_________________________________________________________________________________________

ENEA: National Agency for New Technology, Energy and Environment

INFN: National Institute for Nuclear Physics

_________________________________________________________________________________________

I. The program

II. Status

1. Proton Source

2. Low and Medium Energy Accelerator Section

3. High Energy Accelerator Section

4. Neutron Production for Material Characterization

5. General Safety Criteria and Classification

6. Neutronics

7. Thermal-Hydraulic Analysis

8. Technology of the beam window

9. Material Technology and Compatibility with Lead and/or Lead-Bismuth Alloy

I. The program

It was approved by ENEA (National Agency for New Technology, Energy and the Environment) and INFN (National Institute for Nuclear Physics) in July '97. Was then submitted to MURST (Minister for University and Scientific and Technological Research) and got the final approval at the end of 1997.

The program consists of two main parts, regarding, respectively, the accelerator and the sub-critical system. Although ENEA and INFN will be jointly responsible for the whole program, INFN will essentially manage the first part, and ENEA the second part.

The proposed project will concern all the main subsystems of an ADS (accelerator, window/target, sub-critical reactor). However, due to the limited available financial resources, it has been decided to concentrate efforts on some significant and qualified activities, in view of the goal of participation in an international project for the construction of an ADS prototype, like the Energy Amplifier for waste transmutation.

The main objectives of the research program can be summarised as follows:

· Conceptual design of a 1 GeV - 30 mA proton LINAC.

· Design and construction of the proton source and of the first section of the RFQ, as well as of some prototypical cavities concerning the super-conductive LINAC.

· Development of methods and criteria for neutronics, thermal-hydraulics and plant design for an EA-like sub-critical system, as well as some specific aspects related to the safety analysis of this type of nuclear installation.

· Materials technologies and development of components to be used in a plant in which lead or lead-bismuth acts both as a primary target and as a coolant.

· Experiments to validate and verify proposed technologies for materials compatibility with lead and lead-bismuth alloys.

The foreseen activities will last two years and cost 17 GLire (about 10 M$), 8 of which have already been allocated by the Italian Minister for University and Scientific and Technological Research (MURST), while the other 9 GLire will be provided by the participating bodies.

The following nine research sub-programs have been foreseen; each of them will be carried out by a corresponding research group, involving the research institutes and firms reported in brackets.

1. Final design and construction of the proton source (INFN, SISTEC, HITEC)

2. Low and medium energy accelerator section (INFN, CINEL)

3. High energy accelerator section (INFN, CISE, SAES-Getters, ZANON)

4. Neutron production for material characterisation (INFN, INFM)

5. General safety criteria and classification (ENEA, ANSALDO)

6. Neutronics and transmutation efficiency (ENEA, CIRTEN, CRS4, University of Bologna)

7. Thermal-hydraulic analysis (ENEA, CIRTEN, CRS4, ANSALDO)

8. Beam window technology (ENEA, CIRTEN, ANSALDO, INFM)

9. Materials technology and compatibility with Lead and/or Lead-Bismuth alloy (ENEA, CIRTEN, CRS4, FN, ANSALDO).

II. Status

External collaborations have, also, been or are being activeted. In particular:

1) a collaboration agreement between CERN and INFN, for production and test of rf sc-cavities, is ready to be signed;

2) a draft of a MOU among CEA, CNRS and INFN, on cooperation on high intensity proton linac, has been prepared;

3) an agreement between CEA and ENEA on physics and experimental activities already exists;

4) a collaboration with CERN (Rubbia group) on neutronics and code development is in progress;

5) a MOU among ENEA, IPPE and INPE for a collaboration on physics and thermal-hydraulics has already been signed.

Appendix

Short Description of the TRASCO Sub-Programs

1. Proton Source

Prototypical proton sources of several tens of mA already exist (e.g. at Chalk River National Laboratory, at LANL, and at CEA-Saclay), but R&D is necessary for ensuring the availability and reliability required by an ADS.

The objectives of this sub-program are the feasibility study, design, construction(*) and test of a 2.45 GHz microwaves source which can produce a 50 mA ­ 75 keV proton beam. Taking into account the state-of-the-art of such devices, R&D is required for achieving the required current and voltage stability, as well as a satisfactory controlled low emittance.

The conceptual design will be focused on the study of the following items:

a) off-resonance in microwaves sources;

b) microwaves injection and plasma chamber;

c) magnetic field profile in the plasma chamber;

d) electrode optimisation, making use of the KOBRA-3D code;

e) space-charge neutralisation;

f) emittance minimisation;

g) proton source ­ RFQ matching.

Final design, construction and test of a prototypical proton source will follow the above mentioned preliminary activities. At last, an extended optimisation of the main components of the source is foreseen for achieving the best compromise between different parameters (impedance, energy resolution, proton fraction, electronic density, emittance, etc.).

_____________________________________________________________

(*) The construction will be completed in the frame of other INFN programs.

2. Low and Medium Energy Accelerator Section

The final goal of this research sub-program is the design and construction of critical components for a 100 MeV ­ 30 mA proton LINAC, to be used as an injector for the CW super-conductive LINAC at 350 MHz described in the next section.

Three different options will be analysed and compared:

a) Normal-conductive, continuos wave RFQ (up to 5 MeV), and DTL at 350 Mhz.

b) Normal-conductive RFQ (up to 5 MeV), followed by two-gap, l/4 or l/2, super-conductive cavities at 175 MHz

c) Normal-conductive RFQ, followed by super-conductive cavities at 350 Mhz.

After the conceptual design phase in which the system lay-out will be defined and beam dynamic analyses will be performed, making use of the most advanced codes and methods, the development of a prototypical RFQ is foreseen.

A full-scale aluminium mock-up will be constructed for RF tests at low power. The engineering validation phase will allow the construction of a full-scale section of the RFQ, in which low and high power tests will be performed.

As far as the development of a super-conductive cavity for the medium energy section is concerned, two prototype are foreseen:

a) a steel cavity at room temperature, for developing constructive technologies (such as sputtering, or welding of pre-shaped niobium plates) as well as for performing electrodynamics studies;

b) a niobium cavity, for low and high power tests.

The high energy section accelerates the proton beam from 100 MeV to 1 GeV, thus representing the biggest and most expensive component of the accelerator.

Its design will be based on super-conductive, LEP-like accelerating structures at 350 MHz. Three different families of b-graded multicell cavities are foreseen, corresponding to matched b of about 0.5, 0.65 and 0.85 respectively.

The present research sub-program concerns the conceptual design and the beam dynamic analysis of the whole super-conductive LINAC, as well as the development and construction of prototypical super-conductive cavities.

The first part of the sub-program, while defining the general layout of the accelerator, will be particularly focussed on the detailed study of:

a) the electromagnetic design of the accelerating structures;

b) the thermal and mechanical performances of the same structures;

c) the halo problems, with the goal of minimising the particle losses.

In particular, it is planned to develop a single cell Nb cavity at the lowest b, a complete five-cell copper structure for mechanical and RF warm tests, and a complete five-cell copper, Nb-sputtered, cavity at the highest b.

4. Neutron Production for Material Characterization

The proton beam of an ADS is particularly suitable for testing high intense neutron sources which are currently of great interest for the international scientific community (e.g., the European Spallation Source).

This research sub-program aims to optimise the accelerator design to allow for an efficient "spill-out" of the primary beam for producing a high intensity neutron flux for fundamental studies.

5. General Safety Criteria and Classification

The ADS is a very innovative concept, with higher intrinsic than existing or advanced nuclear reactors. Consequently, some simplifications of the safety issues and relaxation of the requirements to be followed during the design, construction and operation phases, can be achieved.

This subprogram aims to identify the general safety requirements complying with the present national and international regulations. Indeed, codes and standards proposed for the design of innovative reactors likely exceed the needs of sub-critical systems.

However, the identification of general safety requirements and the selection of design regulations will allow to address the subsequent final design.

In this framework four activities will be pursued:

· Identification of general safety issues and requirements. This activity aims to define the safety requirements of the overall process, by emphasising the peculiarities of an ADS plant, relative to current nuclear power plants. Furthermore, general safety functions such as assurance of sub-criticality, residual heat removal, proton beam control, radioactivity confinement, etc. will be analysed, taking into account the innovative features of the system. At last, it will be checked whether the study of standard design basis events (inside and outside the plant) has to be extended to special events (e.g., mutual interaction between ADS and other nuclear installations in the same site).

· Applicable codes and standards. Reference regulations will be established through an in-depth, critical assessment of LWR and LMFBR licensing processes (e.g., by revising existing Regulatory Guides) and of other guides (e.g., industrial standards).

· Safety classification. This activity will be finalised to asssociate structures, systems, and components to the reference standards and codes. On the basis of a functional analysis of design basis events, each item will be classified according to its safety function.

· Mechanical design criteria. Because of the lack or inapplicability of existing regulations, new criteria have to be established for the use of innovative materials, as well as for the operation of nuclear components and structures out of the standard range of applicability.

Many specific aspects of its core, make the neutronics of an ADS different from that of a critical sodium-cooled fast reactor. In particular one has to consider its geometrical complexity, the use of lead or lead-bismuth as a coolant, the neutron energy spectrum, the physics of spallation, as well as the presence of high order harmonics characterising the flux spatial distribution.

Such features require developments both in nuclear data evaluations and in codes for static and kinetic reactor analysis.

In particular, nuclear data models for such nuclides such as Th, Pb, etc. have to be investigated, in an energy range usually not considered in nuclear reactors, and new evaluations are required.

Concerning reactor analysis, it has been recently claimed that for the lead-cooled ADS concept a continuous energy description is necessary in the whole energy range. This is motivated by the large mismatching of the neutron spectrum between the target zone and the sub-critical system (due to the relatively small neutron energy loss per elastic collision) and by the need for a correct evaluation of the coolant void effects. These considerations, along with the geometrical complexity, suggest the use of Monte Carlo codes. On the other hand, faster and suitably simplified deterministic codes (based on homogenisation and energy grouping), after appropriate validation, can play a relevant role for extensive system analyses. Thus, uncertainties coming from standard deterministic multigroup methods will be assessed via an extended comparisons with reference Monte Carlo codes, developed at CERN in the frame of the EA project.

In addition, a new deterministic neutron kinetic model (in full transport theory) will be developed and compared, where possible, with Monte Carlo performances. Such a model will address specifically some reference transients in an ADS

Last, but not least, the overall efficiency of an ADS as actinide and fission product burner, as well as other aspects of its fuel cycle, will be analysed, by using recent developments of Monte Carlo codes coupled with deterministic depletion codes.

7. Thermal-Hydraulic Analysis

The availability of reliable thermal-hydraulic codes is of primary importance for nuclear plant design, both for identifying operational conditions and for analysing system transients.

The proposed ADS concepts present some peculiar aspects which require the development of new thermal-hydraulic models, as well as a deep investigation of some fundamental phenomena, at present far from a complete comprehension. In particular, the use of lead or lead-bismuth alloy as a beam target and nuclear coolant, as well as heat removal based on natural convection have to be carefully studied.

Therefore, the use and development of advanced, 3-D CFD (Computational Fluid Dynamics) codes is necessary, in particular for analysing the boundary layer stability and its interaction with the hot rising flow, the fluid flow in the subchannels, and the formation and stability of fully developed turbulent flow. In addition, transients at start-up and shut-down in a natural convection regime will be investigated.

The above fundamental studies will provide data for establishing correlations to be implemented, after appropriate validation, in any ADS oriented thermal-hydraulic design code.

Plant design requires the development of a thermal-hydraulic system code which can simulate the various reactor transient. Such a code, must include the following modules, some of which have to be developed or validated to include specific features of a lead-cooled ADS:

· neutron source model;

· target and core thermal-hydraulic model (including simplified neutron kinetic model);

· primary loop model;

· secondary loop model;

· residual heat removal model.

8. Technology of the beam window

Being subjected to heavy operational conditions, concerning irradiation and corrosion, the beam window is universally considered as a "key" component of a sub-critical system. Advanced materials and technologies have, thus, to be foreseen and developed for this component.

In this connection, some promising metals or alloys with high mechanical performances such as W, W-Re alloy and Mo, have been proposed. Unfortunately, there is a general lack of data on the mechanical properties of these new materials under the synergetic conditions of high neutron and proton fluence and of the interaction with lead or lead-bismuth.

This subprogram aims to analyse the effects of high fluence proton irradiation, in order to get reliable data on the mechanical proprieties of candidate materials vs. the irradiation dose. Furthermore, new technologies will be investigated for demonstrating the feasibility of windows of actual size.

As far as the theoretical studies are concerned, a finite element model will be developed for mechanical tests interpretation. Calculations performed with such a code will be compared with TEM analyses.

9. Material Technology and Compatibility with Lead and/or Lead-Bismuth Alloy

Due to the heavy operational conditions (e.g., high particle flux, lead temperature and velocity, etc.), qualification of materials and components to be used in future lead-cooled ADS is of primary importance. The present sub-program foresees experimental investigations aiming at increasing the know-how on the performance of candidate window materials and of system components in contact with lead at high temperature and velocity.

An experimental plant able to operate either with lead or lead-bismuth will be designed and constructed. The loop will be shaped like "a figure 8", thus allowing the presence of a hot and a cold leg for corrosion product deposition analyses. Three independent test sections will be constructed for housing different material tests at the same time.

The experimental program includes:

a) Erosion/corrosion and tenso-corrosion tests at high lead temperature (about 600 °C) and velocity (about 4 m3/h) on candidate materials for the beam window ;

b) Mechanical tests on the same materials after extended interaction with flowing lead in relevant thermal-hydraulic conditions (endurance tests);

c) Erosion/Corrosion and mechanical properties degradation studies on structural materials (e.g., martensitic steel);

d) Deposition and distribution of corrosion products between the cold and hot leg of the loop;

e) Development of prevention and protection methods against corrosion, based on superficial coatings and/or inhibitors.