Diffusion-controlled fission product

Spheres Diffusion-Controlled Fission Product Release and Absorption... 

A temperature-stepping diffusion-controlled fission product absorption model, where equilibrium is taken to occur at the surface of the... 

Numerous studies by other workers (I, 10) have shown that the releases of iodine and the noble-gas fission products from pyrolytic carbon-coated fuel particles are controlled by diffusion of these nuclides through grain boundaries, cracks, and defects in the isotropic pyrolytic carbon coating. When coatings are intact, however, the release of these fission product nuclides is low. However, the pyrolytic carbon coating constitutes only a delaying barrier to the metallic nuclides barium and strontium through which they diffuse with diffusion coefficients of the order of 10 9 cm.2/sec. (at — 1400°C.). The steady-state release of these metallic nuclides is controlled instead by diffusion out of the fuel kernel,... 

In summary, essentially 100% of the Pu, 85 — 1(X)% of the Nd, 75 — 90% of the Ru and 60 — 85 % of the Tc were retained within the reactor zones. The migrating fission products were held within a few tens of meters of these zones. Thermodynamic calculations of the temperature dependent solubilities indicate that the loss of fissiogenic elements is diffusion controlled, whereas, retention in the surrounding rocks is due to temperature dependent deposition from an aqueous solution. 

The release of volatile fission products from the still-solid fuel matrix is primarily controlled by diffusion processes, i. e. intragranular diffusion from the interior... 

If the absorbing species is in a condensed phase, intermolecular interactions may arise that control the fate of the excited-state entity, eg when the excited molecule is in a solvent cage and the initial photochemical reaction relies on the homo-lytic or heterolytic bond fission, diffusion of the initial products (radicals) from the same precursor is inhibited. Instead the products remain in the cage for several vibration periods which enables the back reaction to form the substrate or its isomeric form [4-6],... 

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