Tritium Assay Analysis by PVT Mass Spectrometer cont'd

DOE-HDBK-1129-99

Once the quantity of tritium in the container on the Sampling Date is known, the quantity of

tritium in the container for any other date, including the Book Value Date can be calculated.

The number of moles of gas in the container on the Sampling Date (n(TotCSmplDa)) is the sum of

the number of moles of the non-tritiated gases present in the container, which do not change

with time due to decay, (n(Non-tritium)), plus the number of moles of tritium in the container at the

time of the sampling (n(T2CSmplDa)). In equation form

PV/zRT = n(TotCSmplDa)

= n(Non-tritium) + n(T2CSmplDa)

Rearranging the equation it becomes

n(Non-tritium) = n(TotCSmplDa) - n(T2CSmplDa)

{1}

The total number of moles of material in the container on the Analysis Date, (n(TotCAnlDa)) is

n(TotCAnlDa) = n(Non-tritium) + n(T2CSmplDa) x e((t ln(0.5))/4500.88) + 2 x (n(T2CSmplDa) - n(T2CSmplDa) e((t x

ln(0.5))/4500.88)

)

where n(Non-tritium) = sum of the moles of the other gases

(n(T2CSmplDa) (e((t ln(0.5))/4500.88)) = number of moles of T2 decayed

2 x (n(T2CSmplDa) - n(T2CSmplDa) e((t ln(0.5))/4500.88)) = number of moles of 3He created

t = time between the Sampling Date and Analysis Date in days

Factoring, the equation becomes

n(TotCAnlDa) = n(Non-tritium) + n(T2CSmplDa) x (2 - e((t x ln(0.5))/4500.88))

{2}

On the day the gas analysis is performed, the mole percent of tritium (m%(T2MAnlDa)) is

determined by gas analysis. The equation is

m%(T2MAnlDa) is equal to the number of moles of tritium on the sampling date decayed to the

analysis date; i.e., (n(T2CSmplDa) x e((t x ln(0.5))/4500.88)) divided by the number of moles in the sampled

container on the analysis date; i.e., (n(TotCAnlDa)) multiplied by 100 to convert it to percent.

m%(T2MAnlDa)={(n(T2CSmplDa)e((txln(0.5))/4500.88))/n(TotCAnlDa)} x 100

where (n(T2CSmplDa) x e((t x ln(0.5))/4500.88)) = number of decayed moles of T

(n(TotCAnlDa)) = number of moles in the sample on the Analysis Date

t = time between the Sampling Date and Analysis Date in

days

Rearranging the equation it becomes

((t x ln(0.5))/4500.88)

n(TotCAnlDa) = {(n(T2CSmplDa) e

)/m%(T2MAnlDa)} x 100

{3}

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