Nuclear burning rates and Population II stellar models

We discuss theoretical predictions concerning the evolution of globular cluster Population ii stars with respect to current estimates of standard errors in the determination of nuclear burning rates. Numerical evaluations are given for the dependence of the turn-off and horizontal branch luminosities on the rate of the relevant nuclear reactions. We conclude that evolutionary predictions appear rather solid in this respect, with a maximum 3 sigma error of about 1 Gyr in the evaluation of cluster ages derived from the calibration of the difference in luminosity between the horizontal branch and the turn-off, However, current evaluation of the original He content, as given on the basis of the R-parameter, will need to wait for a much better determination of the C-12(alpha, gamma)O-16 reaction before reaching a satisfactory accuracy.