Computational Analysis of the Shutdown of One MCP of VVER-1000 During Operation of the Reactor Facility at Nominal Power

The article considers results of the computational analysis of process with a disturbance in the operation of VVER-1000 reactor facility, caused by the de-energizing of a single Main Circulation Pump (MCP-195).Calculations of de-energizing of the MCP were made with the CORSAR/GP software package developed by Federal State Unitary Enterprise "Alexandrov RESE". This software package is a contour code which allows making calculations of emergency situations taking into account the operation of various systems, including safety systems. CORSAR/GP is certified and verified for facilities with water-cooled reactors including VVER-1000.Developed nodalization scheme (computational scheme) of the first circuit of VVER-1000 allows adding or excluding the operation of protective safety systems and can also be used for a computational analysis of other disturbances of normal operation.To perform the calculations parameters of the core were chosen to ensure conservative results for the parameters determining the current state of the reactor facility (fuel temperature, boiling point, etc.).The computational analysis showed that in case of de-energizing of a single MCP when the reactor is operated at nominal power criteria describing the safety of the facility are fulfilled, protective automatic actions of safety systems transfer the reactor facility to a controlled safe state

Consequences of Channelized and Diffuse Melt Transport in Supra-subduction Zone Mantle: Evidence from the Voykar Ophiolite (Polar Urals)

International audienceThe well-preserved, 6 km thick mantle section of the Voykar ophiolite in the Polar Urals contains numerous dunite bodies as well as dunite and pyroxenite veins within the host harzburgites. These rocks provide evidence of a composite asthenosphere-lithosphere history of partial melting, plastic deformation, multi-stage melt migration and melt-rock interaction. We investigated the petrology and geochemistry of multiple samples of the different mantle lithologies to define the sequence of mantle melting and melt migration events, as well as the composition of the percolating melts. Spinel harzburgites sampled far from dunite bodies and pyroxenite veins have fairly homogeneous bulk-rock, olivine and Cr-spinel compositions and are interpreted as residues after 14-16% of partial melting, most probably at a mid-ocean ridge. Near the contacts with the dunite bodies and pyroxenite veins, spinel peridotites demonstrate distinct compositional changes marking different stages of melt migration in a supra-subduction environment. At the earliest stage, which probably took place in the lithosphere-asthenosphere boundary of the forearc mantle at temperature between 1050 and 1200°C and a pressure of 1-1*7 GPa, the dunite bodies formed as a result of stress-driven focused melt flow. The latest stage melts moved in cracks under a conductive cooling regime within the lithospheric mantle section when it was horizontally displaced towards the trench. The trace element composition of the melts that migrated through the mantle section during dunite formation have geochemical characteristics like those of high-Ca boninites. The role of the slab-derived component progressively increased through time and late-stage, pyroxenite-forming melts were conspicuously rich in SiO2 and H2O. These low-viscosity melts impregnated the surrounding harzburgites, modifying or obliterating their primary composition

Parental melt of the Nadezhdinsky Formation: Geochemistry, petrology and connection with Cu-Ni deposits (Noril'sk area, Russia)

International audienceThe paper addresses genetic relationship between volcanic rocks and ore-bearing intrusions of the Noril'sk area, Siberian Trap Province. Mg-rich rocks were found inside layered the Mikchangdinsky and Ikensky flows at the highest level of the vertical section of a tuff-lava pile in the Nadezhdinsky Formation in the east- ern part of the Noril'sk area. The high La/Sm, Th/U ratios, depletion in Cu, highly radiogenic Sr and unradio- genic Nd isotope compositions suggest their affiliation with the Lower Nadezhdinsky Formation and distinguish them from the Sunduksky layered flow, which has similar internal structure but belongs to the Tuklonsky Formation. The composition of layered Mg-rich basalt flow (the Mikchangdinsky flow) indicates that these rocks likely represent previously unknown parental melt of Nadezhdinsky lavas which are thought to play a crucial role in the genesis of ore mineralisation. Compositionally this melt was significantly different from the parental melt, which formed lavas of the Tuklonsky Formation and this precludes their direct genetic relationship. Olivine composition of the Mikchangdinsky flow indicates rapid depletion of melt by Ni and Cu suggesting early precipitation and fractionation of sulphide melt. Chemical composition and Sr and Nd isotope compositions of rocks from the Mikchangdinsky flow are similar to the Low Talnakh intrusion, while composi- tion of olivine and coexisting spinels manifest significant differences. The compositional differences between the olivine (contents Mn and V) and coexisting spinel (Fe2+/Fe3+ ratios) from the picrite gabbro-dolerites of the Low Talnakh intrusion and picrite of the Mikchangdinsky flow suggest that they may have crystallised from magma of similar composition but at different oxygen fugacity (intrusions being unusually oxidised). The substantial differences in contents of Ca, HREE and Y in olivines from these objects, however, leave open the question of genetic relationship between Nadezhdinsky parental melt and the Low Talnakh intrusion. Although some rocks of the Nadezhdinsky Formation contain unusually low concentrations of chalcophile elements, their role in the ore-forming processes of the Noril'sk district still remains largely uncertain