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The whole picture of decommissioning strategies and issues -grasping of situation in core-

Organization of strategic plans and issues

 A diagram of organized strategies for reducing the risk of Fukushima Daiichi NPS is illustrated in the logic tree below.

Logic tree1

1.Waste adsorption column and waste
sludge from water treatment system

<Reference: Strategic Plan 2015 (NDF)>

  In this, thorough preparations are necessary for safe and sure fuel debris retrieval, and we face the challenges of many difficult problems. to retrieve fuel debris safely without fail in this. Practical scenarios for retrieving it by using various methods (submersion method, partial submersion method) or a combination of them depending on the situation of each plant are under examination.

Logic tree2

<Reference: Strategic Plan 2015 (NDF)>

 A logic tree of more hierarchical strategies for grasping in-core and fuel debris’ situations is presented below.

Logic tree3

<Reference: Strategic Plan 2015 (NDF)>

 In order to grasp in-core situation such as the amount, location and properties of fuel debris and distribution of FP, comprehensive analysis and evaluation are going to be conducted, accompanied with on-going R&D corresponding to three issues below.

  1. Estimation by plant investigation
    Investigations of certain structures such as internal conditions of the PCV/RPV and S/C and torus rooms, and the whole image of the fuel debris using of the muon detection systems.
  2. Estimation by analysis
    Analysis is conducted using accident progression analysis codes.
  3. Estimation based on knowledge and experiments
    Estimation from the knowledge and experiments is conducted by studies based on the past accidents and research and engineering studies on plant data and experiments on simulated debris.

R&D efforts

Comprehensive analysis and evaluation of fuel debris and FP status

Device/equipment development /demonstration for the full scale practical system research and measurement