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The global network of neutron monitors comprises predominantly of the monitor standardised by Carmichael in 1964, the NM-64. The design of these existing monitors and their instrumentation have changed very little over the last sixty years. For example, their neutron detectors rely on gas filled proportional counters that are either filled with highly toxic boron trifluoride (BF3) or helium-3 (3He) in an arrangement not optimised for this detector type. We have designed a new neutron monitor optimised for fully modernised, 1” diameter, gas-filled 3He detectors. Our new design is optimised for cost savings, compactness and efficient use of 3He. Benchmarked against a 6-NM-64, our design has a 71% smaller footprint, 83% smaller volume, and is 55% lighter. It is estimated to be ~50% cheaper, excluding cost reductions associated with the shipping, installation, housing, maintenance and operation of a more compact instrument. It is suited for unattended operation in relatively remote locations and designed to produce comparable results to a 6-counter NM-64 typically used in the existing global network. We provide a progress update and latest validation results relating to the implementation of the new design at the UK Metrological Office’s Camborne observatory near Cornwall. Funded by UK Research & Innovation (UKRI), this research is part of the Space Weather Instrumentation, Measurement, Modelling and Risk (SWIMMR) programme.

The global network of neutron monitors comprises predominantly of the monitor standardised by Carmichael in 1964, the NM-64. The design of these existing monitors and their instrumentation have changed very little over the last sixty years. For example, their neutron detectors rely on gas filled proportional counters that are either filled with highly toxic boron trifluoride (BF3) or helium-3 (3He). Almost the entire global supply of 3He is derived from a waste product of nuclear weapons programmes and, with the termination of such programmes and reducing nuclear weapons stockpile, the supply of 3He has become limited. Consequently, 3He supply became strictly controlled in 2008 and its price has fluctuated since. In some cases, new neutron monitors have reverted to BF3 filled counter tubes when the price of 3He has been at a premium. Helium-3 filled proportional counters are also used extensively in radiation portal monitors deployed for homeland security and non-proliferation; objectives which have increased significantly over the last two decades. The reduced production and increased demand for 3He has led to concerns over its supply and provided the research motivation for alternative neutron detection methods which are viable in terms of sensitivity, stability and gamma-rejection for certain applications. One of these alternative technologies is based on boron-coated straws (BCS) manufactured and supplied by Proportional Technologies, Inc (PTI). The technology is built on a patented low-cost technology that enables long copper tubes, known as ‘straws’, to be coated on the inside with a thin layer of 10B-enriched boron carbide (10B4C). Thermal neutrons captured in the 10B are converted into secondary particles, through the 10B(n, α) reaction. The straws can be of various diameter (circa 4 mm to 15 mm), length (up to 2 m) and shape (round, star or pie) to increase the surface area of 10B. Multiple straws can be packed inside a 1” diameter aluminium tube acting as a single drop-in replacement for traditional 3He detectors or individually distributed directly throughout the moderating medium, thus increasing efficiency by detecting the thermal neutrons at the point that they are created. BCS-based detectors are widely used in systems for homeland security, safeguards and neutron imaging in direct exchange for 3He tubes. This study aims to design a neutron monitor utilising BCS technology that is cheaper, more compact and produces comparable results to the existing network of NM-64 monitors. Monte Carlo simulations using the MCNP radiation transport code to model several BCS-based solutions and an NM-64 computational benchmark are reported. These models are validated experimentally using a standard PTI portal monitor (PTI-110-NDME) to determine its efficiency, dieaway, deadtime and gamma rejection using a combination of bare 252Cf, AmLi and 137Cs sources. The PTI-110-NDME consists of a 12” x 5” x 1 m high density polyethylene (HDPE) slab with thirty ~15-mm diameter straws, 93 cm active length, embedded uniformly throughout the moderator. Funded by UK Research & Innovation (UKRI), this research is part of the Space Weather Instrumentation, Measurement, Modelling and Risk (SWIMMR) programme.

Accurate measurement of the nuclear environment within a test tritium breeding-blanket module of a fusion reactor is crucial to determine tritium production rates which are relevant to self-suffici ...

In preparation for the upcoming deuterium-tritium campaign at the JET tokamak, the ex-vessel fission chamber neutron diagnostics and the neutron activation system will be calibrated in absolute terms at 14 MeV neutron energy, to a required accuracy of less than 10%. Two nominally identical DT neutron generators were chosen as the calibration sources, both of which were fully calibrated and characterized at the UK's National Physical Laboratory. The neutron activation method was adopted as a complementary method for the purpose of determining the absolute value of the neutron yield from the neutron generators and to provide a means of cross check for the active detection methods being employed. The work being presented here shows the derivation of the neutron emission rate from the neutron generators based upon experimental activation foil measurements. © 2017 Elsevier B.V.

Activities under the EURO fusion work package JET3 programme have been established to enable the technological exploitation of the planned JET experiments over the next few years, which culminates in a D-T experimental campaign, DTE-2. In the areas of nuclear technology and nuclear safety the programme offers a unique opportunity to provide experimental data that is relevant to ITER. The key purpose of the collected data will be to support bench marking and validation activities relating to neutronics and activation codes, and associated nuclear data, that are used to predict the nuclear behavior of ITER component and materials, during and after operations. This paper details the status and key issues of the ongoing ACT sub-project under work package JET3, which aims to take advantage of the large 14 MeV neutron fluence expected during JET DTE-2 to irradiate samples of real ITER materials used in the manufacturing of the main in-vessel tokamak components. The materials considered, with specified minor elemental impurity levels, include: Nb3Sn, SS316L steels from a range of manufacturers, SS304B, Alloy 660, W, CuCrZr, OF-Cu, XM-19, Al bronze, NbTi and EUROFER. The activities include provision for measurement of nuclide activities for each material and comparison against the predicted quantities through calculation with the FISPACT-II inventory code. Included here are key pre-analysis results for the selected ITER irradiation samples, and corresponding optimization of dosimetry foils (Ti, Mn, Co, Ni, Y, Fe, Co, Sc, Ta) that will be irradiated at selected positions inside JET irradiation stations in order to determine the neutron spectrum. Preliminary experimental activation results through recent JET D–D operations are discussed.

In the frame of the WPJET3-DT Technology project within the EUROfusion Consortium program, neutronics experiments are in preparation for the future deuterium–tritium campaign on JET (DTE2). The experiments will be conducted with the purpose to validate the neutronics codes and tools used in ITER, thus reducing the related uncertainties and the associated risks in the machine operation. This paper summarizes the status of previous shutdown dose rate benchmarks experiments and analyses performed at JET and focuses on the computational and experimental efforts conducted in preparation of the future DTE2 experiments. In particular, preliminary calculations and studies to select detectors and positions aimed to reduce uncertainties in the shutdown dose rate experiment are presented and discussed.

A novel Shutdown dose rate benchmark experiment has been performed at Joint European Torus (JET) machine during the last high performance Deuterium-Deuterium (DD) campaign in preparation of future ...

In the preparation for the Deuterium-Tritium campaign, JET will operate with a tritium plasma. The T + T reaction consists of two notable channels: (1) T + T -> He-4 + 2n, (2) T + T -> He-5 + ...

This paper details progress in experimental characterisation work at JET for the long-term irradiation station, conducted as part of a project to perform activation experiments using ITER materials. The aim is to take advantage of the significant 14 MeV neutron yield expected during JET operations to irradiate samples of materials that will be used in the manufacturing of ITER tokamak components, such as Nb3Sn, SS316L steels from a range of manufacturers, SS304B, Alloy 660, W, CuCrZr, OF-Cu, XM-19, Al bronze, NbTi and EUROFER. This paper presents an assessment of the nuclear environment at the relevant irradiation locations at JET, measured using a range of high purity dosimetry foils: Ti, Ni, Y, Fe, Co, Sc, and Ta, irradiated with fusion neutrons at JET over a period of 15 months. Experimental results are presented and compared to simulation predictions using a JET MCNP model coupled with the FISPACT-II inventory code. Comparisons are made for a total of 11 nuclear reactions using a range of nuclear data libraries in calculations. © EURATOM 2018.

A calibration of the JET neutron detectors was carried out prior to the upcoming deuterium-tritium experimental campaign. Two Compact DT neutron generators (NGs) were purchased for this purpose from VNIIA, Russia. These generators are capable of producing approximately 2 × 108 neutrons/s with a DT fusion energy spectrum. Preceding the in-vessel calibration measurements, these compact generators were tested and fully characterised at the UK's National Physical Laboratory (NPL). In order to support the characterisation measurements, detailed neutronics models were developed of the NGs, monitoring detectors and remote handling (RH) apparatus. Neutron spectra calculated from these models have been used to help determine NPL long counter efficiencies and effective centres, as well as NPL reference iron and aluminium activation foil reaction rates. The neutron emission rate has been measured for both generators as a function of angle using absolutely calibrated long counters and the relative emission rate by monitoring single crystal diamond detectors. The measured anisotropy profile is shown to be reproducible with a detailed NG MCNP model. Consequently, the neutron source routine and the MCNP model of the NGs can be reliably used for the analysis of the in-vessel calibration at JET.

At the Joint European Torus (JET) the ex-vessel fission chambers and in-vessel activation detectors are used as the neutron production rate and neutron yield monitors respectively. In order to ensure that these detectors produce accurate measurements they need to be experimentally calibrated. A new calibration of neutron detectors to 14 MeV neutrons, resulting from deuterium–tritium (DT) plasmas, is planned at JET using a compact accelerator based neutron generator (NG) in which a D/T beam impinges on a solid target containing T/D, producing neutrons by DT fusion reactions. This paper presents the analysis that was performed to model the neutron source characteristics in terms of energy spectrum, angle–energy distribution and the effect of the neutron generator geometry. Different codes capable of simulating the accelerator based DT neutron sources are compared and sensitivities to uncertainties in the generator's internal structure analysed. The analysis was performed to support preparation to the experimental measurements performed to characterize the NG as a calibration source. Further extensive neutronics analyses, performed with this model of the NG, will be needed to support the neutron calibration experiments and take into account various differences between the calibration experiment and experiments using the plasma as a source of neutrons.