How to estimate the enrichment of U-234 from the enrichment of U-235?

Fresh nuclear fuel made from naturally occurring uranium (i.e. neither MOX nor ERU fuel) is mainly characterised by the enrichment of $\ce{^235U}$. The mass and activity concentrations of $\ce{^235U}$ and $\ce{^238U}$ can be directly calculated from the given level of enrichment. If necessary, the mass and activity concentrations of relevant decay products can also be calculated easily.

However, the gas diffusion or gas centrifuge processes for $\ce{^235U}$ enrichment do not only lead to an increase in the $\ce{^235U}$ concentration in the fuel, but also to a more than proportional increase in the $\ce{^234U}$ concentration. This can be seen from the following table where the mass concentrations of uranium isotopes in natural uranium and typical fresh nuclear fuel (with $3.5\ \%\ \ce{^235U}$) are compared.

$$\textbf{Mass concentration of uranium isotopes (in g/kg HM) in fresh nuclear fuel} \\ \begin{array}{lll} \hline & \text{Natural U} & 3.5\ \%\ \ce{^235U} \\ \hline \ce{^234U} & \hphantom{00}0.06 & \hphantom{00}0.4 \\ \ce{^235U} & \hphantom{00}7.2 & \hphantom{0}35.0 \\ \ce{^238U} & 992.8 & 965.0 \\ \hline \end{array}$$

The corresponding activity concentrations are shown in the second table.

$$\textbf{Activity concentration of uranium isotopes (in MBq/kg HM) in fresh nuclear fuel} \\ \begin{array}{lll} \hline & \text{Natural U} & 3.5\ \%\ \ce{^235U} \\ \hline \ce{^234U} & 13 & 93 \\ \ce{^235U} & \hphantom{0}0.58 & \hphantom{0}2.8 \\ \ce{^238U} & 13 & 12 \\ \hline \end{array}$$

Is there a simple and reliable calculation method or model that can be used to estimate the enrichment of $\ce{^234U}$ from a given enrichment level of $\ce{^235U}$?

• It would depend on the enrichment method used, and how much somebody cared about the $^{234}$U. – Jon Custer May 1 '17 at 15:42
• Could a sequential off-line or continuous on-line monitoring by mass spectroscopy, discerning the isotopes (like $\ce{^{79}Br}$ / $\ce{^{81}Br}$ or $\ce{^{35}Cl}$ / $\ce{^{37}Cl}$ in small molecular organic chemistry) assist to establish a descriptive model about the enrichment of the uranium isotopes? – Buttonwood May 1 '17 at 17:15