Review and discussion of the results of physical start-up investigations of WWER-type reactor cores

During physical start-up of nuclear power plants equipped with WWER-type reactors the following quantities were determined: temperature and pressure coefficients of reactivity in the temperature range 100 to 2600C, differential and integral efficiencies of the control rod groups, and differential efficiency of boric acid for certain temperatures. Moreover, the symmetry of real loading was examined. Measuring results obtained in the nuclear power plants Kola, Novovoronezh, 'Bruno Leuschner' Greifswald/G.D.R., and Kozloduj/Bulgaria are compared with each other and generalized. Problems of experiment planning and performance, data recording, measuring technique, and data evaluation are briefly dealt with. Possible systematic errors are studied. The possibility of applying the differential efficiency of boric acid to the determination of built-in reactivity and of the temperature effect in cores without adding boric acid to the coolant is discussed. (author)