Seismic Base Isolation for Nuclear Power Plants. zhang tao China Nuclear Power Engineer Company

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2 Seismic Base Isolation for Nuclear Power Plants AUG-2014 zhang tao China Nuclear Power Engineer Company

3 Contents Seismic isolation SI for Nuclear Power Plants CNPEC experiences

4 01 Seismic isolation 4

5 Seismic isolation (SI) is a widely used strategy of earthquake-resistant design in civil engineering applications.the fundamental idea behind seismic isolation is to position a horizontal flexible layer of isolation units between the structure and the foundation. With this isolation layer, the dynamic response of the structure is modified through the reduction of the natural frequency of the building. The forces transmitted to the structure (inertial forces and vibrations) are thus reduced. Seismic isolation could also bring benefits for Nuclear Power Plant (NPP). Anti-seismic building SI building

6 Why a SI? Inner SI direct benefit: shift of the frequency and so significant reduction of the acceleration And its consequences: reinforced concrete structure optimization (lower density ratio) homogenization of the FRS use of standard equipments already qualified for other projects under lower seismic level Benefit of isolation (JHR illustration Displacements LARGELY amplified FOR UNDERSTANDING PURPOSE) (Courtesy of CEA) JHR 5% damping ground spectrum and isolation benefit (by courtesy of CEA In a general extent, to building cost reductions and to improved protection of the investment (extra margin in the design).

7 Elastomeric Bearings For the elastomer bearings, the mechanical characteristics consist in horizontal and vertical stiffness. For the three types of elastomer presented here: LDRB, LRB and HDRB LDRB LRB HDRB

8 Low Damping Rubber bearings (LDRB) The horizontal response of a LDRB is depicted in the Figure below. It is characterized by a horizontal stiffness Kh, function of the shear modulus G, the surface area of the elastomer A and the height of the elastomer Tr : Kh = GA/Tr The shear modulus usually varies between 0.4 MPa and 1.4 MPa. The damping ratio of the bearing, characterized by the area under the Force/Displacement curve, is limited to 2 to 5%. This device is usually modeled with three uncoupled linear springs.

9 Lead Plug Rubber bearings (LRB) The LRB is made of a low damping rubber bearing with lead plugs insertions. The experimental response of the LRB bearing is depicted in the Figure below. The lead core is considered as a perfectly plastic material: it has a high horizontal stiffness before yielding. After yielding, the horizontal stiffness is mainly provided by the elastomer.

10 High Damping Rubber bearings (HDRB) HDRB bearings are made of elastomer with additives which modify its stiffness and hardness. A typical experimental response of an HDRB is presented in the Figure below. Compared to the previous case, its response is characterized by the scragging effects (degradation of the stiffness and damping under cyclic loading conditions).

11 02 SI for Nuclear Power Plants 11

12 Cruas-Meysse NPP France

13 Cruas-Meysse NPP Upper Raft Isolation System Lower Raft

14 Cruas-Meysse NPP Implemented by Freyssinet France A common raft for 2 units 1812 pads Deadload is evenly distributed on pads

15 Cruas-Meysse NPP

16 Cruas-Meysse NPP In-operation considerations Ageing of elastomer pads In 2005, as compared to the construction time, the stiffness increase was 37%, against a 30% median value expected from ageing tests carried out in the 70 s. The gap is covered by design margins from far. Samples of elastomer pads are shelved in situ and periodically tested

17 JHR France Experimental and medical research-dedicated reactor Owner CEA, Cadarache, France Elastomeric bearing characteristics Mechanical properties Shape factor S PGA g (hard soil) Number of isolators 195 Mass (t) ~ Isolation frequency (Hz) 0.6 JHR 900x900x181 mm square bearing 6 layers of 20 mm of elastomer 5x 5 mm-thick steel plates + 2 external 15 mm-thick steel plates Dynamic shear modulus: Gd = 1.1 MPa Damping : 5% Service loading (N Sd ) 5.67 MN (σ = 7 MPa) Displacement d bd (mm) 108 Cutaway view of JHR (Courtesy of CEA)

18 JHR France ITER (left) and JHR (right) upper basemat construction

19 ITER France Experimental fusion tokamak Owner IO, Cadarache, France Elastomeric bearing characteristics Mechanical properties Shape factor S PGA g (hard soil) Number of isolators 493 Mass (t) ~ Isolation frequency (Hz) 0.55 ITER 900x900x181 mm square bearing 6 layers of 20 mm of elastomer 5x 5 mm-thick steel plates + 2 external 15 mm-thick steel plates Dynamic shear modulus: Gd = 1.1 MPa Damping : 5% Service loading (N Sd ) 6.4 MN ( = 8 MPa) Displacement d bd (mm) 112 Cutaway view of ITER (Courtesy of F4E/IO

20 ITER France

21 ITER France

22 ITER France

23 European Pressuried Reactor (EPR) In 2009, Italian and French companies ENEL and EDF started to jointly develop a feasibility study, for the seismic isolation of the nuclear island of EPR Nuclear Power Plant.

24 NPP Emergency Response Centre (ERC) The fundamental functions of NPP emergency response centre consist of emergency command after occurrence of severe accidents, technical support, emergency safeguard, maintenance, release of public information and logistic support etc. In the Niigata earthquake in Japan, ERC office and corridor ceilings collapse, the window can not be normal switch, internal facilities damaged also, in addition, sanitary equipment can not be used. Tokyo Electric Power Company according to the Niigata earthquake experience feedback, reconstruction the ERC, using base isolation technology, in Fukushima earthquake, ERC play an important role in the accident rescue.

25 03 CNPEC experiences 25

26 Seismic isolation for CPR 1000 Nuclear Island Purpose of the Preliminary Feasibility Study By adopting seismic isolation solution, meet the target of making the seismic design benchmark of SSE to 0,30g in horizontal direction instead of the original 0,20g Floor response spectra with seismic isolation should be less than CPR 1000 NI design floor response spectra, in order to reduce drawings modification in CPR 1000 NI original design Control displacement between structures and adjust them to a suitable scope

27 Seismic isolation for CPR 1000 Nuclear Island 3D model for global calculation simplified model for FRS calculation

28 Seismic isolation for CPR 1000 Nuclear Island Position of the 759 isolation devices

29 Seismic isolation for CPR 1000 Nuclear Island Without Seismic isolation with seismic isolation Benefit for Equipments Horizontal FRS with and without SI Vertical FRS with and without SI

30 Emergency Response Centre (ERC) emergency command after occurrence of severe accidents, technical support, emergency safeguard, maintenance, release of public information and logistic support etc. Fangchenggang NPP, China 2014

31 Emergency Response Centre (ERC)

32 References Seismic Base Isolation for NPPs Jean-Marc Vezin, Véronique LE CORVEC, Frédéric ALLAIN, Fabien MEMETEAU EDF Experience on Design and Construction of Nuclear Power Plants on Seismic Isolation Systems Pierre Labbé French practice for seismic isolation of nuclear structures M. CONNESSON, S. DIAZ, F. ALLAIN, N. MOUSSALLAM, I. PETRE-LAZAR Construction of reactors on seismic isolation Lesson learnt from ITER and JHR S.Diaz1& L.Patisson2, B.Slee3, C.Beretti4, M.B Syed2, M. Curtido3, G. Louvet4

33 Thank you