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Author:Kalilainen, Jarmo
Title:Chemical reactions on primary circuit surfaces and their effect on fission product transport in a severe nuclear accidents
Kemialliset reaktiot primääripiirin pinnalla sekä niiden vaikutukset fissiotuotteiden kulkeutumiseen vakavissa reaktorionnettomuuksissa
Publication type:Master's thesis
Publication year:2010
Pages:60      Language:   eng
Department/School:Informaatio- ja luonnontieteiden tiedekunta
Main subject:Ydin- ja energiatekniikka   (Tfy-56)
Supervisor:Salomaa, Rainer
Instructor:Auvinen, Ari ; Kärkelä, Teemu
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  14   | Archive
Keywords:aerosol
ionide
primary circuit
severe nuclear accident
aerosoli
jodi
primääripiiri
vakava reaktorionnettomuus
Abstract (eng): The objective of this work was to examine the chemical reactions taking place on primary circuit surfaces and their effect on fission product transport in a severe nuclear accident.
Especially transport of gaseous and solid iodine was studied.
Caesium iodide was used as precursor material for iodine compound.
Also, effects of molybdenum and boron on transport of iodine were investigated.

Six experiments with different precursor materials were conducted.
Before each experiment, precursor materials were placed in an evaporation crucible.
To determine the effect of the surface on the reactions, alumina or oxidized stainless steel were used as evaporation crucible material.
During each experiment, the amount of hydrogen in the carrier gas was varied, in order to determine its effects on reactions of precursor material.
Before each experiment, the crucible was placed inside a furnace which was heated to 650 °C.
The gaseous reaction products formed in the crucible were trapped in bubbling bottles, and aerosol particles were collected in PTFE filters.
The properties of aerosol reaction products, such as mass concentration and particle size distribution, were monitored with online measurement devices, such as TEOM and SMPS.
The aerosol particles, as well as the crosscut samples created from the crucibles after the experiments, were also analysed with SEM and EDS.
The water vapour concentration during the experiments was monitored with FTIR.

The experiments showed that when CsI alone was used as precursor, as much as 20% of the released iodine was in gaseous form and rest was in aerosol particles.
Aerosol particles were most likely caesium iodide.
As the amount of hydrogen in the carrier gas was increased, the fraction of gaseous iodine dropped.
When boron was added to the precursor, a glassy caesium borate glass surface was formed on the crucible.
Boron trapped most of the caesium and some fraction of iodine, causing almost all released iodine to be in gaseous form.
When molybdenum was introduced in the precursor, most of the iodine was again released in gaseous form.
Oxidized Mo reacted with caesium releasing iodine from CsI.
The effect of molybdenum on iodine transport depended much on hydrogen concentration and was observed to be substantially greater on stainless steel surface.
When stainless steel crucible was used, Mo was found in small amounts from aerosol products, indicating that it was probably released as caesium molybdate or as molybdenum oxide.
Abstract (fin): Työn tarkoituksena oli tutkia vakavassa ydinonnettomuudessa primääripiirin pinnalla tapahtuvia kemiallisia reaktioita, ja niiden vaikutusta fissiotuotteiden kulkeutumiseen.
Erityisesti tutkittiin kaasumaisen jodin kulkeutumista.
Jodilähteenä kokeissa käytettiin cesiumjodidia.
Lisäksi tutkittiin molybdeenin ja boorin vaikutusta jodin kulkeutumiseen.

Kokeellinen työ käsitti yhteensä kuusi koetta joissa kaikissa käytettiin eri lähtöaine höyrystysastia yhdistelmiä.
Höyrystysastia materiaaleina käytettiin keraamia sekä ruostumatonta terästä.
Kokeiden aikana kantokaasun koostumusta muutettiin lisäämällä siihen erimääriä vetyä.

Kokeiden alussa höyrystysastia lähtöaineineen asetettiin reaktiouuniin, joka lämmitettiin to 650 °C.
Kokeessa syntyneet kaasumaiset reaktiotuotteet kerättiin kuplituspulloihin, ja aerosolihiukkaset PTFE filtterille.
Aerosolien massa- sekä hiukkaspitoisuuksia mitattiin TEOM ja SMPS mittalaitteilla.
Aerosolihiukkasia sekä höyrystysastioiden poikkileikkaus näytteitä tutkittiin myös EDS analyysin avulla. vesihöyryn pitoisuutta koelaitteistossa mitattiin FTIR mittalaitteella.

Kun pelkkää cesiumjodidia käytettiin lähtöaineena, korkeintaan 20 % kaikesta vapautuneesta jodista oli kaasua.
Loput jodista vapautui aerosolihiukkasina, jotka hyvin todennäköisesti olivat cesiumjodidia.
Kun vedyn määrää kantokaasussa lisättiin, kaasumaisen jodin määrä reaktio tuotteissa putosi.
Kun lähtöaineisiin lisättiin booria, höyrystysastianpinnalle muodostui kokeen aikana cesiumboraatti lasikerros.
Boori pidätti suurimman osan cesiumista sekä pienen osan jodista.
Tämän seurauksena suuri osa vapautuneesta jodista oli kaasumaisessa muodossa.
Kun molybdeenia lisättiin lähtöaineisiin, vapautui suurin osa jodista jälleen kaasuna.
Oksidoitu molybdeeni reagoi cesiumjodidin kanssa, vapauttaen kaasumaista jodia.
Erityisesti ruostumattoman teräksen ollessa käytössä höyrystysastia materiaalina, huomattiin että kaasumaista jodia vapautui hyvin suuria määriä, ilma että muutokset vety konsentraatiossa aiheuttivat siihen suuria muutoksia.
Teräsastiaa käytettäessä, huomattiin myös että pieni määrä molybdeenia vapautui aerosolihiukkasina.
Nämä hiukkaset olivat mitä ilmeisimminkin joko cesiummolybdaattia, molybdeenioksidia tai molempia.
ED:2010-11-15
INSSI record number: 41306
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