Abstract
In pressurized water reactors (PWR) the reactivity control is accomplished through
movement of the control rods and boron dilution, meanwhile in boiling water reactors (BWR) the
importance of boron transport lies in maintaining the core integrity during ATWS-kind severe
accidents in which under certain circumstances a boron injection is required. This is the reason for
implementing boron transport models thermal-hydraulic codes in NRC codes as TRAC-BF1,
RELAP5 and TRACE.
The boron transport models implemented in NRC codes are based on a calculation according
to a first order accurate upwind difference scheme. There is a needing of reviewing and improving
this model.
Four numerical schemes that solve the boron transport model have been analyzed and
compared with the analytical solution that provides the Burgers equation. The studied numerical
schemes are: first order Upwind, second order Godunov, second-order modified Godunov adding
physical diffusion term and a third-order QUICKEST using the ULTIMATE universal limiter
(UL). The modified Godunov scheme has been implemented in TRAC-BF1 source code. The
results using these new schemes are presented in this paper.
