As a burnable absorber, gadolinium oxide (Gd2O3) is widely used in light water reactors due to the high neutron absorption cross section of several gadolinium isotopes and its good solid solubility in UO2. However, some isotopes of natural Gd cause residual reactivity suppression, while some are not efficient neutron absorbers, reducing the efficiency of the burnable absorber when implemented. In this study, fuel assemblies utilizing gadolinium oxide enriched with 157Gd isotope were modelled using Monte Carlo particle transport methods and compared to fuel with a natural Gd based absorber. Reactivity gains were examined over the life of the assembly utilizing 157Gd-enriched absorber as compared to natural gadolinia. A preliminary economic evaluation is also made to assess the commercial benefits of using 157Gd-enriched burnable absorber. Use of enriched gadolinium oxide is shown to eliminate residual reactivity caused by natural gadolinium oxide, and similar reactivity properties (and therefore criticality margins) can be achieved with less burnable absorber in the fuel. The financial cost of incorporating enriched Gd isotopes into nuclear fuel has also been estimated.

A UK National Thermal-Hydraulics Facility (NTHF) dedicated to supporting new reactor and other relevant business is being developed, one of the purposes being to deliver on the government’s carbon emission reduction commitments. The facility site is foreseen to be at Menai Science Park on the isle of Anglesey in North Wales, a region expected to see significant low carbon energy deployment in coming years. The UK NTHF is envisioned to cater for the needs of emerging nuclear in the UK – but also to serve as a hardware platform for international thermal-hydraulics research collaboration. Plans are to construct a platform capable of maintaining several test loops including support for the UK’s on-going, conventional nuclear new build programme as well as Gen-IV systems and associated materials like molten salt and liquid metal coolant media. Motivations are given for NTHF expected capabilities and requirements, which form the basis for its current design and planning state.

The isotopic fractions of plutonium produced in a reactor are of significant value as nuclear forensic signatures, and the mechanisms of their production and alteration should be investigated thoroughly. A series of neutronics calculations were made on a typical UO2 PWR setup, introducing (Th, U)O2 MOX rods gradually, to investigate how the presence of Th affects the 240Pu/239Pu and 242Pu/239Pu ratios in the remaining UO2 fuel rods. A relationship is found that links the percentage change in these ratios, with the burnup and Th content in the configuration. In an extreme case, it was found that the presence of Th may increase the ratio of 242Pu/239Pu by as much as 3.5% at low burnup.

The 235U neutron-induced cross section is widely used as reference cross section for measuring other fission cross sections, but in the resonance region it is not considered as an IAEA standard because of the scarce experimental data covering the full region. In this work, we deal with a new analysis of the experimental data obtained with a detection setup based on parallel plate ionization chambers (PPACs) at the CERN n_TOF facility in the range from 1 eV to 10 keV. The relative cross section has been normalised to the IAEA value in the region between 7.8 and 11 eV, which is claimed as well-known. Comparison with the ENDF/B-VII evaluation and the IAEA reference file from 100 eV to 10 keV are provided.

We present the analysis of the resolved resonance region for the 234U(n,f) cross section data measured at the CERN n_TOF facility. The resonance parameters in the energy range from 1 eV to 1500 eV have been obtained with the SAMMY code by using as initial parameters for the fit the resonance parameters of the JENDL-3.3 evaluation. In addition, the statistical analysis has been accomplished, partly with the SAMDIST code, in order to study the level spacing and the Mehta-Dyson correlation.

The ($n,\ensuremath{\gamma}$) reaction of the radioactive isotope ${}^{93}$Zr has been measured at the n_TOF high-resolution time-of-flight facility at CERN. Resonance parameters have been extracted in the neutron energy range up to 8 keV, yielding capture widths smaller (14$%$) than reported in an earlier experiment. These results are important for detailed nucleosynthesis calculations and for refined studies of waste transmutation concepts.

The neutron-induced fission cross-section of 241Am has been measured relative to the standard fission cross-section of 235U between 0.5 and 20MeV. The experiment was performed at the CERN n_TOF facility. Fission fragments were detected by a fast ionization chamber by discriminating against the \(\alpha\)-particles from the high radioactivity of the samples. The high instantaneous neutron flux and the low background of the n_TOF facility enabled us to obtain uncertainties of \( \approx\) 5%. With the present results it was possible to resolve discrepancies between previous data sets and to confirm current evaluations, thus providing important information for design studies of future reactors with improved fuel burn-up.

The (n, gamma) reaction of the radioactive isotope Zr-93 has been measured at the n_TOF high-resolution time-of-flight facility at CERN. Resonance parameters have been extracted in the neutron energy range up to 8 keV, yielding capture widths smaller (14%) than reported in an earlier experiment. These results are important for detailed nucleosynthesis calculations and for refined studies of waste transmutation concepts. DOI: 10.1103/PhysRevC.87.014622

C.Dom ingo-Pardo, U.Abbondanno, G .Aerts, H. Alvarez, F.Alvarez-Velarde, S.Andriam onje, J.Andrzejewski, P.Assim akopoulos, L.Audouin, G .Badurek, P.Baum ann, F.Be cv a r, E.Berthoum ieux, S.Bisterzo, F.Calvi~ no, M .Calviani, D.Cano-O tt, R.Capote, C.Carrapi co, P.Cennini, V.Chepel, E.Chiaveri, N.Colonna, G .Cortes, A.Couture, J.Cox, M .Dahlfors, S.David, I.Dillm an, R.Dol ni, W .Dridi, I.Duran, C.Eleftheriadis, M .Em bid-Segura, L.Ferrant, A.Ferrari, R.Ferreira-M arques, L.Fitzpatrick, H.Frais-K oelbl, K .Fujii, W .Furm an, R.G allino, I.G oncalves, E.G onzalez-Rom ero, A.G overdovski, F.G ram egna, E.G riesm ayer, C.G uerrero, F.G unsing, B.Haas, R.Haight, M .Heil, A.Herrera-M artinez, M .Igashira, M .Isaev, E.Jericha, F.K appeler, Y.K adi, D.K aradim os, D.K aram anis, M .K erveno, V.K etlerov, P.K oehler, V.K onovalov, E.K ossionides, M .K rti cka, C.Lam boudis, H.Leeb, A.Lindote, I.Lopes, M .Lozano, S.Lukic, J.M arganiec, S.M arrone, C.M assim i, P.M astinu, A.M engoni, P.M .M ilazzo, C.M oreau, M .M osconi, F.Neves, H.O berhum m er, M .O shim a, S.O ’Brien, J.Pancin, C.Papachristodoulou, C.Papadopoulos, C.Paradela, N.Patronis, A.Pavlik, P.Pavlopoulos, L.Perrot, R.Plag, A.Plom pen, A.Plukis, A.Poch, C.Pretel, J.Q uesada, T.Rauscher, R.Reifarth, M .Rosetti, C.Rubbia, G .Rudolf, P.Rullhusen, J.Salgado, L.Sarchiapone, I.Savvidis, C.Stephan, G .Tagliente, J.L.Tain, L.Tassan-G ot, L.Tavora, R.Terlizzi, G .Vannini, P.Vaz, A.Ventura, D.Villam arin, M .C.Vincente, V.Vlachoudis, R.Vlastou, F.Voss, S.W alter, H.W endler, M .W iescher, and K .W isshak

The Am-243 neutron capture cross section has been measured at the n_TOF facility(1) in the 0.7 eV-2 keV energy range. The n_TOF Total Absorption Calorimeter(2) (TAC) composed by 40 BaF2 crystals has been used in the measurement for detecting the electromagnetic cascades produced in the 243Am(n,gamma) reactions. All current evaluations in the resolved resonance region are based essentially in fission measurements and in only one transmission measurement.(3) The analysis of the measurement has been finished recently, and it is ready for its distribution to the EXFOR nuclear database. In addition, the data obtained with the TAC provide valuable information on the level density in the compound nucleus Am-244 and on its electromagnetic de-excitation scheme. In particular, the 243Am data, will be combined with data from previous measurements of Am-241, (240)pu, Np-237 and U-233,U-234,U-236 and with future measurements of U-235,U-238 for a systematic investigation of the photon strength functions in actinides.

Neutron-induced fission cross section measurements of 233U, 243Am and 241Am relative to 235U have been carried out at the neutron time-of-flight facility n_TOF at CERN. A fast ionization chamber has been employed. All samples were located in the same detector; therefore the studied elements and the reference 235U target are subject to the same neutron beam.

We have measured the neutron capture cross sections of the stable magnesium isotopes Mg-24,Mg-25,Mg-26 in the energy range of interest to the s process using the neutron time-of-flight facility n_TOF at CERN. Capture events from a natural metal sample and from samples enriched in Mg-25 and Mg-26 were recorded using the total energy method based on (C6H6)-H-2 detectors. Neutron resonance parameters were extracted by a simultaneous resonance shape analysis of the present capture data and existing transmission data on a natural isotopic sample. Maxwellian-averaged capture cross sections for the three isotopes were calculated up to thermal energies of 100 keV and their impact on s-process analyses was investigated. At 30 keV the new values of the stellar cross section for Mg-24, Mg-25, and Mg-26 are 3.8 +/- 0.2 mb, 4.1 +/- 0.6 mb, and 0.14 +/- 0.01 mb, respectively.

Neutron-induced fission cross section measurements of U-233, Am-243 and Am-241 relative to U-235 have been carried out at the neutron time-of-flight facility n_TOF at CERN. A fast ionization chamber has been employed. All samples were located in the same detector; therefore the studied elements and the reference U-235 target are subject to the same neutron beam.

The neutron time of flight (n_TOF) facility at CERN is a spallation neutron source with white neutron energy spectrum (from thermal to several GeV), covering the full energy range of interest for nuclear astrophysics, in particular for measurements of the neutron capture cross section required in s-process nucleosynthesis. This contribution presents an overview on the astrophysical program carried on at the n_TOF facility, the main results and their implications. 1 Stellar nucleosyntesis The origin of the elements is an important topic to understand the evolution of the universe. Hydrogen and helium, and small amounts of lithium, were formed in the period between about 100 seconds and 20 minutes after the big bang [1]. This period of primordial nucleosynthesis was followed by galactic condensation and the formations of the stars. All elements heavier than lithium have been formed in

The yield of the neutron capture reaction ${}^{232}$Th($n,\ensuremath{\gamma}$) has been measured at the neutron time-of-flight facility n_TOF at CERN in the energy range from 1 eV to 1 MeV. The reduction of the acquired data to the capture yield for resolved resonances from 1 eV to 4 keV is described and compared to a recent evaluated data set. The resonance parameters were used to assign an orbital momentum to each resonance. A missing level estimator was used to extract the $s$-wave level spacing of ${D}_{0}=17.2\ifmmode\pm\else\textpm\fi{}0.9$ eV.

The neutron capture cross section of Np-237 was measured between 0.7 and 500 eV at the CERN n_TOF facility using the 4 pi BaF2 Total Absorption Calorimeter. The experimental capture yield was extracted minimizing all the systematic uncertainties and was analyzed together with the most reliable transmission data available using the SAMMY code. The result is a complete set of individual as well as average resonance parameters [D-0 = 0.56(2) eV, = 40.9(18) meV, 10(4)S(0) = 0.98(6), R' = 9.8(6) fm]. The capture cross section obtained in this work is in overall agreement with the evaluations and the data of Weston and Todd [Nucl. Sci. Eng. 79, 184 (1981)], thus showing sizable differences with respect to previous data from Scherbakov et al. [J. Nucl. Sci. Technol. 42, 135 (2005)] and large discrepancies with data Kobayashi et al. [J. Nucl. Sci. Technol. 39, 111 (2002)]. The results indicate that a new evaluation combining the present capture data with reliable transmission data would allow reaching an accuracy better than 4%, in line with the uncertainty requirements of the nuclear data community for the design and operation of current and future nuclear devices.

The neutron-induced fission cross section of ${}^{245}$Cm was measured at n_TOF in a wide energy range and with high resolution. The energy dependence, measured in a single measurement from 30 meV to 1 MeV neutron energy, has been determined with 5$%$ accuracy relative to the ${}^{235}$U(n,f) cross section. In order to reduce the uncertainty on the absolute value, the data have been normalized at thermal energy to recent measurements performed at ILL and BR1. In the energy range of overlap, the results are in fair agreement with some previous measurements and confirm, on average, the evaluated cross section in the ENDF/B-VII.0 database, although sizable differences are observed for some important resonances below 20 eV. A similar behavior is observed relative to JENDL/AC-2008, a reactor-oriented database for actinides. The new results contribute to the overall improvement of the databases needed for the design of advanced reactor systems and may lead to refinements of fission models for the actinides.

The yield of the neutron capture reaction Th-232(n, gamma) has been measured at the neutron time-of-flight facility n_TOF at CERN in the energy range from 1 eV to 1 MeV. The reduction of the acquired data to the capture yield for resolved resonances from 1 eV to 4 keV is described and compared to a recent evaluated data set. The resonance parameters were used to assign an orbital momentum to each resonance. A missing level estimator was used to extract the s-wave level spacing of D-0 = 17.2 +/- 0.9 eV.