A nonlinear mathematical model for determining the dynamic response of a pressurized water reactor was developed that incorporates both prompt and delayed temperature feedback. The use of a modified form of Hansen's method of largest eigenvalues was employed to obtain the solution. The novel features of this model are that the nonlinearities are treated explicitly, and the temperature dependence of thermal-hydraulic parameters is preserved without approximation. A comparison of power and temperature transients was made with other work.