Simulacija hitre spremembe moči v jedrski elektrarni s tlačnovodnim reaktorjem

Kokalj, Luka (author), Čepin, Marko Tomaž (mentor)

Namen diplomske naloge je preučiti odziv jedrske elektrarne na hitro spremembo moči ter postopek njene zasilne ustavitve. V sklopu naloge je predstavljena tudi osnovna zgradba tlačnovodne jedrske elektrarne s poudarkom na njenih ključnih komponentah. Analiza temelji na simulacijah, izvedenih s programom PCTRAN, ki uporablja poenostavljen model jedrske elektrarne s tlačnovodnim reaktorjem. V primeru hitre spremembe moči je bilo izvedeno zmanjšanje moči iz polne, torej iz 100 \% na 90 \% z gradientom 20 \% na minuto. Znižanje moči je bilo doseženo s postopno, delno vstavitvijo regulacijskih palic. Posledično se je v turbini zmanjšal pretok pare, kar je povzročilo znižanje električne moči. V primarnem sistemu je prišlo do padca temperature reaktorskega hladila, tlak se je znižal za približno 2 bara, nato pa se je postopoma povrnil na začetno vrednost 155 barov. Moč reaktorja se je ustrezno zmanjšala na 90 \%, kar je povzročilo tudi upad temperature goriva. V uparjalniku se je zmanjšal prenos toplote, hkrati pa sta se znižala pretoka napajalne vode in pare. Nivo vode v tlačniku se je znižal, aktivacija grelcev pa je zagotovila ohranjanje tlaka v primarnem sistemu znotraj območja nasičenja. Sistem za uravnavanje kemijske sestave in prostornine je ves čas zagotavljal stabilen nivo vode v tlačniku. Ob znižanju moči se je pretok v tem sistemu začasno prekinil, nato pa se je ponovno vzpostavil, ko so se razmere stabilizirale. Zasilna ustavitev reaktorja se izvede v primeru izrednih razmer z namenom zagotavljanja varnosti. V okviru diplomske naloge je kot povod za ustavitev izbran izklop črpalke reaktorskega hladila v zanki A. Ta dogodek je sprožil avtomatski spust vseh regulacijskih palic, kar je povzročilo takojšnjo in popolno zaustavitev reaktorja. Moč na turbini je v trenutku padla na 0 \%. V primarnem sistemu sta se po zaustavitvi reaktorja znižala tako tlak kot temperatura reaktorskega hladila. Pretok hladiva v zanki A se je zaradi izklopa črpalke ustavil, medtem ko se je v zanki B pretok povečal, da bi vsaj delno nadomestil spremembe v tokokrogu. V uparjalniku je zaradi sprememb v sistemu prišlo do porasta tlaka, hkrati pa sta se zmanjšala pretoka pare in napajalne vode. Neposredno po zaustavitvi reaktorja so se avtomatsko vključili grelniki v tlačniku, ki skrbijo za ohranjanje tlaka v območju nasičenja. Ob tem je nivo vode v tlačniku začel upadati. Sistem za uravnavanje kemijske sestave in prostornine je ob zaustavitvi reaktorja začasno prekinil pretok, ki pa se je kasneje ponovno vzpostavil, ko so se razmere stabilizirale.

• Language: Slovenian
• Keywords: primarni sistem, uparjalnik, tlačnik, reaktor, sprememba moči, jedrska elektrarna, reaktorsko hladilo
• Work type: Bachelor thesis/paper
• Typology: 2.11 - Undergraduate Thesis
• Organization: FE - Faculty of Electrical Engineering
• Year: 2025
• PID: 20.500.12556/RUL-170326
• COBISS.SI-ID: 243370243
• Publication date in RUL: 03.07.2025

Secondary language

• Language: English
• Title: Simulation of a rapid power change in a nuclear power plant with pressurized water reactor

Abstract

The aim of this thesis is to examine the response of a nuclear power plant to a rapid change in power and the procedure for its emergency shutdown. As part of the thesis, the basic structure of a pressurized water reactor nuclear power plant is presented, with an emphasis on its key components. The analysis is based on simulations performed using the PCTRAN program, which employs a simplified model of a nuclear power plant with a pressurized water reactor. In the case of a rapid power change, the reactor power was reduced from full power 100 \% to 90 \% at a rate of 20 \% per minute. This power reduction was achieved through the partial insertion of control rods. As a result, steam flow to the turbine decreased, leading to a reduction in the plant's electrical output. In the primary system, the reactor coolant temperature dropped, and the pressure decreased by approximately 2 bar, then gradually returned to its original value of 155 bar. The reactor power was reduced to 90 \%, which also led to a decrease in fuel temperature. In the steam generator, the heat transfer rate declined, along with the feedwater and steam flow rates. The water level in the pressurizer dropped, and the activation of the electric heaters ensured that pressure in the primary system was maintained within the saturation range. The chemical and volume control system continuously maintained a stable water level in the pressurizer. During the power reduction, flow in this system was temporarily interrupted and later restored once the conditions stabilized. An emergency reactor shutdown is carried out in case of abnormal conditions to ensure safety. In this thesis, the selected initiating event for the shutdown was the trip of the reactor coolant pump in loop A. This event triggered the automatic insertion of all control rods, leading to the immediate and complete shutdown of the reactor. The turbine power instantly dropped to 0 \%. In the primary system, both the pressure and temperature of the reactor coolant decreased following the reactor shutdown. Coolant flow in loop A ceased due to the pump trip, while flow in loop B increased to partially compensate for the changes. In the steam generator, system disturbances caused a pressure increase, while both steam and feedwater flows decreased. Immediately after the reactor shutdown, the pressurizer heaters automatically activated to maintain pressure within the saturation range. At the same time, the water level in the pressurizer began to decline. The chemical and volume control system temporarily stopped its flow during the shutdown but later resumed operation as the system stabilized.

• Keywords: primary system, steam generator, pressurizer, reactor, power change, nuclear power plant, reactor coolant