μ

=

λa2/D=λ/D′

a

=

equivalent-sphere radius, cm

D

=

diffusion coefficient, cm2/cm

D′

=

Do/a2 exp(-Q/RT)×[100(MWd/t)/28000]

Do

=

limiting diffusion coefficient, cm2/s

Q

=

activation energy for diffusion, cal/g-mole

R

=

gas constant, (cal/deg) • (g-mole)

T

=

absolute temperature, °K

MWd/t

=

fuel burnup

For a small G (≈5%)*, i.e., μ>100,

(3–2)

or

(3–2A)

where the subscript i indicates nuclide i. At equilibrium, the release rate of nuclide i into the fuel gap is:

(3–3)

*  

For iodine and noble gas isotopes, an average of <5% was adopted in the Rasmussen report, WASH-1400 (NUREG-75/014). A smaller value has been reported in the most recent experimental measurement.(3,4)



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