Grace Time

Lead Research Organisation: Imperial College London
Department Name: Dept of Mechanical Engineering


Following some fault in a nuclear plant, a safe outcome will nonetheless be achieved so long as adequate cooling can be provided to the plant for a period after the fault, and heat generation has naturally fallen to trivial levels. Some faults may themselves have been associated with external events, such as an earthquake or a tsunami, which might have caused external power supplies to the plant to cease to be available. It is thus plainly desirable for the cooling needed by the plant to be provided by holy "passive" means, not dependent on the availability of either site-generated or externally-generated electricity to drive pumps and so on. Providing cooling by passive means such as natural convection is very attractive and very reliable, but it is not an easy phenomenon to predict reliably; for example, just 'how much' cooling will natural circulation provide?. The main objectives of this piece of research are to develop and validate methods to contribute to reliable prediction of this passive cooling.

Planned Impact

Designers and safety assessors of nuclear plant will benefit as this research will increase our ability to make reliable predictions of passive, post-accident cooling of nuclear power plants. Soundly based licensing judgements will both help avoid inadequately safe plants being licensed, and help avoid the refusal to license plants that are actually safe enough, and thus avoid wasteful additional safety systems and studies.

This should facilitate the design of nuclear plants able better to exploit natural circulation flows and passive cooling. It is to be expected that such plants will be both safer, and cheaper to build cheaper to build than conventional plant that uses engineered, powered intervention to effect such cooling.

Nuclear plants that are safer and cheaper will naturally have great economic and societal benefits, ultimately being reflected in electricity prices and reduced fossil fuel burning.

Licensing assessments of new plant are in hand, and likely to be so for the foreseeable future. These improved methods will be able to be used on a timescale of the grant duration, and thus can be used for this licensing.

Engineers and designers working in areas of industry other than nuclear power, but where natural circulation and buoyancy driven flows are important, will benefit also from the availability of more reliable prediction methods.

People and skills: The project will lead to the development of highly skilled researchers in the general area of nuclear thermal hydraulics. This area of skills has declined greatly in the last few decades in United Kingdom. It is an area also which is enormously in demand to support the United Kingdom government's intended new-built programme for nuclear power stations. Any increase in capability here is to be welcomed.


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Carasik L.B. (2015) URANS simulations of thermal stratification in a large enclosure for severe accident scenarios in International Topical Meeting on Nuclear Reactor Thermal Hydraulics 2015, NURETH 2015

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Colombo M (2016) Accuracy of Eulerian-Eulerian, two-fluid CFD boiling models of subcooled boiling flows in International Journal of Heat and Mass Transfer

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Giustini G (2018) Modelling of bubble departure in flow boiling using equilibrium thermodynamics in International Journal of Heat and Mass Transfer

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Giustini G (2019) Microlayer evaporation during steam bubble growth in International Journal of Thermal Sciences

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Hänsch S (2017) Mechanistic studies of single bubble growth using interface-tracking methods in Nuclear Engineering and Design

Description This work is in progress, and are developing methods to predict these natural-circulation flows for reactor safety analyses.
Exploitation Route In due course we expect these methods will be able to be used by those performing analyses of nuclear power plants, demonstrating their ability to be cooled by natural circulation methods.
Sectors Energy

Description ERCOFTAC workshop 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Study participants or study members
Results and Impact Workshop using the results generated by our study of natural circulation at its basis.
Year(s) Of Engagement Activity 2019