An interatomic potential for W-N interactions

N-2 gas is routinely used as a seeding species in fusion plasma to control the amount of power emitted from the plasma by radiation to the tungsten walls of an ITER-like divertor. Nitrogen atoms interact with the plasma-facing materials beryllium and tungsten, and form chemical bonds with the wall surfaces, as well as with plasma hydrogen isotopes, thus raising a special interest in W-N and N-H interactions in the fusion community. In this work we describe the development of an analytical interatomic potential for W-N interactions and benchmark the potential against DFT calculation results for N defects in tungsten.Peer reviewe

Fuel inventory and material migration of JET main chamber plasma facing components compared over three operational periods

Fuel retention and material migration results from JET ITER-like wall beryllium limiter tiles are presented for three operating periods. Ion beam analysis results support the general picture of erosion during limiter configurations with local deposition on tile ends far into the scrape off layer. Similar trends of fuel concentrations are observed in all JET operating periods; (i) low on surfaces exposed to high heat flux and erosion and (ii) higher in deposits. The pattern of fuel retention and deposition correlates with heat flux and distribution of limiter plasmas touching inner and outer limiters. The D/Be ratio in the thickest deposit is similar to 0.01. Global fuel retention attributed to limiters isPeer reviewe

Determination of retained tritium from ILW dust particles in JET

Quantitative tritium inventory in dust particles from campaigns in the JET tokamak with the carbon wall (2007-2009) and the ITER-like wall (ILW 2011-2012) were determined by the liquid scintillation counter and the full combustion method. A feature of this full combustion method is that dust particles were covered by a tin (Sn) which reached 2100 K during combustion under oxygen flow. The specific tritium inventory for samples from JET with carbon and with metal walls was measured and found to be similar. However, the total tritium inventory in dust particles from the ILW experiment was significantly smaller in comparison to the carbon wall due to the lower amount of dust particles generated in the presence of metal walls.Peer reviewe

Modelling of the effect of ELMs on fuel retention at the bulk W divertor of JET

Effect of ELMs on fuel retention at the bulk W target of JET ITER-Like Wall was studied with multi-scale calculations. Plasma input parameters were taken from ELMy H-mode plasma experiment. The energetic intra-ELM fuel particles get implanted and create near-surface defects up to depths of few tens of nm, which act as the main fuel trapping sites during ELMs. Clustering of implantation-induced vacancies were found to take place. The incoming flux of inter-ELM plasma particles increases the different filling levels of trapped fuel in defects. The temperature increase of the W target during the pulse increases the fuel detrapping rate. The inter-ELM fuel particle flux refills the partially emptied trapping sites and fills new sites. This leads to a competing effect on the retention and release rates of the implanted particles. At high temperatures the main retention appeared in larger vacancy clusters due to increased clustering rate.Peer reviewe

Costs and benefits of pig feed salmonella control programme in Finland

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Salmonellatorjunnan taloudellisten riskien hallinnan tukemisen vaihtoehdot

Salmonellakontaminaatio voi aiheuttaa kotieläintilalla mittavia taloudellisia menetyksiä. Kotieläintilojen, etenkin sika-alan, salmonellasaneerausten kokonaiskustannukset ovat viime vuosina kasvaneet, kun salmonellatapausten määrä on noussut ja tilat ovat kasvaneet yhtä suuremmiksi. Nämä ovat nostaneet salmonellakorvausten kustannuksia, mikä on johtanut suurempiin vakuutusmaksuihin, tiukentuneisiin vakuutusehtoihin ja ryhmäetuvakuutusten irtisanomiseen. Tässä selvityksessä kartoitettiin vakuutuksentarjoajien halukkuutta jatkaa ryhmäetuvakuutuksia sekä valtiontuen mahdollisuuksia ja merkitystä salmonellavakuutusmaksujen tai jälleenvakuuttamisen tukemisen muodossa. Selvityksessä tarkasteltiin useita eri tukiskenaarioita. Keskeisimmät tukivaihtoehdot olivat: • Valtio tukisi vakuutusmaksua siten, että tuki kattaisi 70 % vakuutuksen verollisesta hinnasta ja tukikelpoisuuden tarkastaisi viranomainen. • Vakuutusyhtiö korvaisi yksittäisen vahingon joko 0,5 tai 1,0 miljoonaan euroon asti ja sen ylimenevästä osuudesta vastaisi valtio. Vakuutusmaksua ei tuettaisi vakuutusmaksuverovapaudella. • Vakuutusyhtiö korvaisi vuosittaiset yhteenlasketut vahingot viiteen miljoonaan asti. Ylimenevästä osuudesta vastaisi valtio. Vakuutusmaksu ei tuettaisi vakuutusmaksuverovapaudella. Taloudellisessa analyysissa salmonellavahingot simuloitiin käyttäen tausta-aineistoa 5–10 viime vuoden ajanjaksolta. Sika-alalle simuloidut vahingot olivat 3,5–5,3 prosenttia ja siipikarja- ja nauta-aloilla noin 0,2 % kyseisten tuotantosuuntien vuoden 2021 markkinatuotosta. Sika-alalle salmonellavakuutusten tuki oli tarkastelluissa vaihtoehdoissa tukimallista riippuen 2,1 ja 6,4 miljoonan välillä. Simulaatiotulokset viittaavat siihen, että jälleenvakuuttamisen tukeminen, erityisesti tilakohtaisten vahinkojen korvaaminen valtion varoista tietyn kynnysarvon jälkeen olisi vakuutusten houkuttelevuuden ja toimivuuden kannalta tehokkaampi tapa tukea salmonellavakuuttamista kuin vakuutusmaksutuki. Se voisi auttaa yksityistä vakuutusmarkkinaa säilymään ja kehittymään. ”Jälleenvakuutusmalli” voi kuitenkin aiheuttaa valtion budjetille riskejä, joiden hallinta tulisi ratkaista, sillä sen aiheuttamat menot ovat vaikeasti ennakoitavissa. Aiemmin valmistellun, mutta toteutumatta jääneen salmonellarahaston kehitystyötä tulisi jatkaa tuotantosuuntakohtaisesti valtion ja elinkeinon yhteistyönä. Rahastoon tilojen tekemiä maksuja tulisi harkita porrastettavaksi siten, että eläintä kohti laskettuun maksuun vaikuttaisivat tilan eläinmäärä ja tautisuojauksen taso tilalla. Maksujen porrastaminen yhtäältä kannustaisi tautiriskin vähentämiseen tautisuojausta kohentamalla ja toisaalta auttaisi huomioimaan tilakohtaisen riskin maksuissa. Sika-alan asiantuntijoiden ja vakuutustentarjoajien kanssa käytyjen keskusteluiden perusteella tautisuojaukseen liittyvän tiedon saanti ja etenkin sen käyttäminen vakuutusten hinnoittelussa aiheuttaa haasteita. Tautisuojausluokituksen käyttö vakuutusmaksujen kannustimena on tärkeää, sillä se ohjaa tiloja kohti parempaa tautiriskinhallintaa. Olennaista onkin, että salmonellan esiintymisriskiä saadaan koko toimialan tasolla vähennettyä, sillä se laskee korvattavia vahinkoja ja vakuutusmaksuja. Eräs riskinhallintamahdollisuus on alan salmonellarahasto, jonka mahdollisuuksia on selvitty, ja sen kehitystyötä tulisi jatkaa. Tuotantosuuntien välillä oli melko suuria eroja salmonellakorvauksissa, joten tukimallin ehtoja on tarkasteltava tuotantosuuntakohtaisesti. Salmonellariskinhallinta hyödyttää ensisijaisesti kansanterveyttä, minkä vuoksi haastatellut asiantuntijat kokivat, että valtiovallan tulisi osallistua nykyistä voimakkaammin siitä aiheutuviin kustannuksiin

Deposition in the inner and outer corners of the JET divertor with carbon wall and metallic ITER-like wall

Rotating collectors and quartz microbalances (QMBs) are used in JET to provide time-dependent measurements of erosion and deposition. Rotation of collector discs behind apertures allows recording of the long term evolution of deposition. QMBs measure mass change via the frequency deviations of vibrating quartz crystals. These diagnostics are used to investigate erosion/deposition during JET-C carbon operation and JET-ILW (ITER-like wall) beryllium/ tungsten operation. A simple geometrical model utilising experimental data is used to model the time-dependent collector deposition profiles, demonstrating good qualitative agreement with experimental results. Overall, the JET-ILW collector deposition is reduced by an order of magnitude relative to JET-C, with beryllium replacing carbon as the dominant deposit. However, contrary to JET-C, in JET-ILW there is more deposition on the outer collector than the inner. This reversal of deposition asymmetry is investigated using an analysis of QMB data and is attributed to the different chemical properties of carbon and beryllium.EURATOM 63305

Long-term fuel retention and release in JET ITER-Like Wall at ITER-relevant baking temperatures

The fuel outgassing efficiency from plasma-facing components exposed in JET-ILW has been studied at ITER-relevant baking temperatures. Samples retrieved from the W divertor and Be main chamber were annealed at 350 and 240 °C, respectively. Annealing was performed with thermal desoprtion spectrometry (TDS) for 0, 5 and 15 h to study the deuterium removal effectiveness at the nominal baking temperatures. The remained fraction was determined by emptying the samples fully of deuterium by heating W and Be samples up to 1000 and 775 °C, respectively. Results showed the deposits in the divertor having an increasing effect to the remaining retention at temperatures above baking. Highest remaining fractions 54 and 87% were observed with deposit thicknesses of 10 and 40 μm, respectively. Substantially high fractions were obtained in the main chamber samples from the deposit-free erosion zone of the limiter midplane, in which the dominant fuel retention mechanism is via implantation: 15 h annealing resulted in retained deuterium higher than 90%. TDS results from the divertor were simulated with TMAP7 calculations. The spectra were modelled with three deuterium activation energies resulting in good agreement with the experimentsEURATOM 63305

The influence of carbon impurities on the formation of loops in tungsten irradiated with self-ions

The microstructure changes taking place in W under irradiation are governed by many factors, amongst which C impurities and their interactions with self-interstitial atoms (SIA). In this work, we specifically study this effect by conducting a dedicated 2-MeV self-ions irradiation experiment, at room temperature. Samples were irradiated up to 0.02, 0.15 and 1.2 dpa. Transmission electron microscopy (TEM) expectedly revealed a large density of SIA loops at all these doses. Surprisingly, however, the loop number density increased in a non-monotonous manner with the received dose. Performing chemical analysis with secondary ion spectroscopy measurements (SIMS), we find that our samples were likely contaminated by C injection during the irradiation. Employing an object kinetic Monte Carlo (OKMC) model for microstructure evolution, we demonstrate that the C injection is the likely factor explaining the evolution of loops number density. Our findings highlight the importance of the well-known issue of C injection during ion irradiation experiments, and demonstrate how OKMC models can help to rationalize this effect.Peer reviewe

Efficiency of thermal outgassing for tritium retention measurement and removal in ITER

Proceedings of the 22nd International Conference on Plasma Surface Interactions 2016, 22nd PSIAs a licensed nuclear facility, ITER must limit the in-vessel tritium (T) retention to reduce the risks of potential release during accidents, the inventory limit being set at 1kg. Simulations and extrapolations from existing experiments indicate that T-retention in ITER will mainly be driven by co-deposition with beryllium (Be) eroded from the first wall, with co-deposits forming mainly in the divertor region but also possibly on the first wall itself. A pulsed Laser-Induced Desorption (LID) system, called Tritium Monitor, is being designed to locally measure the T-retention in co-deposits forming on the inner divertor baffle of ITER. Regarding tritium removal, the baseline strategy is to perform baking of the plasma-facing components, at 513K for the FW and 623K for the divertor. Both baking and laser desorption rely on the thermal desorption of tritium from the surface, the efficiency of which remains unclear for thick (and possibly impure) co-deposits. This contribution reports on the results of TMAP7 studies of this efficiency for ITER-relevant deposits.Peer reviewe