Nuclear energy has sparked international attention as one of the most important strategies for reducing emissions thanks to its ability to provide low-carbon power. Based on this interesting fact, the current research explores the effect of nuclear energy on CO2 emissions in the leading countries by nuclear power consumption using a quarterly dataset from 1990 to 2019. The study employs the quantile-on-quantile (QQ) estimator, which accounts for both non-parametric and conventional analyses and enhances the provision of unbiased and consistent estimates. In addition, the Granger causality in quantiles approach is adopted to assess the causality in quantiles between the variables of investigation. The outcomes from the QQ estimator reveals that in the majority of the quantiles, nuclear energy contributes to decreased degradation of the environment in the USA, France, Russia, South Korea, Canada, Ukraine, Germany, and Sweden. Contrawise, the feedbacks from Spain and China expose that Nuclear Energy Consumption (NUC) contributes to the deterioration of the environment. Moreover, the outcomes of the causality test disclose that nuclear energy and CO2 emissions can predict each other in the majority of the quantiles. The findings above provide profound ramifications for policymakers planning nuclear energy and CO2-emission policies towards achieving sustainable environment in the sample countries and beyond..