Self-powered neutron detectors (SPNDs) are widely used for neutron flux monitoring within nuclear reactors. Among them, rhodium-based SPNDs (Rh-SPNDs) exhibit higher signal amplitudes due to the high thermal neutron capture cross-section of rhodium. However, this also results in more significant spatial burnup effects, leading to a nonlinear variation in sensitivity over time. Although previous studies have preliminarily explored the burnup effects of Rh-SPNDs, they have not comprehensively analyzed the impact of spatial burnup effects and their influence on space charge effects, and approximations have been introduced in sensitivity calculations. In this study, based on the SPNDSignal toolkit, a precise and comprehensive analysis of the spatial burnup effects of Rh-SPNDs in the K1 assembly of the VVER reactor has been conducted, incorporating the perspective of space charge effects for the first time. The influence of spatial burnup effects on detector sensitivity was calculated and analyzed. The results show that the influence of the spatial electric field within the detector on burnup calculations is minimal. After 5 years of operation, the spatial burnup effects result in a burnup difference of up to 19.24% between the inner and outer regions of the emitter. Furthermore, the nonlinearity of detector sensitivity changes with burnup is 10.43%, while the contribution of beta particles to sensitivity decreases by 0.72%. These findings provide critical theoretical support for calibrating detector sensitivity.