Improved fuel cycle flexibility and economy: Verification tests with BWR coolant flow range extension

All Swedish and Finnish BWRs have been relicensed to permit operation at lower recirculation flow at rated power than the original design, which corresponded to a 10% ''flow window''. This gives a number of advantages, among which lower fuel costs through spectral shift operation and increased core operation flexibility are the most important. The reduced coolant flow has been made possible by improvements in the core steady state operation leading to lower power peaking. Dynamic reactor characteristics are, however, of vital importance at low flow operation. A thorough theoretical analysis and experimental verification of reactor transients and stability thus form the basis for the applicability of the extended recirculation flow range concept. (orig.)