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Calvert Cliffs Nuclear Power Plant will present its plan for addressing the potential impact of debris blockage in an emergency recirculation situation to the U.S. Nuclear Regulatory Commission and the Nuclear Reactor Regulation on Tuesday, Jan. 8, during a teleconference.
NRC spokesman Neil Sheehan said that in the last decade, studies indicated the possibility of debris blockage on sump screens and flow paths during emergency recirculation.
The safety issue was established to determine whether the transport and accumulation of debris in pressurized water reactor containments, like Calvert Cliffs, following a loss-of-coolant accident or other high-energy line breaks, if recirculation is credited, will impede the long-term operation of the emergency core cooling systems or containment spray systems, according to a 2007 NRC inspection manual regarding the issue.
In a PWR, such as Calvert Cliffs, pressurized water in a coolant loop carries heat generated in the core to the steam generator where heat from the primary coolant loop vaporizes the water in the secondary loop producing steam. The steam is then directed through the streamline to the main turbine, which causes the turbine generator to turn resulting in electricity.
The concern is that materials, such as thermal insulation, coatings and concrete, in the vicinity of a break during a loss-of-coolant accident would be damaged, dislodged and transported to the recirculation sump and accumulate on its screens. This would result in an increased head loss across the sump screens, which has the potential to exceed the net positive suction head margin required to assure the successful operation of the emergency core cooling systems or containment spray systems.
In 2004, in light of the concern, a letter was sent from the NRC to all holders of operating licenses for PWRs requesting an evaluation of the emergency core cooling system and containment spray system recirculation functions, and that additional actions be taken to ensure system function.
Sheehan said solutions for preventing or lessening the debris blockage possibility have included expanding the size of the screens around the pumps and replacing materials that could flow through the pipes as debris.
Calvert Cliffs, Sheehan said, is planning on enlarging the reactor drains and replacing some insulation by 2014 and then by 2016 making other modifications and replacing additional insulation.
The conference call between Calvert Cliffs Nuclear Power Plant, NRC and NRR staff is scheduled for Tuesday from 10 a.m. to noon, and the public is invited to join.
Anyone interested in participating in the conference call must call Nadiyah S. Morgan with the NRR at 301-415-1016 by 4 p.m. Friday, Jan. 4, to receive the telephone number and the passcode.