Dr. Reuven Rachamin
Experimental Thermal Fluid Dynamics

PhD thesis

Conceptual Design of a Pressure Tubes Light Water Reactor with Variable Moderator Control

PhD student:
Reuven Rachamin
Prof. Alex Galperin (BGU – Ben-Gurion University, Israel), Dr. Emil Fridman (HZDR)
Reactor Safety


In the coming decades, the world will need to produce significant amount of energy in order to meet the needs of the growing population and raise the living standards of developing countries. This energy should be produced at a reasonable cost and in a safe, secure and efficient manner. Nuclear energy has the potential to meet these requirements and contribute to a sustainable solution for the world’s growing energy needs and environmental problems. In order for nuclear energy to play a substantial role in the global energy supply, innovative nuclear reactors and fuel cycles need to be developed.


This thesis presents the development of innovative reactor concept named the Pressure Tube light water reactor with Variable Moderator control (PTVM LWR). The basic novelty of the proposed design is an implementation of the "breed & burn" mode of operation by a dynamic variation of the moderator content in the core. The core layout of the novel reactor design is derived from the CANDU line of reactors in general, and ACR-1000 design in particular. It should be stressed however, that while some of the ACR-1000 mechanical design features are adopted, the core design basics of the reactor proposed here are completely different. First, the inter fuel channels spacing, surrounded by the calandria tank, contains a low pressure gas instead of heavy water moderator. Second, the fuel channel design features an additional tube (designated as moderator tube) connected to a separate moderator management system. The dynamic variation of the moderator is a unique and very important feature of the proposed design. The moderator management system is designed to vary the moderator tube content from "dry" (gas filled) to "flooded" (light water filled). The "breed & burn" mode is implemented by keeping the moderator tube empty ("dry" filled with gas) during the breed part of the fuel depletion and subsequently introducing the moderator by "flooding" the moderator tube for the "burn" part.

This thesis assesses the conceptual feasibility of the design and explores its physics characteristics.


  • R. Rachamin, E. Fridman, A. Galperin., “Design and analysis of an innovative pressure tube light water reactor with variable moderator control”, Annals of Nuclear Energy (2013) 60, pg. 248-255. DOI: 10.1016/j.anucene.2013.05.011


Dr. Reuven Rachamin
Experimental Thermal Fluid Dynamics