Fractional-space law for the neutron current density

► The fractional-space law for the neutron current density is investigated. ► The fractional-space neutron balance equation is derived with fractional law. ► The fractional exponent was related with neutronic signals of APRM in BWRs. ► The Forsmark and Laguna Verde Nuclear Power Plant were analyzed. ► The results show that the fractional exponent is between 0.1881 and 0.9399.