Isolamento sismico degli impianti nucleari

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1 Isolamento sismico degli impianti nucleari Massimo FORNI - ENEA Responsabile Unità Tecnica Ingegneria Sismica (UTSISM) Giornata di Studio LEZIONI DAL TERREMOTO DI TOHOKU 1 Luglio 2011, ENEA, Via Giulio Romano, 41, Roma

2 Cruas, France ( ), 4 PWRs - 3,600 Neoprene Isolators (500x500x65 mm) Koeberg, South Africa ( ), 2 PWRs - 1,800 Neoprene bearings (700x700x130 mm ) coupled with sliders

3 Kashiwazaki-Kariwa Nuclear Power Plant, strongly damaged by the Niigata-Chuetsu-Oki earthquake of July 2007, out of service for 3 years La maggior parte delle centrali di II Generazione sono costituite da reattori ad acqua, caratterizzati da una intrinseca resistenza nei confronti del sisma, e sono state progettate con terremoti di riferimento non particolarmente severi.

4 ALMR ISOLATED REACTORS NEW DESIGNS ESFR PRISM KALIMER 4S STAR-LM UPPER BASEMAT DFBR ISOLATOR REACTOR VESSEL

5 Vertical Isolation STAR-LM DFBR ESFR

6 Electrical equipments (and even whole control rooms) can be singularly protected from the vertical component of the acceleration with suitable devices 3D devices vertical devices

7 Examples of possible dispositions of energy dissipators within pipelines to mitigate the effects of vertical accelerations

8 The Jules Horowitz Reactor, under construction with seismic isolation at the French Cadarache Nuclear Center (same site where the ITER machine will be built with isolation)

9 (mancanza di) NORMATIVA Japan Electric Association (JEA), Nuclear Standard Committee of JEA, Design and Technical Guideline of Seismic Isolation Structure for Nuclear Power Plant, JEAG (in Japanese, only) AASHTO - The American Association of State Highway and Transportation Officials, Guide Specifications for Seismic Isolation Design, 2 nd Edition and 2000 Interim National Institute of Standard and Technology (NISTIR 5800), Guidelines for Prequalification, Prototype and Quality Control testing of Seismic Isolation Systems, 1996 NRC??? EUROPA: EN 15129, Anti-seismic devices

10 Validity of EN Anti-seismic devices could be extended to nuclear plants with suitable changes, some of them are minor, other are quite significant: 1) Limit to 100% the shear strain at the design earthquake; 2) Perform type tests on full scale isolators in real 3D dynamic excitations up to failure

11 Eliminate the possibility of exceeding the isolator failure limit with suitable horizontal fail safe system which damps the shock between building and lateral foundation wall in case of extremely violent earthquakes (3-4 times SSE)

12 Expansion joints for pipelines 3-pins System made of 1 Angular and 2 Gimbals Expansion Joints

13 22 m 21 m 23 m IRIS - International Reactor Innovative and Secure 50 m 1 m gap 1 m thick Ground level Flood level (1 m) 56 m

14 The last design solution foresees 99 HDRBs of 2 diameters (1000 & 1300 mm), 100 mm rubber height and 1.4 MPa rubber shear modulus. The stiffness centre of the isolation system coincides with the center of mass of the structure so to avoid eccentricity effects (rotations around the vertical axis). During earthquake the building moves like a rigid body with the same acceleration at any level (no amplification).

15 Displacement (m) Acceleration (m/s2) Behavior of the isolated IRIS building under the design 3D earthquake (0.3g peak). The structure behaves like a rigid body (same acceleration from the base to the top) with 0.2 g max acceleration and 10 cm max displacement. Time history X+Y+Z Dir X roof Dir X isolator Dir X vessel Time (s) Time history X+Y+Z Dir X roof Dir X isolator Dir X vessel Time (s)

16 Acceleration (m/s 2 ) The isolation system can reduce the acceleration of the building (and then the inertial forces on the components) by a factor at the vessel attachment level and even 5 6 at the roof level ROOF (fixed base) GROUND (~ Vessel) ISOLATED BUILDING Time (s)

17 Preliminary cost analysis made by ENEA for IRIS: - The cost of the whole isolation systems ranges between 1.5 and 1.8 M (FIP Industriale S.p.A, Padova, Italy - devices manufacturer) - The cost analysis of the qualification and acceptance tests is still in progress (it could be 0.1 M, but it will strongly depend on the final number of isolators, the standard used...) - No significant costs are expected for maintenance and inspection (replacement of isolators is not necessary even after the design earthquake) -The cost of the sub-foundation and lateral containing wall (for a medium soil) is 5 7 M (Achille Fadalti S.p.A., Pordenone, Italy - construction company) - The cost of the expansion joints for the 8 pipelines is 0.5 M (BOA BKT GmbH, Stutensee, Germany - joints manufacturer) TOTAL COST: 9 10 M

18 CONCLUSIONI Cause che giustificano il limitato numero di impianti nucleari isolati sismicamente: 1) Input sismico relativamente basso assunto nel progetto degli impianti di II Generazione ( 0.2 g), la maggior parte dei quali è composta da reattori ad acqua, dotati di una buona robustezza intrinseca; 2) Impossibilità di proteggere l impianto dalla componente verticale del sisma, almeno allo stato tecnologico attuale; 3) Carenza di normativa specifica; 4) Costi (necessità di realizzare una sottofondazione aggiuntiva, una parete di contenimento del terreno per la parte interrata, giunti di dilatazione, ecc ). Necessità future che richiedono OBBLIGATORIAMENTE l applicazione dell isolamento: 1) Affrontare input sismici sempre più severi; 2) Garantire standard di sicurezza sempre più elevati, specialmente nei riguardi di eventi che vanno oltre le condizioni di progetto (beyond design); 3) Garantire una sempre più spinta standardizzazione dell impianto.

19 SILER (Seismic-Initiated events risk mitigation in LEad-cooled Reactors) Type of funding scheme: Collaborative Projects (CP): Small or medium-scale focused (CP-FP) Work programme topics addressed: Call Identifier: FP7-Fission-2011 Activity/Area: II.2.2.3: Cross-cutting aspects for nuclear systems Topic: Fission : R&D activities in support of the implementation of the Strategic Research Agenda of SNE-TP Partners ENEA (Coordinamento), AREVA, SCK-CEN, FIP Industriale, MAURER-SOEHNE, JRC Ispra, SINTEC, KTH, BOA, IDOM, ANSALDO NUCLEARE, IPUL, NUMERIA, VCE, SRS, EA, CEA, NUVIA External Advisory Committee (EdF, ENEL, NRC, IAEA, KIT, NPS, UCSD)

20 GRAZIE PER L ATTENZIONE massimo.forni@enea.it