Isolamento sismico degli impianti nucleari

Massimo FORNI - ENEAResponsabile Unità Tecnica Ingegneria Sismica (UTSISM)

Giornata di Studio

LEZIONI DAL TERREMOTO DI TOHOKU

1 Luglio 2011, ENEA, Via Giulio Romano, 41, Roma

Cruas, France (1983-85), 4 PWRs - 3,600 Neoprene Isolators (500x500x65 mm)

Koeberg, South Africa (1984-85), 2 PWRs - 1,800 Neoprene bearings (700x700x130 mm ) coupled with sliders

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.

UPPER BASEMAT

ISOLATOR

REACTOR VESSEL

ALMR

PRISM

4S

ESFR

STAR-LM

DFBR

KALIMER

ISOLATED REACTORS “NEW” DESIGNS

DFBR

Vertical Isolation

STAR-LM

ESFR

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

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

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)

(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 4614-2000 (in Japanese, only)

AASHTO - The American Association of State Highway and Transportation Officials, Guide Specifications for Seismic Isolation Design, 2nd Edition and 2000 Interim

National Institute of Standard and Technology (NISTIR 5800), Guidelines for Pre-qualification, Prototype and Quality Control testing of Seismic Isolation Systems, 1996

NRC ???

EUROPA:

EN 15129, Anti-seismic devices

Validity of EN 15129 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

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)

Expansion joints for pipelines

‘3-pins’ System made of 1 Angular and 2 Gimbals Expansion Joints

IRIS - International Reactor Innovative and Secure

50 m

23 m

22 m

21 m

56 m

1 m gap

Ground level

Flood level (1 m)

1 m thick

The last design solution foresees 99 HDRBs of 2 diameters (1000 & 1300 mm), 100 mmrubber height and 1.4 MPa rubber shear modulus. The stiffness centre of the isolationsystem 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 rigidbody with the same acceleration at any level (no amplification).

Time history X+Y+Z

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

0 5 10 15 20 25

Time (s)

Ac

ce

lera

tio

n (

m/s

2)

Dir X roof

Dir X isolator

Dir X vessel

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

-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

0 5 10 15 20 25

Time (s)

Dis

pla

ce

me

nt

(m)

Dir X roof

Dir X isolator

Dir X vessel

The isolation system can reduce the acceleration of the building (and then the inertial forces on the components) by a factor 1.5 ÷ 2 at the vessel

attachment level and even 5 ÷ 6 at the roof level.

-12

-9

-6

-3

0

3

6

9

12

0 2 4 6 8 10 12 14

Time (s)

Accele

rati

on

(m

/s2)

ROOF (fixed base)

GROUND (~ Vessel)

ISOLATED BUILDING

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€

Cause che giustificano il limitato numero di impianti nucleari isolati sismicamente:

1) Input sismico relativamente basso assunto nel progetto degli impianti di IIGenerazione (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…).

CONCLUSIONI

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.

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 systemsTopic: Fission-2011-2.3.1: R&D activities in support of the implementation of

the Strategic Research Agenda of SNE-TP

PartnersENEA (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)

GRAZIE PER L’ATTENZIONE

massimo.forni@enea.it