In this work a fully kinetic model of the JET SOL with tungsten divertor plates has been developed. It includes the dynamics of main-ions (D+) and electrons, the neutrals (D, C, W) and the impurity particles (C+m, W+n). Our simulations show extremely low concentration of W impurity. We identify two reasons which are responsible for this effect: 1. for low temperature divertor plasma the energy of most of the main-ions and the impurities in a low-ionization state impinging the divertor plates is below the W-sputtering threshold energy; 2. with increasing temperature the W-sputtering increases, but the potential drop across the divertor plasma increases too, so that most of the W ions are reabsorbed at the divertors.