Scope and purpose
This standard provides an analytical method for calculating the release of volatile fission products from uranium dioxide(UO2) fuel pellets during normal reactor operation. When used with nuclide yields, this method will give the release-to-birth ratio R/B or the so-called "gap release," which is the inventory of volatile radioactive fission products that could be available for release from the fuel rod if the cladding were breached.
The standard considers high-temperature releases (up to 2500 K) and low-temperature releases (lessthan 1000K where temperature-independent processes dominate) and distinguishes between short-half-life nuclides (half-lives lessthan 1 yr) and long-half-life nuclides (half-lives lessthan1 yr). Therefore, the standard is applicable to fuel under irradiation conditions with fuel temperatures between 620 up to 2500 K. This standard accounts for thermal diffusion and athermal diffusion coefficients that are added together for determining a total R0B ratio.