NUCLEAR POWER NEW NUCLEAR POWER PLANTS IN 2012
AP1000 IN FEBRUARY 2012, THE FIRST NUCLEAR POWER PLANTS IN THE US IN 35 YEARS WERE LICENSCED TO BEGIN CONSTRUCTION. TWO WESTINGHOUSE AP1000 NUCEAR REACTOR PRESSURIZED WATER POWER PLANTS ARE BEING CONSTRUCTED AT THE VOGLE SITE SOUTH OF ATLANTA, GEORGIA.
OBJECTIVE WE WILL DISCUSS THE EVOLUTION OF THE AP1000 WITH EMPHASIS ON THE IMPROVEMENTS IN PLANT DESIGN.
Why Nuclear Power? Greater fuel efficiency (energy release) Fossil fuel a few ev/ reaction Nuclear fuel 200 million ev/fission No carbon emissions No greenhouse gases Baseline power for electricity grid Plants capable of running 24hrs/day, 365 days/year for up to two years Nearly unlimited fuel supply
Fission One neutron activates a Uranium 235 atom The activated U235 breaks apart (splits) releasing on average 2.7 new neutrons and 200mev of energy The neutrons bang around, slow down, some escape, and one neutron activates another U235 atom (Chain Reaction) The energy released heats the coolant
Basic Design PRESSURIZED WATER REACTOR POWER PLANT STEAM GEN TURBINE REACTOR COOLING SYSTEM
AP 1000 SPECIFICATIONS Produces 1154 MWe (net) Same Footprint as AP 600 Reactor Power 3400 MWt Two Loop, Pressurized Water Reactor Design
Safety Features Passive Emergency Cooling Aggressive Design Simplification Probabilistic Risk Assessment Passive Containment System
Sequence of Events AP 600 is designed with passive safety features and simplified plant systems AP 600 is licensed by the NRC (1999) AP 600 is considered not competitive in the US market at 4.1 to 4.6 cents/kwh AP 600 is scaled up to Ap1000 with cost reduced (economies of scaling) to 3.0 to 3.5 cents/kwh
Sequence of Events (cont'd) AP 1000 Design Certified by the NRC in December of 2005 NRC questioned containment building integrity during severe external events such as earthquakes, hurricanes, and airplane collisions In response, Westinghouse prepared a modified containment design NRC approved the amended design certification in September 2011
Sequence of Events (cont'd) NRC approve the construction of two AP 1000 plants at the Vogtle plant site in Georgia on February 12, 2012
Design Simplification The passive safety systems make extensive use of gravity, natural circulation, and other natural phenomena to perform safety related functions
Design Simplification Passive emergency reactor cooling: requires no pumps, or operator action during an accident Passive emergency containment cooling: requires no pumps, sprays, or operator action during an accident In fact there are no pumps, fans, diesel generators or any rotating machinery required for the safety systems
Design Simplification Since there is no rotating machinery in the safety related systems, there is no need for safety related AC power sources ( i.e. Diesel Generators) The Passive Cooling System uses multiple explosively operated and DC operated valves. No human operator action is necessary. Valves don t rely on hydraulic or compressed air system
Design Simplifications Reduced Components needed: 50% fewer safety related valves 35% fewer pumps 85% less control cable 80% less safety related piping
Scaling: AP600 to AP1000 The AP1000 design starts with the same footprint as the AP600. To allow or the increased power, the power plant and containment are scaled upward. The steam generators are taller, the containment building height is raised 25 ft, and the In-containment Refueling Water Storage Tank (IRWST) capacity is increased by increasing its height.
Scaling (cont d) Only minor changes had to be made throughout the plant to accommodate the increase to 1000 MWe The concept of the original AP600 passive safety system design was maintained
LOCA One of the important safety analysis performed is the Loss of Coolant Accident (LOCA) We can use the response to a LOCA type leak in the primary (reactor) coolant system to illustrate the operation of the emergency core cooling system and the containment cooling system
Emergency Core Cooling The first line of defense the event of a LOCA are the Core Make-up Tanks (CMT) As the reactor vessel depressurizes and the CMTs empty, the Accumulators begin draining After depressurization, the In-containment Refueling Water Storage Tank (IWRST) provides water to the reactor vessel to continue decay heat removal
Containment Cooling After one hour the IWRST begins to boil, sending steam into the steel containment shell The steam is condensed by the shell and water is drained back in to the IRWST The shell is cooled by natural air circulation in the containment building and by water drained from a roof tank
Construction Plant to be built using 270 premanufactured modules, built in factories and shipped to the site Construction planned to take 36 months
China Six units planned in Zhejiang, two under construction for operation in 2013 Six units planned in Shandong, two under construction for operation in 2014
USA Two units each planned at: Shearson Harris in North Carolina Lee III in South Carolina Summer in South Carolina Vogtle in Georgia (under construction) Levy County in Florida Turkey Point in Florida Bellefonte in Alabama
Accident Perspective The plant is designed in every detail so that accidents can t happen Probabilistic Risk Assessments (PRA s) are done at integral with the design to reduce failure rates to near zero For Example: The PRA for the AP1000 risk of core melt is calculated to be 2,4E-7/yr
Accident Analysis So nuclear reactor power plants are designed so that the risk of an accident is (near) zero. Then the consequences of the worst kind of accident are analyzed anyway Then the safety systems are designed to mitigate the consequences assuming the accident occurs anyway