Memorandum of UnderstandingDesign, Fabrication, installation and Testing of the

DUNE LAr Membrane Cryostat

DOC Authors: G. Vallone, D. Boettcher, A. Lawrence, M. LeitnerRelease Date: x

LBNL Document Number: x Revision: A.1CERN EDMS Document Number: xxxxxxx Revision: 01Fermilab DocDB Document Number: xxxxx Revision: 01

Document Status: WorkingType: TOPIC

LBNL Category Code: DU1000

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CONTENTS

1. REVISION HISTORY................................................................................................................3

2. APPROVALS.............................................................................................................................3

3. ACRONYMS..............................................................................................................................3

4. INTRODUCTION.......................................................................................................................4

5. CRYOSTAT DESCRIPTION.....................................................................................................4

6. DESIGN, MANUFACTURING, TESTING OF THE CRYOSTAT STRUCTURES.....................5

6.1 DESIGN....................................................................................................................5

6.2 MANUFACTURING AND ASSEMBLY......................................................................6

6.3 TESTS AND COMMISSIONING...............................................................................6

7. REFERENCES..........................................................................................................................8

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1. REVISION HISTORY

Rev Description of ChangeA First revision

2. APPROVALS

Approver Project Role

3. ACRONYMSLAr …. liquid argon

GAr … gas argon

BCR … Project baseline change request

EDMS … CERN document control system

DocDB … Fermilab document control system

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4. INTRODUCTIONThis document is the reference for the design, manufacturing and testing of the DUNE LAr membrane cryostats in the United States. It was written starting from document EDMS 2065403 – Memorandum of Understanding - Design, Fabrication, Installation and Testing of the LBNF Membrane Cryostats.

5. CRYOSTAT DESCRIPTIONThe LAr membrane cryostats are made of a stainless steel cold vessel that contains the cryogens, sensors, insulation panels and a warm steel supporting structure.

The cold primary membrane tank is made of a stainless-steel liner that contains the cryogenic liquid and gas. The liner maintains the leak tightness. The membrane liner is corrugated to provide strain relief, resulting from temperature related expansion and contraction.

The insulation is composed of layers of polyurethane providing a thermal barrier between the membrane at the liquid cryogen temperature and the support structure at ambient temperature. The secondary barrier located at the end of the insulation is a physical protection that contains the liquid cryogen in case of a failure of the first membrane.

The surrounding cryostat warm steel structure support consists of a frame of steel columns and beams. The frame is reinforced locally with corrugated plates. On one side of the cryostat, a composite window replaces the steel structure in order to limit the impact on crossing neutrinos. The window is connected to the steel beams with a scarf joint. The composite window also replaces the secondary barrier, and will provide leak and gas tightness.

An overview of the cryostat and a cross section are shown in Figure 1.

Fig. 1: Cryostat support structure overview (left) and cross-section (right).

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Fig. 2: Scarf joint connecting the steel structure to the composite window.

6. DESIGN, MANUFACTURING, TESTING OF THE CRYOSTAT STRUCTURES

6.1 DESIGNThe LAr cryostat is a membrane tank, designed to operate at a maximum design pressure of 350 mbarg (as defined by the settings of the pressure relief valves) [1].

The external warm structure provides support for all internal and external loads acting on the cryostat. The structure, shown in Fig. 1, is made of steel beams and corrugations, and of a composite window made of a sandwich of fiberglass and high density polyurethane. The steel structure and the window are connected with a scarf joint design, as shown in Fig. 2. The loads from the liquid head and the gas pressure are transferred from the stainless steel membrane vessel to the structural support through the polyurethane insulation.

Per [1], the structural support can be verified using the American Institute for Steel Construction Standard ANSI/AISC 360 [2]. The design of the warm supporting structure is performed per the European standard for steel structure design and construction EN1993 [3], which is equivalent to the U.S. ANSI/AISC 360 [4]. The main design technique is based on the Finite Element Analysis (FEA) method. The design approach is to generate detailed FEA models of the vessel and to perform a detailed stress analysis of each component.

The stiffness and strength of the joints and of the composite window are demonstrated by experiments performed following EN1990 Annex D – Design assisted by testing [6].

The composite window is verified also with detailed FEA models, following the provisions from ASME RTP1 [5] for balsa wood cored plates. However, the window will use a Polyurethane core with equivalent or superior performances. The mechanical properties of the laminate will be experimentally verified, following ASME-RTP1, part 7 [5].

EN1998 – Eurocode 8 is applied to compute the seismic actions [7]. The seismic spectrum considered is from USGS – design maps for FNAL.

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The DUNE LAr Cryostat containment system, is compliant with most of the standards recognizing membrane technology as containment system for refrigerated liquefied gases storage, in particular the European standard EN 14620 part 1 to 5 [8].

The cryostat structure design is independently verified by a U.S. professional structural engineer.

A final verification and certification (where applicable) of the documentation related to examinations, inspections of materials, in-process fabrications, and acceptance tests are performed at the end of the project by the same professional engineer.

6.2 MANUFACTURING AND ASSEMBLYThe DUNE LAr cryostat structure is manufactured and assembled following EN1090-2 [9] providing requirements for the execution of steel structures, to ensure adequate levels of mechanical resistance and stability, serviceability and durability.

The structures follow a strict quality control, inspection and testing plan as per EN1090 (i.e. quality of the welds execution attested by an authorized independent inspection agency).

Quality control of the composite parts (joints and window) will follow ASME RTP1 [5].

6.3 TESTS AND COMMISSIONINGThe tests described below are performed to qualify the warm structure of the cryostat. To proceed from one test stage to the next, the respective authorities of the host laboratory performs an internal review. Their approval is mandatory prior to each test. Prior to each testing campaign:

a risk assessment is performed to verify personnel and equipment safety during the tests

the safety file related to the phase is complete and validated by the safety authorities

The structural static qualification tests are monitored with strain gauges and displacement sensors located on the warm structure of the cryostat. During the tests, the strain gauges and displacement sensors data are compared in real time with the results of the FEA calculations. Any significant deviations from linearity or abnormal stress readings will block the process.

The expected qualification tests are the following:

1. Destructive tests for the weakest structural part of the steel frame are performed to validate the FEA models and the structure mechanical behavior. The weakest connection is identified on the basis of Eurocode 1993 provisions [3]. If required, the FEA models are modified accordingly and an update of the calculations is performed.

2. The stiffness and strength tests of the joint between the composite window and the steel structure are described in detail in [10] and will not be treated here.

3. Structural tests of the window laminate are performed as required by ASME RTP1 [5].

4. Prior to the Liquid Argon filling process and the start of the cryogenics commissioning phase, a pneumatic test is performed at a testing pressure of 200 mbarg, using warm argon gas. Note that the automatic pressure vent valve is set at 150 mbarg in normal control conditions. This test will:

a. verify the quality of the cryogenics controls system and procedures, showing the

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quality and precision of the pressure regulation.

b. validate the FEA analysis and models for 200 mbarg overpressure pure gas load case. If needed, the FEA models will be updated.

c. qualify the cryostat structure for 200 mbarg gas overpressure.

Prior to this pressure test, all feed-through and other external components shall be pressure rated for a design pressure of a least 350 mbarg. The pressure rating shall be obtained through documented qualification process, including design calculations and testing program. Additionally, each feed-through shall be pressure tested prior to installation into the cryostat in an appropriate setup that is described in a separate document.

5. Then, the cryostat will be filled with liquid argon in incremental steps until its service level. The cryostat is instrumented with strain gauges and displacement sensors (dial gauges) to monitor strains and stresses and deformations. The structural behavior of the warm structure is checked all along the filling process by continuous reading of the strain gauges and displacement sensors results (at daily basis). In case of abnormal behavior of the structure, (i.e. large variations from simulated data or large asymmetry in the structural behavior), the filling process is stopped. If required, the cryogen is drained.

The gas overpressure to be additionally applied at the top of the liquid level is defined from the cryogenics system requirements and should be lower or similar to agreed operation pressure.

During the filling of the cryostat, several tests are performed to control the warm structure behavior. Every 2.0 m of LAr level increase in the cryostat, the gas pressure will be increased in steps of 50 mbar up to 200 mbarg. At the beginning of the process (below 4.0 m) measured displacements and deformations may differ (reasonably) from the FEA results. This difference can be related to the initial settling of the structure, likely to occur during the introduction of the first few meters of LAr.

6. Once the filling has reached the service level, the design gas overpressure Pt (350 mbarg) will be applied at the top of the liquid level.

The final value of the test overpressure should be confirmed via the risk assessment of the cryostat and mitigating safety measures. It should remain sufficiently lower than the set up value of the safety valve, in order to avoid any opening or leak of the safety valve.

This test will:

a. qualify the cryostat structure for the characteristic load case: cryostat structure full of LAr (service level) + Pt (350 mbarg) argon gas design overpressure.

b. finish the validation of the FEA models and analysis for the operational type of load case (LAr at service level + Pt (350 mbarg) overpressure). In case of need, the FEA models will be updated.

7. The measurements performed via step number 5 will be used to qualify the FE models. The data will be used to update the models and run them again. An updated estimate of the maximum loads and stresses will be obtained for the design case (LAr full + 350 mbarg) and a final verification of the European and US regulations ([2], [3]) will be performed.

Any modification of the static FE model will be implemented also on the dynamic model used for dynamic analysis, updating the seismic calculations.

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7. REFERENCES[1] FESHM 5031.7: Membrane Cryostats[2] ANSI/AISC 360-16 (July 2016): Specification for Structural Steel Buildings[3] Eurocode 1993 (May 2005): Design of steel structures[4] Acceptance of Steel and Aluminum Structures Designed per the Eurocodes at Fermilab[5] ASME RTP-1-2013 - Reinforced Thermoset Plastic Corrosion-Resistant Equipment[6] Eurocode 1990 (April 2002): Basis of structural design[7] Eurocode 1998 (December 2004): Design of structures for earthquake resistance[8] EN-14620 (December 2006): Design and manufacture of site built, vertical, cylindrical, flat-

bottomed steel tanks for the storage of refrigerated, liquified gases with operating temperatures between 0 °C and -165° C

[9] EN 1090-2: Technical requirements for the execution of steel structures[10] DUNE Doc. DU-1000-XXX – Experimental plan for the qualification of the joints