A centre for Advanced Digital Radiometric Instrumentation for Applied Nuclear Activities (ADRIANA)

Facilities associated with nuclear activities, such as reactors, radioactive substances, wastes and processing systems can often be characterised by the radiation that they emit as a result of the processes going on with them, or residual contamination. This characterisation is very important because it is often impossible to enter such facilities due to the risk to health and, conversely, without characterising them we often do not know the extent of the risk either. Fortunately, because two of the most common forms of radiation - neutrons and gamma rays - are very penetrating, it is usually possible to carry out the necessary measurements without needing to intrude on the facilities under assessment. Indeed, a great deal can be learnt from non-intrusive, non-destructive assessments of these radiation fields.

Until recently, the accepted techniques for assessing gamma-ray and neutron environments were still based on technologies developed at the dawn of the nuclear industry, in the 1950s, 1960s and 1970s. Whilst adequate, these techniques were wholly analogue and as a result only a small proportion of the feasible assessments developed in the laboratory could be transported to industrial environments because extensive setting-up and configuration is needed, and they are not directly compatible with computer systems. Over the last 10 years, work at Lancaster and Liverpool Universities has focussed on digitizing these techniques, which is not easy because the speed with which the radiations interact with detecting systems is extremely fast, and often too fast for current electronic processing systems. The success of this research has enabled environments to be characterized in real-time and without the need for extensive set-up procedures that was the case for analogue apparatus, and in particular has resulted in a number new ways to image nuclear environments in terms of the radiation they emit. Of particular interest to this proposal is that it has become feasible to multiplex a much wider range of detector systems than was previously the case, with many new assay techniques being postulated if these larger, more sophisticated detector systems can be constructed for industrial applications.

Because such detector systems are expensive, there are few if any of a suitable type available in the world despite the potential they hold for analysis in power production, decommissioning, cancer therapy and metrology. In this proposal we intend to construct several of these systems - a gamma-ray spectroscopy system, a neutron imaging system and a gamma-ray imaging system - to establish a cutting-edge group of facilities that can be used by researchers in the UK with an interest in these techniques. This will allow the benefits of digital radiation assay to be brought to bear on a wide range of applications without the need for every researcher to try to fund the expensive equipment necessary, and will be an efficient basis on which to continue Britain's lead in this important area.

Operational requirements in new nuclear build: This proposal is made at a critical time associated with significant investment in nuclear energy facilities in the UK at Hinkley Point, the most significant development for 20 years, when specific apparatus is being selected and at a time of worldwide interest from the nuclear instrumentation community as to the systems that might benefit this renaissance. The impact of the research is likely to be in the influence over the design of next-generation field instrumentation, radiation protection measures and the way in which nuclear environments are characterised and assessed, and perhaps most critically with regard to plans & related policies.

Security & safeguards: The industrial nuclear sector associated with security & safeguards is an important area of potential impact for this investment. For example, the isotope 240Pu (a ubiquitous component of plutonium material by which total plutonium content can be assessed) emits fast neutrons as a result of spontaneous fission. These can be used to assess the quantity of plutonium present. This is particularly useful in nuclear safeguards to prevent the illicit diversion of direct-use nuclear material from nuclear process streams. It is also relevant in nuclear security to detect the illicit transport of nuclear materials.

3He replacement: The assay of mixed field environments is often reliant on the use of 3He gas, due to its large neutron capture cross-section, long-term stability and excellent gamma-ray rejection characteristics. Due to the limited production of this gas there is now a world shortage of 3He. At ~$2000 per litre, it is estimated that to resource just safeguards would cost ~ $12m at current rates, with all stock exhausted in 5 years . Alternatives to 3He, such as boron trifluoride (10BF3), are too hazardous for use and transport in many industrial environments. Other replacement possibilities are too far off in research terms to make a significant impact on this important area in the timescale. Fast scintillators, processed digitally, are the only option to meet this medium-term requirement for neutron detection. This investment has significant potential to make a profound impact in this area: for example, enriched uranium content is often assayed via neutron interrogation with 3He which is highly compatible for replacement with fast scintillators whilst the assay of plutonium material in spent fuel streams could be readily investigated with digital fast scintillators. This is highly complementary to the gamma-ray imaging capability established under this project.

Nuclear safety & post-accident recovery: There are a variety of other environments, such as those associated with operating pressurised water reactors for power and propulsion, where advanced, digital radiation characterisation instrumentation has a significiant role to play, particularly for imaging. We also envisage significant impact could accrue from the outputs of our research in nuclear safety and in post-accident assessment of the integrity of the pressure vessels of stricken reactors, particularly given its merits of stand-off, non-intrusiveness and real-time discrimination of neutron- and gamma-emitting materials.

Coincidence-based assay: this has been used for many years in both neutron and gamma-ray assay but not real-time or in-situ. Where these systems can be installed they have the potential to impact power operations and post-use, post-accident. Tthe distinction between a true coincidence of two fission neutrons emitted by the same nucleus, and the many alternative scenarios, such as a neutron arising from an (alpha, n) reaction, is made on statistical grounds and can be significantly improved upon with digital systems.