Predicting growth of deposits on fuel assemblies of VVER-440 reactors

We discuss issues of simulating the growth of deposits on the surface of the core of VVER-440 reactors, which result in a higher pressure difference of coolant across the reactor and in the need to reduce the reactor power. We also present results of model calculations carried out for one fuel campaign of Unit 4 at the Novovoronezh nuclear power station.     

Results from studies of surface deposits on the claddings of fuel rods used in RBMK-1000 reactors

The results of studies on analyzing the element composition of deposits on the cladding surfaces of fuel rods used in a fuel assembly at the Leningrad nuclear power station are presented. The distribution of elements in deposits over the fuel rod height is analyzed, and the zones of their concentration are revealed. It is shown that deposits of copper penetrating into cracks in the surface layer of zirconium oxide introduce an essential contribution in the development of nodular corrosion of fuel rod claddings.     

The problems of mass transfer and formation of deposits of corrosion products on fuel assemblies of a VVER-1200 reactor

On the basis of examination of materials published both in Russia and abroad, as well as their own investigations, the authors explain the reasons for the occurrence of such effects as AOA (Axial Offset Anomalies) and an increase in the coolant pressure difference in the core of nuclear reactors of the VVER type. To detect the occurrence of the AOA effect, the authors suggest using the specific activity of ⁵⁸Co in the coolant. In the VVER-1200 design the thermohydraulic regime for fuel assemblies in the first year of their service life involves slight boiling of the coolant in the upper part of the core, which may induce the occurrence of the AOA effect, intensification of corrosion of fuel claddings, and abnormal increase in deposition of corrosion products. Radiolysis of the water coolant in the boiling section (boiling in pores of deposits) may intensify not only general corrosion but also a localized (nodular) one. As a result of intensification of the corrosion processes and growth of deposits, deterioration of the radiation situation in the rooms of the primary circuit of a VVER-1200 reactor as compared to that at nuclear power plants equipped with reactors of the VVER-1000 type is possible. Recommendations for preventing the AOA effect at nuclear power plants with VVER-1200 reactors on the matter of the direction of further investigations are made.     

Studying the vibration and random hydrodynamic loads on the fuel rods bundles in the fuel assemblies of the reactor installations used at nuclear power stations equipped with VVER reactors

Random hydrodynamic loads causing vibration of fuel rod bundles in a turbulent flow of coolant are obtained from the results of pressure pulsation measurements carried out over the perimeter of the external row of fuel rods in the bundle of a full-scale mockup of a fuel assembly used in a second-generation VVER-440 reactor. It is shown that the turbulent flow structure is a factor determining the parameters of random hydrodynamic loads and the vibration of fuel rod bundles excited by these loads. The results from a calculation of random hydrodynamic loads are used for estimating the vibration levels of fuel rod bundles used in prospective designs of fuel assemblies for VVER reactors.     

Calculating the solid fuel combustion process in a cyclone reactor

A mathematical model is proposed that describes the combustion of coal particles in the second stage of a cyclone reactor consisting of four cylindrical section. In the first stage, the fuel is additionally dried and supplied from it to the second stage with the temperature T _out and concentration C _out. The parameters of a burning particle were calculated according to the model of concentrated ash residue. A satisfactory agreement is obtained between the calculated data and results from temperature profile measurements in the reactor’s second stage volume.     

Simulating the retention of molten fuel in a fast-neutron reactor during a severe accident

The problem of retaining molten fuel in the fast-reactor vessel during a severe accident is considered. A mathematical model implemented in the BRUT computer code is described and the calculated data obtained using this code are analyzed. Original Russian Text ￠ M.V. Kashcheev, I.A. Kuznetsov, 2007, published in Teploenergetika.     

Tests of a cyclone reactor for firing high-ash fuel

The design of a new furnace device called a cyclone reactor is described, and the results from experiments on studying the processes through which ground fuel mixture is combusted in it are presented. The temperature profiles in the reactor volume are shown, and the results from an analysis of ash residue remaining after combustion of a wood-coal mixture are presented. It is pointed out that unlike combustion of coal, the firing of a wood-coal mixture entails formation of not only fine ash, but also slag.     

Experimental study of burnout in channels with twisted fuel rods

The results of experimental studies of pressure drop and critical heat flux in the models of fuel assemblies (FAs) with fuel rod simulators twisted relative to the longitudinal axis and a three-ray cross section are considered. The experimental data are compared to the results obtained with the use of techniques adopted for design calculations with fuel rod bundles of type-VVER reactors.     

VK-50型汽轮机低压加热器疏水及轴封回汽系统改造

针对辽宁发电厂VK－50型汽轮机低压加热器疏水及轴封回汽系统只能回收工质，而不能回收热量的问题，对其进行改造，改造后均能将热量回收，提高了机组的经济性。运行结果表明系统改造后达到预期效果。     

Using periodical boundary conditions to thermal and hydraulic calculation of fuel assembly with finned fuel rods

A method of calculating velocity and temperature of coolant in a bundle of fuel rods or heat-exchange tubes is proposed. To show its application examples of calculating fuel rod assemblies of BREST-OD-300 and PIK reactors using commercial Flow Vision CFD-code are presented. A satisfactory agreement between calculated and experimental data on friction and heat transfer coefficients is achieved. It is shown that the proposed approach shows possibilities for solving a wide range of three-dimension problems on thermal and hydraulic calculations of infinite lattices of finned fuel rods or finned heat-transfer tubes.     

A modified table for calculating critical heat fluxes in assemblies of triangularly packed fuel rods

A modified table is drawn up and a modified method is developed for describing critical heat fluxes in water-cooled fuel rod assemblies with introduction of a new correction function for the thermal-hydraulic nonequivalence of an assembly.     

Experimental study of the effect of spacer grid on the flow structure in fuel assemblies of the AES 2006 reactor

Results from an experimental study of the local hydrodynamic structure of liquid flow in a 37-cell model simulating a fuel assembly used in the AES-2006 reactor are presented. Special attention is paid to the effect of spacer grid on flow hydrodynamics. Data on variations of the local and integral values of the liquid axial velocity and friction stress on the fuel rod simulator’s wall with distance from the grid are given.     

Kinetics of growth of calcium carbonate deposits in geothermal systems

Results from field investigations into the processes through which suspended particles are formed in geothermal water as a consequence of upset in carbonic acid equilibrium, as well as processes through which solid deposits of calcium carbonate are formed on the inner surfaces of geothermal equipment, are reported.     

Experimental studies of local coolant hydrodynamics using a scaled model of cassette-type fuel assembly of a KLT-40S reactor

The results of experimental studies of local hydrodynamic and mass exchange characteristics of the coolant flow behind the spacer grid in the fuel assembly of a KLT-40S reactor are presented. The experiments were aimed at the investigation of representative domains of the fuel assembly with three tracer injection regions. The studies were performed at the aerodynamic test facility using the tracer gas diffusion method. According to the theory of hydrodynamic similarity, the obtained experimental results can be transferred to full-scale coolant flow conditions in standard fuel assemblies. The analysis of the tracer concentration propagation made it possible to determine in detail the flow pattern and find the main regularities and specific features of the coolant flow behind the plate spacer grid of KLT-40S fuel assembly. The hydraulic resistance coefficient of the spacer grid was experimentally determined. The coefficients of mass exchange between cells for representative cells of the displacer region in the KLT-40S fuel assembly were calculated for the first time; these results are presented in the form of the “mixing matrix.” The results of studies of local coolant flow hydrodynamics in the KLT-40S fuel assembly are used at AO Afrikantov OKBM for estimation of thermotechnical reliability of active cores for reactors of floating nuclear power stations. The experimental data on hydrodynamic and mass exchange characteristics are included in the database for verification of CDF codes and detailed cell-wise calculation of the active core for KLT-40S reactor installation. The results of these studies can be used at FSUE RFNC-VNIIEF for testing and verification of domestic three-dimensional hydrodynamic CFD codes (“Logos”) that are applied for substantiation of newly designed reactor installations. Practical recommendations on the application of the obtained results in thermohydraulic calculations of the active core for the KLT-40S reactor will be worked out. Proposals on further improvement of structural elements of active cores in the considered nuclear power installations will also be presented.     

Formation of corrosion products in the coolant and deposits in the multiple forced circulation circuit of a nuclear power station equipped with an RBMK-1000 reactor

Models used to describe the mechanisms governing the formation of deposits are presented together with calculation results, on the basis of which conclusions are drawn as to how the activity is distributed among radionuclides when the mass concentration of corrosion products is in equilibrium with their specific activity.     

Dual-mode power reactor facility based on a heterophase thermionic converter reactor

The use of a heterophase thermionic converter reactor is suggested as a possible solution to the problem that relates to the development of a dual-mode power reactor facility. Two specialized subsystems of thermionic electricity-generating channels are applied in this thermionic convertor reactor to provide for its extended service life. The thermionic electricity-generating channels of the first subsystem are used to ensure a full power mode in a relatively short period of time, while the thermionic electricity-generating channels of the second subsystem are necessary to provide for a long service life. Under the full power mode, both subsystems of the thermionic converter reactor are connected in parallel to the total load, while in the mode of a durable power supply only the second subsystem acts as a source of electric power. The power reactor facility, based on such a thermionic converter reactor, is capable to ensure the power supply for an electro-propulsion system, with a maximum capacity of 150 kW operating up to 2 years, as well as for a spacecraft apparatus, with a capacity of 60–80 kW and a corresponding service life of 10 years or longer.     

Refinement of a scheme for analyzing sticking of particles and growth of slag deposits

Different submodels used to simulate sticking of particles in deposits are reviewed. A new scheme for sticking of particles is proposed, according to which they stick in deposits if the generalizing viscosity of a particle and deposit surface does not exceed a certain value. The boundary conditions and a method used to calculate the generalizing viscosity are substantiated on the basis of experimental data.     

Predicting the contractual cost of unplanned shutdowns of power stations: An accelerator-driven subcritical reactor case study

This paper discusses analysis of the acute contractual cost of a failure to supply electricity from the perspective of power station owners. It presents a model for analysing the financial cost to an electricity supplier in the context of a national grid when a power station unexpectedly instantaneously shuts down. The model probabilistically samples historical market data and includes analysis of the impact on the system buy price of historic unplanned generator shutdowns. A case study is presented for a potential future nuclear power station concept, the Accelerator-Driven Subcritical Reactor (ADSR), in the UK market. The reliability of ADSRs is a key issue in their future development. The model is used to identify an upper limit on the amount an operator should be willing to pay for reliability improvements that mitigate unplanned shutdowns. The case study results are presented in a form that allows the reader to scale the cost of accelerator system failures for any capacity factor and coefficient of reliability, for a range of discount rates.     

The influence of operational and water chemistry parameters on the deposits of corrosion products on fuel assemblies at nuclear power plants with VVER reactors

The phenomenon involving a growth of pressure drop in the reactor core and redistribution of deposits in the reactor core and primary coolant circuit of a nuclear power station equipped with VVER-440 reactors is considered. A model is developed, the physicochemical foundation of which is based on the dependence of corrosion product transfer on the temperature and pH _t value of coolant and on the correlation between the formation rate of corrosion products (Fe) (after subjecting the steam generators to decontamination) and rate with which they are removed from the circuit. The purpose of the simulation carried on the model is to predict the growth of pressure drop on the basis of field data obtained from nuclear power installations and correct the water chemistry (by adjusting the concentrations of KOH, H₂, and NH₃) so as to keep the pressure drop in the reactor at a stable level.