TotalByCountry =
    CALCULATE(
        COUNTROWS(FactNuclearPowerPlant);
        ALLEXCEPT(FactNuclearPowerPlant;
            FactNuclearPowerPlant[CountryName]
        )
    )

TotalByCountryPercent =
    SWITCH(
        TRUE();
        ISINSCOPE(FactNuclearPowerPlant[ReactorType]);
            DIVIDE([CountFactNuclearPowerPlant];[TotalByCountry]);
        ""
    )