Critical Heat Flux (CHF) is an important safety parameter for the design of nuclear
reactors. The most commonly used predictive tool for determination of CHF is a look-up
table developed using tube data with an average hydraulic test diameter of 8 mm. There
exist in the world today nuclear reactors whose geometry is annular, not tubular, and
whose hydraulic diameter is significantly smaller than 8 mm. In addition, any sub-channel
thermal hydraulic model of fuel assemblies is annular and not tubular.
Comparisons were made between this predictive tool and annular correlations developed
from test data. These comparisons showed the look-up table over-predicts the CHF
values for annular channels, thus questioning its ability to perform correct safety
evaluations.
Since no better tool exists to predict CHF for annular geometry, an effort was
undertaken to produce one. A database of open literature annular CHF values was
created as a basis for this new tool. By compiling information from eighteen sources and
requiring that the data be inner wall, unilaterally, uniformly heated with no spacers or
heat transfer enhancement devices, a database of 1630 experimental values was
produced.
After a review of the data in the database, a new look-up table was created. A look-up
table provides localized control of the prediction to overcome sparseness of data.
Using Shepard's Method as the extrapolation technique, a regular mesh look-up table was
produced using four main variables: pressure, quality, mass flux, and hydraulic diameter.
The root mean square error of this look-up table was found to be 0.8267. However, by
fixing the hydraulic diameter locations to the database values, the root mean square error
was further reduced to 0.2816. This look-up table can now predict CHF values for
annular channels over a wide range of fluid conditions. / Graduation date: 2001
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/32511 |
| Date | 26 April 2001 |
| Creators | Pagh, Richard T. |
| Contributors | Klein, Andrew C. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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