Original scientific paper
Review of Design Extension Conditions Experiments and Analyses for Non-degraded Core
Andrej Prošek,
orcid.org/0000-0003-0641-3474
; Jožef Stefan Institute Jamova cesta 39, SI-1000 Ljubljana, Slovenia
Mitja Uršič
orcid.org/0000-0002-8699-1727
; Jožef Stefan Institute Jamova cesta 39, SI-1000 Ljubljana, Slovenia
Abstract
The second generation nuclear power plants were designed and built to withstand without loss
to the systems, structures, and components necessary to ensure public health and safety during
design basis accidents (DBAs). In the transient and accident analysis the effects of single active
failures and operator errors were considered. There are also accident sequences that are possible but
were judged to be too unlikely and therefore were not fully considered in the design process of
second generation reactors. In that sense, they were considered beyond the scope of design-basis
accidents that a nuclear facility must be designed and built to withstand. Such accident sequences
have been analysed in the past to fully understand the capability of a design.
The requirements to analyse such sequences for existing reactors have been introduced after
Fukushima Dai-ichi accident. In 2012 the design extension conditions (DECs) were introduced in
the International Atomic Energy Agency (IAEA) requirements for the design of nuclear power
plants (NPPs). Western European Nuclear Regulators Association (WENRA) requirements of
existing reactors for DEC were introduced in 2014. The purpose of considering DEC is to further
improve safety by enhancing the plant’s capability to withstand the conditions generated by
accidents that are more severe than DBAs. This concept by IAEA and WENRA (WENRA
definition of DEC is consistent with IAEA definition from 2012, in which DEC with prevention of
core melt is called DEC A) is not completely new, since some multiple failures have already been
considered in the design of existing reactors, for example anticipated transients without scram and
station blackout. The research for beyond design basis accidents with non-degraded core (i.e. DEC
A) for existing reactors has been already done in 80’s and 90’ of the previous century. The purpose
of this paper is to review that research. The tests performed include total loss of feedwater, station
blackout, small break without high pressure safety injection, steam generator tube rupture with no
high pressure safety injection etc. Besides review of experiments performed on integral test
facilities, examples of DEC A tests, which have been analysed at Jožef Stefan Institute using
RELAP5 or TRACE computer code in the last three decades, will be presented too.
Keywords
design extension conditions, RELAP5, TRACE, safety analysis
Hrčak ID:
247094
URI
Publication date:
28.10.2019.
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