Presentation on theme: "James Anderson John Hansen Joshua Perez Clay Taub Small Modular Reactors."— Presentation transcript:
James Anderson John Hansen Joshua Perez Clay Taub Small Modular Reactors
Overview Background and Motivation Toshiba 4S NuScale Babcock and Wilcox mPower Pebble Bed Modular Reactor (PBMR) Hyperion Power Module (HPM) Power Reactor Innovative Small Module (PRISM) Challenges
Background and Motivation Small scale nuclear reactors are classified by the IAEA as delivering less than 300 MWe. Demand for energy continues to increase while heavily centralized grids are strained to provide supply. Remote communities require either dedicated fossil fuel power supply or long power lines, both of which are expensive and inefficient. Modular designs must be versatile, expandable, and safe. “Battery” type designs must be proliferation-resistant, safe and simple to operate.
Toshiba 4S 10 MWe (30 MWt) or 50 MWe (135 MWt) Liquid Sodium Coolant Power control using on mobile reflectors, coolant temperature, and central absorber rod Metallic U-10Zr Fuel (19.9% Enrichment)
Toshiba 4S – Fuel Cycle Fuel can either be metallic Uranium or Uranium and Plutonium, both with 10 wt% Zirconium, with fissile material enrichment at or below 19.9% Fuel is to be bred within the reactor (breeding ratio of 0.69), in order to increase longevity rather than for fuel production. Refueling does not occur. After 30 years, the entire reactor vessel is removed and replaced with a new one (nuclear battery). Fuel Pins Reflectors Gas Cavities Control Rod
Toshiba 4S – Heat Removal Primary and secondary sodium coolant loops cool the core, with steam generation taking place with the second loop. Primary sodium does not leave the reactor vessel, is circulated by EM pump through core and into intermediate heat exchanger (IHX) above core. Secondary coolant flows through top of reactor vessel, out of the core into double wall steam generator. Steam passes through turbine in adjoining facility and is condensed. Electromagnetic pump eliminates mechanical component of cooling within reactor vessel. Double wall steam generator lessens chance of water- sodium leak and interaction.
Toshiba 4S – Reactor Control Reflectors are used to manage neutron population and thermal power output. Six silicon carbide (SiC) reflectors encircle the bottom of core and are slowly moved up the core by 1 mm/day to compensate for burn-up during the reactor lifetime. Core can be shut down by allowing the reflectors to fall below the core. Raising reflectors above the rest inserts negative reactivity, with up to -400 being inserted when 3 reflectors are at the bottom of the core and three are above them. Gas-filled cavities positioned above the reflectors prevent reflection by sodium coolant.
Toshiba 4S – Reactor Control (Cont.) Additionally, core inlet temperature can be reduced by increasing water flow rate through steam generator. This allows for fine control within 10% of rated power. If this is not adequate, reflectors are used for further reactivity control. A boron carbide (B 4 C) control rod is located in the center of the core. For the 50 MWe configuration, this rod is withdrawn after startup and is only used for shutdown of the core. For the 10 MWe configuration, this rod remains in the core for 15 years while the reflectors are moved up the core, then removed and reflector position reset to the bottom of the core for the next 15 years.
Toshiba 4S – Safety Below 350°C, the stainless steel lifting mechanism does not grip Cr-Mo absorbing rod guide, preventing the rod from being withdrawn. Core section of reactor vessel is underground. Negative temperature and void coefficients of reactivity maintained throughout life of core
Toshiba 4S - Safety In the event of a loss of decay heat removal capability, PRACS and RVACS are utilized Primary Reactor Auxiliary Cooling System (PRACS) sinks heat from secondary sodium loop into air cooler; is a partially active system. Reactor Vessel Auxiliary Cooling System (RVACS) drafts heat around structures surrounding reactor vessel; is completely passive. Tests show these systems can operate at below half capacity and still effectively cool core, even in situations such as an aircraft attack.
Toshiba 4S – Regulatory Status and Future The 4S design is currently under pre-application review and Toshiba expects design approval by 2014. The town of Galena, Alaska, hoping to replace its costly diesel generators as the main source of power, approached Toshiba and the US DOE to consider installing a 10 MWe 4S reactor to provide power and stimulate the local economy. The matter is still unresolved, but pending NRC approval, there is hope that the reactor will be in place before 2020.
NuScale Design Created by NuScale Power Inc., is a 45 MWe (160 MWt) PWR which resembles PWR designs currently in use, but at a smaller scale and operating at lower pressure and temperature. Reactor vessel houses the core, primary water loop, and steam generators. RV is surrounded by vacuum in containment vessel, which is submerged in pool of water. Fuel: Uranium Dioxide
Babcock and Wilcox mPower 125 MWe modular plant to be constructed on existing B&W manufacturing infrastructure currently used for US Navy nuclear power equipment. Design is similar to in-use PWR plants, and B&W possesses wealth of experience building small reactors for the Navy. Design certification to be applied for in 2012, and construction expected to begin in 2020.
Pebble Bed Modular Reactor South African design based on German AVR test reactor, using TRISO fuel and helium primary coolant loop, with intended 165 MWe (400 MWt) power output. Lost all government funding in 2010 and its future is in question China is considering a similar design, currently embodied by the HTR-10, acting as a testbed for modular nuclear power and clean hydrogen generation.
Hyperion Power Module (HPM) 25 MWe (70 MWt) transportable design, fueled by uranium nitride and cooled by a lead-bismuth eutectic primary coolant loop within the reactor vessel. Intended to function as a “nuclear battery” (similar to 4S), completely sealed and refueled by replacing entire reactor.
GE Power Reactor Innovative Small Module 311 MWe (840 MWt) modular reactor intended to operate in conjunction with Advanced Recycling Center, where spent LWR fuel is converted into metallic fuel for use in the PRISM reactor. Sodium cooled, with reaction control and shutdown mechanisms similar to the HPM and containment cooling systems similar to the 4S. Intended to burn actinides and breed fuel for further recycling.
n_flux3 Reactor Configuration Uses three regions to simulate the 4S reactor: The “Core” region is a finite cylinder that is 4 meters tall, and.8 meters in diameter. The “Neutron Absorber” region is a finite cylinder 4 meters tall, and.16 meters in diameter. It can be raised and lowered by adjusting parameters in the n_flux3 program. The “Reflectors” region is made up of the six reflectors which are 1.5 meters tall, have a.2 meter radius, and a length of /3 radians. Each reflector position is determined in the n_flux3 function call. Neutron Absorber Core Reflectors
n_flux3 Reactor Configuration n_flux3 uses cylindrical and Cartesian coordinate systems for calculations, with the origin for both at the bottom of the core. Equivalent Core Diameter.8 m Active Core Length4 m Reflector Length1.5 m Reflector Thickness.2 m Absorber Radius.08 m Absorber Height4 m r y x 0 /3 /3 /3 /3
n_flux3 Flux Recording n_flux3 divides up the entire reactor into “small volumes”, which are treated like bins. Each time a neutron interaction occurs in a particular small volume, n_flux3 tallies that interaction in the corresponding bin. The number of neutron interactions in each bin is weighted by the size of that bin’s small volume. The location of each bin is represented as a point in the center of its small volume. r 2D and 3D representation of a small volume
All Reflectors Up Reflectors are all raised to 2.75 1 million neutrons tested (287 seconds to run) Shown: All bins at Z= 2.25, reflector and neutron absorber outlines 3 Reflectors up, 3 Down 3 reflectors raised to center, other 3 reflectors fully lowered. 1 million neutrons tested. Shown: All bins at Z= 2.25, reflector and neutron absorber outlines. All Reflectors Down All reflectors lowered to bottom of core 1 million neutrons tested. Shown: All bins at Z= 2.25, reflector and neutron absorber outlines.
Effect of Reflector Height Reflectors at z=1.0 m, 5 million neutrons.
Effect of Reflector Height Reflectors at z=1.5 m, 5 million neutrons.
Effect of Reflector Height Reflectors at z=2.0 m, 5 million neutrons.
Effect of Reflector Height Reflectors at z=2.5 m, 5 million neutrons.
Effect of Reflector Height Reflectors at z=3.0 m, 5 million neutrons.
Effect of Reflector Height Reflectors at z=3.5 m, 5 million neutrons.
Effect of Reflector Height Reflectors at z=4.0 m, 5 million neutrons.
Edge of the Core Core Reflectors at 2.75 m, 5 million neutrons
Edge of the Core Core Perimeter Reflectors at 2.75 m, 5 million neutrons
Flux in Reflectors Reflector Perimeter Reflectors at 2.75 m, 5 million neutrons
Tabulated Fluxes Location Flux All Reflectors Up3 Reflectors Up1 Reflector UpAll Reflectors Down Neutron Absorber z = 1.75 m 4.36E+074.35E+074.41E+074.46E+07 Inner Core, r =.12 m z = 1.75 m 3.60E+073.52E+073.54E+073.51E+07 Core Perimeter, r =.36 m z= 1.75 m 2.35E+071.82E+071.80E+077.04E+06 Reflector z = 1.75 m 3.85E+062.42E+062.34E+063.40E+04 Inner Core, r =.12 m z = 1.25 m 3.45E+073.44E+073.49E+073.42E+07 Inner Core, r =.12 m z =.75 m 3.30E+073.41E+073.43E+073.39E+07
Conclusions – n_flux3 Fuel, neutron absorber, and reflectors clearly shape the flux in the core. Reflectors raise flux around the core perimeter. Only sections near the reflectors experience substantial changes in flux, allowing control of the reactor. Partial lowering of reflectors has noticeable effect on neutron flux.
Challenges The current regulatory environment heavily favors large power output light water reactor designs very similar to facilities currently in use. Non-proliferation measures and maintaining security become paramount when the intended market includes third-world countries, and significantly add to cost. Down market has dampened hopes for speedy construction and installation, and has claimed casualties (PBMR), but other designs are moving forward.
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