Correct flaw in cooling system of nuclear reactors – orders Nuclear Regulatory Commission

Dangerous Flaw Threatens to Close Nation’s Nuclear Fleet Energy Matters, By Roger Witherspoon, 4 Mar 16 
After four years of increasingly tense internal discussion, seven Nuclear Regulatory Commission engineers have formally petitioned the governing Commissioners to either order the nation’s nuclear power plants to immediately correct a design flaw governing their reactor cooling systems or order them all to shut down.

The flaw is in the original design of the electrical system, and has escaped notice for decades. According to the engineers’ petition, as well as a series of staff analyses on file at the NRC, the design flaw occurs in what is called a “single phase” condition in which little or no electricity is entering the plant to operate its backup cooling systems in the event of a blackout or other event cutting off power from the grid. The result is that the motors of backup generators are underpowered and this can cause their motors to burn out. When that happens, there is no way to keep the reactor core cool.

The seven members of the Electrical Engineering Branch in the Office of Nuclear Reactor Regulation, led by Acting Chief Roy K. Mathew, stated in the petition that “the staff determined that all nuclear facilities are susceptible to this design vulnerability except one plant, and recommended that the NRC take prompt regulatory action.”

As a result, the petition states, if the plants are not ordered to immediately redesign their electrical systems then the Commissioners should “issue Orders to immediately shutdown the operating nuclear power plants since the licensees are operating their facilities without addressing the significant design deficiency…and with inoperable electric power systems….”

The situation evolved from an unplanned shutdown in January 30, 2012 in Unit 2 of the Byron Station Nuclear Power Plant in Illinois. At the time, it was thought that the shutdowns resulted from a string of unfortunate coincidences. But further examination by the NRC’s electrical engineering branch found something more alarming…………

Officials from Exelon, which owns and operates Byron and 10 other nuclear power plants, as well as inspectors from the NRC initially thought that the shutdown was the result of a series of unfortunate coincidences. But On Feb. 28, 2012, there was a similar interrupted and undetected phase which caused a shutdown at Byron’s Unit 1. And, as in the earlier event, it disabled the plant’s cooling systems. That caused Mathews and the  electric unit he led to investigate further and see if there had been any other shutdowns in which an undetected phase disruption disabled the cooling pumps.  Their initial look found identical shutdowns at the Beaver Valley Power Station Unit 1 in Pennsylvania in November, 2007; and in New York, the James Fitzpatrick and the neighboring Nine Mile plants, which share a power substation, shut down in December, 2005.

The staff analysis concluded that the design of the electrical systems was “inadequate because it did not consider the possibility of the loss of a single phase… This situation resulted in neither the onsite nor the offsite electric power system being able to perform its intended safety functions” to provide electric power to the plant’s safety systems. Plants are required to have two separate sets of electrical power lines and monitors for  their core cooling systems so that operators can still control the reactor even if one line, or train, is damaged by fire or another event.

The loss of a single phase of alternating current, the NRC staff found, “can potentially damage both trains of the emergency core cooling system.” In that case, there is nothing to prevent a meltdown………..

Not only does this situation affect the 99 operating reactors, it also applies to the four AP1000 plants under construction at the Vogtle Plant in Georgia and the Sumner plant in South Carolina. That is because these plants are a new design, and while their safety systems appeared sound on paper and in simulations, they do not work as planned when actually built and require design modifications to meet actual operational needs. As a result, a Feb. 26, 2013 staff analysis found that the electrical systems are incomplete and are still being designed.

“In addition,” the staff assessment concluded, “the generic AP1000 plant operating procedures are under development and the licensees’ review of the generic procedures did not identify specific operator actions related to phase voltage verifications of the three phases.”

As a result, the electrical group concluded, all of the nation’s nuclear plants are violating the terms of their operating licenses and must either be brought into compliance or shut down.

According to NRC statutes, this is a major issue.

NRC regulations governing the operating licenses dictate that “the safety systems shall be designed so that, once initiated automatically or manually, the intended sequence of protective actions of the execute features shall continue until completion.”

The group’s petition states “any failures in an offsite power system or onsite power system must not disable the safety functions of emergency core cooling and vital safety systems to protect the health and safety of the public.”

With the current system, they assert, the plants are violating a mandatory condition of their operating licenses ( ).   As the issue was debated within the agency, the Mathews group cast a wider net and began looking at the root causes of shutdowns in the US and abroad, while pushing the agency to more forcefully addresses the design problem. To their surprise, they found 13 “open phase events” over a 14-year period, with the latest taking place at the Oconee Nuclear Power Station in South Carolina in December, 2015…………


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