Patent Number: 041486870
Section: claims

1. In a heavy water moderated and cooled, natural uranium fueled nuclear reactor in which 19 fuel rods are arranged in a fuel bundle having a predetermined lattice pitch of 22.86 centimeters, one of said rods being located centrally within said bundle, the improvement which comprises replacing said central fuel rod with a rod comprising beryllium or its compounds whereby a lattice pitch of the resulting fuel bundle is reduced to 22 centimeters by the utilization of the (n, 2n) reaction effect on the beryllium without substantially detrimentally affecting the neutron multiplication value of the reactor. 2. In a heavy water moderated, light water cooled and natural uranium fueled nuclear reactor in which the fuel for the reactor is in the form of rod bundles each bundle containing 18 fuel rods about an unfueled tubular central tie rod and having a predetermined lattice pitch of about 27 centimeters, the improvement which comprises replacing said unfueled central rod with a rod comprising beryllium or its compounds whereby a lattice pitch of the resulting fuel bundle is reduced to about 25 centimeters by the utilization of the (n, 2n) reaction effect of the beryllium without substantially detimentally affecting the neutron multiplication value of the reactor. 3. A method of reducing the heavy water inventory in heavy water moderated and cooled reactors in which 19 fuel rods are disposed in a fuel bundle, one of said rods being disposed centrally in said bundle, the method comprising replacing said central fuel rod with a rod comprising beryllium or its compounds whereby the lattice pitch of the resulting fuel bundle can be reduced from 22.86 centimeters to 22 centimeters without substantially diminishing the neutron multiplication value of the reactor. 4. A method of reducing the heavy water inventory in heavy water moderated and light water cooled reactors in which the fuel is in the form of rod bundles, each bundle containing 18 fuel rods about an unfueled tubular central tie rod, said method comprising replacing said unfueled central rod with a rod comprising beryllium or its compounds whereby the lattice pitch of the resulting fuel bundle can be reduced from about 27 centimeters to about 25 centimeters without substantially diminishing the neutron multiplication value of the reactor.