Regional Basic Professional Training Course in Korea

❙ 617 ❙
9. Probabilistic Safety Analysis
identification of the modifications required to significantly improve system reliability and
reduce risk. These improvements have been implemented in new plants or proposed as
modifications for back fitting of existing plants.
Although the PSA results show a low risk, possible improvements should be examined,
as soon as the dominating sequences were identified, and the resulting modifications
implemented on systems (e.g. automatic interruption of dilution in progress in the event
of loss of reactor coolant flow, etc.), procedures, and Technical Operating Specifications.
9.6.2.2. An aid in designing future reactors
One of the objectives for the next generation of reactors is an improved overall level of
safety, compared to that of the present generation of reactors. Two major areas of
improvement are expected: the first is a reduction in core damage frequency, taking into
account the lessons learned from the previous PSAs and operating experience feedback.
The second is greater intrinsic resistance in the plant against core damage consequences,
in the event of a severe accident. In each case, probabilistic methods are required to
identify the points that can be improved and quantify the benefits of any new measures.
In the case of EPR, the future European Pressurized Reactor developed by
FRAMATOME, SIEMENS, and EDF, the reason for using PSA very early during the
conceptual and basic design phases of the EPR development work is to provide
reasonable confidence that the design will be consistent and well-balanced, and will
comply with the general safety objectives. In addition, PSA provides a rational basis for
harmonization of the licensing requirements in France and Germany, which are currently
different.
Safety objectives are specified to ensure sufficient safety provisions in the EPR design.
They are not to be interpreted as safety limits. These safety objectives include: