SIAMUF seminar Aspenäs herrgård, Lerum, October 20-21, 2005

Transcription

1 SIAMUF seminar Aspenäs herrgård, Lerum, October 20-21, 2005 Instabilities in Boiling Water Reactors and analysis of flashing-induced instabilities at the CIRCUS test facility C. Demazière Department of Nuclear Engineering Chalmers University of Technology SE Göteborg Sweden C. Demazière SIAMUF seminar, October 20-21, 2005 page -1-

2 1. Introduction 2 predominant types of existing commercial nuclear power plants: Pressurized Water Reactors (PWRs) and Boiling Water Reactors (BWRs). In BWRs, coolant in the primary system allowed to boil. possibility of density wave instabilities. Overview of the presentation: instabilities in forced-circulation BWRs; instabilities in natural-circulation BWRs. C. Demazière SIAMUF seminar, October 20-21, 2005 page -2-

3 2. Instabilities in forced-circulation BWRs Existing commercial BWRs of the so-called Gen-II type: C. Demazière SIAMUF seminar, October 20-21, 2005 page -3-

4 Strong coupling between the neutronics and the thermalhydraulics: Fig. 1. Stability mechanism of a BWR. C. Demazière SIAMUF seminar, October 20-21, 2005 page -4-

5 Possible self-sustained oscillations due to the time delay between the initial perturbation and the corresponding feedback mechanism, which might reinforce the initial perturbation (instead of damping it): Reactivity Neutron flux Void Feedback 1 Fluctuations (AU) Time (s) C. Demazière SIAMUF seminar, October 20-21, 2005 page -5-

6 3 types of instability, all of them involving density waves in the core. 2 (out of 3) modes of instabilities due to the interplay between the neutronics and the thermalhydraulics (the last being a pure thermalhydraulic instability). Decomposition of the neutron flux on a set of orthogonal eigenfunctions ϕ n ( r) in order to understand the radial space-dependence of the coupled instabilities: φ( r, t) = a n ()ϕ t n ( r) n = 0 (1) C. Demazière SIAMUF seminar, October 20-21, 2005 page -6-

7 where for instance in 1-group age+diffusion theory and for a homogeneous reactor one has: a k () t A n0 ( k n 1) t t 0 = exp k k exp( B 2 n τ T ) n = B n L T t n (2) (3) t n = t d B n L T (4) and B 1 < B 2 < B 3 k 1 > k 2 > k 3 (5) (6) (ordinarily only k 1 which can be larger than 1) C. Demazière SIAMUF seminar, October 20-21, 2005 page -7-

8 3 types of instability, all of them involving density waves in the core: Fundamental mode or global (in-phase) oscillation fundamental mode oscillating over the whole core; interplay between the neutronics (destabilizing effect since supercritical mode) and the thermalhydraulics (stabilizing effect due to the damping of the pressure/flow oscillations by the recirculation loop). ± ± P Oscillates P39.cvs C. Demazière SIAMUF seminar, October 20-21, 2005 page -8-

9 Fundamental mode or global (in-phase) oscillation (cont.) fundamental mode oscillating over the whole core; interplay between the neutronics (destabilizing effect since supercritical mode) and the thermalhydraulics (stabilizing effect due to the damping of the pressure/flow oscillations by the recirculation loop). simulation C. Demazière SIAMUF seminar, October 20-21, 2005 page -9-

10 Reactor Pressure 6.92 MPa APRM (A) 100 Unit (%) Coolant Flow 5000 Kg/s Coolant Temperature Celcius Time (s) Fig. 2. Example of an in-phase instability event (Oskarshamn-3, February 1998). C. Demazière SIAMUF seminar, October 20-21, 2005 page -10-

11 Azimuthal mode or regional (out-of-phase) oscillation two first azimuthal (+ axial) modes oscillating over the whole core; interplay between the neutronics (stabilizing effect) and the thermal-hydraulics (destabilizing effect since flow redistribution through the core that always fulfils the boundary conditions imposed by the recirculation loop); eigenvalue separation might be overcome by enough thermal-hydraulic feedback. Core A ± Core B ± P Constant P40.cvs C. Demazière SIAMUF seminar, October 20-21, 2005 page -11-

12 Azimuthal mode or regional (out-of-phase) oscillation (cont.) two first azimuthal (+ axial) modes oscillating over the whole core; interplay between the neutronics (stabilizing effect) and the thermal-hydraulics (destabilizing effect since flow redistribution through the core that always fulfils the boundary conditions imposed by the recirculation loop); eigenvalue separation might be overcome by enough thermal-hydraulic feedback. simulation C. Demazière SIAMUF seminar, October 20-21, 2005 page -12-

13 Azimuthal mode or regional (out-of-phase) oscillation (cont.) possible rotating symmetry or neutral line due to the superposition of the two first azimuthal modes, with a phase shift ϕ() t that can vary with time (or equivalently superposition of the two first azimuthal modes with slightly different oscillation frequencies). + ϕ() t ϕ() t C. Demazière SIAMUF seminar, October 20-21, 2005 page -13-

14 Fig. 3. Example of a stability test with the presence of combined in-phase and out-of-phase oscillations (Ringhals-1, September 2002). C. Demazière SIAMUF seminar, October 20-21, 2005 page -14-

15 Channel instability or Density Wave Oscillation (DWO) or local oscillation due to a purely thermal-hydraulic feedback effect: fluctuations of pressure drop propagating up and down in the channel (fixed pressure drop over the core). C. Demazière SIAMUF seminar, October 20-21, 2005 page -15-

16 Channel instability or Density Wave Oscillation (DWO) or local oscillation (cont.) local noise source in a certain channel; can be induced by an unseated fuel assembly, where some of the coolant bypasses the fuel channel. simulation C. Demazière SIAMUF seminar, October 20-21, 2005 page -16-

17 Fig. 4. Example of a stability test with presence of local oscillations (Forsmark-1, January 1997). C. Demazière SIAMUF seminar, October 20-21, 2005 page -17-

18 3. Analysis of flashing-induced instabilities in natural-circulation BWRs ESBWR (Economic Simplified Boiling Water Reactor) from General Electric: new nuclear reactor type based on natural circulation. Natural circulation enhanced by a long riser possibility of flashing during startup conditions (in addition to the other types of instabilities in forced-circulation BWRs). C. Demazière SIAMUF seminar, October 20-21, 2005 page -18-

19 CIRCUS facility at TU Delft for studying flashing-induced instabilities: Different types of oscillations depending on the inlet temperature. C. Demazière SIAMUF seminar, October 20-21, 2005 page -19-

20 In-phase oscillations: wavelet analysis C. Demazière SIAMUF seminar, October 20-21, 2005 page -20-

21 Chaotic region: wavelet analysis C. Demazière SIAMUF seminar, October 20-21, 2005 page -21-

22 Out-of-phase oscillations: wavelet analysis C. Demazière SIAMUF seminar, October 20-21, 2005 page -22-

23 Continuous flashing in one channel, reverse-flow in the other channel: wavelet analysis C. Demazière SIAMUF seminar, October 20-21, 2005 page -23-

24 Self-similarity between different scales for the chaotic region fractal Estimation of the fractal dimension based on wavelet methods: partition function (based on the structure of the wavelet-transform modulus maxima): Z( q, a) = ( sup ( xa, ) l W ψ [ s] ( xa, ) ) q l L( a) a τ( q) (7) C. Demazière SIAMUF seminar, October 20-21, 2005 page -24-

25 Pseudo frequencies (Hz) Time (min) Fig. 5. Skeleton of the wavelet-transform modulus maxima (i.e. the maxima lines). C. Demazière SIAMUF seminar, October 20-21, 2005 page -25-

26 Boltzmann weights: Ŵψ s [ ]( qla,, ) = ( sup ( xa, ) l W ψ [ s] ( xa, ) ) q ( W ψ [ s] ( xa, ) ) q l L( a) sup ( xa, ) l (8) expectation values: h( qa, ) = Ŵ ψ [ s] ( qla,, ) ln( sup ( xa, ) l W ψ [ s] ( xa, ) ) l L( a) D( qa, ) = Ŵψ[ s] ( qla,, ) lnŵψ[ s] ( qla,, ) l L( a) (9) (10) extraction of: hq ( ) = hqa (, ) lna Dq ( ) = Dqa (, ) lna (11) (12) singularity spectrum Dhq ( ( )). C. Demazière SIAMUF seminar, October 20-21, 2005 page -26-

27 d(h(q)) h(q) Fig. 6. Singularity spectrum (preliminary results). C. Demazière SIAMUF seminar, October 20-21, 2005 page -27-

28 4. Conclusions Presentation of the different types of instabilities in both forced- and natural-circulation BWRs. BWR instabilities still an open issue operating maps inside which the reactor is stable. Wavelet-based methods very good for studying the non-stationary and multifractal character of the BWR instabilities. C. Demazière SIAMUF seminar, October 20-21, 2005 page -28-