# Seismic Analysis for Safety Requirements of SPIRAL2 Accelerator

Cécile Barthe-Dejean, Franck Lutton, Matthieu Michel

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Cécile Barthe-Dejean, Franck Lutton, Matthieu Michel. Seismic Analysis for Safety Requirements of SPIRAL2 Accelerator. 31st Linear Accelerator Conference, Aug 2022, Liverpool, United Kingdom. pp.MOPORI11, 10.18429/JACoW-LINAC2022-MOPORI11. hal-03839863

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# SEISMIC ANALYSIS FOR SAFETY REQUIREMENTS OF SPIRAL2 ACCELERATOR

C. Barthe-Dejean, F. Lutton, M. Michel, GANII-SPIRAL2, Caen, France
M. Dubuisson, ADDL, Paris, France

## Abstract

The SPIRAL2 Accelerator at GANIL is a superconduct-
ing ions continuous wave LINAC with two associated ex-
perimental areas. Mechanical engineers have been highly
involved in the design of SPIRAL2 equipment since the
beginning of the project in 2004. During the development
phase, Computer Aided Design and calculation codes have
been used throughout the complete process: from the ion
sources, the LINAC, the beam transport lines and the ex-
perimental halls equipped with detectors. SPIRAL2 has to
meet different safety requirements, among which seismic
hazard. This involves justifying that the integrity of the ra-
diologic containment barrier is always maintained in case
of earthquake. This paper reports the improvement in de-
sign and calculation methods performed by GANIL engi-
neers to meet the seismic safety requirements, specifically
the non-missility feature of the equipment. The modal-
spectral simulations, used to demonstrate the mechanical
strength of equipment in case of earthquakes, was an im-
portant part of this design activity in the past 10 years. New
methods have been used to calculate welds, fasteners and
the ground anchor of the structural supports of the heaviest
equipment.

## INTRODUCTION

The non-missility criteria consists in preventing equip-
ment weighing more than 500 kg at height 1.5 m to be pro-
jected on ground floor or walls of the building, which is
used as containment barrier. The mechanical supports and
frames have to withstand dynamic load corresponding to
earthquake S.M.S (Security Maximum Seism) [1]. Also,
fasteners and anchors to ground have to be analysed to
prove that they withstand such loads. For example, LINAC
supporting frame had to be reinforced for seismic load after
first installation (Fig. 1).

<figure><img src="image_2.png" /><figcaption>Figure 1: Additional supporting features LINAC A.</figcaption></figure>

All calculation have been performed with the Finite El-
ement Analysis Code ANSYS 2020 R1. The spectral load
in three directions X, Y and Z is provided by Civil Engi-
neering (Fig. 2) and implemented in the Finite Element
Model and combined to gravity. First, a modal analysis is
performed to identify the Eigen modes of the structure.

Then two load cases will be compared to identify the most
severe: gravity + seism or gravity - seism. The X, Y and Z
direction loads are also combined to each others: either by
quadratic combination, or by Newmark combination.

<figure><img src="image_3.png" /><figcaption>Figure 2: Spectral load based on S.M.S.in S3.</figcaption></figure>

## EXAMPLE 1 : NFS DETECTOR

NFS (Neutron for Science) is the first experimental area
linked to SPIRAL2 accelerator. NFS is composed of a
time-of-flight baseline and irradiation stations. A new de-
tection system named FALSTAFF has been installed in the
Time-of-flight NFS area as shown. This detector fully
equipped weighs 592 kg, and hence is subject to
non-missility requirements, has been clamped to ground as
shown in Fig. 3.

<figure><img src="image_4.png" /><figcaption>Figure 3: FALSTAFF detection assembly drawing.</figcaption></figure>

In this example, only the structural frame and the feet of
the vacuum chamber has to be calculated in order to prove
that the FALSTAFF detector will not be projected under
seismic load. We will focus on the fasteners and anchorage
analysis even if welds and stresses are also post-treated.

Figure 3 shows how the equipment is clamped to the
frame with metal plates and to the ground. The bonded an-
chors that have been calculated and selected according to
the method described in [2].
<figure><img src="image_5.png" /><figcaption>Figure 8: Sketch of normal and shear stress in a weld.</figcaption></figure>

The main criteria to meet is based on equivalent stress as described in Eq. (3) and (4):

$$ \sigma_{eq} = [\sigma_{normal}^2 + 3(\tau_{normal}^2 + \tau_{parallel}^2)]^{0.5} \quad (3) $$

$$ \sigma_{eq} \le \frac{f_u}{(\gamma_{M2})} \quad (4) $$

The main difficulty was to find a way to extract the loads and shell stress at the junction element from Finite Element simulation. The transferred load will allow to calculate analytically the shear and tensile stress on the weld area (Fig. 9). To achieve this, a specific computer program has been developed by an external specialised company and code lines inserted in the Finite Element model.

<figure><img src="image_6.png" /><figcaption>Figure 9: Elements corresponding to weld junction.</figcaption></figure>

The code lines applied to the F. E. model generates automatically a table file with the transferred load at each node and elements of the identified junction. The calculation is then performed analytically in an Excel spreadsheet.

<table><caption>Table 1: Calculated Load Stresses on Weld</caption><thead><tr><td></td><td>Load (N)</td><td>Unit</td></tr></thead><tbody><tr><td>Fx from F.E. model</td><td>153</td><td>N</td></tr><tr><td>Fy from F.E. model</td><td>576</td><td>N</td></tr><tr><td>Fz from F.E. model</td><td>12</td><td>N</td></tr><tr><td>Weld length</td><td>125</td><td>mm</td></tr><tr><td>Weld size</td><td>2.5</td><td>mm</td></tr><tr><td>Shear stress τ //</td><td>49</td><td>MPa</td></tr><tr><td>σ equivalent</td><td>85</td><td>MPa</td></tr><tr><td>σ Criteria (st. steel)</td><td>385</td><td>MPa</td></tr></tbody></table>

The calculations show that all criteria are reached [5], and consequently there is no risk of damage or leakage on the tray and on the structure in case of earthquake.

## CONCLUSION

The calculations and analysis described here shows the difficulty to match theoretical Eurocode 3 criteria with global F. E. Simulation. The code lines used to extract relevant values from model was one of the key to solve that problem. The computer program was sub-contracted to an external expert and is now adapted for each new calculation. Each SPIRAL2 heavy equipment is now in line with seismic requirements. A method has been summarized for all seismic calculation at GANIL-SPIRAL2 [6] and [7].

## REFERENCES

[1] V. Cingal, F. Lemaire, N. Alahari, "Rapport de Sureté de l'INB n°113 ", GANIL, SSR-102-B, vol. 1, Partie Descriptive, Chapitre 02, 2017.

[2] Design of Bonded Anchors, EOTA Technical report, EOTA TR029, Edition 2007, Amended Sep. 2010, superseded by EN 1992-4:2018.

[3] Pierre Maitre, *Formulaire de la Construction Mécanique selon l'Eurocode 3*, 4ème édition, Ed. Le Moniteur, 2013.

[4] C. Barthe-Dejean and F. Lutton, "Note de Calculs de Tenue au Séisme du Détecteur FALSTAFF dans NFS", GANIL, France, Note GANIL-04769, 2022.

[5] C. Barthe-Dejean, "Tenue aux séismes du bac de rétention du refroidissement de l'Arrêt faisceau S3", GANIL, France, SP2_AT-218458 V2, 2022.

[6] C. Barthe-Dejean, F. Lutton, "Guide méthodologique pour Calculs de Tenue aux Séismes des équipements mécaniques", GANIL, France, Note STP-535-A, 2021.

[7] C. Barthe-Dejean and F. Lutton, "Mechanical Engineering Design and Simulation for Spiral2 Accelerator at GANIL", in *Proc. MEDSI'18*, Paris, France, 25-29 Jun. 2018.
doi:10.18429/JACoW-MEDSI2018-THOAMA03