Model izračuna reaktorske faze teških nesreća u nuklearnoj elektrani

doctoral thesis

• Title (english): Calculational Model for In-Vessel Phase of Severe Accidents in Nuclear Power Plant
• Author: Siniša Šadek
• Mentor: Nenad Debrecin (mentor)
• Committee member: Nikola Čavlina (predsjednik povjerenstva)
• Committee member: Željko Bogdan (član povjerenstva)
• Granter: University of Zagreb; Faculty of Electrical Engineering and Computing; Zagreb
• Defense date and country: 2010-03-29, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Electrical Engineering
• Universal decimal classification (UDC): 621.3 - Electrical engineering

Abstract

Analiza teške nesreće u nuklearnoj elektrani provodi se sa svrhom kvantificiranja posljedica taljenja jezgre i
ispuštanja fisijskih produkata. S obzirom na multidisciplinarnost problema, izračun je proveden u nekoliko faza pri čemu je
korišteno više računalnih alata. Prva faza izračuna koja obuhvaća procese u reaktorskoj jezgri provedena je korištenjem programa SCDAP/RELAP5 i MAAP4. Radilo se o integralnom izračunu jer je bilo potrebno modelirati kompletni primarni i sekundarni krug elektrane kako bi se osigurali adekvatni termohidraulički rubni uvjeti (tlak, temperatura i protok rashladnog fluida). Rezultati ovih izračuna bili su sastav i masa rastaljenog materijala ispuštenog u donji plenum. Druga faza je bila kombinirana CFD i FEM analiza donjeg plenuma. CFD analiza prirodne cirkulacije rastaljenog materijala provedena je s ciljem određivanja njegove konfiguracije i temperaturne raspodjele. Detaljni FEM model donjeg plenuma razvijen je kako bi se što preciznije odredila temperatura stijenke reaktorske posude na temelju čega se ocijenilo mjesto i vrijeme do pucanja, odnosno taljenja posude. Jedno od nedovoljno istraženih podrucja je izmjena topline zračenjem između rastaljenog materijala i struktura u donjem plenumu. Potporna ploča jezgre direktno je izložena toplinskom zračenju. Njezino bi pregrijanje i eventualni kolaps izazvao propadanje kompletne jezgre i struktura u gornjem plenumu. Model radijacijske izmjene topline implementiran je u postojeći SCDAP/RELAP-ov FEM modul COUPLE. Dodatno je razvijen model potporne ploče jezgre, a rezultati su pokazali da postoji mogućnost njezinog pucanja. Propadanje preostalih neoštećenih struktura u donji plenum dodatno bi mehanički opteretilo reaktorsku posudu i povećalo vjerojatnost pucanja posude.

Abstract (english)

Severe accidents in nuclear power plants are analysed in order to quantify the consequences of a core meltdown and
fission products release. Such a multidisciplinary problem calls for a multiphase calculating process involving various tools.
The first phase focused on the processes within the reactor core and the SCDAP/RELAP5 and MAAP4 codes were used for the analysis. Integral calculation was applied because the whole primary and secondary circuit of the power plant had to be modified in order to ensure the adequate thermal and hydraulic boundary conditions (pressure, temperature and the coolant flow). The results of the calculation defined the composition and mass of the molten material released in the lower plenum. The second phase was a combination of the CFD and FEM analyses of the lower plenum. The CFD analysis of the molten material natural circulation was conducted in order to define its configuration and temperature distribution. A detailed FEM model of the lower plenum was developed with the purpose of calculating the accurate temperature of the reactor vessel wall, which would help determine the precise time and place of vessel breach or meltdown. The radiation heat exchange between the molten material and the lower plenum structures has not been sufficiently studied. The core support plate is directly exposed to radiation heating. If overheated, it might collapse and cause the core and upper plenum structures to fall into the lower head. A radiation heat exchange model was implemented in the existing SCDAP/RELAP5 FEM COUPLE module and a core support plate model was developed. The results indicate the possibility of a plate rupture. A collapse of the remaining undamaged structures into the lower plenum would add extra burden to the reactor vessel and might eventually lead to its breach.

• Keywords: teška nesreća; reaktorska faza; oštećenje jezgre; rastaljeni materijal; donji plenum; prirodna cirkulacija coriuma; prijenos topline; metoda konačnih elemenata; računalna mehanika fluida; izmjena topline zračenjem
• Keywords (english): severe accident; in-vessel phase; core degradation; molten material; lower plenum; corium natural circulation; heat transfer; finite element method; computational fluid dynamics; radiation heat exchange
• Language: croatian
• URN:NBN: urn:nbn:hr:168:993841
• Promotion: 2010
• Study programme: Title: Doctoral study programme "Electrical Engineering and Computing"; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, po-dručje tehničkih znanosti (doktor/doktorica znanosti, po-dručje tehničkih znanosti)
• Type of resource: Text
• Extent: vii, 174 str. : graf. prikazi
• File origin: Born digital
• Access conditions: Open access
• Created on: 2024-03-19 12:15:56