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Author:Nieminen, Anna
Title:Core-melt behaviour inside the reactor pressure vessel during the late-phase of a severe accident
Sydänsulan käyttäytyminen ydinreaktorin paineastian sisällä vakavan onnettomuuden loppuvaiheessa
Publication type:Master's thesis
Publication year:2012
Pages:ix + 66      Language:   eng
Department/School:Energiatekniikan laitos
Main subject:Lämpötekniikka ja koneoppi   (Ene-39)
Supervisor:Lampinen, Markku
Instructor:Lindholm, Ilona
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  4651   | Archive
Keywords:severe accident
late-phase
corium pool
ASTEC
vakava onnettomuus
vakavan onnettomuuden loppuvaihe
sydänsula-allas
ASTEC
Abstract (eng): The severity of nuclear reactor accidents is often classified according to the amount of released radioactive fission products.
The melting of the reactor core, even a partial one, is always related into severe accidents.
This study concentrates specifically to the late-phase of core damage, when a large melt pool is formed into the bottom of the pressure vessel.
The investigations are focused on and limited to the in-vessel phase.

The purpose of the study is to evaluate the effects of the accident scenario and the supposed melt composition -in terms of chemical form and melt layering -into the reactor pressure vessel rupture.
The study brings the information obtained in the international experimental research program MASCA to reactor scale in a sample reactor application.
The tool used for analyses is an integral code ASTEC (Accident Source Term Evaluation Code) purposed for simulation of the whole accident scenario history.
The chemical equilibrium studies for core-melt are performed with Chem Sheet.

It was found that the initial chemical composition of the melt, depending on the accident scenario, has only a minor effect.
However, the actual melt layer arrangement was discovered to be the key point, when considering the vessel failure and especially the place of rupture.
Abstract (fin): Ydinvoimaloissa tapahtuvien onnettomuuksien merkittävyys määritellään radioaktiivisten fissiotuotteiden vapautumisen avulla.
Myös osittainen reaktorisydämen sulaminen on aina vakava onnettomuus.
Tämä työ keskittyy onnettomuuden vaiheeseen, jolloin reaktorisydän on sulanut ja sydänsula on kerääntynyt paineastian pohjalle.
Työssä tehdyt tarkastelut on rajattu paineastian sisäpuolisiin ilmiöihin.

Tarkoituksena on arvioida onnettomuusskenaarion vaikutusta, sekä sulan kemiallisen koostumuksen että sula-altaan kerrostumiseen kannalta, paineastian murtumiseen.
Tässä tutkimuksessa sovelletaan kansainvälisen kokeellisen MASCA-tutkimusohjelman tuloksia reaktorimittakaavaan.
Analyysien tekemisessä on käytetty koko onnettomuusketjuhistorian mallintamiseen kehitettyä ASTEC-ohjelmaa (Accident Source Term Evaluation Code).
Sydänsulan kemiallisen tasapainon määritykseen on käytetty Chem Sheet-ohjelmistoa.

Tutkimuksessa selvisi, että onnettomuusskenaariosta johtuvalla kerrosten kemiallisella koostumuksella ei ole merkittävää vaikutusta paineastian hajoamiseen.
Sen sijaan, kerrosten järjestäytyminen vaikutti olevan ratkaiseva tekijä erityisesti paineastian murtumakohtaan.
ED:2012-05-09
INSSI record number: 44439
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