The design of a compact integral medium size PWR : the CIRIS

[摘要] The International Reactor Innovative and Secure (IRIS) is an advanced medium size, modular integral light water reactor design, rated currently at 1000 MWt. IRIS design has been under development by over 20 organizations from nine countries, led by Westinghouse. IRIS has a standard Westinghouse PWR core, but is an integral reactor, which means the reactor vessel contains all pumps, steam generators, pressurizer and control rod drive mechanisms. This work assesses possible improvements of the plant economics by the allowable power in the IRIS vessel, while maintaining the same or better safety limits, through increasing the power density in the core and heat exchangers. IRIS was designed with 8 Once-Through Helically coiled Steam Generators (OTHSG), located in an annulus near the vessel in the region above the core. The unit size dictates the vessel diameter, or limits the core size for fixed vessel diameter, and thus the reactor power rating. The Printed Circuit Heat Exchangers (PCHE) of HEATRICIm are compact heat exchangers that can provide high power density along with low pressure drop. They are proposed here as replacement for the OTHSG. The PCHEs experience is mostly for single phase heat transfer. A model is developed for the two phase fluid heat transfer in the small horizontal PCHE flow channels. The PCHE performance under IRIS conditions was modeled by a one dimensional nodal code. For the same power output, the PCHEs are found to safely reduce the IRIS vessel diameter by as much as 1.5 m and reduce the pressure drop in the SG by 30 %. The Internally and eXternally cooled Annular Fuel (IXAF) had been investigated as part of MIT;;s Advanced Fuel Project. It was found to maintain the current operating MDNBR margin under steady state IRIS conditions at 150% of nominal power density when the flow rate can be proportionally increased. The MDNBR in the inner channels was sensitive to flow changing flow conditions. A complete RELAP5 model of the IRIS reactor, along with PCHE and IXAF design representation, was developed. The PCHE RELAP model was first benchmarked against the stand-alone code and their agreement was demonstrated successfully. The short and long term responses of IRIS with PCHE and IXAF were analyzed for a Loss Of Flow Accident (LOFA) and a Loss Of FeedWater Accident (LOFWA). Under LOFA the MDNBR margins were found to be acceptable with added inertia to current IRIS pumps configuration. Therefore, the pressure vessel size can be reduced by implementing the PCHE instead of the OTHSG, and IXAF instead of solid fuel rods in addition to increasing the power rating of the reactor by 50% for the same vessel size. The results indicate that a large potential exist to reduce the cost per kilowatt and increase the attractiveness of the IRIS reactor design.

[发布机构] Massachusetts Institute of Technology