Modeling of protection and control functions in the system calculations of nuclear power plants

Razvijen je RELAP5 model zaštitnih funkcija OTΔT, OPΔT i prekoračenja iznosa i brzine promjene nuklearne snage za NE Krško. Razvijen je RELAP5 model sustava automatske regulacije reaktora i trodimenzionalni (3D) model regulacijskih šipki. Napravljene su izmjene u vezanom programskom sustavu RELAP5- QUABOX/CUBBOX koje omogućuju simuliranje kretanja apsorpcijskih šipki promjenljivom brzinom. RELAP5 nodalizacija NE Krško proširena je modelima napojne vode parogeneratora i kontrolnih sistema regulacije nivoa vode parogeneratora. Razvijeni modeli testirani su na primjeru dvije pogonske promjene snage: (100→15) %, (100→90, 90→100) %, i na primjeru akcidenta unošenja pozitivne reaktivnosti najvećom i najmanjom brzinom. Analiziran je nesimetrični tranzijent izolacije napojne vode parogeneratora bez obustave reaktora. Analize su napravljene korištenjem vezanog programskog sustava (3D kinetika) i samostalnog kôda RELAP5 (točkasta kinetika). Analize su pokazale ispravnost razvijenih modela zaštitnih i regulacijskih sustava i unešenih promjena u nodalizaciji elektrane i dobru usklađenost parametara nuklearnog dijela proračuna za točkastu i 3D kinetiku.RELAP5 model of protection functions OTΔT, OPΔT as well as high neutron flux and high neutron flux rate trip functions for nuclear power plant (NPP) Krško have been developed. RELAP5 model of automatic reactor control system and three dimensional (3D) control rod model have been developed. Modifications in the coupled code RELAP5- QUABOX/CUBBOX have been performed in order to simulate variable control rod velocity. RELAP5 nodalization for nuclear power plant (NPP) Krško has been extended with model of feedwater system and steam generator level control system, respectively. The developed models have been tested with two operational power transients: (100→15) %, (100→90, 90→100) %, and two positive reactivity insertion accidents (minimum and maximum reactivity insertion). Asymmetrical transient of feedwater isolation without reactor trip has been analyzed. The analyses were performed using the coupled code (3D kinetics) and RELAP5 stand-alone code (point kinetics). The analyses have proven the appropriateness of developed models of protection and control systems as well as developed nodalization and nuclear parameters for both applied methods (point kinetics and 3D kinetics)