Waste retrieved from the Magnox Swarf Storage Silo (MSSS) at Sellafield is being safely stored in an unencapsulated form for 50-75 years. This has never been done before and it is safety critical that hydrogen generation is measured and managed, especially when the waste first goes into store.

There was no existing technology capable of meeting the requirements of speed of measurement, accuracy, remote access and operations.

In a world first, Wood developed a non-invasive, remote measurement technique to autonomously identify surface bubbles and provide volumetric assessment of hydrogen release rate in a matter of minutes.

The novel system uses machine vision to analyse video of the liquor surface in the skip. A bespoke software program reads camera images and uses light patterns to identify and track bubbles on the surface and to measure their size. The hydrogen release rate is calculated by summing the bubble volumes.

The system accounts for bubbles appearing, disappearing and merging, and will count bubbles on clear or cloudy liquors.

The system has progressed to Technology Readiness Level (TRL) 6 – full-scale inactive demonstration of an integrated system – and is expected to move to TRL 8/9 when it is deployed later this year.

Wood created a fit-for-purpose test rig, which enabled significant schedule and cost savings to be made during development.

The new system ensures that Sellafield Ltd can meet the waste characterisation requirements of the Office for Nuclear Regulation (ONR) in a way which takes only a minimal amount of time and costs very little.

The system has been trialled at full scale and is now being readied for deployment as part of the characterisation capability in two important Sellafield projects: Encapsulated Product Store-Waste Transfer Route and the Box Encapsulation Plant.

Contact
John Maddison, Wood
john.maddison@woodplc.com

Источник: eurosafe-forum 5.2019

Wood’s Regulatory Support Directorate carried out a study into the effect of temperature on the criticality safety of fissile systems for the Office for Nuclear Regulation (ONR), the UK civil nuclear regulator.

Criticality calculations for fissile material transport packages are typically carried out at room temperature.  However, transport packages may encounter a wide range of temperatures, and the IAEA Transport Regulations state that packages shall be designed for ambient temperatures from ‑40°C to +38°C.  Previous work on temperature effects has mainly looked at the high temperatures found in reactors, but this new study also considers temperatures below freezing.

Calculations were carried out using the Monte-Carlo criticality code MONK over a temperature range from 193 ‑ 1073K, (-80^oC – 800^oC) with 273K (0^oC) being calculated for both water and ice.   The interaction of thermal neutrons in water and in ice has been shown to be significantly different, even at similar temperatures. The crystalline structure that forms when water freezes not only leads to a reduction in density but a change to the nature of the interactions between the atomic bonds within a single H₂O molecule and between adjacent molecules. Therefore, the bound thermal scattering data is fundamentally different between water and ice.

The report presents an investigation into the effect of temperature on the reactivity of fissile systems.  An explanation of the important physical phenomena that may result in changes in the reactivity of a fissile system with temperature is provided.  One of the main effects is the Doppler broadening of resonances in the neutron cross sections.

A range of calculations was performed to estimate how a change in temperature influences the neutron multiplication factor, K, in a number of fissile systems.  The range of materials covered in the study included a number of fissile / fissionable species being one or more of U-235, U-238, Pu-239 and Pu-240 combined with different moderator materials (water/ice, polythene or graphite).   The systems were modelled as either an infinite mixture or an infinite array of pin-cells, therefore the measure of neutron multiplication considered in all cases is K_infinity (no leakage of neutrons from the system).

Results are plotted as difference in k against temperature and against moderator-to-fuel ratio.  The example in the graph above is for 5% enriched uranium oxide rods in light water.  The unit cell size was adjusted to give three different water volume to fuel volume ratios V(H₂0) to V(UO₂).

The discontinuity at 273K (0°C) is clear.  For an under-moderated system, reactivity decreases with increasing temperature; for an over-moderated system, reactivity increases with temperature.

The report compares the major criticality codes MONK, MCNP and SCALE-KENO with respect to their current and developing abilities to model the temperature dependence of neutron multiplication. This includes consideration of the limitations of the available nuclear data.

The study concluded that variation of reactivity with temperature is not always intuitive, and those assessing transport safety cases should be aware that for some systems criticality safety margins may be smallest at temperatures below freezing.

A full report on the findings is available on the ONR website here:
http://www.onr.org.uk/documents/2019/onr-rrr-077.pdf

Contact
Steve Power, Wood
steve.power@woodplc.com

Источник: eurosafe-forum 5.2019

When the UK Government published the draft European Union (Withdrawal) Bill on January 26, 2017, it became clear that Brexit would also mean Brexatom. To the surprise of some, the UK signalled its intention to withdraw from the European Atomic Energy Community (Euratom).

This was driven by a desire to leave the jurisdiction of the European Court of Justice and to end the free movement of people, both of which are enshrined in the Euratom treaty.

At the time of writing, the UK and EU’s efforts to reach a negotiated agreement remain frustrated by politics. But the nuclear landscape appears much more settled than anything else on the Brexit horizon.

Andrew Stephenson, minister for nuclear, told the House of Commons in a written statement on May 15, 2019: “Government’s preparations for the UK’s withdrawal from Euratom mean that the UK now has all the necessary measures in place to ensure that the UK nuclear industry can continue to operate with certainty in all situations.”¹

To replace Euratom, the UK government has sought to create alternative arrangements to avoid any lapse in the ability to conduct international nuclear trade if it can no longer rely on Euratom’s nuclear co-operation agreements (NCAs) in a post-Brexit world.

The first task was to take back control of the nuclear safeguarding system, which must demonstrate that civil nuclear materials are not being diverted into military or weapons programmes.

During its membership of Euratom, UK safeguarding measures have been implemented by the European Commission, which also conveys relevant information to the International Atomic Energy Agency in compliance with international standards.

The UK has passed the Nuclear Safeguards Act giving the Office for Nuclear Regulation (ONR) domestic oversight post Brexit. It has also signed two new bilateral agreements on safeguarding with the IAEA, a voluntary offer agreement and an additional protocol.

The legal framework for ONR oversight was codified quickly. Public consultation on the draft Nuclear Safeguards Regulations, which set out the new domestic civil nuclear safeguards regime, closed in September 2018 and the UK Parliament debated and approved the regulations in January 2019.

The ONR met its target for recruiting additional inspectors ahead of the original departure date of 29 March and the delay in reaching a Brexit agreement can only assist in ensuring that the new inspectorate is up and running when Brexatom finally arrives.

The Safeguards Information Management and Reporting System is now running parallel with Euratom to ensure a seamless transition when the time comes and the UK government has committed to meeting in full the set-up costs of the new ONR safeguarding regime.

There is widespread confidence that the new regime will be as thorough and effective as that overseen by Euratom.

The UK’s international nuclear trade will also be protected by newly agreed NCAs with the US, Australia, Canada and Japan which will take effect when the UK leaves the EU and on terms equivalent to the existing Euratom arrangements.

On top of this, the UK government says discussions are going well with Japan on the continuation of a bilateral nuclear trade arrangement which has been in place since 1998.

Despite leaving Euratom, the UK wants to maintain a close association so that mutually successful civil nuclear cooperation is maintained. There are hopes for an enhanced NCA to formalise cooperation between ONR and the European Commission on safeguards, participation in the Euratom Research and Training Programme, contractual arrangements for the supply of nuclear materials, and to minimise trade barriers. Agreement in principle has already been reached on safeguarding mechanisms and the UK’s continued involvement in the Joint European Torus.

If there is no exit deal, the UK still risks losing influence in nuclear cooperation across Europe. And although Britain’s nuclear sector and the Euratom community are equally keen to ensure business as usual, a lot will depend on whether the tangled politics of the withdrawal agreement can be resolved.