PARAMETRIC REACTIVITY TRANSIENT ANALYSES FOR THE FFTF NUCLEAR PROOF TEST REACTOR

Fault tree techniques have been used to identify possible failure paths within the NPTR which could lead to core disassembly. The analysis o f the various faults has led to formulation of design requirements, protective system requirements, and administrative restraints required to prevent accidents from these faults. Transient analyses were performed using the heat transfer-nuclear kinetics codes, Nutiger-II, FORE-II, and MELT-II . To verify results, intercomparison studies were made between the codes. The codes were i n good general agreement. Each code was found to exhibit different advantages and disadvantage. Inherent reactivity feedback effects were assessed in the analysis. With the assumed core parameters, there appears to be sufficient Doppler to prolong a nuclear transient to allow protective action to prevent fuel from melting. The use of average values of the feedback coefficients smeared over the entire core does not appear to be an acceptable method with spacially dependent temperatures. In the thermal analysis, the fuel pin gap coefficient and sodium film coefficient do not appear to be highly sensitive parameters for transient analysis. Power transients resulting from reactivity insertions of from 2$/sec to 20$/sec have been examined in detail. Sodium will be molten before fuel melting occurs for accidents within this range. For the smaller ramp rates (< 4$/sec), sodium nay even reach vaporization temperatures before any fuel melts. Power transients terminated by effective protective action were investigated. It i s believed p o s s i b l e t o design a scram system, with the . present state of the art, to prevent sodium from melting for a reactivity ramp up to at least 6$/sec. This same system would prevent fuel melting for a reactivity ramp up to 15/sec. Sodium thermal expansion will play a very important role in a core disassembly. When the average sodium temperature exceeds 250 {degrees}F, physical core distortion must result to relieve expansion pressures. Rupturing of the fuel assembly cans during a transient increases the probability of a sodium fire. Pressures and temperatures from a sodium fire could easily exceed 20 psig and 1000 {degrees}F. The design basis accident has not been identified. However, the lower limit is a sodium fire involving hot liquid sodium and possible sodium vapor. A fuel vapor explosion would require a large initiating reactivity ramp rate (> 20/sec) with at least 3$ total reactivity worth. No mechanism for introduction of a reactivity insertion of this characteristic has been identified other than a dropped fuel assembly into a vacant core position. This mechanism is discounted as it is believed that sub-criticality of the reactor can be guaranteed during refueling. It is conceivable that a minor accident could be aggravated into an explosive accident by failure of protective system and positive feedback mechanisms. The possibility of this occurring is dependent upon what effects the confined sodium has on the core. It is desirable that the sodium would take the core to a disassembly condition or termination mode. Additional analysis will be necessary before this can be guaranteed

Role of phi decays for K- yields in relativistic heavy-ion collisions

The production of strange mesons in collisions of Ar+KCl at a kinetic beam energy of 1.756 AGeV is studied within a transport model of Boltzmann-\"Uhling-Uhlenbeck (BUU) type. In particular, $\phi, K^+$ and $K^-$ yields and spectra are compared to the data mesured recently by the HADES collaboration and the $\phi$ yield measured previously by the FOPI collaboration. Our results are in agreement with these data thus presenting an interpretation of the subleading role of $\phi$ decays into $K^-$'s and confirming the importance of the strangeness-exchange channels for $K^-$ production.Comment: 24 pages, 19 figure

Buying into myths: free movement of people and immigration

The way in which free movement of people has become the central issue of the British government’s renegotiation and referendum campaign on the UK’s relationship with the EU risks obfuscating at least three central issues: why immigrants are coming to the UK; what impact EU migrants are having on the UK; and what can be done to effectively regulate such inflows. It is, however, not just the Eurosceptics and the British government but also ‘in campaigners’ and other EU member states who risk perpetuating a number of widely-held misconceptions about free movement and immigration for political reasons. Buying into such myths risks to undermine attempts to have a more honest and more evidence-based debate about immigration and migrant integration

Emergency brakes on migration: neither novel nor effective

The ’emergency brake’ is not the first time member states have tried to restrict freedom of movement within the EU. Indeed, after the enlargements in 2004 and 2007, most countries – though not Britain – did not give eastern European workers free access to their labour markets. But ultimately, write Eiko Thielemann (left) and Daniel Schade, the only reliable way to deter labour migrants is to ensure the economy is too weak to offer them worthwhile job opportunities

Jobs are good ones: addressing the factors that attract EU migrants to the UK

As one of the founding principles of the EU’s single market, the right to freedom of movement allows EU citizens to travel freely across the 28 Member States and to take up work in a place of their choosing. With very high numbers of EU citizens arriving in the UK in recent years, advocates of a Brexit often argue that this right has led to higher immigration than the UK can readily absorb, and one of the aims of David Cameron’s renegotiation was to curb the incentives for EU migrants to come to Britain. The purpose of the LSE Commission on the Future of Britain in Europe hearing was to discuss the overall costs and benefits of this fundamental principle of the European Union. It took into account a wide range of expert opinions, while considering different policy options in the context of the forthcoming referendum.The chair Eiko Thielemann (left) and Daniel Schade report.

Catalog of Galaxy Morphology in Four Rich Clusters: Luminosity Evolution of Disk Galaxies at 0.33<z<0.83

Hubble Space Telescope (HST) imaging of four rich, X-ray luminous, galaxy clusters (0.33<z<0.83) is used to produce quantitative morphological measurements for galaxies in their fields. Catalogs of these measurements are presented for 1642 galaxies brighter than F814W(AB)=23.0 . Galaxy luminosity profiles are fitted with three models: exponential disk, de Vaucouleurs bulge, and a disk-plus-bulge hybrid model. The best fit is selected and produces a quantitative assessment of the morphology of each galaxy: the principal parameters derived being B/T, the ratio of bulge to total luminosity, the scale lengths and half-light radii, axial ratios, position angles and surface brightnesses of each component. Cluster membership is determined using a statistical correction for field galaxy contamination, and a mass normalization factor (mass within boundaries of the observed fields) is derived for each cluster. In the present paper, this catalog of measurements is used to investigate the luminosity evolution of disk galaxies in the rich-cluster environment. Examination of the relations between disk scale-length and central surface brightness suggests, under the assumption that these clusters represent a family who share a common evolutionary history and are simply observed at different ages, that there is a dramatic change in the properties of the small disks (h < 2 kpc). This change is best characterized as a change in surface brightness by about 1.5 magnitude between z=0.3 and z=0.8 with brighter disks at higher redshifts.Comment: 53 pages, including 13 figures and 7 tables. Accepted for publication in the Astrophysical Journal Supplement Serie