In the Kamioka mine, there is clean water flowing near the detector and it can be used
freely in large quantities. This water is circulated through the water purification
system. The purpose of this water purification system is:
- To keep the water transparency as high as possible.
Small dust, metal ions like Fe, Ni, Co, and bacteria in the water are removed.
- To remove the radioactive material, mainly Rn, Ra, and Th. Especially, radon is a
serious background for the solar neutrino analysis.
Figure1: The water purification system.
Fig 1 shows the water purification system. The water purification system consists
of the following components,
|Heat exchanger: |
The water temperature rises due to the heat generated by pumps and PMTs. The temperature
is kept at around 14C to suppress bacteria growth.
|Ion exchanger: |
To remove metal ions in the water.
|Ultra-Violet sterilizer: |
To kill bacteria. The documentation states the number of bacteria can be reduced to less
|Vacuum degasifier: |
To remove gas resolved in the water. It is able to remove about 99% of the oxygen gas and
96% of the radon gas
|Cartridge polisher: |
This is a high performance ion exchanger.
|Ultra filter (UF) |
To remove small dust even of the order of nanometers. Fig 2 shows the resistance of
the water sampled at the inlet and the outlet of the Ultra filter. This can be compared
the chemical limit of .
|The resistance of the water sampled at inlet and outlet of the Ultra
filter as a function of time.
Fig 3 shows the number of particles after the UF. After the Ultra filter, the
water is returned to the detector. The UF removes 10% of the water passed through. That
water is recirculated through the water purification system again via the following
equipment, which is shown by the dashed line in Fig 1.
|Reverse osmosis |
|The number of various sizes of particles as a function of time.
The water is taken from the top of the tank using a pump and returned to the bottom of
the tank. Its flow rate is about 50 tons/hour. This system keeps the water transparency
above 70m as described elsewhere.
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