GUINEVERE: Generator of Uninterrupted Intense Neutron at the lead VEnus REactor

The GUINEVERE project

The GUINEVERE project was initiated as a project within IP-EUROTRANS, a programme in the 6th Framework Programme (FP6) of EURATOM.

The IP-EUROTRANS project addresses main issues for Accelerator Driven Systems (ADS) development in the framework of partitioning and transmutation for nuclear waste volume and radiotoxicity reduction.

The GUINEVERE project is devoted to specific experiments for the coupling of an accelerator, a target and a subcritical core. A major item to be investigated by these experiments is the validation of the subcriticality monitoring for an ADS since the guarantee of subcriticality is of fundamental importance for the safety of an ADS.

Analyzing the outcome of the FP5 MUSE project with regard to this issue, two points were left open for significant improvement. To validate the methodology for reactivity monitoring, a continuous beam is needed, which was not present in MUSE. In the definition of MUSE, from the beginning also a strong request was made for a lead core in order to have representative conditions of lead-cooled ADS which were only partially answered by the MUSE programme. For this purpose, there is a need for a lead fast critical facility connected to a continuous beam accelerator.

Since such a programme/installation is not present at the European nor at the international level, SCK•CEN has proposed to use a modified VENUS critical facility located at its Mol-site and to couple it to a modified GENEPI deuteron accelerator working in continuous mode (with and without beam trips) and in pulsed mode: the GUINEVERE project (Generator of Uninterrupted Intense NEutrons at the lead VEnus REactor).

Objectives

During 2008 and 2009, the VENUS facility was modified in order to allow the experimental programme to start in 2010. These experiments aim to provide an answer to the questions of on-line reactivity monitoring, subcriticality determination and operational procedures in ADS.

The execution of the GUINEVERE project consisted of two types of modifications at the SCK•CEN site. First of all, there are the modifications which are connected to the installation of the new GENEPI-3C accelerator at the VENUS critical facility and its coupling to the core. The second type of modifications is linked with the adaptation of the VENUS critical facility to host a fast lead core, further on referred to as VENUS-F.

The construction of the accelerator GENEPI-3C is carried out by the French research centre CNRS. For the penetration of the accelerator into the core, it was decided early in the project to have a vertical penetration because it has significant scientific advantages. An additional floor had to be constructed on top of the existing installation. In the figure at the front you see the drawing of the additional floor with the ventilation system on top of the already existing bunker in the VENUS hall.

The GENEPI-3C (GEnérateur de NEutrons Pulsé Intense-3Continu) accelerator is the third of a series designed for neutronic experiments. The GENEPI machines are 250 kV deuteron accelerators ended by copper targets with titanium-tritium (TiT) or titanium-deuterium (TiD) deposits, providing 14 MeV or 2.5 MeV neutrons via T(d,n)4He or D(d,n)3He reactions.

The new GENEPI-3C machine cumulates specifications of the first GENEPI accelerator, designed for the MUSE experimental programme at MASURCA reactor (CEA Cadarache, France, 2000-2004), i.e. pulsed mode operation with very sharp and intense beam pulses (1 μs, 50 mA peak current), with new continuous mode specifications summed up in the table below. In this new DC mode, it will also be possible to operate with beam interruptions (so-called “beam trips”) with a programmable duration and a low repetition rate for the needs of the foreseen experiments.

 

   

Due to the vertical coupling conditions, the GENEPI-3C machine requires a special design allowing the entire removal of the vertical line partly inserted in the reactor: this is necessary for target changes as well as for reactor or accelerator maintenance. To do so, the vertical line has to be embedded in a supporting structure that can be hosted along guiding structures by means of a crane, and then lifted above the reactor bunker ceiling to be stored on a stand surrounded by working platforms. To allow this structure to move, the 90° bending magnet has to be removable too and is supported by a mobile cart that can be moved along two rail tracks. 

To obtain a fast lead core in the VENUS vessel, all internals were removed and are replaced by a core made of lead and uranium fuel. The fuel is provided by CEA.

A fuel assembly consists of uranium rodlets of about 1,27 cm diameter, lead plates and square lead rodlets of 1,27 cm thickness. The active height of the core region is about 60 cm. About 100 fuel assemblies are needed to obtain a critical configuration.

The core region is contained within a 12 x 12 square of assemblies, consisiting of fuel assemblies and lead assemblies simulating the reflector. To allow a safe shutdown in all situations, 6 safety rods made of boron carbide with a fuel/lead follower are foreseen in the core. The control rods are made of boron carbide only.

 

   

Contact: Jan Wagemans