Integrating STAR-CCM+ with a Systems Analysis Code for Nuclear - PowerPoint PPT Presentation

Integrating STAR-CCM+ with a Systems Analysis Code for Nuclear Reactor Safety Simulations Justin W. Thomas Nuclear Engineering Division Argonne National Laboratory STAR-American Conference Chicago, Illinois June 28, 2011

Why Sodium-cooled Fast Reactors (SFRs)? § All nuclear power plants currently operating the U.S. use water as their coolant – But the first reactor to generate electricity was a fast reactor § Fast reactors get their name because, on average, neutrons are moving faster than in water reactors – Changes the likelihood of the occurrence of various nuclear reactions § Fast reactors can be designed for: – Actinide burning: Continue to produce energy from “used” nuclear fuel from water reactors – Breeding: Produce more fissile fuel than what consumed in the core § As a part of a strategy to recycle used nuclear fuel from water reactors, SFRs help to: – Extract more energy from uranium – Reduce reliance on uranium enrichment – Reduce the amount of used fuel STAR-­‑American ¡Conference, ¡Chicago ¡Illinois, ¡June ¡28, ¡2011 ¡ 2 ¡

Passive safety of SFRs § Nuclear power plant operators must convince regulators that their reactors will remain safe, even under accident scenarios and off- normal events § Even after the nuclear fission reactions have stopped in the reactor, a small amount of heat is still heat being generated – decay heat – which needs to be removed for an extended period of time § If the coolant pumps fail, SFRs can rely on natural circulation to drive coolant through the reactor’s core and remove heat § The potential for SFRs to survive severe accident initiators with no damage was demonstrated in a series of tests at the Experimental Breeder Reactor-II facility in the 1980s – Complete loss-of-flow and loss-of-heat-sink tests were performed – Experimental results from this program will be used to validate the work described here STAR-­‑American ¡Conference, ¡Chicago ¡Illinois, ¡June ¡28, ¡2011 ¡ 3 ¡

Modeling transients in SFRs § Argonne’s safety systems code SAS4A/SASSYS-1 models the dynamic response of a reactor during a posited transient scenario § Physics include: – The core’s response to changes in its environment – Structural mechanics – Fuel performance – Decay heat generation – Fluid mechanics and heat transfer • Natural circulation, buoyancy-driven flow, thermal stratification § By including STAR-CCM+ in SAS4A/SASSYS-1 transient analyses, the goal is to improve the fluid mechanics/heat transfer solution while still maintaining the sophistication of the other models available in SAS4A/ SASSYS-1 – Specific cases where 3-D effects are important – E.g., thermal stratification in large plena STAR-­‑American ¡Conference, ¡Chicago ¡Illinois, ¡June ¡28, ¡2011 ¡ 4 ¡

Example: Loss-of-flow in Toshiba’s 4S reactor § Argonne supported safety analysis for a small SFR concept developed by Toshiba § In a hypothetical loss-of-flow scenario: 1. The pumps stop, reducing the flow rate through the core 2. The reactor scrams, stopping the nuclear fission reactions but decay heat remains § Because of #2, the sodium entering the outlet plenum is now cooler than the bulk sodium in the plenum § Because of #1, the time for the cooler sodium to reach the Intermediate Heat Exchanger (IHX) can be significant à Thermal stratification § This effects the natural circulation head in the system 4S Schematic (Not to scale) STAR-­‑American ¡Conference, ¡Chicago ¡Illinois, ¡June ¡28, ¡2011 ¡ 5 ¡

Example: Loss-of-flow in Toshiba’s 4S reactor § A model of the 4S outlet plenum was built with STAR-CCM+ – 2-D axisymetric for demonstration purposes § Remainder of reactor system modeled with the system code SAS4A/SASSYS-1 § STAR-CCM+ and SAS4A/SASSYS-1 communicate at the flow boundaries § For each core channel, SAS4A/SASSYS-1 sends the outlet temperature and mass flow rate – Temperature and fluid velocity distributed uniformly along STAR-CCM+ boundary § At the IHX inlet, STAR-CCM+ provides the average pressure and temperature 4S Schematic (Not to Scale) STAR-­‑American ¡Conference, ¡Chicago ¡Illinois, ¡June ¡28, ¡2011 ¡ 6 ¡

Temperature predictions in the outlet plenum § SAS4A/SASSYS-1 predicts the low flow rates and cooler temperatures from the core when the transient starts § Cool sodium slowly progresses upward through the plenum towards the heat exchanger To Heat § Important to predict the time delay required Exchanger for cooler sodium to reach the heat exchanger § Note: These results are preliminary and should not be considered to represent the actual performance of the 4S reactor From Core STAR-­‑American ¡Conference, ¡Chicago ¡Illinois, ¡June ¡28, ¡2011 ¡ 7 ¡

Reactor system response § The natural circulation driving head depends on the temperature difference between the heat exchanger (heat sink) and the core (heat source) § Some interesting phenomena were predicted during the coupled simulations of SAS4A/SASSYS-1 and STAR-CCM+ Temperature Secondary-side becomes a heat source rather than a Long delay before heat sink due to flow IHX senses cooler stagnation core temperatures STAR-­‑American ¡Conference, ¡Chicago ¡Illinois, ¡June ¡28, ¡2011 ¡ 8 ¡

Implementation of STAR-CCM+ coupling § Coupling with the SAS4A/SASSYS-1 code is implemented through the STAR-CCM+ client via a Java macro – Portions of Fortran routines developed for STAR-CD coupling preserved – Java calls the Fortran functions via Java Native Access (JNA) § Communication between SAS4A/SASSYS-1 and STAR-CCM+ via file I/O § Synchronize each SAS4A/SASSYS-1 time step – SAS4A/SASSYS-1 determines its time step size using its normal approach • Monitors temperature changes and other conditions, user-input tolerances – STAR-CCM+ time step is the smaller of: • ½ the SAS4A/SASSYS-1 time step • The user-input value in the simulation – Linear interpolation performed as needed STAR-­‑American ¡Conference, ¡Chicago ¡Illinois, ¡June ¡28, ¡2011 ¡ 9 ¡

Implementation of STAR-CCM+ coupling (cont) § At the end of its time step, SAS4A/SASSYS-1 prints for each inlet flow boundary – Mass flow rate – Temperature § STAR-CCM+ assumes a uniform velocity and temperature profile at each flow boundary, computed from the SAS4A/SASSYS-1 data § Just before the next SAS4A/SASSYS-1 time step, STAR-CCM+ prints for all flow boundaries – Area-averaged absolute pressure Reports – Mass-flow averaged temperature § STAR-CCM+ annotates a plot with the current time (from SAS4A/ SASSYS-1) and prints for the animation § Heat transfer at boundaries to be implemented soon – Exchange heat flux or temperature at wall boundaries STAR-­‑American ¡Conference, ¡Chicago ¡Illinois, ¡June ¡28, ¡2011 ¡ 10 ¡

Future Work: EBR-II Analysis § But are these predictions accurate? § Measured data from the EBR-II tests provides a validation exercise of whole-plant response to a loss-of-flow scenario – Cold pool tank modeled with STAR-CCM+ – Remainder of the cooling system modeled with SAS4A/SASSYS-1 § Seven flow boundaries that connect to SAS4A/SASSYS-1 STAR-­‑American ¡Conference, ¡Chicago ¡Illinois, ¡June ¡28, ¡2011 ¡ 11 ¡

EBR-II Initialization STAR-­‑American ¡Conference, ¡Chicago ¡Illinois, ¡June ¡28, ¡2011 ¡ 12 ¡

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Thank you STAR-­‑American ¡Conference, ¡Chicago ¡Illinois, ¡June ¡28, ¡2011 ¡ 16 ¡