atw - International Journal for Nuclear Power | 06/07.2019

atw Vol. 64 (2019) | Issue 6/7 ı June/July
SERIAL | MAJOR TRENDS IN ENERGY POLICY AND NUCLEAR POWER 346
if necessary implementation of properties for new heat
pipe working fluids,
pp
single/two phase flow natural convection, flow
instabilities and transition range between single and
two natural convection,
pp
passive safety systems (special components, start-up
behavior, mutual interaction of different passive safety
systems or trains of one passive safety system, ­extension
of the scope of correlations for containment heat
transfer)
pp
check-valves, in which the opening cross section and
the associated form loss is calculated dependent on the
pressure difference up- and downstream the valve,
pp
3D models for water pools/environment (ultimate
containment heat sink), temperature and velocity
fields, stratification,
pp
heat transfer at bundle surfaces at free convection,
subcooled or saturated boiling conditions,
pp
steam condensation at containment walls, structures
and internals especially for the case of small break
LOCA, inertised containments or containments
operated at near vacuum conditions,
pp
new coupling (strategy) between ATHLET and COCOSYS,
pp
infinite passive containment cooling to an ultimate heat
sink in ocean environment (influence of seawater,
mussel growth, etc.),
pp
heat transfers of horizontally arranged containment
in large water pools or the ocean at RA-numbers of
approx. 1015.
The above mentioned, open issues shall be processed and
closed with national and international research alliances.
One example is the EU project ELSMOR (Towards European
Licensing of Small Modular Reactors), which has received
approval for grant agreement preparations under the
European Union’s Horizon 2020 research and innovation Literature
programme. Scheduled to be launched in the summer of
2019, a total of 15 organisations from 8 countries will
participate in ELSMOR, to which the EU has granted EUR
3.5 million. GRS leads in ELSMOR two important work
packages. The consortium consists of support organisations
of European TSOs, universities, power companies,
and some of the developers of a French SMR design I-150
[CHJ-17]. ELSMOR is developing systematic methods for
the safety assessments of new and innovative reactors
(here especially SMRs). The project shall contribute that
European experimental infrastructures and modelling/­
evidence tools will be ready for use in nuclear licensing
procedures [VTT-19].
5 Summary
Small modular reactors are one interesting option for new
builds in almost all countries worldwide continuing to use
nuclear energy for commercial electricity production.
­Currently four SMRs are in operation, further six SMRs are
under construction and eleven at an advanced stage of
planning. Different European countries (e.g. the United
Kingdem, Russia, Poland) are planning to build and
operate SMRs. Even after nuclear phase-out the German
Federal government would like to assert legitimate nuclear
safety and/or security interests, e.g. by promoting comprehensive
safety reviews and ambitious binding targets
for the new builds (including SMRs) in our neighborhood.
The Gesellschaft für Anlagen- und Reaktorsicherheit
(GRS) gGmbH as the main German technical support
organization in nuclear safety for the German government,
has performed a Study on Safety an International
Development on SMR published in 2015 (GRS-376). In this,
numerous trends of current SMR development were
­identified. They are presented in this publication. The
modelling gaps of the GRS simulation chain were compiled
and a strategy for their closure was developed. The main
findings are: The safety level was increased e.g. by an
advanced, conservative design, implementation of new
safety features (e.g. passive safety systems) and the
­exclusion of accidents (e.g. LBLOCA, control rod ejection).
Therefore, SMR could be – if proven by safety analyses –
among the safest nuclear equipment ever made. Factory
fabrication minimizes the (financial) risk of delay in
construction. Competitiveness e.g. with gas power plants
requires the construction of a large number of identical
SMR units worldwide. Prerequisites for this are that all
entry barriers have been overcome like series production
in factories, which are currently not existing, and a
worldwide harmonization of rules and regulations and
recognition of licenses of foreign nuclear regulators.
­However, currently published figures are fraught with
large uncertainties and not yet reliable. Independently of
the previously mentioned open points, which are irrelevant
from TSO’s point of view, GRS will further develop and
validate its nuclear simulation chain. This allows to
successfully apply the GRS simulation chain in nuclear
licenses procedures and independent safety analyses also
for SMRs.
Acknowledgement
This article contains results of the research project Study
of Safety and International Development of SMR (grant
number RS1521), which was funded by the German
Federal Ministry for Economic Affairs and Energy (BMWi).
ıı
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Serial | Major Trends in Energy Policy and Nuclear Power
SMRs – Overview on International Developments and Safety Features ı Andreas Schaffrath and Sebastian Buchholz