The production reactors operated by Douglas United Nuclear, Inc., use treated Columbia River water as the coolant on a once through basis. Thus, radionuclides formed largely by the neutron activation of river salts are discharged to the river. One method of reducing the quality of radionuclides in the effluent is to increase the efficiency of parent isotope removal during the water treatment process. Prior to 1961 the water treatment process for preparing reactor coolant had been improved to the point that reactor quality coolant could be produced using an average alum flocculent feed rate of 6 ppM. Laboratory experiments carried out in 1959 and 1960 demonstrated that a markedly increased removal of parent isotopes resulted when alum feed rates in the neighborhood of 20 ppM were used. The results were confirmed by two half-plant tests of short duration in July, 1961, all water treatment plants began to use alum at a somewhat arbitrarily selected rate of 18 ppm. The practice Continues to date at all plants except at the K Reactors. The K Reactor alum feed has been limited to a nominal 15 ppM because of the high filtered water requirements. The use of the high alum feed rate did …