
 DOESTD30132000
APPENDIX B
Derivation of Pressure Equation
B.1.
Introduction
This appendix provides a derivation of the equation used to bound the internal pressure of
storage packages loaded with oxide. It also provides guidance on use of the equation. This
equation appears in DOESTD301396 [USDOE 1996] and is similar to the equation in DOE
STD301394 [USDOE 1994b]. For simplicity in comparing the equation derived here with that
used in the 3013 Standard, SI units have not been used. Instead, pressures are given in psi.
It is assumed that the ideal gas law applies to the conditions and gases important to the
calculations. According to that law
PV = nRT
[1]
where P is absolute pressure, V is volume, T is absolute temperature, n is the number of moles
of gas, and R is a constant with units consistent with those chosen for P, V, and T. If a gas is at
some standard condition, described by P0, V0, and T0, then the quantity nR can be evaluated as
n R = P0V0/T0.
[2]
And the pressure under different conditions can be determined by
P1 = nRT1/V1 = P0(V0/V1)(T1/T0).
[3]
In the above equation, T1 is the temperature at which P1 is to be evaluated. V1 is the volume
occupied by the gas at the evaluation temperature.
For ideal gases, the pressure of a mixture of gases can be determined as the sum of the partial
pressures of the individual gases. There are three gas sources that require consideration in a
plutonium storage container: 1) the container fill gas, 2) any gases evolved during storage in
the sealed container through radiolysis, chemical reactions, or desorption, and 3) helium
produced by alpha decay of the contained radioactive species. Thus, the combined effect can
be expressed as:
P = PF + PG + PHe
[4]
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