BWR Stability Issues in Japan

Table 1

Features in frequency-domain and time-domain stability analysis codes.

	Frequency-domain code (reduced-order model)	Time-domain code (3D kinetics model)
Computation speed	Fast	Slower than Freq. model
Numerical diffusion	No	Dependent on numerical scheme
Decay ratio	Determinable by the unique way from the Nyquist curve for the system transfer function	Sensitive to time-step size, disturbance condition to activate transient state, in numerical simulation
Model limitation	1st-order linear perturbation to the nonlinear physical systems	Basically No
Spatial behavior	No	Yes
Nonlinear behavior	No	Yes