Nuclear Data Production for Recycling of Nuclear Power Plant Waste
The advanced in nuclear reactor technologies has bring many advantages in providing nuclear energy for human life. This manifestation requires more advanced treatment in obtaining nuclear data from both calculation and experiments. Nuclear data which is required in advanced nuclear reactor simulation such as fission cross section, mass yield distribution, angular distribution, spectrum continuum and many more could be obtained using direct complete experiment or low cost numerical model calculation.
EMPIRE 2.19 is one of most versatile nuclear code in calculating fission cross section over wide energy range. The scheme of fission cross section calculation involved many reaction models mechanism such as Liquid drop and Shell model in level density calculation, Multi-Step Compound (MSC) and Multi-Step Direct (MSD) in Compound calculation, Monte Carlo pre-equilibrium for nuclear pre-equilibrium state calculation, and many more.
One disadvantage of using EMPIRE 2.19 is lack of mass yield fission distribution calculation which is required in some advanced nuclear reactor simulation. High demand ratio in this kind of nuclear data has lead to the implementation of other physical model into the core of EMPIRE 2.19 nuclear code. One of sophisticated model in describing mass yield distribution has been proposed by Brosa et. al through his magnificent model called Random Neck-Rupture Model. In this model, fission mass distribution are related with three type of fission barrier, that is Superlong Mode I (ST I), Superlong Mode II (ST II) , and Standard Mode(ST) which is affect the fission transmission mechanism and other important parameter in fission reaction. Most important thing pointed out by this model that mass yield distribution is calculated using probabilities of scission path on the neck region induced by deformed nuclei (randomness in neck rupture).
Implementation of RNRM model in EMPIRE 2.19 core has been developed by this research. Complete step or algorithm in mass yield distribution calculation has been implemented as following :
a. Fission Barrier
Determination of fission barrier of fissioning nuclei involved calculation of fission barrier parameter such as fission barrier height and width and also eccentricity. There is a lots of library providing such parameter like RIPL-2 from Gorielly et. al or parameter library from built-in calculation of EMPIRE 2.19.
b. Transmission Coefficient
Transmission coefficients are related with mechanism of particle flux penetrating fission barrier in such ways resulting in two different fission type, that is direct fission and indirect one.
Direct fission occurred when all the particle flux penetrated all the fission barrier hump in direct ways, while indirect fission occurred when all or fraction of particle flux reemitted from isomeric well. For indirect process there is two pathways involving particle flux, first path, incoming particle flux split into two fraction, one fraction is reflected back to the source while the other absorbed by isomeric well. Indirect fission occurred when the fraction of particle flux absorbed in isomeric well is reemitted and penetrating the outer hump. Second path, all incoming particle flux absorbed by isomeric well and reemitted back to penetrate the outer hump.
Transmission coefficient is highly depends on energy of incoming particle, shape of fission barrier (whether single-humped or multi-humped), and fission barrier width and height.
c. Decay probabilities
Decay / fission probabilities derived from procedure of multi-modal fission and highly depends on the mechanism of transmission in the fission barrier.
d. Level Density
Level density is one of most important parameter in fission to provide population parameter of fissioning nuclei. EMPIRE 2.19 offer three formalism approach, that is :
• Gilbert Cameron approach is used to calculate level density for up to 20 MeV nucleon induced reaction.
• Dynamic approach is used to calculate level density using superfluid and Fermi gas model where nucleus deformation factor taken into account.
• Hartree-Fock-BCS approach is used to calculate state density dependent level density. All the factor such as shell correction, pairing correlation, deformation effect and rotational enhancement are taken into account by this approach
e. Mass Distribution
As stated earlier, EMPIRE 2.19 did not include capability to calculate mass yield distribution. To accomplish this need, one should adopt the theoretical prediction of mass distribution using RNRM model from Brosa et. al. which is applicable for most fission reaction. In this model, mass yield distribution is calculated using assumption that fissioning nuclei would undergoes fission at random position at neck.
Calculated mass yield then compared with other mass yield data from nuclear data library such as ENDF B/VI for associated nuclei. Analysis to the result would be focused on physics model and procedure that used in calculation.
HEAD OF RESEARCH TEAM :
Dr. Rizal Kurniadi
TEAM MEMBERS :
Dr. Abdul Waris
OFFICIAL ADDRESS :
Faculty of Mathematics and Natural Sciences
e-mail : rijalk@fi.itb.ac.id