Comparison of material irradiation conditions for fusion, spallation, stripping and fission neutron sources

Abstract

Selection and development of materials capable of sustaining irradiation conditions expected for a future fusion power reactor remain a big challenge for material scientists. Design of other nuclear facilities either in support of the fusion materials testing program or for other scientific purposes presents a similar problem of irradiation resistant material development. The present study is devoted to an evaluation of the irradiation conditions for IFMIF, ESS, XADS, DEMO and typical fission reactors to provide a basis for comparison of the data obtained for different material investigation programs. The results obtained confirm that no facility, except IFMIF, could fit all user requirements imposed for a facility for simulation of the fusion irradiation conditions.

Introduction

During the last few decades, significant efforts were spent on the design of a number of novel nuclear facilities. The major role among them belongs to the fusion prototype reactors ITER and DEMO aimed at demonstrating the technical feasibility of electrical power production by means of the (d,t) fusion reaction. On the other hand, several accelerator-based facilities have been designed either in support of the fusion material development program (IFMIF) or for other scientific purpose (ESS, XADS).

In the present work, several nuclear facilities are compared with respect to materials irradiation conditions. Different types of facilities have been considered: the intense stripping neutron source IFMIF, spallation sources ESS and XADS, fusion prototype reactor DEMO and typical fission reactors HFR and BOR60.

While the purposes of the facilities considered in this work are quite different, there is a common problem of development and testing of the structural materials capable of sustaining hard operating conditions. Assessment of the irradiation conditions for nuclear facilities is required by designers and material scientists to make an optimum and safe choice of the structural materials.

The Future Demonstration Power Reactor, DEMO [11], is a magnetically confined fusion prototype reactor with a power of 2–4 GW and an expected wall loading of the order of 2–3 MW/m². The first inner wall of the facility is exposed to high neutron flux, resulting in about 30 dpa per full-power year of operation. In this work material responses were calculated at the position of the maximum neutron irradiation wall load on the central outward segment of the DEMO Helium-Cooled Pebble Bed Blanket.

The International Fusion Materials Irradiation Facility, IFMIF [3], is the accelerator based deuterium–lithium (d–Li) stripping neutron source for production of high-energy neutrons at sufficient intensity to test samples of the fusion candidate materials up to about the full lifetime of anticipated use in fusion energy reactors. Two deuteron beams (40 MeV, 2 × 125 mA) are striking a common liquid lithium target and produce high-energy neutrons with a peak around 14–16 MeV permitting irradiation of material samples with a damage rate higher than 20 dpa/fpy in 0.5 l volume.

The description of the geometry model and the details of neutronics analysis for IFMIF high and medium flux test modules (HF & MFTM) can be found elsewhere [1], [2], [3].

The European Spallation Source, ESS, is a spallation neutron source driven by a proton linear accelerator (LINAC) with a beam energy of 1.33 GeV and a beam power of 10 MW [4]. It features two target stations, both equipped with a liquid mercury target and operating with 5 MW beam power. The short pulse target station is fed with proton pulses compressed by a factor of 800 to 1.4 μs duration in a double compressor ring (repetition rate 50 Hz). The long pulse target is fed directly with protons from the LINAC (proton pulse length 2.0 ms, repetition rate 16.6 Hz). Since it was suggested [5] to use spallation sources for fusion materials testing to bridge the time until the IFMIF source is available, a related feasibility study has been performed [6]. As a result, for material irradiation in the ESS a useful `high flux' volume of about 0.83 l at the out-of-target reflector position of the short pulse target station has been identified [7]. The geometry model description and neutronics analysis of the ESS can be found elsewhere [6].

The Experimental Accelerator Driven System, XADS, is aimed at reduction of radiotoxicity of a spent nuclear fuel by means of their incineration in accelerator driven systems. The ADS reactor for nuclear waste transmutation is a sub-critical reactor and requires an external neutron source for maintaining a fission chain reaction. Neutrons are initially produced via the spallation reaction induced by a high-energy proton beam impacting on a liquid metal target. In the present work we are considering a liquid metal (lead–bismuth eutectic) cooled design variant with a hot beam window. In this design, the beam goes from the top of the reactor through a beam guide ending with a hemispherical beam window. The guide and the window tightly separate the vacuum of the accelerator from the liquid spallation target. Neutrons penetrating through the liquid target reach fuel assembles and induce fission and transmutation of the long-living radioactive isotopes. The hot window is subjected to a very high irradiation load by source protons and spallation neutrons and protons as well as by fission neutrons.

Fission reactors: The High Flux Reactor (HFR) at Petten is a light water moderated and cooled multipurpose materials testing reactor with a thermal power of 45 MW. The BOR-60 facility is a fast, sodium-cooled reactor designed to test fuel elements and structural materials. At present, both reactors are extensively used for the irradiation testing both in the fusion and in the XADS material programs [12].