The radon levels in the tunnel air surrounding the SK tank excavation
usually reach 2000 ... 3000 Bq/m³ for about 6 to 7 months in a year
during the "hot" season from April/May until October/November. In the
"cold" season, November to April, the radon levels are mostly low at
approx. 100 ... 300 Bq/m³. Click here for an example of air radon
concentration during the year 2000.To keep the radon levels in the SK dome area and water purification system below 100 Bq/m³, fresh air is continuously pumped at approx. 10 m³/min from outside through an air duct along the 1.8 km Atotsu access tunnel to the SK experimental area. This flow rate generates a slight overpressure in the SK experimental air so that any radon coming from the surrounding rock and water is 'pushed' out.
The so-called radon hut was constructed in early winter 1995/1996 at the Atotsu tunnel entrance (SK road access tunnel) to house a 40 hp air blower with 10 m³/min / 15 PSI pump capacity, air dehumidifier, carbon filter tanks, and control electronics. Radon-low air of the radon hut location gets into the air blower, is then pumped through an air dehumidifier, through a carbon filter tank and then finally into an 1.8 km air duct from the Atotsu entrance to the SK experimental areas inside the mountain.
Originally, an additional air blower and air heater were also operated to regenerate the Rn-saturated carbon in the filter tanks at regular intervals in order to lower the radon levels of the output air down to 10 Bq/m³ or below. Maintenance and supervision of the carbon regeneration operation turned out to be too time consuming and too unpractical for continuos running mode. In autumn 1997, an extended intake air pipe was installed at a location approx. 25 meters above the Atotsu tunnel entrance, where radon level concentrations were measured to stay at natural low levels of approx. 10 ... 30 Bq/m³ all year long. It was decided that this low level satisfies the air quality goals so that carbon filter regeneration would become obsolete. As shown in the radon plot of year 2000, the 10 m³/min fresh air flow from the radon hut keeps the radon levels in the SK experimental areas ("Control Room Air" curve) at typical approx. 30 ... 50 Bq/m³ at all time during all seasons.
In the summer 2002, the radon hut underwent major reconstruction. The
carbon tanks and old air dehumidifier were removed and all other items
repositioned. The hut was extended on the north side (facing the tunnel)
by 7 feet to house a the chiller for the new system. A new large blower
in a sound-reducing enclosure was delivered and installed in the fall 2002.
It initially delivered air to the SK experimental areas at a rate of approx. 50
m³/min, which is about factor 5 increased air flow from the original
service blower. Later, in May 2008, the flow rate was further stepped up to
approx. 70 m³/min by changing the blower gears. This air flow increase was
requested by various SK subgroups to improve the air quality in the water
purification system and to distribute fresh radon-low air to additional newly
installed experimental rooms around the SK detector area.
The two original blowers were temporarily left in the hut as spare blowers on
standby in case the new blower would malfunction. They were finally removed in
the summer of 2008.
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NEW!
Web camera in the radon hut
with live video stream (March 2003)
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System performance logs during the most recent hour.
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automated plots of the radon monitor boxes' data.
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Radon DAQ monitor plots.
The Radon Hut system is controlled by a Series 90-30 State Logic
Control System (by General Electric FANUC Automation, ADATEK State
Logic Products) running ECLiPS software.
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Hypermail Archive of E-mails about the Radon Hut.
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are for collaboration members only: either your suketto login & password or
the SuperK login & password are required.
