I can suggest you to measure the text you want to set to a cell and then set the cell preferred width to the width of the text content. This way the width of the columns you want will be enough to show their values without the need to wrap the text. This can be done by finding the max width of the cells of the column and set the widths to the found max value. The following code snippet will help you achieve what you want:
var table = new Telerik.Windows.Documents.Fixed.Model.Editing.Tables.Table();
var row = table.Rows.AddTableRow();
var cell = row.Cells.AddTableCell();
var block = cell.Blocks.AddBlock();
cell.PreferredWidth = block.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity)).Width;
I hope this works for you.