A possible application of catastrophe theory to boiling water reactor instability

• It is known that the stability of boiling water reactors (BWRs), when quantified with the so-called decay ratio as the stability parameter, may show seemingly abrupt changes, despite the smooth variations of the control parameters (reactor power and core flow). There is also evidence of the fact that the stability properties can exhibit a hysteresis effect when moving back and forth on the same path on the power-flow map. The most common explanation of the abrupt change is based on the co-existence of two different types of instabilities (global and regional), and their interplay (van der Hagen et al., 1994; Pázsit, 1995). In this paper we suggest an alternative phenomenological explanation, which only assumes the existence of one single mode of instability. We propose the hypothesis that the decay ratio of one single mode of a complex, many-variable non-linear system might obey a cusp catastrophe as a function of the control parameters. Such a phenomenological model can explain both the discontinuous variation of the decay ratio, as well as the hysteresis effect. Since a cusp-type behaviour implies that the decay ratio is many-valued in a certain region of the power-flow map, a mechanism is suggested how a Hopf bifurcation with multiplicative noise can lead to such a behaviour.

Ämnesord

NATURVETENSKAP  -- Fysik -- Annan fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Other Physics Topics (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Strömningsmekanik och akustik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Fluid Mechanics and Acoustics (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Elektroteknik och elektronik -- Annan elektroteknik och elektronik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Electrical Engineering, Electronic Engineering, Information Engineering -- Other Electrical Engineering, Electronic Engineering, Information Engineering (hsv//eng)

Nyckelord

BWR stability

Catastrophe theory

Ringhals-1 instability

Decay ratio

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