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-20 experiment with BWR test bundle [in press]

The experiment QUENCH-20 with BWR geometry simulation bundle was successfully conducted at KIT on 9th October 2019 in the framework of the international SAFEST project. The test bundle mock-up represented one quarter of a BWR fuel assembly with 24 electrically heated fuel rod simulators and two B4C control blades. The rod simulators were filled with Kr to an inner pressure of 5.5 bar. The pre-oxidation stage in a flowing gas mixture of steam and argon (each 3 g/s) and system pressure of 2 bar lasted 4 hours at the peak cladding temperature of 1250 K. The Zry-4 corner rod, withdrawn at the end of this stage, showed the maximal oxidation at elevations between 930 and 1020 mm with signs of breakaway. During the transient stage, the bundle was heated to a maximum temperature of 2000 K. The coolability of the bundle was decreased by its squeezing due to the shroud ductile deformation caused by an overpressure outside the shroud. The cladding radial strain and failures due to inner overpressure (about 4 bar) were observed at temperature about 1700 K and lasted about 200 s. During the period of rod failures also the first absorber melt relocation accompanied by shroud failure were registered. The interaction of B4C with the steel blade and the ZIRLO channel box were observed at elevations 650…950 mm with the formation of eutectic melt. The typical components of this melt are (Fe, Cr) borides and ZrB2 precipitated in steel or in Zr-steel eutectic melt. Massive absorber melt relocation was observed 50 s before the end of transition stage. Small fragments of the absorber melt moved down to the elevation of 50 mm. The melting point of Inconel spacer grids at 500 and 1050 mm was also reached at the end of the transition stage. The Inconel melt from the elevation 1050 mm relocated downwards through hot bundle regions to the Inconel grid spacer at 550 mm and later (during the escalation caused by quench) to 450 mm. This melt penetrated also under the damaged cladding oxide layer and formed molten eutectic mixtures between elevations 450 and 550 mm. The test was terminated by quench water injection 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 due to the strongly exothermic oxidation reactions. As result, the metal part (prior β-Zr) of the claddings between 550 and 950 mm was melted, partially released into space between rods and partially relocated in the gap between pellet and outer oxide layer to 450 mm. In this case, the positive role of the oxide layer should be noted, which does not allow the melt to completely escape into the inter-rod space. It is thereby limiting the possibility of interactions of a large amount of melt with steam, which could significantly increase the exothermic oxidation processes and the escalation of temperatures. The distribution of the oxidation rate within each bundle cross section is very inhomogeneous: whereas the average outer ZrO2 layer thickness for the central rod (#1) at the elevation of 750 mm is 465 µm, the same parameter for the peripheral rod #24 is only 108 µm. The average oxidation rate of the inner cladding surface (due to interaction with steam and with ZrO2 pellets) is about 20% in comparison to the outer cladding oxidation. The bundle elevations 850 and 750 mm are mostly oxidized with average cladding ECR 33%. The oxidation of the melt relocated inside the rods was observed at elevations 550…950 mm. The mass spectrometer measured release of CO (12.6 g), CO2 (9.7 g) and CH4 (0.4 g) during the reflood as products of absorber oxidation; the corresponding B4C reacted mass was 41 g or 4.6% of the total B4C inventory. It is significantly lower than in the PWR bundle tests QUENCH-07 and QUENCH-09 containing central absorber rod with B4C pellets inserted into a thin stainless steel cladding and Zry-4 guide tubes (20% and 50% reacted B4C correspondingly). Hydrogen production during the reflood amounted to 32 g during the reflood (57.4 g during the whole test) including 10 g from B4C oxidation

First results of the bundle test QUENCH-19 with FeCrAl claddings

The QUENCH-19 bundle experiment with FeCrAl(Y) claddings and 4 FeCrAl(Y) spacer grids as well as 8 KANTHAL APM corner rods and KANTHAL APM shroud was conducted at KIT on 29th August 2018. This was performed in cooperation with the Oakridge National Laboratory (ORNL). The test objective was the comparison of FeCrAl(Y) and ZIRLO™ claddings under similar electrical power and gas flow conditions. In common with the previous QUENCH-15 experiment, the bundle was heated by a series of stepwise increases of electrical power from room temperature to a maximum of ≈600 °C in an atmosphere of flowing argon (3.45 g/s) and superheated steam (3.6 g/s). The bundle was stabilised at this temperature, the electrical power being ≈4 kW. During this time the operation of the various systems was checked. In a first transient, the electrical power was controlled with the same electrical power history as the QUENCH-15 test. As a result, the bundle was heated to peak cladding temperature of about 1000 °C reached at about 4000 s. It showed a slowed bundle heating than for the QUENCH-15 bundle (1200 °C reached at about 3000 s). In this test phase about 0.3 g of hydrogen were produced (QUENCH-15: 23.3 g). In the following phase, the power was increased continuously to 18.12 kW (corresponds to maximal power of the QUENCH-15 test). After reaching of this value the power was kept constant during about 2000 s. At the end of this phase the maximal peak cladding temperature of Tpct≈1500 °C was reached. Much lower heating rate in comparison to QUENCH-15 was measured. Exceeding Tpct≈1400 °C sharp increase of hydrogen release rate was observed. Then reflood was initiated at ≈9100 s, connected with switching the argon injection to the top of the bundle, first rapidly filling the lower plenum of the test section with 4 kg of water, and continuing by injecting ≈48 g/s of water. The electrical power was reduced to 4.1 kW during the reflood. A temperature excursion was not observed. The temperatures at all elevations decrease immediately after water injection. The total hydrogen release during the whole test was 9.2 g compared to 47.6 g in the QUENCH-15 test with much shorter high electrical power phase. The videoscope observation of the bundle at the positions of the withdrawn corner rods showed the damage of several claddings at the bundle elevations between 850 and 1000 mm. The claddings were failed either due to interaction with melted thermocouples (mostly) or by spalling of small annular cladding parts

First results of the QUENCH-ALISA bundle test

Experiment QUENCH-18 on air ingress and aerosol release was successfully conducted at KIT on 27 September 2017. This test was performed in the frame of the EC supported ALISA programme. 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 (OD=9.5 mm, wall thickness 570 µm) 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-phase bundle degradation (companion test to the QUENCH-13 experiment), and two pressured unheated rod simulators (60 bar, He). The low pressurised 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 pressurised rods were burst at temperature of 1045 K. The attainment of Tpct ≈ 1400 K marked the start of the pre-oxidation phase to achieve a maximum cladding oxide layer thickness of up to 120 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 phase. 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 0.2 g/s. The change in flow conditions had the immediate effect of reducing the heat transfer so that the temperatures began to rise again. After some time measurements demonstrated a gradual increasing consumption of oxygen. 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 steam caused release of additional chemical energy (power about 4 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 was occurred and was followed by almost complete steam consumption and partial consumption of the nitrogen, indicating the possibility of bundle. Following this the temperatures continued to increase and stabilised at melting temperature of Zr bearing materials until water injection. The total uptakes of oxygen, steam and nitrogen were 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. 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

Latest Developments from the S-DALINAC*

The S-DALINAC is a 130 MeV superconducting recirculating electron accelerator serving several nuclear and radiation physics experiments as well as driving an infrared free-electron laser. A system of normal conducting rf resonators for noninvasive beam position and current measurement was established. For the measurement of gamma-radiation inside the accelerator cave a system of Compton diodes has been developed and tested. Detailed investigations of the transverse phasespace were carried out with a tomographical reconstruction method of optical transition radiation spots. The method can be applied also to non-Gaussian phasespace distributions. The results are in good accordance with simulations. To improve the quality factor of the superconducting 3 GHz cavities, an external 2K testcryostat was commissioned. The influence of electro-chemical polishing and magnetic shielding is currently under investigation. A digital rf-feedback-system for the accelerator cavities is being developed in order to improve the energy spread of the beam of the S-DALINAC. * Supported by the BMBF under contract no. 06 DA 820, the DFG under contract no. Ri 242/12-1 and -2 and the DFG Graduiertenkolleg 'Physik und Technik von Beschleunigern

Genetic variations in VEGF and VEGFR2 and glioblastoma outcome

Vascular endothelial growth factor (VEGF) and its receptors (VEGFR) are central components in the development and progression of glioblastoma. To investigate if genetic variation in VEGF and VEGFR2 is associated with glioblastoma prognosis, we examined blood samples from 154 glioblastoma cases collected in Sweden and Denmark between 2000 and 2004. Seventeen tagging single nucleotide polymorphisms (SNPs) in VEGF and 27 in VEGFR2 were genotyped and analysed, covering 90% of the genetic variability within the genes. In VEGF, we found no SNPs associated with survival. In VEGFR2, we found two SNPs significantly associated to survival, namely rs2071559 and rs12502008. However, these results are likely to be false positives due to multiple testing and could not be confirmed in a separate dataset. Overall, this study provides little evidence that VEGF and VEGFR2 polymorphisms are important for glioblastoma survival

Measurements of fiducial and differential cross sections for Higgs boson production in the diphoton decay channel at s√=8 TeV with ATLAS

Measurements of fiducial and differential cross sections are presented for Higgs boson production in proton-proton collisions at a centre-of-mass energy of s√=8 TeV. The analysis is performed in the H → γγ decay channel using 20.3 fb−1 of data recorded by the ATLAS experiment at the CERN Large Hadron Collider. The signal is extracted using a fit to the diphoton invariant mass spectrum assuming that the width of the resonance is much smaller than the experimental resolution. The signal yields are corrected for the effects of detector inefficiency and resolution. The pp → H → γγ fiducial cross section is measured to be 43.2 ±9.4(stat.) − 2.9 + 3.2 (syst.) ±1.2(lumi)fb for a Higgs boson of mass 125.4GeV decaying to two isolated photons that have transverse momentum greater than 35% and 25% of the diphoton invariant mass and each with absolute pseudorapidity less than 2.37. Four additional fiducial cross sections and two cross-section limits are presented in phase space regions that test the theoretical modelling of different Higgs boson production mechanisms, or are sensitive to physics beyond the Standard Model. Differential cross sections are also presented, as a function of variables related to the diphoton kinematics and the jet activity produced in the Higgs boson events. The observed spectra are statistically limited but broadly in line with the theoretical expectations