atw 2017-12

atw Vol. 62 (2017) | Issue 12 ı December
sodium­ cooled fast reactor designs.
Uncertainties for the VHTRC turned
out to be moderate and not much higher
than for LWR systems, while for the
fast-spectrum assemblies, much larger
uncertainties were obtained (e.g.
more than 1.5 % in the multiplication
factor uncertainty). This is of particular
relevance, since for fast reactors
there is only very scarce operational
experience in comparison to LWR.
She emphasized the participation of
GRS in corresponding international
activities, namely the HTR-CRP and
the OECD/NEA Benchmark for Uncertainty
Analysis in Modelling of Sodium­
Cooled Fast Reactor Systems,
and the current development of multigroup
cross section and covariance
data libraries especially dedicated to
the simulation of fast reactor arrangements.
Evgeny Ivanov (Institut de Radioprotection
et de Sûreté Nucléaire, France)
presented the next paper The Role of
Data Assimilation in V&UQ Process.
He talked about validation and uncertainty
quantification which plays an
important role in simulation and prediction
of complex systems behaviour
and is also an essential part of safety
margins verification and of characterization
of the maturity of different
design solutions. The V&UQ process
comprises the application domain,
where the model is specified and the
target accuracy is established, the validation
domain, where representative
integral experiments are identified,
and the transposition methodology,
with which knowledge is propagated
from the validation to the application
domain. Thus, by using integral experiments,
information is propagated
back from the macroscopic level to the
microscopic scale, and the original
uncertainties from microscopic measurements
can be reduced by data
assimilation (DA) techniques. An
example was the application of a
Bayesian approach with respect to
nuclear data uncertainties in criticality
benchmarks, which led to a
reduction of the result uncertainties
and to an improved agreement
between calculated and measured
values. The conclusions of the presentation
were that propagation of
non-reducible uncertainties such as
manufacturing tolerances, burn-up
uncertainties etc. gives knowledge on
target accuracies; that DA technique
at the same time provides analysts
with a consistent evaluation of accessible
accuracy of modelling; that DA
is the only way to put assessment of
uncertainty/accuracy on the basis
of evidence, e.g. on integral experiments;
and that Bayesian data
assimilation can help in the planning
of dedicated experimental and other
relevant research and development
programmes.
The last presentation of the session,
Experience in Using S/U Analysis
for Basic Data Validation and Other
Fission/Fusion Reactor Applications,
was given by Ivo Kodeli (Institut
“Jožef Stefan”, Slovenia). He gave an
overview of the sources of uncertainties
which can influence the results of
neutron transport calculations. For
the validation of nuclear data and
methods, comprehensive collections
of evaluated integral experiments are
available, in large part coordinated
and sponsored by OECD/NEA; these
cover criticality, reactor physics, radiation
shielding, and fuel performance
experiments. In addition, sensitivity
and uncertainty analyses should be
performed, in particular for design
and safety margins for new or improved
reactor designs, where little or
no experi mental information is available,
such as GEN-IV or acceleratordriven
system designs. At IJS, the
SUD3D code, based on perturbation
theory, has been developed for such
analyses. After analysing a wealth of
benchmarks with respect to the results
for various output quantities, he concluded
that powerful codes for nuclear
data sensitivity and uncertainty analysis,
both based on deterministic and
Monte Carlo methods are available
which, combined with benchmark
experiments, offer an efficient tool
for evaluation and testing of nuclear
data. The application of sensitivity and
uncertainty tools to the kinetic and
shielding benchmarks demonstrated
that the sensitivities of multiplication
factors and effective delayed neutron
fractions and shielding benchmark
measurements show complementary
features, suggesting that a combined
use of these measurements can be optimal
for the validation and improvement
of modern nuclear data. The use
of shielding, criticality, and kinetics
benchmarks offers a more complete
picture needed for nuclear data validation.
Challenges are that benchmark
data evaluation requires much more
effort than just providing inputs for
simulation codes; that improved,
mathematically and physically consistent
covariance matrices are needed,
e.g. containing correlations among
isotopes, secondary angular and energy
distributions; and that a reduction
of experimental uncertainty for the
effective delayed neutron fractions is
required.
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AMNT 2017
Key Topic | Enhanced Safety & Operation
Excellence: Technical Session: Operation
and Safety of Nuclear Installations, Fuel
Thorsten Hollands
Fuel and Materials
The sessions Fuel and Materials and Containment and SFP, as part of the Technical Sessions Operation and Safety
of Nuclear Installations, Fuel implemented in the Key Topic Enhanced Safety & Operation Excellence were chaired
by Dr. Thorsten Hollands (Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH) and Dr. Erwin Fischer (Preussen-
Elektra GmbH) who was the keynote coordinator for the Technical Sessions. Both sessions consist of a keynote lecture
followed by technical presentations.
The keynote lecture of the session
Fuel and Materials titled The Role
of Safety Regulator for Excellence
in Safety of Nuclear Power Plant
Operation was given by MinR
Volker Wild (Federal Ministry for the
AMNT 2017
Key Topic | Enhanced Safety & Operation Excellence: Technical Session: Operation and Safety of Nuclear Installations, Fuel ı Thorsten Hollands