Localized deformation in spent nuclear fuel disposal canisters

Antti Forsström

Localized deformation in spent nuclear fuel disposal canisters

Julkaisun otsikon käännös: Muodonmuutoksen paikallistuminen käytetyn ydinpolttoaineen loppusijoituskapseleissa

Antti Forsström

Energia- ja konetekniikan laitos

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Suomessa ja Ruotsissa käytetty ydinpolttoaine tullaan loppusijoitettamaan kuparikapseleissa maanalaiseen loppusijoitusluolaan. Mekaanisen kestävyyden näkökulmasta loppusijoitukseen liittyy vielä joitakin epävarmuustekijöitä esimerkiksi muodonmuutoksen paikallistumisen ja ympäristön vaikutusten (korroosio, vedyn vaikutus, jne.) suhteen, erityisesti johtuen loppusijoituksen pitkästä kestosta. Kapselit suljetaan kitkatappihitsaamalla (FSW), jolloin saadaan aikaan luja hitsi suhteessa perusaineeseen, mutta tämä voi toisaalta johtaa muodonmuutoksen paikallistumiseen, jos hitsi on huomattavasti lujempi kuin perusaine. Tämän takia venymän paikallistumista kapselihitseissä tutkittiin optisella venymämittauksella digitaalisen kuvakorrelaation (DIC) avulla. Kapselien hitsausmenetelmää on kehitetty hitsin valmistajan toimesta ottamalla käyttöön suojakaasu hitsauksenaikaisen hapettumisen vähentämiseksi. Tämä vähentää merkittävästi hitsiin sekoittuvien oksidipartikkelien määrää verrattuna vanhaan ilmassa hitsattuun hitsiin, jolloin myös hitsin mikrorakenne muodostuu tasalaatuisemmaksi. DIC-kokeet kuitenkin osoittavat, että verrattuna vanhaan hitsiin venymä paikallistuu uudessa hitsissä voimakkaammin kannenpuoliselle hitsin rajalle. Mikrorakennetutkimusten mukaan tämä johtuu kansien erilaisesta lähtötilasta, joka on aiheutunut todennäköisesti erilaisista takomisolosuhteista, ja lujemmasta hitsiaineesta, jolloin lujuusero hitsin ja perusaineen välillä muodostuu suuremmaksi kuin vanhassa hitsissä. Tämän ilmiön vähentämiseksi olisi varmistettava, että kuparikapselien valmistusmenetelmä takaa mahdollisimman tasalaatuiset mekaaniset ominaisuudet sen eri osissa. Venymän paikallistumisen lisäksi tutkittiin vedyn vaikutusta kuparihitsien ja sisäosan valuraudan mekaanisiin ominaisuuksiin. Hitsin oksidipartikkelit toimivat vedyn "absorptionloukkuina", mutta sillä ei ollut näissä kokeissa vaikutusta kuparin makroskooppiseen sitkeyteen. Kapselin sisäosan valurauta sen sijaan on hyvinkin altista vetyhauraudelle. Venymien paikallistumisen havaitseminen DIC-kokeessa riippuu mittauksen erotuskyvystä ja häiriön määrästä, joiden suhteen vallitsee riippuvuus toisistaan. Kumpaakin voidaan parantaa näytteen kuvioinnilla ja paremmilla mittausolosuhteilla. Tämän takia kuparille kehitettiin kuviointimenetelmä, joka mahdollistaa sekä suurten venymien mittaamisen että pienten venymien havaitsemisen. Tämän lisäksi kehitettiin menetelmä DIC-kokeen erotuskyvyn ja häiriön määrän arvioimiseen. Menetelmä mahdollistaa erotuskyvyn ja mittatarkkuuden arvioimisen mittadatasta itsestään, eikä vaadi keinotekoisten siirtymien tietämistä etukäteen. Sen takia menetelmää voidaan käyttää tietämättä etukäteen yhtään mitään vallinneista mittaolosuhteista tai siirtymien määrästä.

Julkaisun otsikon käännös	Muodonmuutoksen paikallistuminen käytetyn ydinpolttoaineen loppusijoituskapseleissa
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Bossuyt, Sven, Vastuuprofessori Hänninen, Hannu, Vastuuprofessori
Kustantaja	Aalto University
Painoksen ISBN	978-952-60-8699-6
Sähköinen ISBN	978-952-60-8700-9
Tila	Julkaistu - 2019
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

digitaalinen kuvakorrelaatio
DIC
erotuskyky
kuviointi
venymän paikallistuminen
ydinjätteen loppusijoitus
kuparikapseli
valurautasisäke
vetyhauraus

Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-60-8700-9

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@phdthesis{de891e6ba23a48eca96d169f4a04751c,

title = "Localized deformation in spent nuclear fuel disposal canisters",

abstract = "Spent nuclear fuel disposal in copper canisters in a deep geologic repository will be the main disposal method of spent nuclear fuel in Finland and Sweden. The long timespans involved in the disposal bring certain uncertainties, for example, when considering localized deformations and environmental factors, such as corrosion and hydrogen effects on the mechanical properties. The canisters are sealed by friction stir welding (FSW), which results in strong welds, but the variation in cross-weld microstructure may lead to localized deformations during the long disposal of the canisters. Thus, localization of plastic deformation in the canister welds was studied by digital image correlation (DIC). The FSW welding method has recently been modified by argon shielding gas to reduce oxidation during welding. When compared to the old weld, which was welded without shielding gas, the new weld exhibits considerably less oxide particles, and the weld microstructure is more uniform. However, DIC testing indicates more pronounced localization of plastic deformation on the weld boundary on the lid side of the canister. This is attributed to the combined effect of softer lid material and stronger weld material, which leads to worse mechanical performance in terms of strain localization. To minimize this effect, the strength mismatch between different parts of the copper shell should be minimized. In addition to localized deformations, studies were conducted on hydrogen effects on mechanical properties of the copper welds and the cast iron insert. Hydrogen charging of the copper FSW welds indicates that oxide particles trap considerable amounts of hydrogen, but it did not compromise the ductility of the copper welds. However, the cast iron insert of the canisters exhibits a significant sensitivity to hydrogen. In the context of detecting localized deformations by DIC, the trade-off between spatial resolution and noise level of the measurement is critical. Thus, methods for quantifying that trade-off, as well as for improving the DIC data quality were developed. Patterning of copper, by utilizing copper oxide and a photolithographic method, enables the measurement of large deformations in copper, as well as detection of small deformations due to improved data quality. The improvements were quantified by extracting the noise level and autocorrelation length of the noise, which allows the evaluation of precision and spatial resolution of the DIC measurement based on the DIC data itself, and does not require imposing known displacements beforehand.",

keywords = "digital image correlation, DIC, spatial resolution, patterning, localized deformation, spent nuclear fuel disposal, copper canister, cast iron insert, hydrogen embrittlement, digitaalinen kuvakorrelaatio, DIC, erotuskyky, kuviointi, venym{\"a}n paikallistuminen, ydinj{\"a}tteen loppusijoitus, kuparikapseli, valurautasis{\"a}ke, vetyhauraus, digital image correlation, DIC, spatial resolution, patterning, localized deformation, spent nuclear fuel disposal, copper canister, cast iron insert, hydrogen embrittlement",

author = "Antti Forsstr{\"o}m",

year = "2019",

language = "English",

isbn = "978-952-60-8699-6",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "158",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - Localized deformation in spent nuclear fuel disposal canisters

AU - Forsström, Antti

PY - 2019

Y1 - 2019

N2 - Spent nuclear fuel disposal in copper canisters in a deep geologic repository will be the main disposal method of spent nuclear fuel in Finland and Sweden. The long timespans involved in the disposal bring certain uncertainties, for example, when considering localized deformations and environmental factors, such as corrosion and hydrogen effects on the mechanical properties. The canisters are sealed by friction stir welding (FSW), which results in strong welds, but the variation in cross-weld microstructure may lead to localized deformations during the long disposal of the canisters. Thus, localization of plastic deformation in the canister welds was studied by digital image correlation (DIC). The FSW welding method has recently been modified by argon shielding gas to reduce oxidation during welding. When compared to the old weld, which was welded without shielding gas, the new weld exhibits considerably less oxide particles, and the weld microstructure is more uniform. However, DIC testing indicates more pronounced localization of plastic deformation on the weld boundary on the lid side of the canister. This is attributed to the combined effect of softer lid material and stronger weld material, which leads to worse mechanical performance in terms of strain localization. To minimize this effect, the strength mismatch between different parts of the copper shell should be minimized. In addition to localized deformations, studies were conducted on hydrogen effects on mechanical properties of the copper welds and the cast iron insert. Hydrogen charging of the copper FSW welds indicates that oxide particles trap considerable amounts of hydrogen, but it did not compromise the ductility of the copper welds. However, the cast iron insert of the canisters exhibits a significant sensitivity to hydrogen. In the context of detecting localized deformations by DIC, the trade-off between spatial resolution and noise level of the measurement is critical. Thus, methods for quantifying that trade-off, as well as for improving the DIC data quality were developed. Patterning of copper, by utilizing copper oxide and a photolithographic method, enables the measurement of large deformations in copper, as well as detection of small deformations due to improved data quality. The improvements were quantified by extracting the noise level and autocorrelation length of the noise, which allows the evaluation of precision and spatial resolution of the DIC measurement based on the DIC data itself, and does not require imposing known displacements beforehand.

AB - Spent nuclear fuel disposal in copper canisters in a deep geologic repository will be the main disposal method of spent nuclear fuel in Finland and Sweden. The long timespans involved in the disposal bring certain uncertainties, for example, when considering localized deformations and environmental factors, such as corrosion and hydrogen effects on the mechanical properties. The canisters are sealed by friction stir welding (FSW), which results in strong welds, but the variation in cross-weld microstructure may lead to localized deformations during the long disposal of the canisters. Thus, localization of plastic deformation in the canister welds was studied by digital image correlation (DIC). The FSW welding method has recently been modified by argon shielding gas to reduce oxidation during welding. When compared to the old weld, which was welded without shielding gas, the new weld exhibits considerably less oxide particles, and the weld microstructure is more uniform. However, DIC testing indicates more pronounced localization of plastic deformation on the weld boundary on the lid side of the canister. This is attributed to the combined effect of softer lid material and stronger weld material, which leads to worse mechanical performance in terms of strain localization. To minimize this effect, the strength mismatch between different parts of the copper shell should be minimized. In addition to localized deformations, studies were conducted on hydrogen effects on mechanical properties of the copper welds and the cast iron insert. Hydrogen charging of the copper FSW welds indicates that oxide particles trap considerable amounts of hydrogen, but it did not compromise the ductility of the copper welds. However, the cast iron insert of the canisters exhibits a significant sensitivity to hydrogen. In the context of detecting localized deformations by DIC, the trade-off between spatial resolution and noise level of the measurement is critical. Thus, methods for quantifying that trade-off, as well as for improving the DIC data quality were developed. Patterning of copper, by utilizing copper oxide and a photolithographic method, enables the measurement of large deformations in copper, as well as detection of small deformations due to improved data quality. The improvements were quantified by extracting the noise level and autocorrelation length of the noise, which allows the evaluation of precision and spatial resolution of the DIC measurement based on the DIC data itself, and does not require imposing known displacements beforehand.

KW - digital image correlation

KW - DIC

KW - spatial resolution

KW - patterning

KW - localized deformation

KW - spent nuclear fuel disposal

KW - copper canister

KW - cast iron insert

KW - hydrogen embrittlement

KW - digitaalinen kuvakorrelaatio

KW - DIC

KW - erotuskyky

KW - kuviointi

KW - venymän paikallistuminen

KW - ydinjätteen loppusijoitus

KW - kuparikapseli

KW - valurautasisäke

KW - vetyhauraus

KW - digital image correlation

KW - DIC

KW - spatial resolution

KW - patterning

KW - localized deformation

KW - spent nuclear fuel disposal

KW - copper canister

KW - cast iron insert

KW - hydrogen embrittlement

M3 - Doctoral Thesis

SN - 978-952-60-8699-6

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -

Localized deformation in spent nuclear fuel disposal canisters

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