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We present the results of a study of the AGN density in a homogeneous andwell-studied sample of 167 bona fide X-ray galaxy clusters ($0.1<z<0.5$) fromthe XXL Survey. The results can provide evidence of the physical mechanismsthat drive AGN and galaxy evolution within clusters. The XXL cluster samplemostly comprises poor and moderately rich structures ($M=10^{13} -4\times10^{14} M_{\rm o}$). Our aim is to statistically study the demographicsof cluster AGNs as a function of cluster mass and host galaxy position. Toinvestigate the effect of the environment on AGN activity, we computed thefraction of spectroscopically confirmed X-ray AGNs ($L_{\rm X[0.5-10\,keV]}>10^{42}$ erg cm$^{-1}$) in bright cluster galaxies, up to$6r_{500}$ radius. To study the mass dependence and the evolution of the AGNpopulation, we further divided the sample into low- and high-mass clusters andtwo redshift bins (0.1-0.28 and 0.28-0.5). We detect a significant excess ofX-ray AGNs, at the 95% confidence level, in low-mass clusters between$0.5r_{500}$ and 2$r_{500}$, which drops to the field value within the clustercores ($r<0.5r_{500}$). In contrast, high-mass clusters present a decreasingAGN fraction towards the cluster centres. The high AGN fraction in theoutskirts is caused by low-luminosity AGNs. It can be explained by a highergalaxy merging rate in low-mass clusters, where velocity dispersions are nothigh enough to prevent galaxy interactions and merging. Ram pressure strippingis possible in the cores of all our clusters, but probably stronger in deepergravitational potentials. Compared with previous studies of massive orhigh-redshift clusters, we conclude that the AGN fraction in cluster galaxiesanti-correlates strongly with cluster mass. The AGN fraction also increaseswith redshift, but at the same rate with the respective fraction in fieldgalaxies.

The XXL survey XXXV. The role of cluster mass in AGN activity