1. Thermal Hydraulic Simulation of a SuperCritical-Water-Cooled Reactor Core Using Flownex F.A.Mngomezulu, P.G.Rousseau, V.Naicker School of Mechanical and Nuclear Engineering North-West University Energy Postgraduate Conference 2013 Cape Town, South Africa

2. Outline 1.Introduction and Objectives of Study. What is the SCWR? A SCWR Core Layout. 2. Methodology. Flownex Fuel Assembly Network. 3. Results and Discussion. Mass and Energy Balances. Dittues-Boelter vs Bishop Correlation. 4. Conclusion and Future Work.

3. Objectives  Gain insight into Generation IV reactor technologies specifically for SCWR.  Establish methodology in light water reactor technology analysis. Using neutronics and thermal hydraulics.  Use this reactor layout to obtain a working thermal hydraulic model using Flownex ® SE.

4. Description of the SCWR  The Supercritical Water- Cooled Reactor (SCWR) is one of the Gen IV reactor concepts.  It operates above the critical point of water (374 o C, 22.1 MPa).  Simplified plant. No steam dryers, steam separators, recirculation pumps, and steam generators.  Thermal efficiency up to 44% relative to 35% for current LWRs, due to higher steam temperatures.

5. Description of the SCWR (cont.)  The fluid behaves both like a liquid and a gas and no phase change is observed, therefore no critical boiling phenomenon observed.

6. A SCWR Core Layout  Reactor consists of 249 fuel assemblies, only 1/8 of the core was modeled.

7. Methodology  Thermal hydraulic Flownex ® SE code was used.  Fuel assemblies were modelled as three types: full (24), half (14) and quarter (1).  Each assembly was modelled using three parallel channels from top to bottom: fuel, moderator and the gaps between assemblies.  Each channel was then modelled using four different pipe elements: upper plenum, steam plenum, reactor core and mixing plenum.

8. Results and Discussion Pipe Increment Q_n (KW) Heat fraction Q_fp (KW) Q_f (KW) Q_m (KW) 4*Q_g (KW) Q_tot (KW) 1185990.0815241551-2.07-6.331524 40.12222122268.313.482221 70.101872185916.80.791872 100.03490.746222.91.54491 Sum185991758173371.318599  The outlet steam temperature for the reactor is 507.9 o C and the mass flow rate is 7.9 kg/s compared to 508 o C and 7.3 kg/s from Liu and Cheng 2009. Energy balance for fuel assembly 48

9. Results and Discussion (cont.) Fig 5. Cladding temperature distribution of the fuel assembly 48 Dittus-Boelter correlation gives a maximum cladding temperature above the design limit while Bishop correlation give a maximum cladding temperature well below the design limit (650 o C). The maximum peak is observed at the lower part of the active core.

10. Conclusions and Future Work  A working thermal hydraulic model was obtained capable of determining the temperature distribution in the 1/8 of the core.  Bishop heat transfer correlation proposed by Liu and Cheng 2009 was used and implementation of correlation reduced the maximum fuel and surface temperatures.  Mass and energy balances were obtained.  Remaining Work Energy balances for the whole core. Acknowledgements This work is based upon research supported by the South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation.