Analyses of the OECD Main Steam Line Break Benchmark with the Codes DYN3D and ATHLET

Analyses of the OECD Main Steam Line Break Benchmark with the Codes DYN3D and ATHLET

Grundmann, U.; Kliem, S.

The OECD Main Steam Line Break (MSLB) Benchmark was defined to validate the thermal-hydraulic system codes coupled with three-dimensional neutron kinetic codes. The reference problem is a MSLB in a pressurized water reactor (PWR) at end of cycle (EOC). The analyses were performed with the three-dimensional core model DYN3D, the thermal-hydraulic system code ATHLET and the coupled code DYN3D/ATHLET. The results of the DYN3D and ATHLET simulations based on the specification are compared with the results of other participants in the final OECD reports. The effect of the thermal-hydraulic nodalisation of the core, i.e. the number of coolant channels, and the influence of the coolant mixing inside the pressure vessel are studied in the paper. Calculations with a reduced number of coolant channels are performed often in coupled calculations for saving
computational time. Results of a 25-channel model were compared with the 177-channel calculation (1 channel/assembly). The results for global parameters like nuclear power show only small differences for the two models, however the prediction of local parameters such as maximum fuel temperatures requires a detailed thermal-hydraulic modeling. The effect of different coolant mixing within the reactor pressure vessel is investigated. It is shown that the influence of coolant mixing mitigates the accident
consequences when three-dimensional neutron kinetics is applied. In case of point kinetics, coolant mixing leads to an opposite effect. To profit from the three-dimensional core model, a realistic description of the coolant mixing in the coupled codes is a topic of further investigations.

Keywords: coupled neutron kinetics/thermal-hydraulics codes; main steam line break analyses; coolant mixing

  • Nuclear Technology 142(2003) 146-153

Publ.-Id: 4278