The effect of bound and free hydrogen cross section of fuel temperature reactivity co-efficient of 3MWt TRIGA research reactor

The temperature reactivity co-efficient, α1, of TRIGA core has been calculated using the code WIMS-D/4 for three different burnups viz. 0 MWd, 1000 MWd, and 2000 MWd. The effect of scattering cross section of H bound in ZrH and free hydrogen on the fuel temperature reactivity co-efficient has been studied rigorously as function of burnup and temperature. It was found that the use of these two cross sections yields entirely different fuel temperature characteristics. Specially in lower temperature region if the cross section of H in ZrH in fuel are used as against for hydrogen bound in water as in WIMS/D-4 old library the difference in α1 is just opposite. The difference converges with the increase in energy. Hence for correct calculation of α1, and to avoid misleading results the cross section of H in ZrH and cross section of free hydrogen (as in water) should be treated separately