DRAFT
Removal of Rock Septum and Cavern Configurations
Scope
This documentconcerns the configuration of the far detector cavern to detector installation and work space required for the installation.
Objective
The present configuration of the cavern is not optimal for detector installation. It is hereby proposed to make a change in the cavern construction in order to make detector installation feasible. In addition, this document describes the configuration phases of the cavern during cryostat and detector construction.
Motivation
The present configuration of each cavern is shown in figure below. The cavern includes two chambers excavated between the 4850 ft and 4910 ft levels with a 14m septum in between. Each chamber houses one cryostat, within which a detector is constructed.
It has been planned that the top of this septum is used for staging of material during cryostat and detector construction. The top of the septum is at the 4850 level and is accessible through the north and south drifts.
The final design of the cryostat requires that all material and detector components enter at the ends which is the space between the cryostat and the septum. As seen above, this space is 3.3 m. With the near-final design of APA and CPA installation units being 12.7 m high and 2.5 m wide, it is very clear that the space is not adequate.
Each of the APA installation units is constructed from two APAs that are transported to the cavern in horizontal on-edge orientations. They are then rotated to a vertical condition and assembled together to form the installation unit as shown to the right.
In addition, a cleanroom is required to install the detector components. Constructing and working in a narrow (3.3 m), tall (18 m) and wide (20 m) is not feasible and safe.
It is proposed to remove the septum between the two chambers down to the 4910 level and, in effect, construct on chamber housing two cryostats. It is further proposed to reduce the total length of the cavern by 9 m. By doing so, the distance between the two cryostats will be 12m and the total volume of the excavation will be roughly equal. The proposed configuration is shown below.
In order to access the cavern from the drifts, and to access the central utility cavern, it is proposed to build a bridge between the north and south drifts at the 4850 level. The space under the bridge and between the cryostats will then be used for detector installation. It is high enough to rotate and assemble APAs and CPAs prior to installation.
Cavern Configurations
The following sections describe the overall phases for cavern configuration during cryostat construction and detector installation. These configurations will be used to design and implement the access, life safety and other equipment. Details of these systems are under development.
Additionally, lifts and stairs will be constructed from the 4850 level down to the 4910 level for access during construction. Details of such systems are also under development and not presented here.
Phase 1
In this phase steel construction for west cryostat is taking place. The east part of the cavern is free. The general direction of airflow is through the cavern at the 4850 level. An appropriate portion of the airstream is diverted to the 4910 level at appropriate locations and flows openly back to the 4850 level.
Phase 2
In this phase steel construction for east cryostat is taking place. The membrane for the west cryostat is constructed in this phase also.During both phases of 1 and 2, the methods employed are those for general construction and strict cleanliness conditions are not required.
Airflow into the west cryostat is through the access hatches on the west end and out the cryostat opening into the area between the two cryostats.
Phase 3
In this phase the construction of the west cryostat is finished and it is cleaned. The only opening into the west cryostat is through the opening and the access hatches. The west cryostat is turned over to the detector group.
In order to achieve the cleanliness requirements of the detector, a cleanroom is constructed immediately to the east. The airflow direction is through the cryostat and the cleanroom. In addition, the air is filtered before entry into the cryostat.
There may be a need to construct a temporary riser at the 4910 level in order that equipment may be rolled in and out of the cryostat. The need for this riser is being determined in conjunction with the detector installation planning.
Phase 4
In this phase, detector construction for the west cryostat is completed and cryostat is closed. Installation of the LAr recirculation pumps and associated equipment will take place at this time and LAr filling will begin.
The cleanroom and infrastructure is moved to the east cryostat and east detector installation will proceed as with the west.
Airflow for the west cryostat is reconfigured to be around the outside of the cryostat and through the external cryostat steel structure.
Phase 5
This is the final configuration phase when east detector construction is also complete and the cryostat is closed. Final installation of the LAr recirculation pumps will proceed at this phase and filling of east cryostat will commence.
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