Measuring neutrons to reduce nuclear waste
Credit: ©2024 NASA'S GODDARD SPACE FLIGHT CENTER/CI LAB
DETECTIONS OF GRAVITATIONAL WAVES FROM MERGING NEUTRON STARS TIPPED OFF RESEARCHERS HERE ON EARTH THAT IT SHOULD BE POSSIBLE TO PREDICT HOW NEUTRONS INTERACT WITH ATOMIC NUCLEI.
Newswise — Nuclear power is considered one of the ways to reduce dependence on fossil fuels, but how to deal with nuclear waste products is among the issues surrounding it. Radioactive waste products can be turned into more stable elements, but this process is not yet viable at scale. New research led by physicists from the University of Tokyo reveals a method to more accurately measure, predict and model a key part of the process to make nuclear waste more stable. This could lead to improved nuclear waste treatment facilities and also to new theories about how some heavier elements in the universe came to be.
The very word “nuclear” can be a bit of a trigger for some people, understandably so in Japan, where the atomic bomb and Fukushima disaster are some of the pivotal moments in its modern history. Yet, given the relative scarcity of suitable space in Japan for renewable forms of energy like solar or wind, nuclear power is considered to be a critical part of the effort to decarbonize the energy sector. Because of this, researchers are hard at work trying to improve safety, efficiency and other matters relating to nuclear power. Associate Professor Nobuaki Imai from the Center for Nuclear Study at the University of Tokyo and his colleagues think they can contribute to improving a key aspect of nuclear power, the processing of waste.
“Broadly speaking, nuclear power works by boiling water using self-sustaining nuclear decay reactions. Unstable elements break apart and decay, releasing heat, which boils water, driving turbines. But this process eventually leaves behind unusable waste that is still radioactive,” said Imai. “This waste can remain radioactive for hundreds of thousands of years, so it is usually buried deep underground. But there is a growing desire to explore another way, a way in which unstable radioactive waste can be made more stable, avoiding its radioactive decay and rendering it far safer to deal with. It’s called transmutation.”
Transmutation is like the opposite of nuclear decay; instead of an element breaking apart and releasing radiation, a neutron can be added to an unstable element changing it into a slightly heavier version of itself. Depending on the initial substance, this new form can be stable enough to be considered safe. The problem is, though this process has been generally known for some time, it has been impossible to quantify sufficiently accurately to carry the idea on to the next stage and ideally produce prototype new-generation waste management facilities.
“The idea actually came from a surprising source: colliding stars, specifically neutron stars,” said Imai. “Following recent observations of gravitational waves emanating from neutron star mergers, researchers have been able to better understand the ways neutrons interact and their ability to modify other elements. Based on this, we used a range of instruments to narrow our focus on how the element selenium, a common nuclear waste product, behaves when bombarded by neutrons. Our technique allows us to predict how materials absorb neutrons and undergo transmutation. This knowledge can contribute to designs for nuclear waste transmutation facilities.”
It's difficult for researchers to make these kinds of observations; in fact, they are not able to directly observe acts of transmutation. Rather, the team can observe how much of a sample does not transmute, and by taking readings to know that transmutation did in fact take place, they can estimate, albeit very accurately, how much of the sample did transmute.
“We are confident that our measurements accurately reflect the real rate of transmutation of unstable selenium into a more stable form,” said Imai. “We are now planning to measure this for other nuclear waste products. Hopefully, this knowledge will combine with other areas required to realize nuclear waste treatment facilities, and we might see these in the coming decades. Though our aims are to improve nuclear safety, I find it interesting that there is a bidirectional relationship between this research and astrophysics. We were inspired by colliding neutron stars, and our research can impact how astrophysicists look for signs of nuclear synthesis, the creation of elements in stars, to better understand how elements heavier than iron were made, including those essential for life.”
Waste issues need consideration in SMR deployment, says CoRWM
14 February 2024
Waste management issues need to have a significantly greater prominence in the process of developing and deploying small modular reactor and advanced modular reactor designs, according to the UK's Committee on Radioactive Waste Management (CoRWM).
The six contenders in the UK SMR contest (Image: Composite of each firm's visuals)"There is considerable impetus for the development of small modular reactor (SMR) and advanced modular reactor (AMR) designs and their commercial deployment, both for energy security and for environmental reasons, particularly given the historic difficulties of deploying reactors at gigawatt scale," CoRWM notes in a new position paper.
However, it says the issue of managing the used fuel and radioactive waste from these new reactors "appears, with some exceptions ... to have been largely ignored or at least downplayed up to now". It adds that the issue "must be considered when selecting technologies for investment, further development, construction and operation".
The paper says: "This must involve addressing the uncertainties about such management at an early stage, to avoid costly mistakes which have been made in the past, by designing reactors without sufficient consideration of how spent fuel and wastes would be managed, and also to provide financial certainty for investors regarding lifetime costs of operation and decommissioning."
CoRWM says it is essential to know: the nature and composition of the waste and, in particular, of the used fuel; its likely heat generation and activity levels; how it could feasibly be packaged and its volume; and when it is likely to arise.
"So far there is little published material from the promoters and developers of new reactor types to demonstrate that they are devoting the necessary level of attention to the waste prospectively arising from SMR/AMRs," it notes.
The position paper provides recommendations to the UK government, Great British Nuclear (GBN), and Nuclear Waste Services and regulators to consider as SMR and AMR deployment is progressed.
"There are many questions to be answered concerning the radioactive waste and spent fuel management aspects of the design and operation of SMRs and AMRs," CoRWM says. "This paper begins the process of raising them, with the caveat that our knowledge of the reactor designs and their fuel requirements is relatively immature compared with large GW reactors."
CoRWM says there are various mechanisms by which these questions could be addressed in the process of obtaining approval for the new reactors. These are principally: the process of justification, which will be mandatory for all new reactor types; Generic Design Assessment which is optional and non-statutory; nuclear site licensing; and environmental permitting.
"The last two stages of control may in some cases come too late in the process to allow for effective optimisation of designs and the selection of materials that reduce waste," CoRWM says. "It remains to be seen how effective these mechanisms will be and whether they will occur sufficiently early in the decision-making process to ensure that radioactive waste management is fully and responsibly addressed."
CoRWM was established in 2003 as a non-statutory advisory committee and is classed as a non-departmental public body. Its purpose is to provide independent advice to the UK government, and the devolved administrations based on scrutiny of the available evidence on the long-term management of radioactive waste, arising from civil and, where relevant, defence nuclear programmes, including storage and disposal.
The UK government has plans to expand nuclear energy capacity to 24 GW by 2050, with a fleet of SMRs a key part of that strategy. Last year, the government and the new GBN arms-length body set up to help deliver that extra capacity began the selection process for which SMR technology to use. In October, EDF, GE Hitachi Nuclear Energy, Holtec, NuScale Power, Rolls Royce SMR and Westinghouse were invited to bid for UK government contracts in the next stage of the process.
Researched and written by World Nuclear News
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