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Fission Product Yields

#3751


Complete Data Library on Nucleon-Induced Fission Product Yields for Applications in Wide Energy Region

Tech Area / Field

  • FIR-MAT/Materials and Materials Conversion/Fission Reactors
  • FIR-REA/Reactor Concept/Fission Reactors
  • PHY-ANU/Atomic and Nuclear Physics/Physics

Status
8 Project completed

Registration date
19.04.2007

Completion date
04.04.2012

Senior Project Manager
Tocheny L V

Leading Institute
Khlopin Radium Institute, Russia, St Petersburg

Collaborators

  • CEA / DSM / DAPNIA/CEN Saclay, France, Saclay\nInternational Atomic Energy Agency, Austria, Vienna

Project summary

Needs in the extension and improvement of on fission yields (FY) data is first at all related with a large scale usage of the data in different applied fields including the global security problems. In this kind of application the data on FY for main fissile materials (uranium, plutonium) for neutron-induced fission with energies from thermal to 14-15 MeV (in use of deuteron-tritium mixture in a device) allow through on-site inspection of possible underground explosion and with measurement of a relative abundance of isotopes in the rock samples to make a conclusion on a potential violation of a Comprehensive Test Ban Treaty as well as to determine the time of the test [1]. The FY data are also used for the analysis of a spent fuel to provide guarantee of nuclear materials nonproliferation [2]. Moreover, such a data are necessary for calculations of fission product accumulation and inventory at various stages of the nuclear fuel cycle, for the definition of criticality and reactivity at reactor core management, and for estimation of decay heat after reactor shutdown and in the spent fuel assemblies.

The problem of the data accumulation on fission yields has gained a new urgency at the development of the new nuclear technologies based on the usage of the beams of secondary neutrons with energies up to 200-300 MeV generated on thick spallation targets by high energy proton beams. It is expected that the new hybrid technologies will be used for the solution of such a fundamental problem as the transmutation of a radioactive waste. Besides, these data are needed for the solution of a number of basic problems of a nuclear physics at transition to higher energies stimulated by the commissioning of new high energy neutron sources and updating of existing machines as well as for astrophysics research.

In the heavy nuclei fission more than 300 isotopes of about 40 elements of the periodic table is created ranging from nickel to erbium, and about 25 % of them are creating in both ground and isomeric states. Besides, the significant contribution comes from light fission products (tritium, helium) generated in the ternary nuclear fission.

For neutron-induced fission with neutron energy up to 14-15 MeV there are three main evaluations collected in the ENDF-B/VI, UKFY2/3 (JEF-2), and CENDL nuclear data libraries mainly for thermal and fast energy region. In spite of large volume of evaluated FY there are evident gaps in the data as well as significant discrepancies even for main fission products with large yields.

It is well known that for higher energies the data on fission yields are very scarce. For example, for neutron induced fission only one experiment has been carried out for 238U(n,f) from 2 MeV to 450 MeV (C.M. Zoller, Ph.D. thesis, TH Darmstadt, 1995). For proton induced fission the situation is slightly better but there is also no systematic data for main isotopes of fuel cycle.

The number of experimental efforts to supply these data is now undertaken including two new ISTC projects #3192 and #3363 devoted to FY measurements for intermediate neutron and proton induced fission. However, by virtue of labour input and seller's prices of experiments the data have a rather separated character and can be used in main only for development and testing of model and codes being the main tool for datafile creation.

Evaluations used in the main nuclear data libraries for low-energy fission up to 14-15 MeV have been based on the fitting of fragment mass distributions by several Gaussians. This method allows to fill the gaps in the data in the model-independent way. The lack of the data for higher energy fission disables this kind of evaluations and the reliable physical models of nuclear fission have to be applied for the nucleon induced fission in 20-200 MeV energy region. Needs in the theoretical models for FY calculations stated in the IAEA documents as early as 1998 [3,4]

There are two main problems to be solved for the description of fission fragment (FF) formation in the nucleon-induced fission reactions. The first one lies in the accurate definition of the reaction mechanism including all reaction stages, i.e. direct, precompound and statistical processes, the role of different stages depending on a beam energy. The second problem is the proper model of fragment formation.

Formation of fragments in nuclear fission is closely tied with the important and still incompletely studied process of nuclear matter fragmentation from both low excited (spontaneous and thermal fission) and excited and highly excited states in the cases of intermediate and high energy nucleon-induced fission.

It is clear at present that the formation of FF mass distributions is first of all connected with the properties of potential energy surface on the stage of saddle-to-scission descent. Dynamical effects exert less influence on the mass spectra and manifest themselves in widths of mass distributions mainly. In the given project the new model of FF formation based on the notion of shape oscillations of fissionning nucleus on mass and charge asymmetry degree of freedom in the collective nuclear potential will be used, the model has being successfully applied for the calculations of FF mass spectra for the nucleon-induced nuclear fission in a wide energy diapason (Yavshits S., Grudzevich O., Proc. of 3rd Int. Workshop on Nuclear Fission and Fission Product Spectroscopy, Cadarache, France, May 11-14, 2005, AIP Conference Proceedings, v.798, 2005, p.373). The Hauser-Feshbach statistical approach will be used for calculations of neutron emission from FF excited states and population probability of the isomeric states (Grudzevich O. et al., Journal of Nuclear Science and Technology, Suppl.2, 2002 - Proc. of Int. Conference on Nuclear Data for Science and Technology, Oct. 7-12, Tsukuba, Japan, 2001, vol.2, p.44). The improved version of dynamic model of the ternary fission (Rubchenya V., Yavshits S., Z.Phys. 1988, v.329, p.217) will be applied for the calculations of light fission products. The standard activation approach will be also used for the computing of the chain yields.

The intermediate energy nucleon-induced fission is characterized by a broad distribution of fissionning nuclei on mass and charge numbers and excitation energies at the final stage of the reaction and the total yields of fission fragments is the sum of different contributions from different fissionning nuclei, the weights of this contributions depending on the reaction mechanism. The main model codes for the calculation of nucleon-induced reaction mechanism can be pided into two main classes. In the field of low energies the main tool is the statistical model realized in such well-known software packages as GNASH and STAPRE. For higher energies the methods based on the intranuclear cascade model (CEM, INC etc.) or the model of quantum molecular dynamics (QMD) are used. Despite of the reasonable physical assumptions underlying the codes the combined description of the nuclear data in practical calculations meets with large difficulties leading to necessity of variations of large number of model parameters. The reason of these difficulties lies in the originally narrow orientation of the approaches. For low energies there is no necessity to take into account the contribution of direct processes, while for high energies intranuclear interactions are taken into account but with rather simplified description of the preequilibrium and equilibrium reaction stages.

To overcome these kind of obstacles the new computational system TALYS (A.J. Koning, S. Hilaire and M.C.Duijvestijn, Proc. of Int. Conference on Nuclear Data for Science and Technology, Sept. 26 – Oct.1, Santa Fe, USA, AIP Conference Proceedings, v.769, 2005 p.1154) has been developed within the framework of the European project HINDAS, where the complex of nuclear models was included in the code to be able the estimation of nuclear reaction and fission data from the region of the unresolved resonances to intermediate energies.

The code system MCFx joining advantages of the intranuclear cascade model with the detailed description of preequilibrium and equilibrium stages of reactions induced by nucleons in a wide energy range has been developed in the Khlopin Radium Institute within the framework of the ISTC projects #964 “Development of model code and theoretical data library on heavy nuclei fission cross-sections in a wide energy range” and #2524 “Development of nuclear data library for nucleon-induced reactions on heavy nuclei in wide energy region” (Yavshits S., Report IAEA-NDS-153 (February 2002) - htpp://www-nds.iaea.org/reports/nds-153.pdf). The performed calculations of fission cross sections, spectra and multiplicity of secondary particles have shown the good description of experimental data with the model parameters determined on the base of the modern physical assumptions. This code similar in the main points to the TALYS code will be used for the description of reaction mechanism in the project proposed.

The problem of nuclear data for the reactions induced by nucleons is a traditional field of V.G. Khlopin Radium Institute where the large experience on experimental and theoretical study of the various reaction and fission is accumulated, including 6 completed and ongoing ISTC projects (##17, 183, 540, 554, 609, 964, 2524). Moreover, the results of the project will supply the theoretical support of the experimental investigations of fission observables started in the Khlopin Radium Institute in the framework of ISTC projects #3192 and #3363 and give us possibility to develop the ENDF-6-formatted data library on the fission yields based on the both experimental and theoretical results. The project proposed is a development of the ISTC project #964, #2524 and the work will be performed by the same team of experts which has the high qualification and consists mainly of the candidates and the doctors of physical and mathematical sciences working in the field of theoretical nuclear physics.

The project duration is 30 months. For this period the following results will be obtained:

  • The analysis of existing experimental and theoretical results on fission yields for the nucleon-induced reactions on the heavy nuclei for beam energy higher than fission spectra (~ 1 MeV);
  • The new calculation models will be developed and calculations for the proton-induced reaction up to 1 GeV and neutron-induced reactions up to 500 MeV on nuclei from Pb to Cf will be performed;
  • The nuclear data files on absolute values of independent and cumulative (after neutron emission) fission product yields in the ground and isomeric states, ternary fission yields and chain yields will be formed in the ENDF-6 format.

References
  1. Li Bin, “Analysis of Fission Products – a Method for Verification of a CTBT during On-Site Inspections” – Science and Global Security, 1998, vol.7, p.195;
  2. “Compilation and evaluation of fission yield nuclear data” – IAEA-TECDOC-1168, IAEA, 2000;
  3. M.Lammer, A.L.Nichols, “IAEA Coordinated Research Project on Fission Product Yield Data for Minor Actinides up to 150 MeV”, Proc. of 3rd Int. Workshop on Nuclear Fission and Fission Product Spectroscopy, Cadarache, France, May 11-14, 2005, AIP Conference Proceedings, v.798, 2005, p.285
  4. “Progress in fission product data” – INDC(NDS)-379, IAEA, 1998


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