Study on advanced control rod; Study on the main design parameters of large scale FBR core characteristics

*; *; *; *; *; Nakanishi, Seiji; *

PNC TN9410 88-060, 74 Pages, 1988/07

PNC-TN9410-88-060.pdf:6.39MB

The aims of this work are to give the specifications of the control rod having a good performance under a long term irradiation and a high temperature condition of outlet coolant, and also to get a rough estimation of the allowable maximum irradiation period and outlet temperature at the base of the reference core designed in the year before last. The hoop stress of a cladding tube and the dimension of interference between an absorber pin bundle and an inner duct tube surrounding the bundle (BDI) are evaluated in the period after the time that ACMI begins. In addition, the maximum temperature of a cladding tube is evaluated at the beginning stage of irradiation. These evaluations are done for the several specifications which change in the number of pins, the arrangement of pins, the gap width between BC pellet and cladding tube, the spacer wire thickness or wrapping pitch, etc. It is found that a diametral gap width between pellet and cladding tube may be expanded to about 0.8 mm if a 37 pins bundle is selected, and that ACMI begins at three years irradiation and BDI reaches the magnitude of wire thickness at additional one-year irradiation if that width of 0.8 mm is selected. Through the additional irradiation, the hoop stress of a cladding tube does not exceed the allowable maximum value owing to an irradiation creep, but it increases rapidly at a reactor shutdown or when the control rod is removed from the core. It is also found that the 37 pins bundle whose pins are located on concentric circles is superior in view of making an coolant outlet temperature high to the 31 pins bundle whose pins are located with a regular triangle lattice pattern. As a conclusion, the prospect is obtained that about 450C is realized as an coolant outlet temperature by selecting the 37 pins bundle whose pins are located on concentric circles. But it is found that the irradiation creep behavior of a cladding tube must be clarified in order to evaluate the ...