Results of Severe Fuel Damage Experiment QUENCH-15 with ZIRLO cladding tubes. (KIT Scientific Reports ; 7576)

The QUENCH-15 experiment investigated the effect of ZIRLO™ cladding material on bundle oxidation and core reflood from maximum bundle temperature of 2150 K. The molten cladding metal at the hottest elevation was localized between outer and inner oxide layers. The analyses of the QUENCH-15 test data indicate a similar global bundle behavior as of bundle experiments QUENCH-14 (M5® claddings) and QUENCH-06 (Zircaloy-4 claddings)

Social networks and citizen election forecasting: the more friends the better

Most citizens correctly forecast which party will win a given election, and such forecasts usually have a higher level of accuracy than voter intention polls. How do citizens do it? We argue that social networks are a big part of the answer: much of what we know as citizens comes from our interactions with others. Previous research has considered only indirect characteristics of social networks when analyzing why citizens are good forecasters. We use a unique German survey and consider direct measures of social networks in order to explore their role in election forecasting. We find that three network characteristics – size, political composition, and frequency of political discussion – are among the most important variables when predicting the accuracy of citizens’ election forecasts

Decreasing time consumption of microscopy image segmentation through parallel processing on the GPU

The computational performance of graphical processing units (GPUs) has improved significantly. Achieving speedup factors of more than 50x compared to single-threaded CPU execution are not uncommon due to parallel processing. This makes their use for high throughput microscopy image analysis very appealing. Unfortunately, GPU programming is not straightforward and requires a lot of programming skills and effort. Additionally, the attainable speedup factor is hard to predict, since it depends on the type of algorithm, input data and the way in which the algorithm is implemented. In this paper, we identify the characteristic algorithm and data-dependent properties that significantly relate to the achievable GPU speedup. We find that the overall GPU speedup depends on three major factors: (1) the coarse-grained parallelism of the algorithm, (2) the size of the data and (3) the computation/memory transfer ratio. This is illustrated on two types of well-known segmentation methods that are extensively used in microscopy image analysis: SLIC superpixels and high-level geometric active contours. In particular, we find that our used geometric active contour segmentation algorithm is very suitable for parallel processing, resulting in acceleration factors of 50x for 0.1 megapixel images and 100x for 10 megapixel images

Reconfigurable nanophotonic devices using phase-change materials

This is the final version of the article. Available from E\PCOS via the URL in this record.Nanophotonic integrated circuits enable realizing functional optical devices using efficient design and fabrication routines. Their inherent stability and scalability makes them attractive for applications where optical signal processing is combined with coupling to external light stimuli. A majority of nanophotonic devices is, however, based on passive materials, which do not provide low-power tuning options or knobs for reconfigurability. We address this shortcoming by combining passive silicon nitride photonic devices with tunable phase-change materials [1]. Such a platform allows realizing both on-chip optical data storage [2] and active photonic components. Implementing on-chip photonic memories has been pursued for a long time, in particular for fabricating memory devices which are able to retain their state after the storage process. Photonic data storage would dramatically improve performance in existing computing architectures by reducing the latencies associated with electrical memories and potentially eliminating optoelectronic conversions. Furthermore, multi-level photonic memories with random access would allow for leveraging even greater computational capability. Thus far, photonic memories have been predominantly volatile, meaning that their state is lost once the input power is removed. We exploit hybrid photonic-phasechange materials to implement robust, non-volatile, all-photonic memories. By using optical near-field coupling within on-chip waveguides, we realize bit storage of up to eight levels in a single device that readily switches between intermediate states. We show that individual memory elements can be addressed using a wavelength multiplexing scheme. Such multi-level, multi-bit devices provide a pathway towards eliminating the von Neumann bottleneck and portend a new paradigm in all-photonic memory and non-conventional computing. We further show that such devices can be operated with short optical pulses, both for write and read operations

Integrated phase-change photonics for all-optical processing

This is the final version of the article. Available from E\PCOS via the URL in this record.Embedding phase-change materials (PCMs) in on-chip photonic circuitry enables nonvolatile alloptical operation of integrated optical devices. This hybrid system has been used so far in terms of memory applications. However, it also provides the capability to all-optically process light signals. Here, we use picosecond pulses to demonstrate both all-optical routing and all-optical arithmetic operations within the on-chip photonic circuitry

First results of the QUENCH-20 test with BWR bundle

Experiment QUENCH-20 with BWR geometry simulation bundle was successfully conducted at KIT on 9th October 2019. This test was performed in the framework of international access SAFEST infrastructure with the users from Swedish Radiation Safety Authority (SSM) in cooperation with Westinghouse Sweden, GRS and KTH. The test objective was the investigation of a BWR fuel assembly degradation including a B4C control blade. The test bundle mock-up represents one quarter of a BWR fuel assembly. The 24 electrically heated fuel rod simulators were filled separately with krypton (overpressure of 4 bar). According to the pre-test calculations performed with ATHLET-CD, the bundle was heated to a temperature of 1230 K at the cladding of the central rod at the hottest elevation of 950 mm. This pre-oxidation phase in steam lasted 4 hours. Towards the end of this phase, the reference rod was extracted from the test bundle for determination of the oxide thickness axial distribution. During the transient stage, the bundle was heated to a maximal temperature of 2000 K. The cladding failures were observed at temperature about 1700 K and lasted about 200 s. Massive absorber melt relocation was observed 50 s before the end of transition stage. The test was terminated with the quench water injected with a flow rate of 50 g/s from the bundle bottom. Fast temperature escalation from 2000 to 2300 K during 20 s was observed. The mass spectrometer measured release of COx and few CH4 during the reflood as products of absorber oxidation; corresponding production of B2O3 should be about 97 g. Hydrogen production during the reflood amounted to 32 g (57.4 g during the whole test) including 10 g from B4C oxidation

Results of the QUENCH-18 Bundle Experiment on Air Ingress and AgInCd absorber behavior

The experiment QUENCH-18 on air ingress and aerosol release in an electrical heated test bundle with 24 rods and a length of about 2 m was successfully conducted at KIT on 27 September 2017. This test was performed in the frame of the EC supported ALISA program. It was proposed by XJTU Xi’an (China) and supported by PSI (Switzerland) and GRS (Germany). The primary aims were to examine the oxidation of M5® claddings in air/steam mixture following a limited pre-oxidation in steam, and to achieve a long period of oxygen and steam starvations to promote interaction with the nitrogen. QUENCH 18 was thus a companion test to the earlier air ingress experiments, QUENCH-10 and -16 (in contrast to QUENCH-18, these two bundle tests were performed without steam flow during the air ingress stage). Additionally, the QUENCH 18 experiment investigated the effects of the presence of two Ag-In-Cd control rods on early-stage bundle degradation (companion test to the QUENCH-13 experiment), and of two pressurized unheated rod simulators (60 bar, He). The low pressurized heater rods (2.3 bar, similar to the system pressure) were Kr-filled. In a first transient, the bundle was heated from the peak cladding temperature Tpct ≈ 900 K in an atmosphere of flowing argon (3 g/s) and superheated steam (3.3 g/s) by electrical power increase to the peak cladding temperature of Tpct ≈ 1400 K. During this heat-up (with the heat-up rate 0.3 K/s), claddings of the two pressurized rods burst at a temperature of 1045 K. The attainment of Tpct ≈ 1400 K marked the start of the pre-oxidation stage to achieve a maximum cladding oxide layer thickness of about 80 µm. Then the power was reduced from 9 to 3.8 kW (simulation of decay heat) which effected a cooling of the bundle to Tpct ≈ 1080 K, as a preparation for the air ingress stage. In the subsequent air ingress stage, the steam flow was reduced to 0.3 g/s, the argon flow was reduced to 1 g/s, and air was injected with the flow rate of 0.21 g/s. The change in flow conditions had the immediate effect of reducing the heat transfer so that the temperatures began to rise again. The first Ag-In-Cd aerosol release was registered at Tpct = 1350 K and was dominated by Cd bearing aerosols. Later in the transient, a significant release of Ag was observed along with continued Cd release, as well as a small amount of In. In contrast to the QUENCH-16 test (performed with the air ingress stage without steam flow), oxidation of bundle parts in air and steam caused release of higher chemical energy (power about 8 kW) and consequently acceleration of bundle heat-up. A strong temperature escalation started in the middle of the air ingress stage. Later a period of oxygen starvation occurred and was followed by almost complete steam consumption and partial consumption of the nitrogen, indicating the possibility of formation of zirconium nitrides. Following this the temperatures continued to increase and stabilized at melting temperature of Zr bearing materials until water injection. The total consumption of oxygen, steam and nitrogen was 100±3, 450±10 and 120±3 g, respectively. During the starvation period a noticeable production (about 25 mg/s, totally 45±1 g) of hydrogen was measured. Almost immediately after the start of reflood there was a temperature excursion in the mid to upper regions of the bundle, leading to maximum measured temperatures of about 2450 K with cladding melt release, relocation and oxidation. Reflood progressed rather slowly and final quench was achieved after about 800 s. A significant quantity of hydrogen was generated during the reflood (238±2 g). Nitrogen release (>54 g) due to re-oxidation of nitrides was also registered. Zirconium nitrides and re-oxidized nitrides were found in the middle part of the bundle. In this bundle region, the claddings and cladding melt were strongly oxidized, the melt was collected mostly inside the grid spacer. Partially oxidized Zr-bearing melt was found down to elevation 160 mm; this elevation was the lowest with evidence of relocated pellet material. At the bundle bottom, only frozen metallic melt containing Zr, Ag, In and Cd was observed between several rods. The data of the experiment are used for validation of severe accident code systems