atw 2018-09v3


atw Vol. 63 (2018) | Issue 8/9 ı August/September



hardly be attributed to the primary

water inlet temperature variations,

which remain relatively well known

since decades, because the noise has

essentially no time shift dependence

along the water flow through the

assembly channel. The high neutron

flux noise is concentrated essentially

in one quarter of the core, radial and

azimuthal correlations build a consistent

picture supporting this observation.

The model explaining the increase

of the neutron flux noise is at the

present time associated with the

replacement of FOCUS fuel assemblies

by the HTP assemblies, which took

place basically since 2010. The current

core configuration has no longer

FOCUS assemblies, and the (high)

neutron noise achieved seems to be

saturated, bracketing the period of

insertion of the HTP-assemblies well.

The reason for the neutron noise

increase is associated to the thermalhydraulics

pattern in the core, not fully

symmetric (3 loops with asymmetries),

probably promoting a more

intense cross flow towards one specific

loop that exercises a lateral dragging

force on the HTP assemblies. Since

these assemblies hold the fuel rods in a

less fixed way than the previous

FOCUS, with the purpose of minimising

the rod-to-grid fretting potential

further, the guiding tubes do not

count in HTP assemblies with the

stiffness of the fuel rods themselves to

give a combined, stronger assembly

stiffness, as it was the case of the

FOCUS assemblies. HTP are considered

to be mechanically more prone

to elastic lateral oscillations. The

­increase of neutron flux noise would

be the result of larger variations of

the water gap thickness between

HTP assemblies, an effect that was

enhanced as the core was loaded

increasingly with HTP assemblies.

Further work is ongoing to

bring complementary information to

support or discard this assembly

behaviour model. In particular, KKG

participates in the CORTEX international

research programme within

the Horizon 2020 EU Framework

Programme for Research and Innovation,

and a different organisation

will take independent new measurements

to refine the analyses available.


The authors would like to thank

the Electrical Division at KKG for

their support and collaboration, in

particular R. Härry, K. Heydecker

and A. Ploner for performing several

additional measurements during last

cycle. We are also thankful to the

director of the Nuclear Fuel Division,

B. Zimmermann, for his support

during the course of this research.


[1] Neutronenflussrauschen, R. Meier,

ANO-D-41205, 2010. Restrictive.

[2] Noise Analysis of KKG’s neutron flux

detector signals, A. Alander, Studsvik

Scandpower, TN-04/2011, Document

Kernkraftwerk Gösgen-Däniken AG.

2011. Restrictive.

[3] Studie des Neutronenflussrauschens im

Zyklus 36, G. Girardin, Kernkraftwerk

Gösgen-Däniken, BER-F-78937, Internal

Document Kernkraftwerk Gösgen-

Däniken AG, 2015. Restrictive.

[4] Use of Neutron Noise for Diagnosis Of

In-Vessel Anomalies in Light-Water Reactors,

ORNL/TM-8774, 1984.

[5] KKGG – Reaktorphysikalische

Rechnungen für den 36. Zyklus; FS1-

0016977 v1, Endgültiger Umsetz plan

für den 35. BE-Wechsel (Stand:

10.06.2014), Internal Document Kernkraftwerk

Gösgen-Däniken AG, 2014.


[6] Handbook of statistical Distributions

with Applications (Statistics: A Series of

Textbooks and Monographs),

K. Krishnamoorthy,



Dr. Gaëtan Girardin

Fuel Assembly Design

Dr. Rudolf Meier

Nuclear Technic

Phys. Lukas Meyer

Core Surveillance

Phys. Alexandra Ålander

Transport and Storage

Dr.-Ing. Fabian Jatuff

Projects and Processes

Kernkraftwerk Gösgen-Däniken AG


4658 Däniken, Switzerland


For further details

please contact:

Nicolas Wendler


Robert-Koch-Platz 4

10115 Berlin


E-mail: presse@

First half of 2018:

Electricity production

in Germany

For the first half of 2018, the seven nuclear

power plants in Germany produced about

34.8 billion kWh (net) electricity and had

therefore a share of 12.9 % of the whole


Although five power plants were

tem porarily shut down due to scheduled

inspections, the nuclear energy shows a

rise of 9 % relating to its electricity

pro duction of the first half of 2017.

Net electricity production (269.5 billion kWh)

for first half of 2018 in percent








20.4 Wind power

8.5 Biomass

8.3 Photovoltaics

4.2 Hydro power






Hard coal

Quelle: VGB; AG Energiebilanzen; Fraunhofer ISE

DAtF Notes

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