Reactor physics calculations in the Nordic countries: Proceedings of the 7th Nordic Reactor Physics Meeting

The seventh biennial meeting on reactor physics calculations in the Nordic countries was arranged by VTT Energy in Otaniemi, Espoo on May 8 - 9, 1995. Recent development and verification of the program systems of ABB Atom, Risø, Scandpower, Studsvik and VTT Energy was of course the main topic of the meeting. Benchmarking of the two assembly codes CASMO-4 and HELIOS is proceeding. Cross section data calculated with CASMO-HEX have been validated for the Loviisa reactors. On core analysis, ABB Atom described its latest core simulator version POLCA7 with the calculation environment Core Master 2 and the BWR core supervision system Core Watch. Transient calculations with HEXTRAN, HEXTRAN-PLIM, TRAB, RAMONA, SIMULATE-3K and a code based on PRESTO II/ POLCA7 were presented. The importance of an efficient core monitoring system for detection of various anomalies, as excessive crud accumulation or assembly bowing, was demonstrated. It was furthermore shown that reactor physics methods can be successfully applied to other problems, as charged particle transport, that core stability can be considerably improved through careful fuel and core design as well as optimum use of control rods, that ordinary diffusion theory sometimes may be surprisingly accurate also in extreme conditions, but that on the other hand even sophisticated programs can have a hard time when confronted with the exotic geometries of a test reactor. The old four-factor-formula was revived in an attempt to obtain better agreement between measurements and an uncomplicated theory. Criticality safety studies performed at VTT Energy and ex-core neutron flux calculations at ABB Atom were reported. Finally, both the calculation and measurement of void fractions were discussed during the meeting.