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Reçu aujourd’hui — 16 janvier 2026 6.5 📰 Sciences English

India turns to small modular nuclear reactors to meet climate targets

16 janvier 2026 à 13:30

India has been involved in nuclear energy and power for decades, but now the country is  turning to small modular nuclear reactors (SMRs) as part of a new, long-term push towards nuclear and renewable energy. In December 2025, the country’s parliament passed a bill that allows private companies for the first time to participate in India’s nuclear programme, which could see them involved in generating power, operating plants and making equipment.

Some commentators are unconvinced that the move will be enough to help meet India’s climate pledge to achieving 500 GW of non-fossil-fuel based energy generation by 2030, Interestingly, however, India has now joined other nations, such as Russia and China, in taking an interest in SMRs. They could help stem the overall decline in nuclear power, which now accounts for just 9% of electricity generated around the world – down from 17.5% in 1996.

Last year India’s finance minister Nirmala Sitharaman announced a nuclear energy mission funded with 200 billion Indian rupees ($2.2bn) to develop at least five indigenously designed and operational SMRs by 2033. Unlike huge, conventional nuclear plants, such as pressurised heavy-water reactors (PHWRs), most or all components of an SMR are manufactured in factories before being assembled at the reactor site.

SMRs, typically generating less than 300 MW of electrical power but — being modular – additional capacity can be brought on quickly and easily given their lower capital costs, shorter construction times, ability to work with lower-capacity grids and lower carbon emissions. Despite their promise, there are only two fully operating SMRs in the world — both in Russia — although two further high-temperature gas-cooled SMRs are currently being built in China. In June 2025, Rolls-Royce SMR was selected as the preferred bidder by Great British Nuclear to build the UK’s first fleet of SMRs, with plans to provide 470MW of low-carbon electricity.

Cost benefit analysis

An official at the Department of Atomic Energy told Physics World that part of that mix of five new SMRs in India could be 200 MW Bharat Small Modular Reactor, which are based on pressurized water reactor technology and use slightly enriched uranium as a fuel. Other options are 55 MW Small Modular Reactor and the Indian government also plans to partner with the private sector to deploy 220 MW Bharat Small Reactors.

Despite such moves, some are unconvinced that small nuclear reactors could help India scale its nuclear ambitions. “SMRs are still to demonstrate that they can supply electricity at scale,” says Karthik Ganesan, a fellow and director of partnerships at the Council on Energy, Environment and Water (CEEW), a non-profit policy research think-tank based in New Delhi. “SMRs are a great option for captive consumption, where large investment that will take time to start generating is at a premium.”

Ganesan, however, says it is too early to comment on the commercial viability of SMRs as cost reductions from SMRs depend on how much of the technology is produced in a factory and in what quantities. “We are yet to get to that point and any test reactors deployed would certainly not be the ones to benchmark their long-term competitiveness,” he says. “[But] even at a higher tariff, SMRs will still have a use case for industrial consumers who want certainty in long-term tariffs and reliable continuous supply in a world where carbon dioxide emissions will be much smaller than what we see from the power sector today.”

M V Ramana from the University of British Columbia, Vancouver, who works in international security and energy supply, is concerned over the cost efficiency of SMRs compared to their traditional counterparts. “Larger reactors are cheaper on a per-megawatt basis because their material and work requirements do not scale linearly with power capacity,” says Ramana.  This, according to Ramana, means that the electricity SMRs produce will be more expensive than nuclear energy from large reactors, which are already far more expensive than renewables such as solar and wind energy.

Clean or unclean?

Even if SMRs take over from PHWRs, there is still the question of what do with its nuclear waste. As Ramana points out, all activities linked to the nuclear fuel chain – from mining uranium to dealing with the radioactive wastes produced – have significant health and environmental impacts. “The nuclear fuel chain is polluting, albeit in a different way from that of fossil fuels,” he says, adding that those pollutants remain hazardous for hundreds of thousands of years. “There is no demonstrated solution to managing these radioactive wastes—nor can there be, given the challenge of trying to ensure that these materials do not come into contact with living beings,” says Ramana.

Ganesan, however, thinks that nuclear energy is still clean as it produces electricity with much a lower environmental footprint especially when it comes to so-called “criteria pollutants”: ozone; particulate matter; carbon monoxide; lead; sulphur dioxide; and nitrogen dioxide.  While nuclear waste still needs to be managed, Ganesan says the associated costs are already included in the price of setting up a reactor. “In due course, with technological development, the burn up will significantly higher and waste generated a lot lesser.”

The post India turns to small modular nuclear reactors to meet climate targets appeared first on Physics World.

Gravitational lensing sheds new light on Hubble constant controversy

16 janvier 2026 à 11:00

By studying how light from eight distant quasars is gravitationally lensed as it propagates towards Earth, astronomers have calculated a new value for the Hubble constant – a parameter that describes the rate at which the universe is expanding. The result agrees more closely with previous “late-universe” probes of this constant than it does with calculations based on observations of the cosmic microwave background (CMB) in the early universe, strengthening the notion that we may be misunderstanding something fundamental about how the universe works.

The universe has been expanding ever since the Big Bang nearly 14 billion years ago. We know this, in part, because of observations made in the 1920s by the American astronomer Edwin Hubble. By measuring the redshift of various galaxies, Hubble discovered that galaxies further away from Earth are moving away faster than galaxies that are closer to us. The relationship between this speed and the galaxies’ distance is known as the Hubble constant, H0.

Astronomers have developed several techniques for measuring H0. The problem is that different techniques deliver different values. According to measurements made by the European Space Agency’s Planck satellite of CMB radiation “left over” from the Big Bang, the value of H0 is about 67 kilometres per second per megaparsec (km/s/Mpc), where one Mpc is 3.3 million light years. In contrast, “distance-ladder” measurements such as those made by the SH0ES collaboration those involving observations of type Ia supernovae yield a value of about 73 km/s/Mpc. This discrepancy is known as the Hubble tension.

Time-delay cosmography

In the latest work, the TDCOSMO collaboration, which includes astronomers Kenneth Wong and Eric Paic of the University of Tokyo, Japan, measured H0 using a technique called time-delay cosmography. This well-established method dates back to 1964 and uses the fact that massive galaxies can act as lenses, deflecting the light from objects behind them so that from our perspective, these objects appear distorted.

“This is called gravitational lensing, and if the circumstances are right, we’ll actually see multiple distorted images, each of which will have taken a slightly different pathway to get to us, taking different amounts of time,” Wong explains.

By looking for changes in these images that are identical, but slightly out of sync, astronomers can measure the time differences required for the light from the objects to reach Earth. Then, by combining these data with estimates of the distribution of the mass of the distorting galactic lens, they can calculate H0.

A real tension, not a measurement artefact

Wong and colleagues measured the light from eight strongly lensed quasars using various telescopes, including the James Webb Space Telescope (JWST), the Keck Telescopes and the Very Large Telescope (VLT). They also made use of observations from the Sloan Lens ACS (SLACS) sample with Keck and the Legacy Survey (SL2S) sample.

Based on these measurements, they obtained a H0 value of roughly 71.6 km s−1 Mpc−1, which is more consistent with current-day observations (such as that from SH0ES) than early-universe ones (such as that from Planck). Wong explains that this discrepancy supports the idea that the Hubble tension arises from real physics, not just some unknown error in the various methods. “Our measurement is completely independent of other methods, both early- and late-universe, so if there are any systematic uncertainties in those, we should not be affected by them,” he says.

The astronomers say that the SLACS and SL2S sample data are in excellent agreement with the new TDCOSMO-2025 sample, while the new measurements improve the precision of H0 to 4.6%. However, Paic notes that nailing down the value of H0 to a level that would “definitely confirm” the Hubble tension will require a precision of 1-2%. “This could be possible by increasing the number of objects observed as well as ruling out any systematic errors as yet unaccounted for,” he says.

Wong adds that while the TDCOSMO-2025 dataset contains its own uncertainties, multiple independent measurements should, in principle, strengthen the result. “One of the largest sources of uncertainty is the fact that we don’t know exactly how the mass in the lens galaxies is distributed,” he explains. “It is usually assumed that the mass follows some simple profile that is consistent with observations, but it is hard to be sure and this uncertainty can directly influence the values we calculate.”

The biggest hurdle, Wang adds, will “probably be addressing potential sources of systematic uncertainty, making sure we have thought of all the possible ways that our result could be wrong or biased and figuring out how to handle those uncertainties.”

The study is detailed in Astronomy and Astrophysics.

The post Gravitational lensing sheds new light on Hubble constant controversy appeared first on Physics World.

Reçu hier — 15 janvier 2026 6.5 📰 Sciences English
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