P. N. Alekseev

Manifestation of quark clusters in the emission of cumulative protons in the experiment on the fragmentation of carbon ions

The proton yields at an angle of 3.5° have been measured in the FRAGM experiment on the fragmentation of carbon ions with the energies T0 = 0.6, 0.95, and 2.0 GeV/nucleon on a beryllium target at the heavy-ion accelerator complex TWAC (terawatt accumulator, Institute for Theoretical and Experimental Physics). The data are represented in the form of the dependences of the invariant cross section for proton yield on the cumulative variable x in the range of 0.9 < x < 2.4. This invariant cross section varies within six orders of magnitude. The proton spectra have been analyzed within the theoretical approach of the fragmentation of quark clusters with the fragmentation functions obtained in the quark-gluon string model. The probabilities of the existence of six- and nine-quark clusters in the carbon nuclei are estimated as 8–12 and 0.2–0.6%, respectively. The results are compared to the estimated of quark effects obtained by other methods.

Aqueous Nanofluid as a Two-Phase Coolant for PWR

Density fluctuations in liquid water consist of two topological kinds of instant molecular clusters. The dense ones have helical hydrogen bonds and the nondense ones are tetrahedral clusters with ice-like hydrogen bonds of water molecules. Helical ordering of protons in the dense water clusters can participate in coherent vibrations. The ramified interface of such incompatible structural elements induces clustering impurities in any aqueous solution. These additives can enhance a heat transfer of water as a two-phase coolant for PWR due to natural forming of nanoparticles with a thermal conductivity higher than water. The aqueous nanofluid as a new condensed matter has a great potential for cooling applications. It is a mixture of liquid water and dispersed phase of extremely fine quasi-solid particles usually less than 50 nm in size with the high thermal conductivity. An alternative approach is the formation of gaseous (oxygen or hydrogen) nanoparticles in density fluctuations of water. It is possible to obtain stable nanobubbles that can considerably exceed the molecular solubility of oxygen (hydrogen) in water. Such a nanofluid can convert the liquid water in the nonstoichiometric state and change its reduction-oxidation (RedOx) potential similarly to adding oxidants (or antioxidants) for applying 2D water chemistry to aqueous coolant.

On Voltage-Sensitive Managing the Redox-Potential of MSR Fuel Composition

The principles for optimal managing a composition of base solutions for the molten-salt reactor are formulated here for ensuring the given properties and exchange processes as a selective extracting of salt components. The correction of melt properties can be carried out by means of impurity additives parallel with the forced and controllable variation of reduction-oxidation (redox) potential of the non-stoichiometric salts. The accent is done on a possible application of the potentiometer for monitoring and managing of the properties of MSR fuel compositions. For this, one can use the precision methods of e.m.f and the coulomb-metric titration of sodium (lithium) in a galvanic cell upon the base of Na+ (Li+ )-β″ -Al2 O3 solid electrolyte with cation conductivity.Copyright

Evolution of isotopic composition of reprocessed uranium during the multiple recycling in light water reactors with natural uranium feed

A complex approach based on the consistent modeling of neutron-physics processes and processes of cascade separation of isotopes is applied for analyzing physical problems of the multiple usage of reprocessed uranium in the fuel cycle of light water reactors. A number of scenarios of multiple recycling of reprocessed uranium in light water reactors are considered. In the process, an excess absorption of neutrons by the 236U isotope is compensated by re-enrichment in the 235U isotope. Specific consumptions of natural uranium for re-enrichment of the reprocessed uranium depending on the content of the 232U isotope are obtained.

Light fragments from (C + Be) interactions at 0.6 GeV/nucleon

We measured nuclear fragments emitted at 3.5° in 12C fragmentation at 0.6 GeV/nucleon. We also used the spectra obtained to test the predictions of four ion-ion interaction models: INCL++, BC, LAQGSM03.03 and QMD as well as for the comparison with the analytical parametrization in the framework of thermodynamical picture of fragmentation.

Electrochemical Sensor for Monitoring RedOx Potential of Molten Salts

A precise monitoring of reductionoxidation (RedOx) potential is necessary for using molten salts as fuel compositions and coolants in molten-salt reactors as well as for pyrochemical processing of a spent fuel. So, low over-potentials (~10 mV) are required for rigorously selective extraction of impurities out of the molten salt due to a permanent diffusive cathode polarization in galvanic cell. At the same time, a weak identification of cationic disproportionation (Mk+ Ml+) of metal impurities in liquid salts reflects the common defect of all known internal monitoring tools using salt as a sensor: realizing high over-potential and thereby strong polarization of the cathode. It leads to appreciable energy deformation of allowed electron states in the molten salt near the electrodes so that metal components of the basic salt are extracted out of the salt solution together with the selected impurity. Obviously, such the kinetic monitoring of RedOx potential cannot be a precise method since there is impossible eliminating the uncertain polarizing cathode effects in the galvanic cell with the molten salt as an electrolyte. Therefore a monitoring of the RedOx potential of liquid salts by means of an external potentiometer is necessary. This method is based upon the using of a gauge with Na+βAl2O3 electrolyte as a solid membrane with unipolar sodium conductivity assigned for monitoring a thermodynamic activity, , of neutral sodium atoms (Na0) in the molten salt. The principle of operation of such the gauge is based on the e.m.f. method. A measuring electrode, Pb [N (a thin layer of liquid lead on the solid electrolyte), directly contacts with the molten salt, easily exchanges by dissolved sodium atoms, and corrosive protects the solid electrolyte. The e.m.f., E, of this electrode is defined relatively a reference electrode (liquid sodium) located on the other side of solid electrolyte, Na+βAl2O3, in the four-layer galvanic cell: NaNa+βAl2O3Pb [Nsalt [], by equation, E = (RT/F) ln, where R is the universal gas constant, T is Kelvin temperature, F is Faraday constant.

Nuclear fragmentation study at ITEP heavy ion facility

In an experiment performed at ITEP TWA heavy ion accelerator, the yields of hydrogen (p,d,t) and helium (from 3He to 8He) isotopes at 3.5? from fragmentation of 12C at T0 = 0.2 ? 3.2 GeV/nucleon on a Be target have been measured. Momentum spectra of the fragments in the projectile rest frame have been obtained in larger momentum intervals than in the previous experiments with heavy ion beams. The main attention was given to the region of high momentum where fragment velocity exceeds the velocity of the projectile nucleus. The obtained data cover about 6 orders of the differential cross section magnitude. It made possible the observation of a transition from the Gaussian shape of the longitudinal momentum spectra in projectile rest frame, expected for the evaporation mechanism, to the exponential shape, typical for the cumulative (pre-equilibrium) processes. The Feynman x distributions for protons are analyzed in the framework of quark-gluon string model. The probabilities of existence of six-and nine-quark clusters are estimated and compared with the results on two- (three-) nucleon short range correlations in nuclei measured at Jefferson Laboratory.

Temperature parameters in the fragmentation of carbon ions at the energy of 0.6 GeV/nucleon

Momentum distributions of nuclear fragments at an angle of 3.5° in the interaction of 0.6-GeV/nucleon carbon ions with a beryllium target are measured in the FRAGM experiment on the ITEP-TWAC facility. The measured spectra are used for testing predictions of four ion–ion interaction models: BC, QMD, INCL, and LAQGSM03.03, and for comparison with the analytical parameterization within the thermodynamic concept of fragmentation.

The procedure and results of calculations of the equilibrium isotopic composition of a demonstration subcritical molten salt reactor

A subcritical molten salt reactor with an external neutron source is studied computationally as a facility for incineration and transmutation of minor actinides from spent nuclear fuel of reactors of VVER-1000 type and for producing 233U from 232Th. The reactor configuration is chosen, the requirements to be imposed on the external neutron source are formulated, and the equilibrium isotopic composition of heavy nuclides and the key parameters of the fuel cycle are calculated.

Multiple recycle of REMIX fuel at VVER-1000 operation in closed fuel cycle

The basic features of loading the VVER-1000 core with a new variant of REMIX fuel (REgenerated MIXture of U–Pu oxides) are considered during its multiple recycle in a closed nuclear fuel cycle. The fuel composition is produced on the basis of the uranium–plutonium regenerate extracted at processing the spent nuclear fuel (SNF) from a VVER-1000, depleted uranium, and the fissionable material: 235U as a part of highly enriched uranium (HEU) from warheads superfluous for defense purposes or 233U accumulated in thorium blankets of fusion (electronuclear) neutron sources or fast reactors. Production of such a fuel assumes no use of natural uranium in addition. When converting a part of the VVER-1000 reactors to the closed fuel cycle based on the REMIX technology, the consumption of natural uranium decreases considerably, and there is no substantial degradation of the isotopic composition of plutonium or change in the reactor-safety characteristics at the passage from recycle to recycle.