Using antineutrinos to monitor nuclear reactors

Dr. Nils Haag developed an experimental setup that allowed him to determine the missing spectrum of uranium 238. 

Credit: Wenzel Schuermann / TU München 

When monitoring nuclear reactors, the International Atomic Energy Agency (IAEA) has to rely on input given by the operators. 

In the future, antineutrino detectors may provide an additional option for monitoring.

However, heretofore the cumulative antineutrino spectrum of uranium 238 fission products was missing.

Physicists at Technische Universität München have now closed this gap using fast neutrons from the Heinz Maier Leibnitz Neutron Research Facility.

In addition to neutrons, the fission reaction of nuclear fuels like plutonium or uranium releases antineutrinos.

These are also electrically neutral, but can pass matter very easily, which is why they can be discerned only in huge detectors.

Recently, however, detectors on the scale of only one cubic meter have been developed. They can measure antineutrinos from a reactor core, which has generated great interest at the IAEA.

Prototypes of these detectors already exist and collect data at distances of around 10 meters from a reactor core.

Changes in the composition of nuclear fuels in the reactor e.g., when weapons-grade U-239 is removed, can be determined by analyzing the energy and rate of antineutrinos.

This would free the IAEA from having to rely on representations of reactor operators.

Antineutrino spectrum of uranium 238 revealed
In the 1980s the antineutrino spectra of three main fuel isotopes, uranium 235, plutonium 239 and plutonium 241, were determined.

However, the antineutrino spectrum of the fourth main nuclear fuel, uranium 238, which accounts for approximately 10 percent of the total antineutrino flux, remained unclear.

It had only been estimated using inaccurate theoretical calculations and thus limited the accuracy of the antineutrino predictions.

Dr. Nils Haag

Dr. Nils Haag from the Chair of Experimental Astroparticle Physics at TU München recently developed an experimental setup at the FRM II that allowed him to determine the missing spectrum of uranium 238.

"I needed a high flux of fast neutrons to induce the fission of the U-238," says the physicist. This is why he located his experimental setup at the NECTAR radiography and tomography station of the FRM II, a source of fast neutrons.

Second detector allows background-free measurement
The neutrons induce nuclear fission in a film of U-238. The radioactive decay products then emit electrons and antineutrinos.

The electrons were investigated using a scintillator – a block of plastics that converts the kinetic energy of the electrons into light. A photomultiplier then translates this into electrical signals.

The nuclear decay also generates gamma radiation that produces unwanted events in the scintillator.

Therefore, Haag placed a second detector right in front of the scintillator: a so-called multi-wire proportional chamber.

Since only charged particles like electrons trigger a signal in the gas detector, the researcher was able to determine and subtract the proportion of gamma radiation.

Haag then inferred the antineutrino spectrum using this background-free measurement data.

Method allows better monitoring of reactor cores
The measurement of the antineutrino spectrum can be used to monitor the status, performance and even composition of reactor cores.

"Our results open the door to predict with significantly higher accuracy the expected antineutrino spectrum emitted by a reactor running on a fuel composition reported by the operator," explains Dr. Nils Haag.

"Deviations of antineutrino detector measurement data from expected reactor signals can thus be exposed."

The development of this methodology is embedded in basic research on the phenomenon of so-called "sterile" antineutrinos.

Comparing previously made measurements and predictions of reactor antineutrino spectra gave rise to the assumption that some of the antineutrinos turned "sterile" after being produced.

They were then no longer able to react with other matter. A better understanding of this effect would expand our knowledge of elementary physical processes.

More information: 
Experimental Determination of the Antineutrino Spectrum of the Fission Products of U238, N. Haag, A. Gütlein, M. Hofmann, L. Oberauer, W. Potzel, K. Schreckenbach, and F. M. Wagner, Phys. Rev. Lett. 112, 122501 (2014), DOI: 10.1103/PhysRevLett.112.122501

Akademik Lomonosov: Russians to deploy floating nuclear power plant

The general director of one of Russia's largest shipbuilders, Aleksandr Voznesensky, has announced to reporters that a floating nuclear power plant is currently under construction at one of Russia's ship yards. 

He added that it will likely be ready for use by 2016. 

The Russians are calling it a "floating power" station, abbreviated to PEB. The vessel has been given the name Akademik Lomonosov.

Several countries, including the United States and China have considered building floating nuclear power plants but until now, no other known vessels have reached the construction phase.

The advantages of a floating nuclear power station are obvious—electrical power could be brought to areas that are not currently being served by other means.

Russia in particular has many far-flung outposts in its eastern region that have had difficulty flourishing due to the financial constraints of building power plants so far away from everything else.

The Akademik Lomonosov will have two KLT-40 naval propulsion reactors modified to serve as power providers for an external location—with a displacement of 21,500 tons.

Lomonosov noted that nuclear powered marine vessels have a proven safety record going back 50 years. Many nations now routinely deploy nuclear powered ships, submarines and even ice-breakers.

He also stressed that the design of the vessel will be such that the platform will be capable of withstanding a tsunami or even a collision with land or a ship.

The Akademik Lomonosov will not be able to power itself however, which means it will be towed to wherever it's needed.

The vessel will be operated by a crew of 69 people and will also conform to regulations set by the International Atomic Energy Agency (IAEA).

Lomonosov said that plans are underway to build a fleet of the floating platforms to provide cities and towns across Russia with electricity for general use and more specifically for heating homes and businesses.

The Akademik Lomonosov will be capable of generating 70 MW of electricity—enough to power a city of 200,000 people.

He noted also that such vessels could also be used to power desalination plants, providing 240,000 cubic meters of fresh water daily.

IAEA: Nuclear science to fight Tse fly sleeping sickness

The International Atomic Energy Agency on Friday announced an agreement to help African nations battle the tsetse fly, the main carrier of parasites that causes sleeping sickness with its bites.

The IAEA, which has been working on the problem with African countries for 30 years, can make available a Sterile Insect Technique (SIT), a nuclear-based pest control technology that is often described as "biological birth control for insects", according to the agency's website.

The IAEA signed a memorandum of understanding on Wednesday with the African Union, extending cooperation in a range of domains. Work on sleeping sickness follows an effective trial in Zanzibar in the late 1990s.

Sleeping sickness, or trypanosomosis in animals, is a deadly disease found in 35 African countries, where it kills 400,000 people a year, along with some three million head of cattle.

Apart from the cost in lives, the disease is seen as a major obstacle to development, causing an estimated loss in earnings of about four billion dollars (2.7 billion euros) a year.

"In SIT-supported pest suppression and prevention campaigns, millions of sterilized male insects are released into targeted areas. They mate with wild females in the field, but no offspring are produced. Eventually, the pest population is suppressed and steadily reduced over time," the IAEA explained.

Medical cooperation is part of the brief of the IAEA, which is based in Vienna and is responsible for promoting peaceful uses of atomic energy.