The BK kaon parameter in the 1/Nc expansion

We present work going on calculating the kaon BK parameter in the 1/Nc expansion. The goal of this work is to analyze analytically in the presence of chiral corrections this phenomenologically very important parameter. We present the method used and preliminary results for the chiral limit value for which we get the invariant BKchi=0.29 +- 0.15. We also give some analytical indications of why the large N_c prediction of BK= 3/4 may have small 1/Nc corrections in the real case