The distribution of fissions within one fuel pin of a cluster is asymmetrical because of self-shielding and neutron streaming phenomena. An implicit solution of the integral form of the Boltzmann equation indicates that, for a given neutron spectrum, this distribution is primarily a function of three dimensionless parameters: (1) pin radius/neutron mean free path in pin material; (2) pin circle radius/pin radius; and (3) pin radius/fuel element radius. The actual distribution was determined experimentally by detector foils and autoradiographic techniques for various seven-pin, cluster type, gas-cooled fuel elements. The experimental fuel pins were fabricated by winding alternate 0.001 in. thick layers of pure aluminum and enriched uranium (93% U235) on a solid core until the desired pin diameter was reached. Seven of these pins, assembled into a fuel element, were irradiated in the thermal column of a research reactor. The layers of uranium and the uranium detector foils (which had been exposed concurrently) were subsequently autoradiographed and the resulting x-ray film optical density measured on a microdensitometer. The detector foils were also counted in a gamma detector, thus providing a key between relative radioactivity and optical density. It was found that the fission distribution within the center pin of the cluster was symmetrical and could be represented by The fission distribution in the outer pins of the cluster was asymmetrical with respect to the pin center but could be represented by Values of the constants in the above equations are correlated by the first two dimensionless parameters given above but appear to be independent of the third.