Summary of Work for February 1999 (Project #14-08239-F)

Computational Support for the HEU to LEU Conversion of the UMLRR

Dr. John R. White
Chemical and Nuclear Engineering Department
University of Massachusetts Lowell
February 25, 1999

Most of the effort during this period was devoted to getting data and information for constructing a 3-D VENTURE model to provide computational support for the HEU to LEU conversion effort. The 3-D model will extend current 2-D XY computational models to include the axial direction. The development of a 3-D model is a major undertaking, and this project will take several weeks of full-time effort (probably 2-3 months of calendar time for a part-time effort).

In gathering data to initiate the actual 3-D model development, it was decided that a rough regulating rod model should be incorporated into the existing 2-D model before this is extended to 3-D. There are many difficulties here because of the small poison material regions in the actual regulating blade. This detail can not be modeled explicitly, and some geometry approximations and homogenization of the poison are needed. This will result in an over prediction of the actual worth because the poison material is smeared over a larger region of space. However, even with this expected uncertainty in the absolute results, variations from one configuration to another should be informative.

The modifications to the 2-D models are now complete and the computed worths of the regulating blade in various configurations are summarized below:

Location and Orientation
of the Regulating Blade

Blade Worth

D8 facing away from core

0.58

D8 facing towards from core

0.81

D9 facing away from core

0.12

D9 facing towards from core

0.17

Thus, there is a relatively large difference between the regulating blade worths in D8 versus D9, as expected. Also, orienting the blade so that the poison faces the fueled core increases reactivity somewhat. Note, however, that all these worths are expected to be high by as much as 20-40 %. Thus, the best estimate of the D9 worth is probably only slightly greater than 1 with the "reference" LEU core configuration. Possible configuration changes can be explored to see if this worth can be increased somewhat. This will be attempted over the next few months.

The new 2-D VENTURE model with regulating rod simulation capability in locations D8 and D9 is now considered the base XY model for the LEU configuration. This computational model will be extended to 3-D over the next few months.

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