New Methods for HTR Fuel Waste Management

International audienceConsidering the need to reduce waste production and greenhouse emissions by still keeping high energy efficiency, various 4th generation nuclear energy systems have been proposed. As far as graphite moderated reactors are concerned, one of the key issues is the large volumes of irradiated graphite encountered (1770 m3 for fuel elements and 840 m3 for reflector elements during the lifetime (60 years) of a single reactor module [1]). With the objective to reduce volume of waste in the HTR concept, it is very important to be able to separate the fuel from low level activity graphite. This requires to separate TRISO particles from the graphite matrix with the sine qua non condition to not break TRISO particles in case of future embedding of particles in a matrix for disposal. According to National Regulatory Systems, in case of limited graphite waste production or of short duration HTR projects (e.g. in Germany), direct disposal without separation is acceptable. Nevertheless, in case of large scale deployment of HTR technology, such approach is not economical and sustainable. Previous attempts in graphite management (furnace, fluidised bed and laser incinerations and encapsulation matrices) dealt with graphite matrix only. These are the reasons why we studied the management of irradiated compact-type fuel element. We simulated the presence of fuel in the particles by using ZrO2 kernels. Compacts with ZrO2 TRISO particles were manufactured by AREVA NP. Two original methods have been studied. First, we tested high pressure jet to erode graphite and clean TRISO particles. Best erosion rate reached about 0.18 kg/h for a single nose ending. Examination of treated graphite showed a mixture of undamaged TRISO particles, particles that have lost the outer pyrolytic carbon layer and ZrO2 kernels. Secondly, we studied the thermal shock method by immerging successively graphite into liquid nitrogen and hot water to cause fracturing of the compact. This produced particles and graphite fragments with diameter ranging from several centimetres to less than 500 µm. This relatively simple and economic method may potentially be considered as a pre-treatment step and be coupled with other method(s) before reprocessing and recycling for example

Performance of prototypes for the ALICE electromagnetic calorimeter

The performance of prototypes for the ALICE electromagnetic sampling calorimeter has been studied in test beam measurements at FNAL and CERN. A $4\times4$ array of final design modules showed an energy resolution of about 11% /$\sqrt{E(\mathrm{GeV})}$ $\oplus$ 1.7 % with a uniformity of the response to electrons of 1% and a good linearity in the energy range from 10 to 100 GeV. The electromagnetic shower position resolution was found to be described by 1.5 mm $\oplus$ 5.3 mm /$\sqrt{E \mathrm{(GeV)}}$. For an electron identification efficiency of 90% a hadron rejection factor of $>600$ was obtained.Comment: 10 pages, 10 figure

Alignment of the ALICE Inner Tracking System with cosmic-ray tracks

37 pages, 15 figures, revised version, accepted by JINSTALICE (A Large Ion Collider Experiment) is the LHC (Large Hadron Collider) experiment devoted to investigating the strongly interacting matter created in nucleus-nucleus collisions at the LHC energies. The ALICE ITS, Inner Tracking System, consists of six cylindrical layers of silicon detectors with three different technologies; in the outward direction: two layers of pixel detectors, two layers each of drift, and strip detectors. The number of parameters to be determined in the spatial alignment of the 2198 sensor modules of the ITS is about 13,000. The target alignment precision is well below 10 micron in some cases (pixels). The sources of alignment information include survey measurements, and the reconstructed tracks from cosmic rays and from proton-proton collisions. The main track-based alignment method uses the Millepede global approach. An iterative local method was developed and used as well. We present the results obtained for the ITS alignment using about 10^5 charged tracks from cosmic rays that have been collected during summer 2008, with the ALICE solenoidal magnet switched off.Peer reviewe

Transverse momentum spectra of charged particles in proton-proton collisions at s=900\sqrt{s} = 900 GeV with ALICE at the LHC

The inclusive charged particle transverse momentum distribution is measured in proton-proton collisions at $\sqrt{s} = 900$ GeV at the LHC using the ALICE detector. The measurement is performed in the central pseudorapidity region $(|\eta|<0.8)$ over the transverse momentum range $0.15<p_{\rm T}<10$ GeV/$c$. The correlation between transverse momentum and particle multiplicity is also studied. Results are presented for inelastic (INEL) and non-single-diffractive (NSD) events. The average transverse momentum for $|\eta|<0.8$ is $\left<p_{\rm T}\right>_{\rm INEL}=0.483\pm0.001$ (stat.) $\pm0.007$ (syst.) GeV/$c$ and \left_{\rm NSD}=0.489\pm0.001 (stat.) $\pm0.007$ (syst.) GeV/$c$, respectively. The data exhibit a slightly larger $\left<p_{\rm T}\right>$ than measurements in wider pseudorapidity intervals. The results are compared to simulations with the Monte Carlo event generators PYTHIA and PHOJET.Comment: 20 pages, 8 figures, 2 tables, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/390

The ALICE experiment at the CERN LHC

ALICE (A Large Ion Collider Experiment) is a general-purpose, heavy-ion detector at the CERN LHC which focuses on QCD, the strong-interaction sector of the Standard Model. It is designed to address the physics of strongly interacting matter and the quark-gluon plasma at extreme values of energy density and temperature in nucleus-nucleus collisions. Besides running with Pb ions, the physics programme includes collisions with lighter ions, lower energy running and dedicated proton-nucleus runs. ALICE will also take data with proton beams at the top LHC energy to collect reference data for the heavy-ion programme and to address several QCD topics for which ALICE is complementary to the other LHC detectors. The ALICE detector has been built by a collaboration including currently over 1000 physicists and engineers from 105 Institutes in 30 countries. Its overall dimensions are 161626 m3 with a total weight of approximately 10 000 t. The experiment consists of 18 different detector systems each with its own specific technology choice and design constraints, driven both by the physics requirements and the experimental conditions expected at LHC. The most stringent design constraint is to cope with the extreme particle multiplicity anticipated in central Pb-Pb collisions. The different subsystems were optimized to provide high-momentum resolution as well as excellent Particle Identification (PID) over a broad range in momentum, up to the highest multiplicities predicted for LHC. This will allow for comprehensive studies of hadrons, electrons, muons, and photons produced in the collision of heavy nuclei. Most detector systems are scheduled to be installed and ready for data taking by mid-2008 when the LHC is scheduled to start operation, with the exception of parts of the Photon Spectrometer (PHOS), Transition Radiation Detector (TRD) and Electro Magnetic Calorimeter (EMCal). These detectors will be completed for the high-luminosity ion run expected in 2010. This paper describes in detail the detector components as installed for the first data taking in the summer of 2008

Μεταφορά πυρηνικών πρωτεϊνών μέσω των μικροσωληνίσκων της πυρηνικής ατράκτου

Διατμηματικό, συνεργαζόμενα Τμήματα Βιολογίας και Ιατρικής.Αρκετές από τις πρωτεΐνες του πυρηνικού φακέλου συνδέονται περιστασιακά με τους μικροσωληνίσκους της πυρηνικής ατράκτου κατά την διάρκεια της μίτωσης προκειμένου να μοιραστούν στα δυο θυγατρικά κύτταρα με τρόπο ανάλογο με αυτόν που μοιράζονται τα χρωμοσώματα. Η πρόσδεση πρωτεΐνών του πυρήνα με την μιτωτική άτρακτο είναι πολύ εκλεκτική και δεν συμβαίνει για όλες τις πρωτεΐνες. Η μετακίνηση των πρωτεϊνών αυτών προς τους πόλους της μιτωτικής ατράκτου διαμεσολαβείται από πρωτεΐνες κινητήρες και/ή λόγω της δυναμικής των μικροσωληνίσκων. Παρατηρήθηκε παραπάνω ότι η β2-τουμπουλίνη συγκεντρώνεται στην μιτωτική άτρακτο, στους αστέρες και στο μεσαίο σωμάτιο (midbody) έχοντας ενεργό ρόλο στον σχηματισμό της μιτωτικής ατράκτου, ενώ η παρουσία της στον πυρήνα κατά την μεσόφαση δεν φαίνεται να εξυπηρετεί μια προφανή λειτουργία του κυττάρου. Μια πιθανή ερμηνεία είναι ότι ένα αρκετά μεγάλο ποσοστό της β-τουμπουλίνης που έχει συγγένεια για πρωτεΐνες του πυρηνικού φακέλου εντοπίζεται στον πυρήνα κατά την μεσόφαση και μόλις το κύτταρο εισέλθει στην μίτωση να στρατολογείται άμεσα για τη συγκρότηση της μιτωτικής ατράκτου. Εκεί η β2-τουμπουλίνη χρησιμοποιείται ως συστατικό της μιτωτικής ατράκτου για τη μεταφορά των χρωμοσωμάτων, καθώς και κυστιδίων του πυρηνικού φακέλου και συστατικών του πυρηνοπλάσματος στους πόλους του κυττάρου. Οι πρωτεΐνες κινητήρες όπως η δυνεΐνη, η κινεσίνη, κ.α. είναι μέρος του κυτταροσκε-λετού και συνδεόμενες με τους μικροσωληνίσκους παίζουν ενεργό ρόλο στην μετα-κίνηση πρωτεϊνών. Τα παραπάνω αποτελέσματα δείχνουν ότι υπάρχει σύνδεση της δυνεΐνης με την έξω πυρηνική μεμβράνη, γεγονός που ενισχύει το συμπέρασμα ότι η δυνεΐνη έχει ρόλο κλειδί στην διάρρηξη του πυρηνικού φακέλου στο τέλος της πρόφασης και την αρχή της προμετάφασης. Το γέγονός ότι η δυνεΐνη δεν συνδέεται με την έσω πυρηνική μεμβράνη θέτει υπο αμφισβήτηση την πιθανότητα η μετακίνηση των συστατικών του πυρηνοπλάσματος να διαμεσολαβείται από την δυνεΐνη και ενισχύει την άποψη ότι η διαδικασία διαμεσολαβείται από την δυναμική των μικροσωληνίσκων. Προφανώς για να αποσαφηνιστεί το θέμα αυτό θα πρέπει να προστεθούν ακόμη αρκετά πειραματικά δεδομένα