Speaker
Description
Neutronics study is the backbone for the reactor Physics design. In both, fission and fusion reactor neutrons play an important role to the generation of electricity, by the conversion of their kinetic energy to heat energy. Fission neutrons have a maximum energy 2-3 MeV, while fusion neutrons coming from D-T plasma have a maximum energy of ~ 14.6 MeV. The Dynamics of fusion reactor neutrons is going to play a crucial role for the upcoming fusion reactor; International thermonuclear experimental reactor (ITER), DEMO, IFMIF and others. Out of the many neutrons induced reactions that take place inside a fusion reactor, the ones that produce gaseous elements like hydrogen and helium are of utmost importance for the study of structural integrity of reactor materials. The production of hydrogen and helium gases takes place mainly through (n, xp) and (n, xα) reactions. These reactions are induced on the first wall, structural and blanket materials of the fusion reactor. In addition to the production of hydrogen and helium, the other processes such as atomic displacements and transmutations can produce microstructural defects and modify physical properties of the materials. The materials suitable for the reactor structures are stainless steel with Cr, Fe, and Ni as main constituents (in SS316(LN)-IG content of Fe ≈ 65%, Ni ≈ 12%, Cr ≈ 17%). As the neutrons continuously coming from plasma interact with the various wall of the reactor made up of SS. There will be generation of various long-lived radionuclides like 55Fe (t1/2= 2.737 years), 59Ni (t1/2= 7.6×104years), 59Fe(t1/2 = 44.5 days), 60Co (t1/2 = 5.27years), 60Fe (t1/2= 2.6×106 years), 53Mn (t1/2=3.74×106 y), 54Mn (t1/2 = 312.16 days) inside reactor environment. The neutrons coming from plasma interacts with various long-lived radionuclides already generated in reactor environment during its operation, such types of reaction are called second generation reaction. These radionuclides play crucial role in damage of the reactor material, because of their long time presence inside reactor. As there is no experimental and theoretical study on the neutron induced reactions of various radionuclides produced inside the reactor environment during the reactor operation. As they are radionuclides, their properties such as decay heat, activity, dose rate, ingestion dose, inhalation dose, will effect normal lattice sites. The cross sections of the neutron induced reaction of various radionuclides are not measured and studied till now. So, there is a large gap in the nuclear data library .
The determination of reaction cross-section for long-lived radionuclide and short lived nuclei is a very challenging task . For the very first time, I have studied and experimentally verified the use of surrogate ratio method for the determination of (n,xp) reaction cross-sections. The cross-sections of 59Ni(n,xp) (t1/2 = 7.6 × 104 year) has been measured for the very first time using surrogate ratio method. Also, there exist no experimental data for the neutron induced charged particle reaction on 60Co. Excitation function of 60Co(n,p)60Fe and 60Co(n,α) have been obtained from threshold to 20 MeV using Hauser Feshbach model calculations with pre-equilibrium contribution using TALYS code. Major pathways (nuclear reaction channels) and their production cross-section for the formation of long-lived radionuclides 55Fe, 60Co, 63Ni, 59Ni have been calculated using activation code-ACTYS and nuclear reaction modular codes TALYS-1.8 code. During the present study, it has been recognized that the 59Ni(n,α)56Fe and 55Fe(n,α)52Cr reactions may also generate significant displacement damage as the recoil energy of 56Fe and 52Cr are 2.476 MeV and 2.497 MeV (for fast neutrons), respectively. A two step neutron reaction sequence 58Ni(n,g)59Ni(n,α)56Fe and 56Fe(n,2n)55Fe(n,α) result in an important contribution to the helium production in reactor environment.
The detail explanation of the methods used and results obtained during the present research work, will be presented during conference.