Issue Number:FDR-217
Phase: Design
Decommissioning Process Fuel Debris Retrieval
Investigation Subject Retrieval method and system
Issue Establishing access route to fuel debris


① Removing interfering obstacles

Desired state and reasons for it

In order to load, install and unload of equipment and devices for fuel debris retrieval, it is desirable to reduce radiation dose in the environment to the extent that allow work and remove interfering obstacles safely.
In order to safely remove interfering obstacles (in-building structures, in-core structures) for fuel debris retrieval, it is desirable to establish a method for removing interfering obstacles so that the release of radioactive materials from the PCV and the RPV is suppressed and that the integrity of the existing structure is maintained.

Gap between ideal and current state/Issues to be resolved

In top entry method, structures on the upper part of the PCV and structures inside the RPV become interfering obstacles, while, in the side entry method, the equipment outside the pedestal becomes an interfering obstacle. Also, both entry method, the equipment in the pedestal and structures in the reactor building become interfering obstacles. Therefore, it is necessary to develop technology to dismantle, remove, recover, and carry them out remotely. In particular, it is important to ensure the feasibility of processing in narrow areas and the workability of remote operation. Therefore, it is necessary to establish a function to prevent contact with the surrounding environment during operation of a multi-degree-of-freedom robot.
In order to maintain the integrity of existing structures, it is necessary to prevent damage to the equipment and surrounding structures caused by cutting.
Compared to machining operations, other operations such as positioning the machining tool, grasping the object, and changing tools, require a great deal of time. In this respect, it is necessary to develop tools for supporting the operation of workers.
Decontamination is necessary when equipment is carried out from the work cell to control the release of radioactive materials, so that it is necessary to improve decontamination by taking measures to prevent contamination by foreign substances.
For remote work and monitoring, it is necessary to establish a method to construct work equipment, peripheral equipment, and monitoring equipment remotely including installing a camera in narrow areas remotely).
② Specifying how to build access routes with safety in min

Desired state and reasons for it

It is desirable to develop a specific access route construction method for the safe delivery and installation (e.g., without exceeding the load-bearing capacity) of the equipment and devices for fuel debris retrieval.
Considering systems sustaining an inevitable increase in high-dose waste and a significant increase in exposure, it is desirable to establish appropriate access routes to retrieve fuel debris that may exist in the lower part of the pedestal, at the bottom of the RPV, and at other locations.

Gap between ideal and current state/Issues to be resolved

In Unit 1, functional tests of the equipment related to access route construction using the X-2 penetration have been conducted. In the future, it will be necessary to verify the field applicability of such equipment through mock-up tests.
In Unit 2, functional tests have been conducted on the isolation room and the hatch opening device, which are part of the equipment used to construct access routes using the X-6 penetration. In the future, it will be necessary to conduct mock-up tests and verify their applicability to the field. It is also necessary to manufacture extension pipes and deposit removal devices and conduct functional tests on them.
Unit 3 is expected to build an access route using X-6 penetration, but since it is submerged in water, the water level needs to be lowered before installing the equipment.
It is necessary to build a remote transport system and conduct mock-up tests and operation training on the system.
A functional test of the measurement system to be installed on the fuel debris detection robot has been conducted. It is necessary to verify its applicability to the field through mock-up tests.
In the construction of access routes, it is necessary to minimize the amount of secondary waste (additional amount of waste generated) generated by processing.

Relevant Issues


※ Please note that this English text is a provisional translation of the Japanese original.