SNOLAB Underground Facilities

SNOLAB _underground_900.jpg

Photo by Gerry Kingsley

The SNOLAB underground laboratory is an expansion of the original SNO facility which consisted of a large experimental cavern 22 m in diameter and 34 m high (72' dia x 112' height), ancillary spaces in mining drifts (tunnels) for the experiment and personnel infrastructure. The SNO Detector is located at 46° 28'30'' N, 81° 12'04'' W. The main level of the laboratory is located on the 6800 ft level of the mine with 2070 m of granitic rock overburden consisting mainly of norite. The ambient rock temperature at this depth is 42C. The 2km of norite overburden corresponds to 6010m water equivalent. Surface elevation at the site is 309 m (1014 ft) above mean sea level. The surface topology is approximately flat. Access to the 6800 Level and SNOLAB is via #9 Shaft located 1.8 km from the laboratory entrance. A key feature of the original laboratory was that all the experimental spaces and personnel spaces were maintained as one large clean room. Personnel entering the laboratory would pass through showers and change into clean room clothing. Equipment entering the laboratory is either cleaned in a "carwash'' before entering the laboratory or is brought underground in sealed containers that are opened after being washed and brought into the clean space. It was decided to keep this highly successful approach for the SNOLAB expansion.


The SNOLAB expansion adds an additional 6,300 m2 of excavations of which 3,700 m2 is clean room space contiguous with the existing facility. The clean/dirty boundary will be relocated for the expanded laboratory and some already existing excavations will be converted to additional clean room space. The resulting SNOLAB underground laboratory will have 5,000 m2 of clean space. Of this 3,100 m2 will be experimental laboratory space. There will be an additional 2,600 m2 of excavation outside the clean room used by SNOLAB for the service infrastructure and material transportation and storage. The nominal finishes inside the clean spaces of the laboratory will be shotcreted and painted walls and painted concrete floors. Nominal shotcrete thickness will be 7.5 cm and nominal concrete floor thickness is 10 cm. Outside the lab most areas will be bolted and screened but not shotcreted or painted. Material handling areas such as immediately outside the laboratory entrance will have concrete pads. Other areas will have bare gravel on the drift (tunnel) floors. In most instances services (ventilation, water, wiring) will be exposed in pipe and cable trays at the back (top) of the drifts.

The SNOLAB construction is taking place in two phases. Phase I adds a new laboratory entrance and service facilities (chiller, generator, waste water treatment) and new experimental areas: a network of drifts ("Ladder Labs") for small and medium sized experiments and a large experimental hall (the "Cube Hall") and ancillary spaces for a larger experiment. Phase II consists of the addition of another lager experimental space dubbed the "Cryopit" and ancillary spaces. The design of the Cryopit envisions its use for an experiment using a large volume of cryogenic liquid where it is desirable to isolate it from the rest of the laboratory. In addition to the new laboratory space created by SNOLAB, there is also the existing SNO detector cavern and its associated Utility Drift and control room. As well, the relocation of the personnel facilities in Phase I will make the existing South Drift used for the SNO personnel facilities available for experiments or laboratory infrastructure. The experimental spaces that will be created for SNOLAB are listed below.

Laboratory Space Style Length (ft) Width (ft) Height Area

SNO+ Cavern (Existing)


Utility Drift

Control Room













South Drift (Existing)






Ladder Labs (Phase I)

Drift C1

Drift C2

Drift B&D













Cube Hall (Phase I)


Utility Drift

Staging Area

Control Room

















Cryopit (Phase II)


Utility Drift

Staging Area

Control Room

















Existing Phase I

Phase II








Entrance and Personnel Facilities

photo-lunch-room-110302-03.jpgThe laboratory entrance is the transition region from the dirty mine environment to the CLASS 2000 clean room interior of the laboratory. Initially adjacent to the SNO facilities, it is being relocated 80 m to the east of its present location to encompass the new experimental facilities. Its capacity is also being increased by a factor of two to accommodate the larger work force that will be present in the completed underground laboratory. Material being brought into the laboratory transition through a "carwash" where it is cleaned before entering the laboratory. Materials that can't be cleaned underground are brought down in "blue boxes" - sealed shipping containers that keep mine dust out. Personnel entering the laboratory must shower and change into clean room clothing in the personnel facility. In addition to showers and change rooms, the personnel facility has a lunch room, meeting rooms and a laundry facility. The personnel facility also serves as a refuge station in the event that there is a fire in the mine. The personnel facilities are intended to host 50 people underground during a shift.


Ladder Labs

img_7827.jpgThe Ladder Labs is a network of drifts ranging from 15ft (4.5m) to 25 ft (7.6m) in width intended to house two medium scale experiments where the detectors are of order 5m in size. The Ladder labs are located north of the laboratory entrance and south of the Cube Hall. The southern "rail" of the ladder is intended as an access way with the rungs being used for ancillary spaces for the experiments. The experiment detectors would be located in the northern rail which is asymmetric. One half is 20 ft (6m) wide by 19 ft (5.8m) high while the other half is 25 ft (7.6m) wide by 23 ft (7m) high. Services for the Ladder Labs (HVAC, power, water) are located to the west of the Ladder Labs in an access drift running from the lab entrance to the Cube Hall. A small chemistry facility will be located at the east end of the Ladder Labs. The Ladder Labs will be kept clean with with HEPA filtered air exchanged 10 times per hour. Ventilation walls will be located at the ends of the rails of the ladder labs to pressurize them relative to the access drift to help exclude dust.


Cube Hall

cubehall-110711.jpgThe Cube Hall is a large cavern 18m long by 15m wide by 20m high intended for large experiments. The base of the hall is 15m below the main level of the laboratory with access via a stair well. A ramp to the base of the hall was constructed for excavation and will continue to be available using an air lock to provide "dirty" access for civil work in the hall. A 10 tonne monorail crane is situated along the spine of the hall. A series of 20 tonne attachment points are situated on the back (roof) and sides of the hall for attaching lifting devices. Access to the hall is through a staging area and control room space. The hall will be ventilated with HEPA filtered air exchanged 5 times per hour. Adjacent to the hall is a "Utility Drift" where ancillary equipment for experiments in the hall can be located. The Cube Hall is intended for either a single large scale (15m) detector or two or more smaller scale detectors.



Cryo.jpgLocated near the Cube Hall, the Cryopit is a cylindrical cavity 15 m in diameter and 20 m high. It is intended to house a large spherical or cylindrical detector immersed in a water shield. Because such a detector may contain a large volume of cryogen, the Cryopit is designed to be isolated from the main part of the laboratory. Pressure bulkheads placed around the hall isolate it from the habited areas of the laboratory while a ventilation system would duct boil off gas into the mine return air system. Excavation is well along with the top sill and approximately half of the utility area completed. Excavation will continue into the middle of 2008 and outfitting is expected to be completed by the end of 2008.


SNO+ Cavern

photo-sno-cavity-070906-17.jpgThe SNO+ Cavern is the original barrel shaped cavity excavated for the SNO experiment. At 30m tall by 22m diameter at its waist, this is the largest cavern at this depth in the world. Situated in the cavern is the SNO+ detector which was originally designed to detector Solar Neutrinos using 1000 tonnes of heavy water as the detecting medium. The heavy water was contained in an acrylic vessel 12 m in diameter 5 cm thick which was bonded together out of 122 separate panels and polished to optical quality. The interactions of neutrinos in the heavy water were detected by 9600 PMTs (Photomultiplier Tubes) mounted in a geodesic sphere 18.4 m in diameter which surrounded the acrylic vessel. The entire assembly was submerged in 7000 tonnes of ultra pure "ordinary" water. The heavy water was returned to Atomic Energy of Canada in 2007 and the SNO detector is now being converted to hold liquid scintillator for the SNO+ experiment. Adjacent to the SNO cavern is the SNO Utility Drift which contains the Ultra Pure Water (UPW) processing plant used to purify the heavy water and the (ordinary) light water used in the SNO experiment. The SNO UPW system will be available for use by other experiments in the laboratory.


Utility Area

SNOLAB235.jpgThe SNOLAB Utility Area contains the support systems for the underground laboratory that are not required to be in the clean room space. This includes a chiller to cool the laboratory, a mine power centre (electrical substation), potable and waste water treatment centres and in future an emergency generator. A 320 ton chiller system provides cooling to the laboratory using a chilled water loop that circulates throughout the laboratory. Waste heat from the chiller is removed by 100 CFM of ventilation air that is directed into the mine return air system. The return air system is also used to provide an exhaust for any process systems in the laboratory that need to be isolated from personnel such as boil off from large cryogenic systems. Potable water is provided by mine water distribution system but is prefiltered prior to being brought into the clean laboratory space where it is used for personnel consumption and as the source water for the SNOLAB Ultra Pure Water (UPW) plant. Waste water is treated in a membrane bioreactor. Normal power to the chiller systems and the new experimental spaces is provided by a 1500kVA Mine Power Centre (MPC) located adjacent to the Chiller. Provision is made for the future installation for a 150kVA generator to provide emergency power to critical systems in the laboratory.