MYRRHA a new future for nuclear research

SCK•CEN (the Belgian Nuclear Research Centre) is a candidate for hosting a European fast spectrum experimental facility for demonstrating efficient transmutation and associated technologies using a system that works in sub-critical and/or critical mode. With this in mind, SCK•CEN started, in 1998, designing the MYRRHA facility as an accelerator driven system (ADS) with the following objectives:

To demonstrate ADS technology, full-scale, within the framework of research into the transmutation of high-level waste
To serve as a flexible fast spectrum irradiation facility for testing materials and innovative fuels for ADS and GEN IV systems and fusion reactors
To contribute to the technological demonstration of the GEN IV Lead Fast Reactor
To perform fundamental and applied physics research making use of SCK.CEN’s high power proton accelerator

MYRRHA should be operational in 2020 and is designed as an open user facility for the international research community in the fields of physical science, waste transmutation, nuclear engineering, radioisotope research and production, as well as for material and nuclear fuel science.

Since the start of the FP6 EUROTRANS integrated project launched by the European Commission in 2005, MYRRHA has served as a basis for a small-scale, short-term experimental facility demonstrating the technical feasibility of “Transmutation in an Accelerator Driven System (XT-ADS)” machine. The main parameters and characteristics of the MYRRHA facility are as follows:

The MYRRHA accelerator is based on LINAC technology in order to fully demonstrate the industrial scale ADS and to meet the very demanding conditions in terms of beam reliability (reduction of the number of beam trips longer than 1 second, up to a maximum of 10 to 20 trips per year)
The windowless spallation target concept of MYRRHA has progressed in terms of design and demonstration on the basis of an important international experimental programme complemented by an international Computational Fluid Dynamics (CFD) effort for the free surface treatment. The evidence of the feasibility of the proposed design is no longer questioned with respect to its fundamental aspect, but some issues still remain open with regards to its fine tuning and advanced design, which will be addressed over the next 3 years
The core maximum sub-criticality level of k_eff ~ 0.95 assures a comfortable margin for safe operation. The total power ranges from between 50 to 80 MWth (depending on the core loading and the experimental rigs inserted). The total neutron flux levels (1 10¹⁵ to 5 10¹⁵ n/cm².s) achieved in large irradiation volumes in the core (about 20.000 cm³ in total) enable very high performance testing conditions
The MYRRHA fuel design is based on fast reactor (FR) MOX fuel technology (30% Pu contents) with T91 ferritic-martensitic steel for the cladding and for the fuel assembly wrapper. The inlet temperature is 300°C and the outlet temperature is 380°C. The targeted fuel residence time is 3 years. Nevertheless, the MYRRHA core is designed to accept minor actinide based fuel assemblies whenever these are made available
The primary system of the MYRRHA facility is based on a pool design cooled with Pb-Bi as a primary coolant (see figure 1) and boiling water as a secondary fluid. The heat exchangers and primary pumps are immersed in the reactor vessel in dedicated casings. Interim fuel storage inside the primary vessel can host the used fuel for decay heat before transfer out of the vessel
The MYRRHA building was conceived from the very beginning to take into account remote handling and robotics based operation and maintenance within a controlled atmosphere, limiting the LBE contamination by O₂ trapping. The remote handling for both out-of-vessel and in-vessel operation and maintenance was developed using existing and demonstrated technology in the Joint European Torus (JET) fusion facility.

Figure 1: Vertical cut of the MYRRHA/XT-ADS sub-critical reactor

In April 2008, SCK•CEN, together with its European partners, answered a FP7 call for establishing a Centralised Design Team for a Fast Spectrum Transmutation Experimental Facility to be able to work in sub-critical and/or critical mode. Within this framework and starting in 2009, the MYRRHA/XT-ADS design will be updated to allow for critical mode operation. The partners involved are the following research organisations: CEA (FR), CNRS (FR), FZK (DE), FZD (DE), CIEMAT (ES), ENEA (IT), NRG (NL) and ITN (PT). From the nuclear industry the partners involved are: Ansaldo Nucleare (IT), Del Fungo di Giera Energia S.p.A. (IT), AREVA NP S.A.S (FR), Empresarios Agrupados (ES), SENER (ES), ADEX (ES), OTL (UK) and CRS4 (IT). Also involved are two universities: UPM (Spain) and UPV (Spain). Since the MYRRHA project is moving to an industrialisation phase, the partners leading the major work-packages are from the nuclear industry.

The MYRRHA project (technical description and business plan) has been submitted to the Belgian minister of energy with a request for financial support for a significant part of the cost of the initial engineering phase of MYRRHA and for its final realisation at a later stage. As a result, in the governmental agreement signed by the new "Leterme I" Belgian federal government, which was formed in March 2008, support for the MYRRHA project is regarded as an international research infrastructure that serves research programmes looking at the reduction of long-lived waste and the production of radio-isotopes for medical applications. Currently, SCK•CEN is in discussion with the Belgian government to set the specific requirements and conditions of this support.

A detailed business plan for MYRRHA exists (MYRRHA Project – Business Plan 2007, SCK•CEN Report, reference ANS/HAA/DDB/3900 B043000/85/07-17, April 2007). From the plan it is possible to identify a total investment cost, expressed in 2007 values and spread over 12 years, of ~700 M€. The operational costs are estimated to be 38 M€ per year.

The 2007 R&D programme for MYRRHA at SCK•CEN features various highlights. Here are some of them:

The primary and secondary system component configurations were further elaborated and optimized. The system components were calculated in detail. The diaphragm separating the hot and cold lead-bismuth coolant in the reactor vessel was largely simplified. This new configuration of vessel components resulted in an enhanced capacity for natural circulation in emergency situations. The specifications for the experimental devices (in pile sections) were formulated according to the MYRHA/XT-ADS objectives and adapted to the actual core and core support structure design
The neutronic calculations for MYRRHA/XT-ADS were mainly focused on two topics. Firstly, the estimation of the neutron induced damage (dpa) on the core barrel and top grid. This led to a recommendation to increase the core by two extra rows, thereby increasing the space between the last row of fuel assemblies and the core barrel. Secondly, calculations were performed to estimate the neutron fluxes in the eight in-pile-positions. In addition, scoping calculations for a burn-up cycle and reshuffling scheme were made
The issues of vacuum and lead-bismuth conditioning for the windowless spallation target were addressed through dedicated experiments, including experiments simulating the proton beam surface heating with an electron beam (WebExpIr). It was shown that the high intensity heating has no distortive effect on the target surface flow and that the vacuum conditions remain well within the operational limits
One of the fundamental design options is that all maintenance and in-service inspection and repair duties in MYRRHA will be performed by remote handling. In view of this, a first version of the Remote Handling Design Catalogue (RHDC) for MYRRHA/XT-ADS was released. This RHDC provides information and guidance to engineers, CAD designers and technicians with a view to ensuring that the MYRRHA/XT-ADS machine, as well as its remote maintenance system, is designed in a way that is fully compatible with the remote handling requirements. The catalogue contents were finalised in cooperation with Oxford Technologies, taking advantage of their experience with the fully remote maintenance of the EFDA-JET Fusion Tokamak project
Significant progress was made with the development of ultrasonic techniques for visualisation in liquid lead-bismuth under gamma radiation. An acoustic computer model was developed and validated on a mock-up in water. The research to improve the diffusion bonding process to obtain a reliable ultrasonic transducer for application in LBE is ongoing
Material irradiations in stagnant lead-bismuth in the BR2 reactor have been performed to investigate the behaviour of the fuel cladding and structural materials, considered for MYRRHA/XT-ADS, in representative conditions. The samples are being analysed during the course of 2008
As a first step towards the development of MYRRHA the GUINEVERE project was launched and formally accepted by the Governing Council of IP-EUROTRANS, in December 2006. GUINEVERE is a zero-power mock-up of the MYRRHA/XT-ADS with, as its main objectives, the qualification of the sub-criticality monitoring techniques and its role as a validation model for the core neutronic design. GUINEVERE should provide answers to these questions by 2009-2010. To achieve this goal, the zero-power critical facility VENUS facility at SCK•CEN is being adapted to a zero-power lead fast reactor and coupled to a modified GENEPI deuteron accelerator delivering 14 MeV neutrons by bombarding deuterons on a tritium-target
An important milestone reached was the delivery of CEA fuel for GUINEVERE to SCK•CEN, in October and November 2007. Also a derogation to the standard licensing procedures was requested in November 2007. This request was approved by the Minister of Internal Affairs, in March 2008. The construction permit has been received in April 2008. The first phase of the licensing procedure was successfully completed in May 2008.
A full plant layout of the MYRRHA complex has been drawn up on the SCK•CEN technical site at Mol, see figure 2