On 20 October the Quince robot being used to conduct a radiation survey became stranded in the reactor building at unit 2 of the Fukushima Daiichi nuclear power station, according to reports from plant operator Tepco.
Quince had been conducting a survey, when it ‘became inoperable on the 3rd floor in the reactor building,’ said Tepco, which is currently working on 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 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.
Regular updates, including in this case a video clip of the stranded robot, may be found on the website of our sister journal, Nuclear Engineering International, reachable on <www.neimagazine.com> or by clicking on the link in the navigation bar to the left of this page.
The following sites are also posting continuing updates:
<http://www.tepco.co.jp/en/index-e.html>
<http://www.iaea.org/>
<http://www.jaif.or.jp/english/>
<http://bravenewclimate.com/2011/03/15/tepco-reactor-status/>
<http://www.world-nuclear-news.org/>
<http://www.kantei.go.jp/foreign/index-e.html>
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