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.
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