Robot breaks down during radiation survey

24 October 2011

The Quince robot has become stranded in the reactor building at unit 2 of the Fukushima Daiichi nuclear power station, according to reports from plant operator TEPCO.

Quince inside Fukushima Daiichi nuclear power plant in June 2011.


Quince had been conducting a radiation survey on 20 October, when it ‘became inoperable on the 3rd floor in the reactor building,’ TEPCO said. TEPCO says it studying what action to take next. The radiation levels measured by Quince during the 20-October survey ranged from 9mSv/hour on the first floor to 40mSv/hour on the third floor.

The radiation level survey was being carried out to confirm the conditions around the area where TEPCO is planning to install a primary containment vessel (PCV) gas control system. As nitrogen is injected into the PCV, a similar amount of gas will be extracted, dehumidified, filtered, monitored and then discharged. The goal is to maintain PCV pressure at atmospheric levels. PCV (drywell) pressures as of 20 October was 0.119 MPa, according to Japan Atomic Industrial Forum's Atoms in Japan news service. (Standard atmospheric pressure is 0.1013 MPa.)

Meanwhile, TEPCO has reported its results from investigating the damage to the Local Power Range Monitors (LPRMs), neutron detectors installed in the core with the purpose of measuring reactor power. Surveys were carried out on 6-7 October at unit 2 and 11 October at unit 3.

TEPCO reported that due to the effects of high temperature during the accident, the cables between connector to detector of LPRM cables were damaged and as a result they were short-circuited or disconnected. It was therefore difficult to estimate the situation of lower part or inside of RPV from the survey results, TEPCO said.

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