The possibility to improve confinement in tokamaks by seeding of impurities has been successfully realized in several devices [1, 2, 3]. However earliest trials on JET [4] were not encouraging and sowed doubts that this mode of operation can be achieved in large machines. New series of experiments performed during the past year have shown that also in JET a positive effect of impurity seeding can be attained through an optimization of the puffing scenario. E.g., carefully dozed puffs of argon allowed to maintain good confinement in the H-mode discharges at an electron density close to the Greenwald limit.In this contribution we present the results of theoretical analysis and numerical modelling of another scenario performed on JET with neon impurity seeded into L-mode discharges. This choice is explained by several reasons. First, the theoretical models applied for our study were developed to analyze the results from TEXTOR [2] and DIII-D [3] where the stage of improved confinement, the so called Radiative Improved (RI) mode, was achieved starting from the L-mode conditions. Up to now these models do not include the edge barrier and are limited in applications to the H-mode conditions. Second, although transiently the most characteristic features of the classical RI-mode such as peaking of density and pressure have been seen in JET namely under these conditions. As an example Fig.1 shows the radial profiles of plasma parameters measured in Pulse No: 50329 before and after Ne puff.