Although performing a nonsafety-related function, the steam dryer in a BWR plant must maintain its structural integrity to avoid loose dryer parts from entering the reactor vessel or steam lines and adversely affecting plant operation," the commission said.

Other parts of the power plant might also be affected by increased vibration. In addition to the BWR steam dryers, "flow-induced vibration during nuclear power plant operation above the OLTP level can potentially damage other plant components," Beckner wrote.

Jim Dyer, director of the commission’s Office of Nuclear Reactor Regulation, said the agency, "will not allow an increase in Vermont Yankee's operating power level unless we are certain the change could be done safely.”

This is a higher level of assurance than previously stated by the NRC, which says in the section on its website about the Vermont Yankee uprate, "We will only approve a license amendment request if there is reasonable assurance that the health and safety of the public can be protected by operation in the proposed manner."

Early in the review process, the commission says its staff made it clear that operating experience from other plants, which had performed uprates similar to what Vermont Yankee proposes, "raised an important generic issue for the review concerning the potential for steam dryer failures following implementation of a power uprate."

The commission has repeatedly requested more information from the company, but is still not satisfied.

In a letter to Entergy, Ledyard Marsh, director of NRC's Office of Nuclear Reactor Regulation, said, “During the review, in an attempt to resolve our steam dryer concerns, the NRC staff has requested additional information, held three public meetings with Entergy, and performed an audit of the steam dryer analysis at the General Electric office in San Jose, California."

"Based on review of the information provided in the application, the supplements received through October 7, 2004, and the results of the audit, the NRC staff has determined that the information submitted by the licensee to date does not yet provide sufficient assurance that the VYNPS [Vermont Yankee Nuclear Power Station] steam dryer will remain capable of maintaining its structural integrity under [uprate] conditions."

Even without the added vibrational load that an uprate would impose, in April Vermont Yankee outage workers identified minor hairline cracking in the plant's steam dryer. The condition was found in a inspection conducted by the General Electric company, Vermont Yankee's original designer, after similar conditions were found at other U.S. boiling water reactors.

Entergy Vermont Yankee Site Vice President Jay Thayer said the cracks were not in the areas of the steam dryer that had presented problems at other plants. "These were in non-stressed areas of the dryer that are not exposed to heavy steam flows. In fact, the components of the dryer that carry most of the load - the ones that presented problems at other plants - are in good shape."

"However," said Thayer, "in accordance with our uprate engineering analysis, those will be replaced with heavier steel plates."

During the audit and the most recent public meeting, Entergy staff indicated that further information will be submitted to address the NRC staff concerns related to steam dryer integrity.”

The additional information is needed before NRC staff can complete a draft safety evaluation on the proposed uprate, and will therefore delay review by the Advisory Committee on Reactor Safeguards, an independent group of nuclear experts.

Once Entergy provides the information and NRC staff carefully reviews it, a more definitive schedule for completing the uprate review will be available, the commission said.

Residents who oppose the uprate reminded NRC officials at the March public hearing that the Vermont Yankee already has generated more than 500 tons of nuclear waste, now stored beside the Connecticut River. An uprate, they warned, would mean the power plant would create more waste, at a faster rate, with no good disposal solution in sight.

To see the NRC's Vermont Yankee FAQs page click here.

The read Entergy's uprate application click here.