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Design and test of a reactivity modulation system for the accurate measurement of the zero p H/F

Vacancy details

General information


The French Alternative Energies and Atomic Energy Commission (CEA) is a key player in research, development and innovation in four main areas :
• defence and security,
• nuclear energy (fission and fusion),
• technological research for industry,
• fundamental research in the physical sciences and life sciences.

Drawing on its widely acknowledged expertise, and thanks to its 16000 technicians, engineers, researchers and staff, the CEA actively participates in collaborative projects with a large number of academic and industrial partners.

The CEA is established in ten centers spread throughout France

Reference number


Job details


Neutronics and reactors physics



Job title

Design and test of a reactivity modulation system for the accurate measurement of the zero p H/F

Socio-professional category


Contract duration (months)

12 mois renouvelable

Job description

Currently, inconsistencies are observed between the delayed neutron group constants from the main evaluated nuclear data libraries, JEFF-3.2, JENDL-4.0 and ENDF/B-VII.1. In addition to the difference in the number of groups used to define the time dependence of delayed neutron emissions, the relative abundances associated to the decay constants lead to strongly different average delayed neutron lifetimes. Such differences may be responsible for excessively large safety margins in design studies of nuclear systems. The post-doctoral position is addressing this issue.

The challenge of this work is to design a neutron absorbing rotating rod, allowing a reactivity modulation over a wide frequency range, in order to measure the corresponding reactor zero power transfer function (ZPTF). The interest of using such design is to cover a much larger frequency domain, typically 1mHz to 1kHz than with a translation device. Moreover, the system will have to be sufficiently versatile to be used in different experimental reactor conditions.

The work will be divided into five steps:
- Neutronics design of the system: Monte-Carlo simulations will be done to meet various requirements: small reactivity amplitude, linearity vs. rotation angle, mitigation of the safety impact in accidental conditions …
- Mechanical and electro-technical design of the system: With the help of technicians, the candidate will have to determine the most appropriate engine to drive the system to maximize the stability of rotation period. Some experience in electronics and servo-drive mechanisms would be welcome.
- Theoretical study of the impact of the flux perturbation induced by the system on the ZPTF: as the zero power transfer function is usually determined under the assumption of a point kinetics model, the current work will have to re-evaluate the relevance of such a simplified approach. Recent developments in the Monte-Carlo code TRIPOLI4® for kinetics calculations will be used for that purpose.
- Test of the system in experimental conditions: the candidate will be in charge of organizing an experimental campaign, to take place in one of the available zero power reactors in partner institutes, for instance VENUS (SCK-CEN), LR-0 (CV-REZ), CROCUS (EPFL).
- Experiments analysis and data processing: we will extract the effective delayed neutron parameters and compare them with the ones obtained from evaluated nuclear data. A sensitivity analysis will be perform to estimate trends and associated covariances on the delayed neutron group constants.

These first tests of a prototype system will help to design a more elaborate one, to be used in the ZEPHYR zero power reactor that CEA is planning to build in the next decade.

Applicant Profile

Applicants are required to have a PhD in reactor physics, experimental physics or nuclear physics.

Job location



Job location

France, Provence-Cote d'Azur


CEA Cadarache

Candidate criteria

Recommended training

PhD in Physics

Requesting party

Position start date