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  • Writer's pictureErez Gilad

Published: our new paper, on nuclear fission chain reaction during core meltdown in future reactor d

Studies related to severe core accidents constitute a crucial element in the safety design of Gen-IV systems. A new experimental program is proposed for the ZEPHYR future reactor, aiming at studying reactivity effects at high temperature during degradation of Gen-IV cores by using critical facilities and surrogate models. The current study introduces the European Lead-cooled SYstem (ELSY) as an additional Gen-IV system into the representativity arsenal of the ZEPHYR reactor.

Climate change is probably the most challenging issue humanity is currently facing and will face in the coming years. To meet the global warming targets, set by the Paris agreement of 2015, nuclear energy must play a key role in the decarbonization of the energy sector. However, the currently operating nuclear power reactors fleet is aging and will eventually fail to meet future safety requirements. Therefore, new types of reactors are developed. These future reactor designs are known as Generation IV. The lead and sodium-cooled fast reactors are among these future designs. These reactor designs are attracting a great deal of attention among the nuclear community, as not all challenges related to their safe operation during accidental conditions are resolved. 

This is exactly the focus of our recent paper, which was published recently in International Journal of Energy Research, entitled: “Modeling representative Gen‐IV molten fuel reactivity effects in the ZEPHYR ZPR ‐ LFR analysis” ( This research is the result of a collaborative program between Ben-Gurion University of the Negev (Israel) and the French Atomic Energy Commission (CEA) at Cadarache (France). Scientists from the two institutes developed an innovative approach to study the nuclear fission chain reaction during severe accidents and core meltdown in Gen-IV reactors, which occur at a temperature of more than 2500°C.

An image from the study was chosen to be featured on the front cover of the International Journal of Energy Research, volume 43, issue 2. Shown in the image is the distribution of the neutron flux inside a nuclear fuel assembly in the reactor core during the progress of a severe core accident and at different stages of the core meltdown. Hot shades denote high nuclear fission rate, whereas light (white) shades denote thermal neutron flux density. The images were generated using Monte Carlo calculations and the Serpent2 code.

  1. Left: Undamaged nuclear fuel assembly

  2. Middle: Molten nuclear fuel assembly without lead above it

  3. Right: Molten nuclear fuel assembly with liquid lead above it

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