Nuclear Data of Vanadium
Execution of the Complex of Benchmark Experiments for Testing the Nuclear Data of Vanadium - Main Component of Low-Activation Structural Materials for Perspective Nuclear Energetics
Tech Area / Field
- FIR-NOT/Nuclear and Other Technical Data/Fission Reactors
8 Project completed
Senior Project Manager
Tocheny L V
Kurchatov Research Center, Russia, Moscow
- VNIIEF, Russia, N. Novgorod reg., Sarov\nFEI (IPPE), Russia, Kaluga reg., Obninsk
- International Atomic Energy Agency / Division of Physical and Chemical Sciences, Austria, Vienna\nForschungszentrum Karlsruhe Technik und Umwelt / Institut für Neutronenphysik und Reaktortechnik, Germany, Karlsruhe
Project summaryFrom estimations it follows that more than 90 % of fusion reactor induced radioactivity is generated in area of high 14-MeV neutron flux - in the first wall and blanket. In case of use in these elements of a traditional material (stainless steel) the masses of high-activated wastes after reactor shutdown will be comparable with ones generated in fission reactors. If the wastes after initial cooling are disposed of, in the long-term this results in disappearance of valuable reserves of materials and creates a disposal problem. The alternative is recycling of materials executed remotely or by "hand-on" processing. In the latter for conventional materials the waiting time to required doze rate 25 mSv/h might be approximately 1000 years. The perspective of creation of low-activation structural materials for recycling in fusion reactors at present is mainly connected with the use of alloys on Vanadium basis (for example, V-5Cr-5Ti), as far as Vanadium does not give significant concentration of long-lived g-emitters.
The use of Vanadium in fusion reactors is accompanied with high demands to accuracy of its nuclear data, relevant to transport of radiation induced by 14-MeV neutrons in reactor blanket and shield, to nuclear heating and activation. The most advanced nuclear data library for fusion reactor calculations at present is FENDL-1 library, containing the best versions of evaluated data, tested on integral experiments with pure materials. However, a status of Vanadium data at present can not be determined, as the integral experiments for their testing are absent.
The min purpose of proposed project consists in creation of benchmark-experiments set for testing the Vanadium nuclear data by performing the complex of integral experiments with specially made composite spherical sample 150 mm of total thickness. The experiments are to be done on facilities with 14-MeV neutron generators as well as on simple spherical critical assembly from metal 235U (90%), and with isotopic neutron sources. On completion of experiments the testing and evaluation of Vanadium data are to be carried out.
1. `The measurement of neutron leakage spectra from Vanadium spheres with thickness of spherical layers of 5, 10, 15 cm with the following neutron sources:
- 14-MeV neutron generators (NG-150M);
- fission neutron source (stand FKBN-2M, assembly from 235U (90%));
- 252Cf isotopic source.
3. The measurement of neutron leakage multiplication in spheres with 14-MeV and isotopic sources.
4. The measurement of reactivity coefficient (Keff) for multiplying assembly containing V and 235U (90%).
5. The measurement of activation and fission rates on thickness of spheres.
6. The measurement of absorbed g-ray doze rate on thickness of spheres.
7. The activation measurement of pure Vanadium samples and samples from perspective Vanadium alloys placed in Vanadium spheres (under 14-MeV neutrons, fission spectrum neutrons and thermal neutrons) with detailed analysis of impurities activation.
8. The calculation testing of various versions of Vanadium evaluated data on integral experiments.
9. The re-evaluation of transport and activation data of Vanadium according to results of their testing.
Technical Approach and Methodology
The Vanadium benchmark-model, consisting from a set of semi-spheres of different optical thickness having technological channels with plugs, will be manufactured on special technology, ensuring high geometrical accuracy of its details. The study of element contents of the sample by method of Roentgen-Fluorescent Analysis (RFA) allows accurately taking into account the corrections on effects, stipulated by impurities. It is proposed to investigate the density non-uniformity of the Semispheres material by a technique being used in VNIIEF.
The neutronics researches will be conducted with use of different neutron sources:
- the neutron generator NG-150 certified as the reference neutron source En=14.3 MeV with the accuracy of neutron fluence certification not worse than ± 1.5 % (2 s);
- the critical stand FKBN-2 M with spherical assembly from 235U (90%);
- the pulsing fission reactor BIR-2 - a metrologically certified source of fast neutrons (0.5 eV < E <18 MeV) and thermal neutrons (d = 2.5 %, (2 s)).
The measurements of neutron leakage spectra will be carried out by several independent techniques:
- the time-of-flight method with use of pulsing operating mode of the generator. The time resolution of ~1 ns/m provides the resolution in area of evaporation spectrum maximum (~ 1 MeV) approximately of DE=30 keV. The energy range of measurements is 0.5 - 14 MeV;
- the method of nuclei recoil in gas proportional counter with unfolding of energy spectrum by the method of direct pergence. The theoretical and calculation components of the technique are well developed and validated on measurements with 252Cf source and critical assemblies. The technique is effective in the neutron energy range of 50 keV - 10.0 MeV;
- the method of nuclei recoils in scintillation detector on base of stilben with separation of n-, g-registration. The technique has high efficiency in the neutron energy range of 1 - 14 MeV;
- the method of threshold, nonthreshold and fission detectors activation, enabling to measure the neutrons spectra from thermal energy to 14 MeV. The technique is well validated on series of experiments and can be used for measurements of neutron spectra as inside of spherical sample, as on its surface.
The measurements of g-ray leakage spectra from Vanadium spherical samples of various thickness will be conducted with help of total absorption spectrometer on base of NaI (Tl) with use of time-of-flight technique on pulsing generator of 14.3 MeV neutrons and on electrostatic generator EGP-10.
The measurements of neutron leakage multiplication factor, as well as of reactivity coefficient (Keff), from spheres of various thickness will be executed with the developed techniques, numerously used for determining the BENCHMARK experimental data for neutron multiplying systems, containing fission materials.
The activation researches of samples from pure Vanadium and from Vanadium alloys irradiated under 14 MeV neutrons, fast neutrons, generated in spherical shells of various thickness, thermal neutrons (in graphite prism on reactor BIR-2 M), as well as in the central cavity of assembly from 235U (90 %), will be conducted with help of g-spectrometry on Ge-detectors of high energy resolution. The methods of complicated g-spectra analysis with exact account of absorption peak form and of a matrix of cascade g-transitions in nucleus will be applied.
The dose characteristics of gamma-fields in spherical samples will be measured with help of thermoluminiscent g-dosimeters of types IKS-A, TLD-500K.
The accompanying calculations and testing of various versions of evaluated data on results of experiments will be conducted with help of Monte-Carlo methods. This enables accurate statement and execution of experiments and development of recommendations on correction of evaluated data.
The work will result in comprehensive information for international testing of evaluated data of Vanadium that in final will ensure the data qualities on a level of requirements for designing the perspective fusion reactors and other units of potential nuclear energetics.
The execution of the mentioned complex of researches will ensure alternate employment of former weapon scientists, engineers and technicians in peaceful researches, first of all of their most vulnerable in conditions of economic instability category - highly experienced specialists in area of neutronics researches, having perfect experimental equipment and precise measurement techniques in their disposal.
Potential role of foreign collaborators
The cooperation in frame of the Project with foreign interested Institutions in areas of task definition, working discussions and uses of the Project activity results, as well as subsequent use of the manufactured Vanadium sphere in similar experiments, is possible. The direct comparison of some experimental results received in the Project with the similar measurements on Vanadium spheres expected to be carried out in Japan and Germany will be available.
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