A1 Journal article (refereed), original research

Experimental observation of adverse and beneficial effects of nitrogen on reactor core cooling

Publication Details
Authors: Riikonen Vesa, Kouhia Virpi, Kauppinen Otso-Pekka, Sjövall Heikki, Hyvärinen Juhani
Publisher: Elsevier
Publication year: 2018
Language: English
Related Journal or Series Information: Nuclear Engineering and Design
Volume number: 332
Start page: 111
End page: 118
Number of pages: 8
ISSN: 0029-5493
eISSN: 1872-759X
JUFO-Level of this publication: 3
Open Access: Not an Open Access publication


Noncondensable gases, if present in the reactor cooling
system, affect the coolability of the nuclear reactor core. In
Loss-Of-Coolant Accidents (LOCA), nitrogen from hydroaccumulators will
enter the reactor systems, and can temporarily alter the water level in
the core by a piston effect. The piston effect on the downcomer side can
increase water level in core and improve core cooling (Damerell et al.,

The effect of nitrogen on core cooling in LOCA
situations was studied experimentally in the PWR PACTEL facility. The
main goal of this testing was to independently verify whether the
claimed positive effect of nitrogen on the core cooling can be
reproduced and to generate data for the development and validation of
thermal–hydraulic system codes.

Four experiments with
an accumulator injection to a cold leg were performed with the PWR
PACTEL facility. In two of the experiments, the break was in the other
cold leg and in the other two in the hot leg. The cold leg injection
experiments confirmed that nitrogen injection had a small positive
impact on the core cooling, but not by shortly redistributing water
masses in the vessel as expected. The presence of nitrogen reduced the
break water flow rate, delaying the core level depletion and thus
postponing core heatup by few minutes. In contrast, with the hot leg
break, the injection of the accumulator nitrogen into the primary side
had a negative impact on the core cooling. The nitrogen accumulated in
the steam generator tubes, blocking the primary side depressurization
and causing a core heatup.

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Last updated on 2019-13-03 at 12:00