Аннотация:New data on microstructure of 16 years old (La, Pu)PO4 monazite ceramics doped with8.1 wt% of 238Pu are presented. It is shown that the sample consists from at least two phasesdiffering in La/Pu ratio and small precipitates of Pu-phosphate. Possible mechanisms of thecompositional heterogeneity are discussed. Formation of Pu-containing rhabdophane aftersample storage in air is observed. This phenomenon together with gradual mechanicaldestruction of the ceramic pellet formation of submicron particles will likely increase rate ofradionuclides loss from the monazite-based waste form. X-ray emission lines produced byrecoil uranium ions from Pu decay are analysed. It is suggested that careful examination oftheir relative intensities may provide important information about behaviour of "hot" recoilsin nuclear waste forms.