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Author:Ahtinen, Esa
Title:Development and validation of a new noncondensable gas transport model for the APROS simulation software
Lauhtumattomien kaasujen kuljetusmallin kehittäminen ja testaus APROS-simulaattorilla
Publication type:Master's thesis
Publication year:2008
Pages:108      Language:   eng
Department/School:Teknillisen fysiikan laitos
Main subject:Ydin- ja energiatekniikka   (Tfy-56)
Supervisor:Salomaa, Rainer
Instructor:Routamo, Tomi ; Kontio, Harri
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark TF80     | Archive
Keywords:non-condensable gases
convective transport
PRISE
APROS
process simulation
lauhtumattomat kaasut
primääri-sekundäärivuoto
APROS
konvektiivinen kulkeutuminen
Abstract (eng): This Master's Thesis is a development and validation project of a new non- condensable gas transport model for the APROS simulation software.
Earlier APROS versions were able to model non-condensable gas transport only in gas phase.
After this thesis user can model convective non-condensable gas transport also in the liquid phase with absorption and release phenomena between phases.

Non-condensable gases have several physical properties that make them important to take into account in certain types of nuclear safety analyses.
Typical PWR has passive accumulators that contain borated water under pressurized nitrogen gas cushion.
The accumulator water is gradually saturated with dissolved nitrogen.
If this saturated water is injected into the primary circuit during pressure reduction, some of the dissolved nitrogen might be released from the primary coolant and form gas pockets.
These gas pockets might terminate the natural circulation and hinder the heat transfer in the steam generators.

In this thesis the new model is validated against old PACTEL and PKL experiments.
After validation cases the new transport model is used to simulate primary to secondary circuit leak (PRISE) with one unisolated accumulator by using full-scale Loviisa APROS model.
These simulations will give information about the local dissolved nitrogen concentrations against theoretical saturation concentrations.
Abstract (fin): Tämä diplomityö on osa Fortum Nuclear Services:n ja VTT:n projektia, jossa kehitetään APROS-simulaattorin 6-yhtälömallin lauhtumattomien kaasujen kulkeutumisen laskentaa.
Ennen diplomityön aloittamista APROS mallinsi ainoastaan kaasufaasin mukana tapahtuvaa lauhtumattomien kaasujen konvektiivista kulkeutumista.
Diplomityön jälkeen lauhtumatonta kaasua voi kulkeutua myös nestefaasin mukana liuenneena.
Faasien välillä voi tapahtua lauhtumattoman kaasun vapautumista sekä liukenemista.

Ydinvoimalaitoksen turvallisuussuunnittelun kannalta tärkeä ilmiö on liuenneen kaasun vapautuminen nestefaasista kaasufaasiin paineen laskiessa.
Vapautumisilmiö voi keskeyttää painevesilaitoksen luonnonkierrolla tapahtuvan jälkilämmön poiston, jos paineakuista primääripiiriin injektoitunut liuennutta typpeä sisältävä vesi joutuu alhaiseen paineeseen muodostaen suuria kaasutilavuuksia.

APROS:iin rakennettu malli validoitiin PACTEL- ja PKL-kokeilla, joista varsinkin PACTEL-kokeista oli saatavilla laadukasta mittausdataa.
Validoinnin jälkeen simuloitiin Loviisan VVER-laitosta kuvaavalla APROS-mallilla PRISE-onnettomuus, jossa yksi paineakuista jäi eristämättä.
Simuloinnista saatiin selville primääripiirissä oleva typen määrä ajan funktiona sekä paikallisten typpikonsentraatioiden suhde saturaatiotilaan.
Paikallisten konsentraatioiden todettiin jäävän kauas saturaatiotilasta, joten kaasua ei vapautunut.
Loviisa-mallilla tehtyjen simulointien aikana saatiin myös uusia ideoita typpiakkujen mallinnukseen.
ED:2009-02-19
INSSI record number: 36778
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