Apparatus and methods for adjusting the weight of a velocity limiter for a control rod of a nuclear reactor

Abstract

The control rod includes an upper absorber section and a lower velocity limiter comprised of a socket, a vane, a transition piece and a set of fins. To adjust the weight of the control rod, lighter and heavier sets of fins, as well as lighter and heavier transition pieces are provided. By suitable selection of the lighter and heavier sets of fins and the lighter and heavier transition pieces, the weight of the velocity limiter can be selectively adjusted in accordance with the weights of differently designed sections to obtain a predetermined control rod weight. Additionally, the heavier transition piece may have material removed therefrom to decrease its weight to provide an infinite adjustment of weight within a predetermined range of weights for the velocity limiter.

What is claimed is:  
     
         1 . A method of adjusting the weight of a control rod for use in a nuclear reactor, the control rod having an upper, generally cruciform absorber section and a lower velocity limiter attached to said section and including a vane, a transition piece and fins, comprising the steps of: 
 providing first and second sets of fins with said second set of fins being heavier than said first set of fins;    providing first and second transition pieces, with said second transition piece being heavier than said first transition piece;    selecting one of said first and second sets of fins and one of said first and second sets of transition pieces; and    forming a velocity limiter for said control rod containing said vane and said selected ones of said fins and said transition pieces thereby selectively adjusting the weight of the control rod.    
     
     
         2 . A method according to  claim 1  including selecting said second heavier transition piece and adjusting the weight of said second heavier transition piece to further selectively adjust the weight of the control rod.  
     
     
         3 . A method according to  claim 2  wherein the weight of the second heavier transition piece is adjusted by removing material from said heavier transition piece.  
     
     
         4 . A method according to  claim 3  wherein said transition piece has a generally cylindrical configuration about an axis and a bore through said transition piece along said axis, the weight of the heavier transition piece being adjusted by removing material from within said bore.  
     
     
         5 . A method according to  claim 1  wherein the difference in weight of said sets of fins is provided solely by a change in size of the first and second sets of fins.  
     
     
         6 . A method according to  claim 1  including a socket and welding said selected one of said transition pieces and said socket to one another.  
     
     
         7 . Apparatus for selectively adjusting the weight of a control rod for use in a nuclear reactor comprising: 
 an upper control rod body;    a lower velocity limiter including a vane;    a first set of fins;    a second set of fins heavier than said first set of fins;    a first transition piece;    a second transition piece heavier than said first transition piece;    said control rod being formed with one of said first and second sets of fins secured to said vane and one of said first and second transition pieces secured to said vane whereby a control rod of selected adjusted weight is formed.    
     
     
         8 . Apparatus according to  claim 7  including a socket, said one of said transition pieces and said socket being welded to one another.