Fission fragment recoil

Search for fission fragment recoils in Allende sulfides. Geochim Cosmochim Acta 43 1743-1752 Lewis RS, Srirrivasan B, Anders E (1975) Host phase of a strange xenon component in Allende. Science 190 1251-1262... 

The structure of a typical coated particle is shown in Fig. 5.4. The fuel kernel is a sphere of uranium carbide with a diameter in the range of 100-400 pm. The innermost coatihg consists of a layer of pyrolytic carbon laid down by deposition from hydrocarbon gases in a high-temperature fluidized bed. This inner layer absorbs fission fragment recoils and is made relatively porous to provide voidage for the accommodation of fission gases. The next layer is made up of silicon carbide, which is particularly effective in the... 

Xenon in chondritic metal. Marti et al. (1989) have identified a xenon component (FVM-Xe) in a metal separate of the Forest Vale (H4) chondrite which appears to be distinct from xenon identified in other solar system reservoirs. It is characterized by relative abundances of the heaviest isotopes with unusually high " Xe. A possible e mlanation is recoil of fission fragments into the metal grains, possibly from Pu, " Tm or neutron induced fission of (Marti et al. 1989). This suggestion is consistent with the observed grain size dependence of FVM which favors a near-surface location. 

The activity due to accidental exposure of core material, resulting from loss of A1 cladding from a fuel plate, is calculated as follows The fractional escape of fission recoils from the surface of a slab source is l/4a, where a is the ratio of the mass thickness of the slab to. the range of the fission fragments, or 5.6 10 /1.05 10" = 54. Thus the fraction 1/4(54) 1/216 will escape from an exposed surface. At 30 mw there are 10 fissions/sec or 6.7 10 fissions/cc-sec. The number oi fission fragments escaping per square centimeter is therefore 3 10. Since the flow rate per plate is 28 gpm, the activity in the water is 1.75 10 fissions/cc-sec. 

The velocity of the fission fragments is changed due to the recoil of the neutrons, which are emitted with an energy of about 1 MeV. This effect is small (about 0.01 MeV) and since the emission of neutrons is isotropic from the fragments in flight, it does not change the mean velocity but widens the distribution and leads to a loss in mass resolution. 

The recoil phenomenon, which is intimately related to hot atom chemistry, was first observed by H. Brooks (1904) in 1904 at the McGill University (O Table 24.1). She noticed severe contamination with radioactivity of Pb and Bi in the ionization chamber she used. In 1905, Rutherford (1951) (Nobel Prize 1908) who supervised her work concluded that the phenomenon observed by her was based on the recoil energy of the residual nucleus introduced by a particle emission on the nuclear disintegration of Po (in other words, implantation in the wall material occurred). Then the technique using nuclear recoil was successfully employed by Hahn (Nobel Prize 1944) and Meitner (1909) for the separation of short-lived T1 (half-life 1.32 min) in 1909. The same technique was absolutely effective to separate a new element Np (Z= 93) from fission fragments with high kinetic energy when uranium (Z= 92) was irradiated with neutrons by Mcmillan (Nobel Prize 1951) and Abelson (1940). 

Besides the fuel, the closed chemical system fuel rod includes the fuel pellet -cladding gap and the upper and lower gas plenum, which are filled with helium overpressure (about 2 MPa at ambient temperature) in the course of fuel rod fabrication. During reactor operation, a certain gap inventory of radionuclides is generated which is of interest in the event of an operational fuel rod failure as well as in a loss-of-coolant accident. In typical LWR fuel rods, this gap inventory is mainly formed by fission product recoil from the fuel pellets. According to Wise (1985), one quarter of the fission fragments generated within a recoil length i from the... 

---