Publications
Advanced Nuclear Power Program
Supercritical Water Reactor Cycle for Medium Power Applications
B.D. Middleton and J. Buongiorno
MIT-ANP-TR-110 (June 2006)
Executive Summary
Scoping studies for a marine power conversion system based on a direct-cycle supercritical water reactor have been conducted. The electric power range of interest is 5-30 MWe with a design point of 20 MWe. The overall design objective is to develop a system that has minimized physical size and performs satisfactorily over a broad range of operating conditions. The design constraints are as follows:
- Net cycle thermal efficiency ≥20%
- Steam turbine outlet quality ≥90%
- Pumping power £2500 kW (at nominal conditions)
Three basic cycle configurations were analyzed. Listed in order of increased plant complexity, they are:
- Simple supercritical Rankine cycle
- All-supercritical Brayton cycle
- Supercritical Rankine cycle with feedwater preheating
The sensitivity of these three configurations to various parameters, such as reactor exit temperature, reactor pressure, condenser pressure, etc., was assessed. The Thermoflex software package was used for this task. The results are as follows:
- The simple supercritical Rankine cycle offers the greatest hardware simplification, but its high reactor temperature rise and reactor outlet temperature may pose serious problems from the viewpoint of thermal stresses, stability and materials in the core.
- The all-supercritical Brayton cycle is not a contender, due to its poor thermal efficiency.
- The supercritical Rankine cycle with feedwater preheating affords acceptable thermal efficiency with lower reactor temperature rise and outlet temperature.
- The use of a moisture separator improves the performance of the supercritical Rankine cycle with feedwater preheating and allows for a further reduction of the reactor outlet temperature, thus it was selected for the next step.
Preliminary engineering design of the supercritical Rankine cycle with feedwater preheating and moisture separation was performed. All major components including the turbine, feedwater heater, feedwater pump, condenser, condenser pump and pipes were modeled with realistic assumptions using the PEACE module of Thermoflex. A three-dimensional layout of the plant was also generated with the SolidEdge software. The results of the engineering design are as follows:
- The cycle achieves a net thermal efficiency of 24.13% with 350/460°C reactor inlet/outlet temperatures, ~250 bar reactor pressure and 0.75 bar condenser pressure. The steam quality at the turbine outlet is 90% and the total electric consumption of the pumps is about 2500 kWe at nominal conditions.
- The overall size of the plant is attractively compact for the intended application and can be further reduced if a printed-circuit-heat-exchanger (vs shell-and-tube) design is used for the feedwater heater, which is currently the largest component by far.
Finally, an analysis of the plant performance at off-nominal conditions has revealed good robustness of the design in handling large changes of thermal power and seawater temperature.
