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

GABRIELA : a new detector array for gamma-ray and conversion electron spectroscopy of transfermium elements

With the aid of the Geant4 Monte Carlo simulation package a new detection system has been designed for the focal plane of the recoil separator VASSILISSA situated at the Flerov Laboratory of Nuclear Reactions, JINR, Dubna. GABRIELA (Gamma Alpha Beta Recoil Investigations with the Electromagnetic Analyser VASSILISSA) has been optimised to detect the arrival of reaction products and their subsequent radioactive decays involving the emission of alpha- and beta-particles, fission fragments, gamma- and X-rays, and conversion electrons. The new detector system is described and the results of the first commissioning experiments are presented.Comment: 24 pages, Submitted to NIM

Hydrozirconium reaction in heterogeneous compositions

The research results presented in this article show the behavior of a hydrozirconium reaction for hydrogen generation at temperatures below 100°C in heterogeneous compositions containing zirconium and chemical activators (e.g., hydrated sodium metasilicate, sodium water glass, or quicklime). The hydrogen yield increases with a temperature increase up to 95°C and is about 0.1–0.2l per 1g of zirconium. Zirconium processing with γ-radiation as well as exposure to acidic and neutral aqueous media increases the hydrogen yield by about 1.2 times. A hydrozirconium reaction is caused by the chemical activators removing the passivating protective zirconium oxide ZrO2 layer from the metal surface. The possibility of a hydrozirconium reaction occurrence should be considered in the organization of technical measures to ensure hydrogen explosion protection at NPPs

On-line separator for γ\gamma-spectroscopic studies at FLNR JINR

International audienceA JINR — IN2P3 collaboration project named “GABRIELA” aimed at the nuclear spectroscopy of transfermium elements using the recoil separator VASSILISSA was launched in 2004 at JINR in Dubna. In the close future the FLNR cyclotron U400M will go through a major upgrade with the goal to deliver heavy ion beams at the energy close to the Coulomb barrier in a new experimental area. Here we report about R&D of the new separator for spectroscopic studies which we plan to install at the beam of the modernized accelerator and which will allow to realize new possibilities of the GABRIELA project

GABRIELA setup for nuclear spectroscopy of the transfermium element isotopes at the VASSILISSA separator

The JINR (Dubna)-IN2P3 (France) Collaboration project aimed at the alpha, beta, gamma spectroscopy of the transfermium element isotopes using heavy-ion beams of the U-400 cyclotron and the modernized recoil separator VASSILISSA was launched at Dubna. During the first full-scale experiment in September-October 2004, nobelium and lawrencium isotopes produced in the Ca-48 + Pb-207,Pb-208 -> No-255,No-256* and Ca-48 + Bi-209 -> Lr-257* reactions were studie

Spontaneous-fission decay properties and production cross-sections for the neutron-deficient nobelium isotopes formed in the \chem{^{44,48}Ca +\,^{204,206,208}Pb} reactions

Heavy-ion fusion reactions $^{48}$Ca + $^{204}$Pb and $^{44}$Ca + $^{208}$Pb leading to the same compound nucleus $^{252}$No$^{*}$ were run in attempts to produce new neutron-deficient spontaneous-fission isotopes of $^{249,250}$No using the electrostatic separator VASSILISSA. Production cross-sections for the spontaneous-fission activities with the half-lives 5.6 and 54 $\mu$s observed in these reactions are compared with the measured ones for the well-known isotopes of $^{251 - 255}$No formed in the heavy-ion fusion reactions $^{48}$Ca + $^{206}$Pb and $^{48}$Ca + $^{208}$Pb. The obtained excitation functions for the reaction products formed after the evaporation of 1–4 neutrons from the corresponding compound No nuclei have been compared with similar data obtained earlier and results of statistical model calculations

Half-life and excitation energy of the IπI^{\pi}=13/2^+ isomer in 209^{209}Ra

An isomeric state in $^{209}$Ra has been observed for the first time, using the GABRIELA setup at the focal plane of VASSILISSA, to decay to the ground state of $^{209}$Ra via a cascade of 238-keV (M2) and 644-keV transitions. The half-life of the isomer has been measured to be 117(5) $\mu$s and from systematics is assigned as a neutron i ^{-1}_{13/2} excitation