tsutsuji said:
The 1 March report (
http://www.tepco.co.jp/cc/press/betu12_j/images/120302a.pdf ) is divided into two parts. The first half, down to page 43 is about the plan to install alternative measurement tools. The second half from page 44 to the end is the assessment of existing thermometers.
I translate the last part of the 1 March report's first part, on
http://www.tepco.co.jp/cc/press/betu12_j/images/120302a.pdf pages 8 and 9 (what follows is attachments) :
(3) working plan for alternative thermometer equipments
a. Selection of alternative thermometer equipments and sending devices
After making comparative studies of the thermometers that are to be inserted into the pipes connecting to the RPV, and of the devices to perform such insertion, from the perspective of resistance to radiations or maximum temperature, we selected two kinds of metal sheath thermocouples and two kinds of sending devices and industrial endoscopes.
« metal sheath thermocouples »
* A company's metal sheath thermocouple : φ1.0mm×150m (maximum temperature 650°C)
* B company's metal sheath thermocouple : φ0.5mm×300m (maximum temperature 650°C)
« sending devices »
* wiring equipment : φ4.5mm×30m (inserted by hand)
* industrial endoscope : φ4.0mm×30m (inserted by hand. The bending wire on the extremity can be [remote] controlled)
(attachments 5 [page 38/91], 6 [page 39/91])
b. The work's implementation plan and problems
At present, the alternative means having the highest probability of implementation is the one inserting a thermometer inside the jet pump instrumentation line. Based on this, we selected a detailed working procedure and extracted the relevant engineering and feasability problems. Many problems cannot be settled unless a field study is performed, but if at least the following problems are not solved, it will be difficult to perform the work:
« Problems »
* Being able to lower the radiation in the work area to 15 mSv/hour or below
* In order that the RPV gasses do not flow out from the instrumentation pipe that is being cut, we plan to use an engineering method where the pipe inside is frozen (filling it with water) while cutting, but as the distance between the PCV penetration end plate and the closing valve is short (300 mm or less), the working space is narrow. Working must be possible in such a narrow space.
A survey will be performed to find detailed radiation data in the working location. After this, we will plan decontamination and shielding, and the results will be checked on location. Also, we plan to diminish the work risks by testing the frozen cutting method on a mock-up and to develop tools to enable working in a narrow space. Please note that the problems encountered if we use the routes selected as priority level 2 (through the water level gauge line, liquid control system (SLC) differential pressure detector line, or the Traversing Incore Probe (TIP)), will be nearly the same as if we use the jet pump instrumentation line, so we wrote here the detailed plans for the jet pump instrumentation line work as a representative case.
(attachment 7 [page 40/91 - 42/91])
c. Working schedule
The earliest start of work is at the beginning of July, bringing the completion of work at the end of July. The following schedule is based on the prerequisite that the working environment's radiation is lowered to a level where working is possible, that new technologies do not need to be developped (application of existing technologies), and that the conclusions drawn from the mock-up test's results do not require more than simple modifications.
The completion of tasks that have major consequences on the schedule are noted below as "hold points" (HP). We shall pay attention to the completion of each hold point, and in case the conditions are changed, we shall quickly change the plan, and head toward the installation of alternative thermometers within the shortest time as possible. Please note that there is a high probability of performing the priority level 2 works (through SLC, or TIP), so that, if possible, the field studies about those will be performed at the same time as the one for the priority 1 work (through jet pump instrumentation line).
HP1 : field study 1 (checking the working area's radiation and space) : mid March
HP2 : study of engineering method (assess if it is possible using existing technology) : mid April
HP3 : confirm an effective decrease of radiations after decontamination and shiedling : end of May
HP4 : end of the mock-up : beginning of July
(attachment 8 [page 43/91])
