Reliability enhancement of RODOS results for a BWR NPP
urn:nbn:de:0221-2009042353 BfS-RESFOR-11/09
Abstract
Decision support systems such as RODOS aim to support the responsible authorities by providing estimates for the possible radiological consequences in case of an event in a nuclear plant. The prognosis of quantity, composition and time of occurrence of a release from the plant ("source term") in the so-called "pre-release phase" is one of the foundations with high relevance for this purpose.
Within previous projects source term prognosis tools have been developed and applied exemplarily for a PWR. At the end of 2005 GRS has finalized a PSA level 2 for a plant of the SWR-69 type. On this basis improved versions of the source term prognosis tools QPRO (probabilistic) and ASTRID (deterministic) have been created for a BWR and tested in an emergency exercise in a BWR.
The further development of QPRO has been related in particular to the structure of the probabilistic network and the precalculated source terms. The activities for the adaptation of ASTRID focus on the creation of the dataset for the BWR coolant loop and the containment.
In the emergency exercise the manageability of QPRO but also of ASTRID has been proven. Further, the first phases of the accident progression have been well identified. However, the exercise scenario developed into a very unlikely sequence with partial core melt, and the reactor building ventilation was shut off just at a critical moment. Therefore the source term prognoses deviate from the exercise scenario.
Starting from these experiences with the development and application of QPRO and ASTRID recommendations are given for the further improvement of the reliability of the source term prognosis for RODOS.
In general it can be stated that the development status of QPRO and ASTRID is definitely advanced compared to the presently still prevailing source term prognosis methods. Therefore it is recommended to develop plant-specific versions of these codes and to apply them.
