Cooling without pumps: New measurement data for modular reactors

Paul Scherrer Institute

Facebook

XLinkedInWeChatBlueskyMessageWhatsAppEmail

 

image: 

Yago Rivera Durán from the PSI Center for Nuclear Engineering and Sciences has investigated passive cooling systems for small modular reactors. The experiments provide important insights for the development of future generations of reactors.

view more 

Credit: © Paul Scherrer Institute PSI/Markus Fischer

Small modular reactors are compact nuclear power plants with an electrical capacity of up to 300 megawatts. These are significantly smaller than current plants, which have a capacity of around 1,000 megawatts and more. They can be mass-produced and are considered promising for flexible deployment scenarios. A key feature of many of these reactors is their safety concept: Instead of relying on active systems that require external energy, they use passive cooling. Physical effects such as condensation, gravity, and density differences can keep the reactor safe in an emergency.

Up to now, however, the simulation of such complex cooling processes has required experimental data that have so far been limited. A new study at the Paul Scherrer Institute PSI now provides important contributions to help close this gap. At PSI’s PANDA test facility, researchers have for the first time investigated passive cooling systems for small modular reactors under realistic conditions. The experiments, carried out with scientific support from cooperation partners in more than ten countries, provide high-resolution measurement data that can be used to validate such systems in simulations. The results have been published in the journal Nuclear Engineering and Design.

Cooling steam through natural heat exchange

The experiment at PSI addressed a central question in the design of nuclear power plants: What happens if, in an accident, steam is released from the reactor into the power plant’s outer containment structure? This steam has to be cooled, or it will increase pressure on the containment structure. In conventional reactors, active safety measures such as water spray systems, which require pumps and valves, handle these tasks. They dissipate heat and keep the pressure in the containment vessel under control. However, these systems depend on a reliable power supply. If that fails, their function can be impaired. Therefore, researchers are increasingly looking into passive means of cooling steam. 

To further that line of research a project team with Yago Rivera Durán from the PSI Center for Nuclear Engineering and Sciences, tested a closed cooling circuit. This consists of a vertical pipe, approximately six metres high, through which cold water flows. If steam were to escape into the containment vessel during an incident, it would strike the cold surface of the pipe, condense there, and drip back into the reactor as liquid water.

The heat released in this process is transferred to the water inside the pipe. Because warm water is less dense than cold water, it naturally rises and releases its heat to a water reservoir. The cooled water then flows back down. This creates a natural cycle based solely on the density difference between warmer and colder water – entirely without pumps or electricity.

Previous experiments had already shown that such systems work. The PSI team has now gone a step farther and presented, for the first time, highly detailed measurement data showing precisely how the physical processes inside a system on the scale of a nuclear power plant would unfold. Using high-speed cameras, the researchers even documented in detail tiny droplets of water that condense on the surface of the pipe.

 For the first time, the researchers were able to observe how gases inside the containment vessel separate: More air collects in the lower section, while more steam remains at the top. This finding is important for both reactor design and computer simulations. If this effect were not taken into account, the system would be less effective at dissipating heat.

Furthermore, the researchers tracked tiny particles in the gas and demonstrated that it moves very slowly near the pipe. In this area, therefore, condensation is determined not by larger currents, but primarily by diffusion: The water vapour reaches the surface of the pipe only slowly and condenses there. This means that the cooling process is highly dependent on local conditions.

PANDA – no “real” reactor, but realistic data

The experiments were carried out at the globally unique PANDA research facility. PANDA, a German acronym, stands for “passive residual heat removal and pressure relief.” The test facility extends over five floors, reaching a height of 25 metres. It consists of several containers, with a total volume of roughly 500 cubic metres, in which processes that occur in nuclear reactors can be realistically simulated.

PANDA contains no radioactive material. The steam, which reaches temperatures of up to 200 degrees Celsius and pressures as high as 10 bar, is generated by an electric heater with a power output of 1.5 megawatts. At more than 80 different points, gas mixtures from different areas of the facility can be extracted and analysed with a mass spectrometer.

PANDA’s forte is its flexibility. For small modular reactors, several dozen design concepts are currently under discussion. Many of them can be replicated in this experimental facility. There are roughly 1,450 sensors ready to provide valuable data. “Until now, researchers developing simulations couldn’t be certain that their calculations matched reality,” says Yago Rivera Durán. “We're closing the gap with PANDA.” This will make data crucial for safety assessments and the licencing of future reactors available for the first time.

Fully booked into the 2030s

Because PANDA is unique, it has drawn together research institutes, universities, and regulatory authorities from ten countries around the world. Currently, national projects are under way with Swissnuclear, the association of Swiss nuclear power plant operators, along with projects for the European Union and international collaborations with partners from Europe, America, and Asia.

The latest publication marks the launch of an international benchmarking initiative based on PANDA data. Twenty-five institutions are already participating in this global collaboration, using the experimental results to verify and improve their simulation methods. A follow-up project, PANDA-2, will build on this work and focus even more intensely on complex scenarios as well as the long-term autonomous operation of passive safety systems. This international project is currently expected to run until 2030, while national and EU projects are already planned well into the 2030s.

Text: Bernd Müller

  

Eighty valves enable the analysis of different gas mixtures: In the PANDA test facility at PSI, passive cooling systems for small modular reactors are being investigated under realistic conditions. This globally unique facility allows researchers to simulate processes as if in a real reactor – entirely without radioactivity.

Credit

© Paul Scherrer Institute PSI/Markus Fischer

About PSI

The Paul Scherrer Institute PSI develops, builds and operates large, complex research facilities and makes them available to the national and international research community. The institute's own key research priorities are in the fields of future technologies, energy and climate, health innovation and fundamentals of nature. PSI is committed to the training of future generations. Therefore about one quarter of our staff are post-docs, post-graduates or apprentices. Altogether PSI employs 2300 people, thus being the largest research institute in Switzerland. The annual budget amounts to approximately CHF 450 million. PSI is part of the ETH Domain, with the other members being the two Swiss Federal Institutes of Technology, ETH Zurich and EPFL Lausanne, as well as Eawag (Swiss Federal Institute of Aquatic Science and Technology), Empa (Swiss Federal Laboratories for Materials Science and Technology) and WSL (Swiss Federal Institute for Forest, Snow and Landscape Research).

---

Journal

Nuclear Engineering and Design

DOI

10.1016/j.nucengdes.2026.114919 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Publication Date

7-May-2026

 

Seasonal COVID-19 vaccination in 2025/26 reduced risk of illness by half in Canada

Vaccine protection especially meaningful for people with a high risk of severe COVID-19

European Centre for Disease Prevention and Control (ECDC)

Facebook

XLinkedInWeChatBlueskyMessageWhatsAppEmail

An interim analysis published on Eurosurveillance estimates that the COVID-19 vaccine for the 2025/26 season reduced the risk of illness in Canada by about half at about 9 weeks after vaccination, offering protection beyond the vaccine’s target strain.

Seasonal COVID-19 vaccination is recommended in Canada as in several other countries for people older than 6 months with an increased risk of severe illness from the infection, and for all adults aged 65 or older. In the 2025/26 respiratory virus season, the vaccine was updated to target the LP.8.1 strain as recommended by the World Health Organization (WHO), but other strains were also circulating during that period.

Estimating vaccine effectiveness during a challenging respiratory season

The research was conducted through the Canadian Sentinel Practitioner Surveillance Network, which sought to perform an early estimate of COVID-19 vaccine effectiveness for the 2025/26 season and to explore the effect that influenza and other respiratory infections might have on these estimates.

Skowronski et al. analysed data from respiratory samples collected from 5,400 patients aged 12 years and older who presented with acute respiratory illness between October 2025 and March 2026 in three Canadian provinces. The COVID-19 vaccination status for patients was extracted from provincial registries, and the samples were tested for COVID-19 and other respiratory illnesses.

The authors assessed vaccine effectiveness with a test-negative study design. They compared vaccination rates among patients seeking care for respiratory symptoms who had laboratory-confirmed COVID-19, with the rates of patients who also sought care but  tested negative and served as controls. This comprised a total of 310 COVID-19 cases and 3,492 controls.

To determine the SARS-CoV-2 variants involved in infections, whole genome sequencing of the virus was performed for 76% of COVID-19 patients. To judge the possible effect of influenza and other respiratory virus infections, vaccine effectiveness was also estimated by excluding these infections from findings for COVID-19 cases and/or controls, in light of a particularly intense influenza season.

Vaccine especially beneficial for older adults

The study found that the vaccine was most beneficial for the groups it targets. The vaccine was shown to be 48% effective (95% confidence interval: 21─66) at a median of 9 weeks after vaccination. Vaccine effectiveness was estimated to be slightly higher for those aged 65 years or older compared to those between 12 and 64, but with overlapping confidence intervals: 53% (95% confidence interval: 21─73) vs 44% (95% confidence interval: 12─72).

Genetic analysis also found that the 2025/2026 vaccine provided protection against virus variants that circulated beyond the vaccine’s target LP.8.1 lineage, including among older patients.

Excluding influenza infections from controls had little effect on effectiveness estimates among people aged 65 or older, but incremental exclusion of other respiratory infections increased vaccine effectiveness estimates among patients aged between 12 and 64. The authors suggest routinely testing for other respiratory illnesses in COVID-19 vaccine effectiveness studies, to help address the possible role of co-infections or other vaccine-preventable infections in the under-estimation of the protection offered by immunisation.

---

Journal

Eurosurveillance

DOI

10.2807/1560-7917.ES.2026.31.18.2600331 

Method of Research

Data/statistical analysis

Subject of Research

People

Article Title

Interim 2025/26 LP.8.1 vaccine effectiveness estimates against COVID-19 from the Canadian Sentinel Practitioner Surveillance Network (SPSN): insights into possible impact of influenza and other respiratory virus co-circulation

Article Publication Date

7-May-2026

COI Statement

DMS is Principal Investigator on grants received to her institution from the Public Health Agency of Canada, Canadian Institutes of Health Research, and Pacific Public Health Foundation in support of this work. She has also received grants from the Canadian Institutes of Health Research and the Michael Smith Foundation for Health Research for unrelated work, also paid to her institution. SC reports funding from the Public Health Agency of Canada paid to her institution, but not pertaining to the current study. Other authors have no conflicts of interest to declare.

 

Understanding Japan’s complex religious landscape

Researchers analyze how Japanese people describe their religious identity, what they believe in, and how they practice

Doshisha University

LinkedInWeChatBlueskyMessageWhatsAppEmail

 

image: 

A recent study explores the plural, layered, and culturally rooted aspects of religion in Japan. This graphical representation shows the population distribution of Japanese people across different religious and nonreligious domains.

view more 

Credit: Assistant Professor Koki Shimizu from Doshisha University, Japan, https://doi.org/10.1111/jssr.70065

On New Year’s Day, millions of people in Japan visit Shinto shrines to pray for good fortune. In summer, many return to their hometowns to honor ancestors in Buddhist rituals. Families often maintain household altars, and seasonal festivals remain a central part of community life. Though this may look like a religious practice, many of them may identify themselves as nonreligious. This apparent contradiction reflects Japan’s unique religious history, shaped by centuries of blending between Buddhism, Shinto, and folk traditions. Moreover, the term “shūkyō” (often translated as “religion”) tends to evoke organized and exclusive institutions, something many people do not associate with their everyday practices.

This disconnect creates a problem when trying to measure religiosity in Japan. Social scientists have long relied on survey questions built around the assumption that being religious means having a clear affiliation, holding defined beliefs, and regularly practicing. These categories work reasonably well in societies shaped by Western Christianity, but they fit Japan poorly. Although qualitative research has already shown that many Japanese people engage in rituals without thinking of themselves as religious, no study had measured this gap rigorously at the national level, looking at identity, belief, and ritual practice all at once.

To this end, a research team comprising Assistant Professor Koki Shimizu from the Department of Sociology, Doshisha University, and Professor Yoshihide Sakurai from Hokkaido University, Japan, set out to address this gap. Their study, published online in the Journal for the Scientific Study of Religion on April 12, 2026, carefully analyzes data from a nationally representative survey conducted in Japan in 2024. The project is part of the broader Global East Survey of Religion and Spirituality, an international project led by Professor Fenggang Yang of Purdue University, USA, to better understand forms of religiosity that do not fit conventional Western frameworks.

The researchers analyzed responses from more than 4,000 participants, examining three dimensions simultaneously: how people identify themselves religiously, what rituals they took part in, and what they believe about concepts such as gods or the afterlife. Participants could select multiple religious identities, and questions were carefully worded to avoid assumption that belief, affiliation, and practice must align.

Overall, the findings revealed a complex and layered picture. Over 40% of respondents described themselves as nonreligious or atheist. At the same time, a large portion of these individuals reported participating in rituals, such as shrine visits or ancestral rites. Even among those with no religious identity, participation rates for such activities remained high. The researchers also noted that people commonly identify with more than one tradition, such as both Buddhism and Shinto, without perceiving any contradiction.

Respondents’ personal beliefs were similarly varied. “Beliefs in gods and the afterlife are diverse and do not align neatly with conventional categories of religious identity,” remarks Dr. Shimizu. “These results highlight how religiosity in Japan is often expressed through culturally embedded practices and inherited traditions, rather than through formal belief or institutional membership.”

The study also uncovered a methodological issue with broad implications for social science. When the researchers compared their findings with other national surveys, they found that small differences in wording—such as asking whether someone “believes in” or “has” a religion—can produce very different results. Estimates of the nonreligious population varied dramatically depending on the phrasing used. “This insight can help improve the design and cross-cultural comparability of future surveys on religion, spirituality, and values, both within East Asia and in broader international comparisons,” notes Dr. Shimizu.

Beyond its technical contributions to sociology, this research offers a more nuanced way of understanding religion in Japan. Rather than viewing the people as largely nonreligious, the findings suggest a form of religiosity that is diffuse, culturally embedded, and not tied to formal institutions. This has practical implications for how religion is discussed and understood outside academic settings. “A more nuanced and context-sensitive understanding of Japanese religiosity may contribute to better discussions of religion-related issues in the media, classrooms, and cross-cultural dialogue,” concludes Dr. Shimizu.

By documenting how identity, belief, and practice can diverge, this study challenges conventional assumptions about what it means to be religious. It also points to the need for more flexible tools in global research that can capture the various ways in which people engage with religion in different cultural contexts.
 

---

About Assistant Professor Koki Shimizu from Doshisha University, Japan
Dr. Koki Shimizu obtained a master’s degree from Aoyama Gakuin University in 2015 and a doctoral degree from Hokkaido University in 2020. He currently serves as an Assistant Professor at the Faculty of Social Studies of Doshisha University. He specializes in sociology, and his research interests center around values, religiosity, and subjective well-being. Dr. Shimizu has published 20 scientific papers and several books and book chapters on these topics.

About Professor Yoshihide Sakurai from Hokkaido University, Japan
Dr. Yoshihide Sakurai obtained a Ph. D from Hokkaido University in 2002 and he has served as a Professor of Sociology since 2004 at the Graduate School of Humanities and Social Sciences of Hokkaido University. He specializes in comparative sociology, and his research interests center around religious culture in Southeast and East Asia. Dr. Sakurai has published 44 scientific books and more than 150 papers on these topics. 

Funding information
This study was supported in part by a grant from the John Templeton Foundation, Grant number 61951, “Global East Religiosity and Changing Religious Landscapes,” to Purdue University.

 

 This graph shows that many people who identify themselves as nonreligious still participate in ritual practices.

Credit

Assistant Professor Koki Shimizu from Doshisha University, Japan. https://doi.org/10.1111/jssr.70065

---

Journal

Journal for the Scientific Study of Religion

DOI

10.1111/jssr.70065 

Method of Research

Data/statistical analysis

Subject of Research

People

Article Title

Ambiguous Boundaries of Religious Belief, Behavior, and Belonging in Japan: A Descriptive Analysis of Plural and Cultural Religiosity

Children’s Hospital of Philadelphia researchers find diagnostic delays are common for US pediatric patients with malaria

Delays in the diagnosis of malaria can lead to more severe illness and longer hospital stays

Children's Hospital of Philadelphia

LinkedInWeChatBlueskyMessageWhatsAppEmail

Philadelphia, May 8, 2026 – Researchers from Children’s Hospital of Philadelphia (CHOP), in collaboration with colleagues across the country, found that more than one in four pediatric patients treated for malaria in the United States had a delay in their initial diagnosis, increasing the risk of more severe infection. The findings, published today in the journal Pediatrics, emphasize the continued need for malaria prevention prior to international travel and more prompt diagnosis of imported cases to improve patient outcomes.

Malaria is a life-threatening disease that infects more than 250 million people each year, resulting in more than 600,000 deaths, the majority of which occur in children under the age of 5. Although malaria is no longer endemic to the United States, approximately 2,000 cases of imported malaria are diagnosed in the country each year, 10-20% of which occur in children. The number of cases in the United States has risen over the past few decades, largely due to increased travel to and immigration from malaria-endemic countries.

The disease trajectory for these pediatric malaria patients in the U.S. was relatively unknown. Since many doctors in the United States may have never encountered a pediatric patient with malaria, there was a desire to better understand risk factors for developing malaria, as well as outcomes in these patients.

“Children are not little adults,” said Sesh A. Sundararaman, MD, PhD, an attending physician with the Division of Infectious Diseases at CHOP and one of the study’s co-first authors. “They are not traveling for work, but more frequently travel internationally to visit relatives and friends and acquire malaria during those trips.”

This retrospective study analyzed pediatric patients treated for malaria at nine hospitals across the United States from 2016 to 2023 to better understand patient demographics, clinical outcomes and risk factors for severe malaria. A total of 171 patients were identified, 73% of whom had traveled to West Africa to visit friends and relatives.

Fever was the most common symptom reported, affecting 90% of patients, and two-thirds of patients reported at least one abdominal symptom. While no deaths occurred in this population, nearly one-third of patients were diagnosed with severe malaria.

The study also found that 26% of patients had a delay in the diagnosis of malaria, and this rate was similar across all hospitals in the study.

“It’s important to note that you can't tell who's got malaria just by symptoms,” said senior study author Audrey R. Odom-John, MD, PhD, chief of the Division of Infectious Diseases at CHOP. “Children who come in and are suspected of having malaria essentially have fever, but they can also present with a wide range of symptoms. They can have cough, they can have tummy symptoms, they can have headache, they can have almost anything. That’s why rapid and precise testing is necessary to confirm these cases.”

That delay in diagnosis could be caused by a variety of factors, like not asking about recent travel or a lack of familiarity with the disease among U.S. pediatricians. Whatever the case, the longer the time interval, the more likely a patient will develop more severe disease.

“Severe disease results in longer hospital stays,” Sundararaman said. “Children with severe malaria are more likely to require blood transfusions and often receive antibiotics in addition to the treatment for malaria. And these longer hospital stays can create substantial costs for both the patient and the hospitals.”

The researchers emphasized that healthcare providers should discuss planned international travel with patients and make sure to check for potential malaria infection in any patients with fever who have recently traveled to malaria-endemic regions around the world.

This study was supported by the Pediatric Infectious Diseases Society-St. Jude Children’s Research Hospital Fellowship Award in Basic and Translational Science, Pediatric Infectious Diseases Society Stanley and Susan Plotkin and Sanofi Pasteur Fellowship Award, the Thrasher Research Fund, the CHOP Foerderer Award, the National Institutes of Health grants T32AI118684, T32AI007532, T32AI060519, and R01AI103280, the Doris Duke Foundation Paragon of Research Excellence Award and Children’s Hospital of Philadelphia.

 

Sundararaman SA, Roper B et al, “Malaria in Children at 9 U.S. Hospitals: 2016-2023.” Pediatrics. Online May 8, 2026. DOI: 10.1542/peds.2020-000123.

About Children’s Hospital of Philadelphia: 
A non-profit, charitable organization, Children’s Hospital of Philadelphia was founded in 1855 as the nation’s first pediatric hospital. Through its long-standing commitment to providing exceptional patient care, training new generations of pediatric healthcare professionals, and pioneering major research initiatives, the hospital has fostered many discoveries that have benefited children worldwide. Its pediatric research program is among the largest in the country. The institution has a well-established history of providing advanced pediatric care close to home through its CHOP Care Network, which includes more than 50 primary care practices, specialty care and surgical centers, urgent care centers, and community hospital alliances throughout Pennsylvania and New Jersey. CHOP also operates the Middleman Family Pavilion and its dedicated pediatric emergency department in King of Prussia, the Behavioral Health and Crisis Center (including a 24/7 Crisis Response Center) and the Center for Advanced Behavioral Healthcare, a mental health outpatient facility. Its unique family-centered care and public service programs have brought Children’s Hospital of Philadelphia recognition as a leading advocate for children and adolescents. For more information, visit https://www.chop.edu.

 

---

Journal

PEDIATRICS

DOI

10.1542/peds.2020-000123 

Method of Research

Observational study

Subject of Research

People

Article Title

Malaria in Children at 9 U.S. Hospitals: 2016-2023

Article Publication Date

8-May-2026

 

New material technology boasts high-performance carbon dioxide absorption

Tohoku University

Facebook

XLinkedInWeChatBlueskyMessageWhatsAppEmail

 

image: 

Synthesis of PILs based on P[DADMA][Cl]. 

view more 

Credit: Kouki Oka et al.

A joint research team from Nitto Boseki Co., Ltd. (Nittobo) and Tohoku University has revealed that Poly(ionic liquid)s (PILs) can achieve high carbon dioxide (CO₂) adsorption when their counter anions are exchanged. This discovery provides a critical new design guideline for the development of high-performance CO2 recovery devices and gas separation membranes.

The research was led by Associate Professor Kouki Oka of the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, with the results published online in the chemical engineering journal Reaction Chemistry & Engineering on March 9, 2026.

PILs are known for their strong ability to attract CO₂ and for their stability as solid materials. However, conventional anion exchange methods struggle to remove inorganic salts, which are by-products of the manufacturing process. These impurities make it difficult to accurately evaluate the materials' true performance.

The joint research team--which also includes Kazuhiko Igarashi, Senior Technical Supervising SV at Nittobo--successfully removed inorganic salts by precisely purifying the PILs. They discovered that increasing the size of the counter anion significantly improves the CO2 adsorption capacity. Notably, the material using the largest anion achieved an adsorption capacity seven times greater than the raw material.

Developing efficient ways to capture and separate CO₂ from the atmosphere and industrial emissions is an urgent challenge in addressing global warming. PILs are considered promising materials for this purpose because they combine the high CO₂ affinity of ionic liquids with the stability and ease of processing of polymers. In particular, PILs with a quaternary ammonium structure are known to perform well. However, until now, the effects of residual metal ions from inorganic salts formed during synthesis have not been fully studied.

In this work, the researchers focused on poly(diallyldimethylammonium chloride) (P[DADMA][Cl]), a material with a high density of positive charges. They replaced the chloride (Cl⁻) ion with three anions of different sizes--acetate (AcO⁻), thiocyanate (SCN⁻), and trifluoromethanesulfonate (TFMS⁻)--to examine how anion size affects CO₂ adsorption.

A key achievement was completely removing inorganic salt impurities. The researchers used Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDX) to confirm the total disappearance of chlorine from the raw material and any reaction by-products, ensuring the production of high-purity PILs.

The results clearly showed that CO₂ adsorption increases as the size of the anion increases. The material with the largest anion (TFMS⁻) achieved the highest performance, with an adsorption capacity seven times greater than the starting material.

This research has established a new performance-enhancing approach of "precisely designing the anion size" for PILs. The findings are expected to contribute significantly to the future enhancement of CO2 capture systems and gas separation membranes.

 

CO₂ and N₂ adsorption isotherms of P[DADMA][Cl] (black), P[DADMA][AcO] (green), P[DADMA][TFMS] (red), measured at 298 K

 

Estimated based on DFT calculations (B3LYP/6-31+G (d,p)). b: CO₂ adsorption amount at 100 kPa. c:N₂ adsorption amount at 100 kPa. CO₂ and N₂ adsorption amount of PILs.

Credit

Kouki Oka et al.

---

Journal

Reaction Chemistry & Engineering

DOI

10.1039/D5RE00535C 

Article Title

Reaction Chemistry & Engineering