Isotopes formation during fission

During the operation of nuclear power reactors, which are fuelled with ceramic UO2 fuel rods, the fission of the nuclei leads to die formation of fission products which are isotopes of elements in all of tire Groups of the Periodic Table. The major fission products, present in 1-10% abundance, fall into five groups divided according to the chemical interaction of each product with the fuel ... 

Some of the metallic fission products are plated out to a large extent onto the outer surfaces of the fuel rod claddings in the immediate vicinity of the defect this means that only small fractions of them are transported into the coolant. This is true in particular for tellurium, probably due to an electrochemical reaction on the Zircaloy surface resulting in the formation of the compound SnTe. The rather long-lived Te (halflife 76.3 h) decays there under the production and continuous release of its daughter to the coolant this mechanism is assumed to be the reason for the specific release behavior of this radionuclide, which is markedly different from that of the other iodine isotopes, both during constant load operation and during transients. 

Nuclear reaction(s) producing noble gas isotope(s) from stable or long-lived isotope during an irradiation in a nuclear reactor, or parent isotopes with half-lives less than 10 years, typical or suspected abundance at the time of formation of the solar system. For longer-lived parent isotopes, current abundance (%) of element. For actinides, " He yields are the number of atoms produced per decay chain, fission Xe yields are branching ratio for Xe. Yields for other isotopes are given in Table 2. 

The radionuclides incorporated into the oxide layers, which lead to a radiation field in the surrounding area, are mainly the activated corrosion product nuclides, above all Co and Co. Out of the fission products present in the primary coolant during plant operation with failed fuel rods in the reactor core, iodine and cesium isotopes are not deposited into the surface oxide layers this reactor experience is consistent with the general chemical properties of these elements which do not allow the formation of insoluble compounds under the prevailing conditions (with the sole exception of Agl, see Section 4.3.3.1.2.). On the other hand, fission product elements that are able to form insoluble compounds (such as oxides, hydroxides or ferrites) in the primary coolant are incorporated almost quantitatively into the contamination layers (see Section 4.3.3.1.4.). However, because of the usually low concentrations of polyvalent fission products in the primary coolant, only in very rare cases will these radionculides make a measurable contribution to the total contamination level for this reason, they will not be treated in this context. 

During the irradiation of a standard fuel like UO2 oxides or MOX, a significant part of nuclear reactions are not fission reactions, but capmre reactions or more complex nuclear transmutations. Thus, in the conrse of time, a part of the isotopes transforms into plutonium Pu, a fissile material which will increasingly contribute to the supply of power. However, some of these reactions will lead to the formation of isotopes difficult to recover (isotope pairs of Pu, Am and other minor actinides, etc.), whose accumulation would cause major concern. The fission of these isotopes can be achieved by irradiation in certain reactors whose neutron characteristics will be adapted to this functioa We must however avoid the recreation of similar isotopes as and when they are burnt . This could lead to striving for fuel designs where the fissile material is dispersed not in the UO2 oxide, but in a neutronically inert matrix. 

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