CERN
CH1211 Geneva 23
Switzerland
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WA105
CERN NEUTRINO PROJECT
Date : 2014-03-16
Technical specification for
construction of a LAr cryostat (17 m3) at
CERN
DOCUMENT PREPARED BY:
DOCUMENT CHECKED BY:
DOCUMENT APPROVED BY:
[prepared by]
[Checkers]
[Approvers]
Adamo Gendotti
Andre Rubbia
Andre Rubbia
Andre Rubbia
Marzio Nessi
Marzio Nessi
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HISTORY OF CHANGES
REV. NO.
DATE
PAGES
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DESCRIPTIONS OF THE CHANGES
First draft for internal circulation.
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TABLE OF CONTENTS
1.
Introduction.......................................................................................................................................... 4
2.
Acronyms and Abbreviations ......................................................................................................... 5
3.
GTT Licence and Agreements ......................................................................................................... 6
4.
Project Requirements ....................................................................................................................... 7
5.
Geometrical Layout ............................................................................................................................ 8
7.
Bill of material .................................................................................................................................... 14
8.
Outer structure ................................................................................................................................... 16
8.1.
8.2.
8.3.
9.
Requirements................................................................................................................................................ 16
Layout, material and dimensions ............................................................................................................ 16
Nitrogen system............................................................................................................................................ 16
Acceptance criteria ............................................................................................................................ 16
10.
List of Norms to be adopted ....................................................................................................... 17
11.
Annexes ............................................................................................................................................ 17
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1. Introduction
The Project’s purpose is to design and construct a tank to contain liquid Argon (LAr) for the WA105 experiment at
CERN. WA105 mandate is to prove the feasibility of a new detector technology for neutrino particles. The new device
is a double phase LAr Large Electron Multiplier Time Projection Chamber (LAr LEM-TPC). Neutrinos will be detected
when arriving on the device. The measure instruments will be used to detect the faint light or the electric charges
produced when neutrinos interact in the liquid.
The experiment requires LAr levels to be extremely stable and pollution of the LAr to be prevented. This is why GST (c
GazStorage & Technigaz) technology has been chosen: in addition to being adapted to cryogenic conditions it ensures
that the Argon (liquid or gas) is in contact only with metal. GST technology is strictly under licence by the GTT
company (Gaztransport & Technigaz, 1 route de Versailles, 78470 St-Remy-les-Chevreuse, France).
This document contains the general requirements for the project and will present the solutions GTT is putting forward
to meet them. Most of this document is issues from a design report which was contracted as a feasibility study to GTT.
The drawings of the pre-design of the containment system and the cap are presented in appendixes, as well as a
description of the assembly procedure.
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2. Acronyms and Abbreviations
BOG : Boil-Off Gas
BOR : Boil-Off Rate
GST : GazStorage & Technigaz
LAH : High Level Alarm
LAHH : High High Level Alarm
LAL : Low Level Alarm
LALL : Low Low Level Alarm
LNG : Liquefied Natural Gas
MDLL : Maximum Design Liquid Level
DOL : Design Operating Level
LAr : Liquefied Argon
ArG : Argon Gas
PAH : High Pressure Alarm
PAHH : High High Pressure Alarm
PAL : Low Pressure Alarm
PALL : Low Low Pressure Alarm
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3. GTT Licence and Agreements
Please not that GST® technology can only be implemented by Licensed EPC contractors.
Additionally, GTT is in the process to License “Outfitters” companies for the installation of the GTT Membrane
systems. Additionally, some European Outfitters are currently going through the Licensing process.
This document contains information from testing, experience and know-how of GTT, which are protected under the
legal regime of undiscosed information, trade secret and Copyright law. This document is strictly confidential and can
not be copied or used improperly.
The parts coming directly from GTT have been negotiated with GTT itself.
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4. Project Requirements
As mentioned above, the expected function is to store LAr under its liquid form at atmospheric pressure. The tank will
be placed inside a CERN facilities. This will require to store the LAr at a temperature between 86.7 K and 87.7 K at a
pressure inside the tank of 950 < P < 1050 mbar. A special emphasis has been made on the thermal fluxes. They
have to be controlled and have to be kept under 5 W/mÇ on the lateral sides.
The tank will contain a new TPC. The active detector will be supported by the cap.
The cap has therefore to ensure a mechanical function as it will have to support the weight of the insulation and of the
device. It will also have to ensure the proper tightness: ultra-high vacuum, Helium tight. There will be 16 crossing
pipes going through the cap. In addition 8 threaded rods will be linked to the cap for extra sustainment of the drift
cage
The crossing pipes have been arranged in positions and diameters. They have been differentiated into two
main groups according to their function and the thermal stresses they will be submitted to: whether they can be used
to support the weight of the cap or not.
Three chimneys are used to hang the device (electrodes, anode etc.) to the top cap.
The cap will be opened and closed four times in its life time.
4.1 Storage characteristics
The dimensions have been adapted in order to ensure that all crossing pipes are arranged as requested and that
there is enough space for maintenance.
The final inner volume is 3*4.8*2.4 (height*length*width): 35m . The volume of LAr stored is 1.5*4.8*2.4: 17m .
Tank capacity (LAr volume) : 17 m
LAr level : 1.5 m from bottom
Minimum liquid level for pump restart : 0.7 m (indicative)
Residual Heat Input (RHI) : 5 W/mÇ
Insulation density : 70 kg/m (PU Aged HFC245)
Insulation Thickness : 1 m
BOR : 0.069 % (Calculated for indication)
Design pressure : Max 1050 mbar / Min 950 mbar
Design / operating temperature : 77 K / 87K
3
3
3
3
4.2 Thank liquids alarm
It has to be clarified with Client how the level of liquid is to be monitored.
According to the GTT database and usual practice in Land Storage different levels of alarms are used to avoid overfill
and ensure that pumps can operate. These elements are given as indication.
MDLL : Maximum design liquid level
Duration between LAHH and MDLL : 5 min
Duration between LAH and LAHH : 5 min
Duration between DOL and LAH : 15 min
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5. Geometrical Layout
Figure 1 : overall experimental layout in bldg 182 at CERN
The new cryostat will be placed and operated in the CERN building 182. Figure 1 shows its lyout as weel of
the space available around it during installation.
5.1. Cryostat layout
Figure 2 : cryostat general view. 1) outer vessel, 2) corrugate membrane, 3) insulating structure, 4) the cap
For this particular Project the structural function will be ensured by an outer structure to be defined by WA105.
The gas and liquid tightness is ensured by the primary membrane.
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The thermal insulation is ensured by the foam insulation in between the membrane and the outer structure.
- The outer structure (number 1 in Figure 2) ensures the structural resistance to contain the LAr, to resist to gas
pressureand structural weight loads. It will work at ambient temperature and therefore will not be submitted to thermal
stresses. The current design has considered that this structure will be set on pedestal to allow bottom convection.
- The corrugated membrane (number 2 in Figure 2) acts as primary barrier. It is a liquid and gas tight barrier. The
membrane is not a structural component of the system and has a tightness function only. It is a double network of
orthogonal corrugations allowing its free contraction/expansion, in two directions, under thermal solicitations.
- The insulating structure (number 3 in Figure 2) located between the membrane and the outer structure, maintains the
outer tank structure at ambient temperature and keeps the thermal fluxes within the required limit; the insulation is said
to be "load bearing" in the sense that it transmits the LAr loads from the inner containment to the outerstructure. This
insulation compartment is tight from inside (by the membrane) and outside by the outer structure.
It is considered as a closed space (insulation space). This space is permanently maintained under nitrogen atmosphere,
which enables a permanent monitoring. Nitrogen breathing allows a control of the integrity of the
inner containment tightness.
- The Cap (number 4 in Figure 2) will ensure the tank tightness from the top and will allow instrumentation to be
supported. Inaddition it has been designed specifically for this Project in order to limit as much as possible the thermal
fluxes.The cap will entirely be made out of steel so as to prevent any pollution of LAr and lateral sides will have
corrugations in order to compensate for thermal contractions.
5.2. Cryostat dimensions
da le dimensioni e fa referenza a dei disegni in cad che daremo
metti un capitol per l’accettanza geometrica e un capitol per le welding specs e accettanza.
6. GST Membrane full integrity system
6.1. Generalities
The principle of the membrane system is to uncouple the structural, thermal and tightness functions of the tank. The
insulating panels are “sandwich type” made of rigid closed cells polyurethane foam inserted between two plywood
faces bonded to the foam.
Figure 3 : Detail of the insulation panel
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6.1.1. Anchoring system
Due to the dimensions of the Project the panels will be maintained in their desired position through the use of rods and
tightening plates. The panel rods will be fixed to the outer vessel on the bottom, in the corners and on the lateral sides.
The arrangement of the panels has been thought to limit thermal bridges.
6.1.2. Insulating system
The insulating structure protects the structural elements from the extreme temperatures. Moreover, it enables to limit
ingress of heat and moisture inside the tank. The insulating system is composed of prefabricated insulating panels and
flat joints:
Figure 4 : Insulating panels
The thickness of the insulating panels has been determined upon the required thermal fluxes. The total thickness is
1m divided into three panels (as illustrated: 300 + 300 + 400 mm). The definite specific thicknesses can be adapted to
supplier’s requirement. The size and shape of the panels are optimized to fit easily and properly the whole area of the
inner side of the tank. After panel erection, the gap must be filled with glass wool blankets (flat joints) to ensure that no
convection effects or thermal bridges occur.
Figure 5 : Inter panel arrangement
6.1.2.1 Thermal fluxes
GTT in its report has carried out preliminary calculations in one dimension of the thermal fluxes in order to determine
the thickness and density of the insulating panels to be used. The results are presented in the table below. The thickness
of the insulation has been estimated at 1 m and the density considered is 70 kg/m .
3
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Figure 6 : Model in one dimension for thermal exchange (example for lateral sides)
6.1.3. Tightness system
The metallic membrane ensures the containment of the liquid and the tightness of the inner container under normal
operating condition. It consists of a stainless steel corrugated membrane
tank surfaces.
The membrane panels will be displayed on top of the inner containment and lap welded together for liquid and gas
tightness. The corrugations are continuous and cross each other in the form of “knots”. The corrugations are formed by
dedicated tools using a cold folding process in order to minimize the thickness reduction in the folded parts. One of the
families of corrugations is larger than the other one. The sheets shape are optimized to fit easily and properly the
whole area of the inner tank.
Figure 7 : Metallic membrane panel
The metallic membrane consists mainly of flat rectangular sheets. Other shapes are used in the angles of the tank to
achieve a proper covering of the corners. When necessary, the corrugations are terminated with dedicated pieces.
The junctions between the corrugations of two adjacent walls are achieved by dedicated angle pieces.
For indication, GTT’s procedure for testing the tightness is as follows: after the inner container erection is completed,
the tightness of all the welds of the membrane is tested by ammonia test. A mixture of nitrogen (75%) and ammonia
(25%) is introduced in the insulating space, behind the membrane. Welded membrane joints are coated with a
reactive paint which changes colour in case of leak in the membrane. All leak test points must be checked to ensure a
complete distribution of the N 2 /NH3 mixture. Detected leaks must be repaired, leak test points are welded and a new
full or global tightness test is carried out. After completion of the test, the insulation space is purged using nitrogen,
several vacuum/purging operations are necessary. Finally, the membrane is cleaned and the paint completely
removed and evacuated. Other tests can also be considered, using Helium for example.
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Then, a global test (maintaining the pressure in the insulation spaces) shall be carried out during the dismantling of
the scaffolding and another one just before the closing of the tank.
6.2. TOP CAP
The cap will be welded on its periphery to ensure the tightness. In addition all crossing pipes will be welded to ensure
that no pollution of the Argon occurs (please refer to Appendix 2).
As mentioned above, the crossing pipes have been differentiated into two main types (excluding the chimneys used
for the anode hanging and the extra hangers for the Drift cage):
- Signal and HV feed through Chimneys
- Cryogenic Chimneys
The first type will be used to support the weight of the cap (with the insulation) and the weight of the measuring
device. The weight of the entire device (anode, electrodes, Drift cage etc.) is 600kg. Insulation thickness has been set
at 1 m using 70kg/m3 foam, but might be adapted to limit thermal exchanges in the next stages. The crossing pipes
will therefore be welded to the lower part of the cap through reinforced rings. A plywood layer can be inserted between
the insulation and the steel to ensure that the weight is evenly distributed.
The overall estimated weight of the top cap will be:
- Insulation + plywood: 1050kg + 234kg
- Pipes : 671 kg
- Flanges: 804 kg
- Membrane + invar: 152 kg + 281 kg
The result is an estimated weight of 3.2 tons, adding the device it will amount to 3.8 tons. This estimation was used to
design the crossing pipes and determine how much weight they would have to support. More precise approximations
will be carried out during the next stages. It is to be noted that the top plate is not considered in this weight estimation
as it will be designed and dimensioned to support the cap with the outer structure.
The cryogenic chimneys have been designed to allow thermal contractions to occur and are also welded to ensure
tightness.
6.2.1. Cap thermal analysis
Special attention has to be given to the cap of the tank. As mentioned before the integrity of the LAr has to be carefully
ensured. The requirement is that extreme vacuum conditions are met: Ultra-high vacuum, Helium tight.
The space between the cap and the lateral sides has been reduced to a minimum. If necessary the thermal fluxes on
the cap can be regulated with insulation blocks.
Insulation layers will be displayed inside the cap. Thermal conductivity calculations through the steel of the crossing
pipes will have to be carried out in the detail stage. Preliminary calculation of these conductive effects are annexed to
this document.
(Dove sono questi calcoli?)
6.2.2. Cap supports
The top cap weight is supported by adapting the design of the crossing pipes and the use of reinforcements at the
bottom on the lower plate (invar). Another solution that is explored is to use suspension rods on the cap to enable a
better distribution of the weight. 8 additional rods have been introduced to support the cage from the Cap.
The outer structure that has been considered will have to have a reinforcement in order to support the top cap and to
ensure not only the tightness welding but the structural function of supporting the whole cap (3.8 t).
(da spiegare meglio)
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6.3. Interface requirements
On the walls the insulation panels are maintained in their desired position through the use of dedicated rods and
fastening plates. The rods are fixed to the outer structure (either welded or anchored depending on its design). They
do not have a structural function.
On the bottom the rods have a similar function; they are used for the positioning of the panels.
The membrane panels are welded to one another but are not fixed to the insulation panels. The purpose is to enable a
free contraction of the steel membrane without transmitting any stress on the insulation panels.
The load is therefore transmitted to the outer structure and it will have to be designed to withstand the hydrostatic
pressure.
The steel membrane is fixed to the corner panels on every corner (bottom and angles) and welded on the top to the
membrane closing inserts. The corner panels are in turn fixed to the outer structure through dedicated rods. These
rods have been designed to keep the membrane in position during operation and will have to cope with the thermal
contractions through the steel springs.
The density of the insulation foam chosen is 70kg/m3 and the estimated volume (1m of thickness) is 120m i.e. 8.4 t.
The membrane total surface is estimated at 58 m2 i.e. 542 kg.
An estimated weight for the fastening elements is 718kg.
The steel insert for tightness is a layer of steel to support the top cap to the outer structure (please refer to figure
below) is estimated at 320 kg.
3
The volume of LAr is 17 m i.e. 24.3 t.
Total estimated weight (full) 34.3 t.
3
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7. Bill of material
According to the GTT initial study here is an assessment of the quantities required for the inner tank.
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Figure 8 : Inner tank example of bill of material
8. Outer structure
The outer structure is not part of this procurement, but has to be considered as an option.
8.1.
Requirements
8.2.
Layout, material and dimensions
8.3.
Nitrogen system
Nitrogen is used for the pressurization of the insulation spaces, for sealing of cryogenic pumps and for blowing and
purging of equipments and lines.
Considering the dimensions of the Project the insulation monitoring system could be designed to have one penetration
for nitrogen supply and an one opening for nitrogen exhaust. Relief valves will also be displayed in order to ensure
adequate pressure in the insulation spaces (cap and containment).
Special arrangements for the nitrogen lines have not been represented in this feasibility stage. They have nonetheless
been taken into account in the design of the cap and containment system leaving adequate space for the layout.
Please note that the outer structure will have to de adapted to this need.
9. Acceptance criteria
Qui metti la lista dei documenti che ti devono dare e I criteri di accettanza geometrical e del welding.
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10. List of Norms to be adopted
Qui dai una lista delle norme da usare nella costruzione
11. Annexes
-
Drawings
-
GTT Basic Installation Sequences