RAVE code system for 3-D core non-LOCA accident analysis

Full text of publication follows: This paper provides an overview of the application of the Westinghouse updated RAVE three dimensional (3-D) core transient analysis code system for PWR non-LOCA accident analysis. The RAVE code system consists of a linkage of the following USNRC-approved codes: the EPRI RETRAN-02 (RETRAN) system transient analysis code, the Westinghouse SPNOVA (also referred to as ANC-K) reactor core neutron kinetic nodal code, and the EPRI VIPRE-01 (VIPRE) reactor core thermal-hydraulic (T/H) code. The RETRAN code is used for calculating transient conditions in the reactor coolant system (RCS), including reactor vessel, RCS loops, pressurizer and steam generators. RETRAN also models reactor trips, engineering safety feature (ESF) functions, and the control systems. The SPNOVA code is used to perform 3-D core neutronic calculations for core average power and power distributions in the core. Its reactivity feedback calculation is based on transient fluid conditions and fuel temperatures obtained from the VIPRE code. Based on core inlet temperature, inlet flow and core exit pressure from RETRAN, and the nodal nuclear power from SPNOVA, VIPRE provides back to RETRAN transient nodal heat flux in the reactor core region. An effective 3-D analysis requires RETRAN, SPNOVA and VIPRE calculations to be closely linked for the entire reactor core. The linking architecture uses a standard external communication interface protocol for communication among the running programs on the same or different computers. The RAVE code system currently uses the Parallel Virtual Machine (PVM) software for the data transfer. Besides the necessary changes for data transfer, no other changes were made to RETRAN, SPNOVA or VIPRE fundamental code algorithms or solution methods. The RETRAN model in the RAVE system uses the same detailed reactor vessel, RCS loops, pressurizer, and steam generator, and control and protection models as has been licensed for current plant Safety Analysis Reports (SARs) using the point-kinetics model. The SPNOVA core model is the same as the current core design model used with the ANC code. For fluid solutions, the number of radial and axial nodes in the VIPRE model is typically the same as the SPNOVA code. This results in up to 772 coupled core neutronic and T/H channels for a four-loop plant. The VIPRE fuel rod model uses multiple radial mesh points in the fuel pellets and in the clad for each core node. The fuel pellet-to-clad gap heat transfer accounts for changes in fuel dimensions and fill gas pressure during the transient. The VIPRE code is also used in a separate calculation to determine the hot rod minimum Departure from Nucleate Boiling Ratio (DNBR) and fuel temperature versus time. A code application topical report has submitted for licensing review demonstrating the application to several non-LOCA SAR accidents events. The use of the RAVE code system has also been demonstrated by predicting the core and RCS responses of the Phase III main steam-line break (MSLB) benchmark problem sponsored by the Organization for Economic Cooperation and Development (OECD). The RETRAN, SPNOVA and VIPRE licensing models were adjusted in accordance with the OECD problem specifications. The RAVE-system predicted core and RCS responses were in good agreement with the published results from other participants. The results of the OECD MSLB benchmark problem confirm the robustness of the RAVE code system in analyzing the non-LOCA accidents. (authors)