EXPERIMENTAL INVESTIGATIONS RELEVANT FOR HYDROGEN AND FISSION PRODUCT ISSUES RAISED BY THE FUKUSHIMA ACCIDENT

Experimental Investigations Relevant for Hydrogen and Fission Product Issues Raised by the Fukushima Accident

Author Information

• Sanjeev Gupta, Becker Technologies GmbH, Koelner Strasse 6, 65760 Eschborn, Germany

• Article history: Received 13 January 2015, Accepted 13 January 2015, Available online 21 January 2015.

• Keywords: Computational fluid dynamics and lumped-parameter codes, Fission products, Hydrogen, Large-scale experiments, Passive autocatalytic recombiners, Severe accident, THAI test facility

Abstract

• The Fukushima Daiichi nuclear power plant accident in March 2011 was caused by an earthquake and tsunami.

• Failure of power systems led to the cooling reactor's inability resulting in fuel melting, containment pressurization, and hydrogen explosions.

• Escaped radioactivity affected the atmosphere and ocean.

• Issues identified: containment venting problems, leakage, malfunctioning of standby systems, and unmanaged hydrogen accumulation.

• The accident emphasized the need for better control measures and assessment of existing mitigation systems.

Introduction

Overview of the Fukushima Daiichi Accident

• Date: March 11, 2011

• Trigger: Earthquake and tsunami caused loss of heat removal leading to core melting and radioactive release.

• Confirmed need for robust safety measures to protect against severe events.

Fukushima Daiichi Plant Details

• Comprised six boiling water reactors (BWRs) with varying containment designs (Mark 1 for Units 1-5 and Mark 2 for Unit 6).

• Challenges: Inadequate systems to manage post-earthquake tsunami effects.

Consequences of the Accident

• Established need for worldwide safety reassessments and protocol improvements across nuclear plants.

• Highlighted deficiencies in hydrogen and fission product management.

Hydrogen Issues in Severe Accidents

Generation and Risks

• Hydrogen produced via metal-water reactions and core-concrete interactions.

• Risk of flammable and detonable hydrogen mixtures in confined spaces, necessitating detailed studies of production, distribution, and behavior.

• The production rate of hydrogen from zirconium oxidation can reach between 3,000-4,000 kg in BWRs.

Combustion Behavior

• Hydrogen combustion can transition from deflagration to detonation based on conditions.

• Ranges of hydrogen concentration critical for combustion safety need to be explored.

Past Incident Analysis

• Previous accidents (e.g., Three Mile Island) illustrate the consequences of hydrogen mishandling in containment.

• The Fukushima accident led to insights into hydrogen transport behavior that informed safety improvements.

THAI Test Facility

Overview

• THAI (thermal hydraulics, hydrogen, aerosols, iodine): A 60 m3 test facility in Eschborn, designed for analyzing multi-compartment containment behavior.

• Equipped with advanced instrumentation and capabilities for simulating reactor building scenarios.

Fission Product Issues

Environmental Impact

• Significant radionuclide release during the Fukushima incident included xenon-133 and cesium-137.

• Emphasis on understanding fission product behavior for accurate predictive modeling during accidents.

Research Needs

• Investigation into aerosol behavior, iodine transport, retention, and spray system performance for effective radionuclide management.

• Exploring means to enhance source-term mitigation measures.

Conclusion

• The Fukushima accident revealed critical gaps in understanding hydrogen and fission product management.

• Ongoing research is essential to improve safety measures, predictive capabilities of safety analysis tools, and effective accident response protocols.

Acknowledgments

• The research was funded by the German Federal Ministry for Economic Affairs and Energy, supported by OECD/NEA THAI and THAI 2 projects.