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For the decommissioning of damaged cores of Fukushima Daiichi NPS, the retrieval operation of solidified core melt (corium) and its safe management are essential tasks. To understand characteristics of corium specific to the 1F cores, we have prepared and analyzed various types of simulated corium specimens in laboratory scale. To verify the effect of cooling condition found on the simulated corium, we revisit the actual corium specimens collected from the TMI-2 accident core, which have been stored at the Reactor Fuel Examination Facility (RFEF) in JAEA Tokai since 1991. Comparing the phases and microstructure, rapid-cooled specimens have dense microstructure and consist of single phase of cubic structure. On the other hand, the slow-cooled specimens consist of U-rich cubic and Zr-rich tetragonal phases distributed minutely. From these observations we have confirmed the similar dependence of microstructure and mechanical property on the cooling condition.

Oral presentation

Criticality control of fuel debris / TMI-2 review and Fukushima expectation

Tonoike, Kotaro; Yamane, Yuichi

no journal, ,

It is conceivable that a large amount of fuel debris has been produced in the reactors of Fukushima Daiichi Nuclear Power Station (1FNPS) due to the severe core damage and melting. The amount is far beyond minimum critical mass, and essentially subject to criticality control. This presentation will outline the criticality control of fuel debris in the Three Mile Island Nuclear Station, Unit 2 reactor (TMI-2). Then, criticality control problems of fuel debris during the 1FNPS decommissioning will be described contrasting with the TMI-2 case. Finally, technical expectations and research activities of the fuel debris criticality control for the 1FNPS will be presented. It is possible that the fuel debris will be retrieved under nonborated water at the risk of criticality. In this scenario, the risk control, mitigation measures in case of criticality, would be a key factor in safety of the decommissioning.

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Visualization of simulated molten-fuel behavior in a pressure vessel lower head using high-frame-rate neutron radiography

Research plan on in-vessel debris coolability in ALPHA program

High-frame-rate video visualization of simulated lower head behavior during TMI accident using neutron radioscopy

In-vessel debris coolability experiments in ALPHA program

Core melt behaviors and thermal properties in LWR severe accident

Validation of COSTA on predicting core damage accident progression with the TMI-2 accident data

Present status of research related to in-vessel debris coolability and experimental plan in ALPHA program at JAERI

Results and lessons from the accident study and recovery actions for TMI-2; Introduction to TMI special volume of the Nuclear Technology

Results of OECD LOFT program

A Translation of NUREG-1355 the status of recommendations of the Presidents Commission on the accident at Three Mile Island; A Ten year review

Method of estimating liquid velocity in a hot leg during reflux cooling of natural circulation in a pressurized water reactor

Post-facta analysis of the TMI accident, I; Analysis of thermal hydraulic behavior by use of the RELAP4/MOD6/U4/J2

Post-facta analysis of the TMI accident, II; Analysis of fuel rod behavior or core damage estimation by use of the TOODEE2-J

Thermal-Hydradulic Analysis of TMI Accident; On the Results of the First to Third Analysis

Prompt Technical Assessment Report for TMI-2 Accident by JAERI Task Force

Study on dissolution technique for fuel debris in Fukushima Daiichi Nuclear Power Station, 2; Dissolution test of fuel debris sample of TMI-2

Dose evaluation of adsorption vessels for contaminated water treatment by using radiation transport and shielding calculation codes

Characterization of fuel debris (27'A), 9; Microhardness of simulated fuel debris and TMI-2 debris

Revisiting the TMI-2 core melt specimens to verify the simulated corium for Fukushima Daiichi NPS

Criticality control of fuel debris / TMI-2 review and Fukushima expectation