1. Idaho National Engineering and Environmental Laboratory Analysis of the SCWR Core with Water Rods Cliff Davis, Jacopo Buongiorno, INEEL Larry Conway, Westinghouse April 29, 2003 Madison, Wisconsin

2. Idaho National Engineering and Environmental Laboratory Introduction Steady-state thermal-hydraulic and neutronic analyses were performed for a SCWR design with water rods Thermal-hydraulic analysis concentrated on determining the density distribution in the water rods Thermal-hydraulic calculations were made with RELAP5 and neutronic calculations with MCNP4B Economic calculations used to evaluate acceptability of thermal-hydraulic results

3. Idaho National Engineering and Environmental Laboratory The core average density should exceed 500 kg/m 3 for acceptable fuel cycle cost MCNP4B model

4. Idaho National Engineering and Environmental Laboratory Heat transfer significantly affects fluid density in the water rods Core average density: 409 kg/m 3 391 kg/m 3 270 kg/m 3

5. Idaho National Engineering and Environmental Laboratory Results insensitive to the fraction of flow diverted to the water rods

6. Idaho National Engineering and Environmental Laboratory Water rod fluid density can be increased with insulation Core average density: 409 kg/m 3 444 kg/m 3 510 kg/m 3 (Reference) 566 kg/m 3 605 kg/m 3

7. Idaho National Engineering and Environmental Laboratory Water Rod Reactor Internals Feasibility Develop preliminary design of down-flow water rod RV internals (25x25 sq assembly with 36 water rods) Current Westinghouse concept uses calandria above fuel assemblies to connect upper head region to water rods in the fuel assemblies Feasibility issues are: –Minimum leakage calandria tube to water rod connection –Minimum leakage seal between upper head and T hot fluid –Thermal stresses

8. Idaho National Engineering and Environmental Laboratory Conclusions Heat transfer across the bare water rods results in unacceptably low core average water density Core average water density insensitive to the fraction of flow diverted to the water rods Insulation needed for acceptable fuel cycle cost and thermal stability RPV internals being developed by Westinghouse