Interdisciplinary
Research

Faculty Spotlights

Arthur Motta

Professor of Nuclear Engineering and Materials Science and Engineering
http://www.mne.psu.edu/motta/

Prof. Motta has worked in the area of radiation damage and environmental degradation of materials with specific emphasis in Zr alloys for the last fifteen years. He received a B.Sc. in Mechanical Engineering, a M.Sc. in Nuclear Engineering from the Federal University of Rio de Janeiro, Brazil, and a Ph.D. Nuclear Engineering from the University of California, Berkeley. He worked as a research associate for the CEA at the Centre for Nuclear Studies in Grenoble, France, for two years and as a post-doctoral fellow for AECL at Chalk River Laboratories, Canada, before joining Penn State in 1992.

Q. - Your work seems to have some real social and environmental benefits. Could you tell us about them?

Motta - Nuclear power is a controversial subject in America. The polls tell us that nuclear power is not generally accepted by the public, but, in fact, it is a more benign source of energy than most other methods of power production. Unlike fossil fuels, such as coal, that produce and release large amounts of toxic waste, nuclear waste, although toxic, is well contained and not dispersed into the environment. Safe nuclear waste might sound like an oxymoron, but because the volume of waste is so small, extensive measures can be made to ensure it is completely isolated and contained.

Q. - Why is there such a fear?

Motta - The general public's perception is that nuclear is far more dangerous than it actually is. In fact research shows that nuclear power shows the greatest disparity in the perception of risk by the public and technical experts. This discrepancy may be because the introduction of nuclear energy to the public was the destruction caused when two atomic bombs were dropped on Japan. So we are dealing with the perception of a Frankenstein monster deep in our souls. In popular culture, especially in movies from the fifties, we had giant ants and mutant creatures created by radiation, such as Godzilla, and the Incredible Hulk.

In fact, genetic engineering occupies the same "place" in risk perception space as nuclear power. To illustrate this last parallel, while I was talking about this subject in class and said that in the original Spiderman comic it was a radioactively mutated spider that bit Peter and caused him to mutate, one of my students pointed out that in the current movie version the spider was genetically engineered. This appears to reflect an aversion to things that might deal with the fabric of nature, especially a Faustian bargain in which we get a benefit from daring to go beyond what appear to be natural limits.

Q. - How justified is that fear?

Motta - People are within their rights to make their own judgments and have any fears they want. It is understandable why nuclear energy is fearsome. Radiation is invisible, and that makes it more frightening. You can see some of the pollution from a coal burning plant, but radiation, even though it can be detected at thousands of times below the danger level, is not detected by the five senses. Plus, we are still dealing with the fallout, as it were, of the secrecy that surrounded nuclear science stemming from its military origins. The vocation of the Atomic Energy Commission was not one of openness; people in charge were telling the public "We're doing okay with nuclear safety," when really we weren't.

To top it all, a nuclear power plant is very complex. As a result, it is very hard to explain to the general public even relatively simple concepts, such as why a nuclear reactor cannot explode like a nuclear bomb. Energy is released in a power plant in a controlled chain reaction in which the power output is constant. A nuclear weapon's output is exponentially more sudden, and requires more than an order of magnitude higher enrichment than what is found in commercial nuclear fuel.

Q. - Some countries don't seem to have the same fear of nuclear energy as we do.

Motta - That's true, for example, France is more accepting of nuclear power (although also there opposition is increasing). Eighty percent of their electric power is generated by nuclear, whereas we are at about 20 percent.

Q. - I'm surprised it's that much.

Motta - Nuclear is second behind coal. We have over 100 nuclear plants in the U.S. In Pennsylvania, about 40 percent of our electricity comes from nuclear. Most new production capacity is in the form of natural gas, but we are limited by price and availability. In renewable energy resources, hydro power is the biggest current contributor, but there is a limit to how many rivers are available and how many of those free-flowing rivers we want to dam. Solar can help in heating houses, but the power production of solar is still very low. It would also require covering large areas with solar panels and dealing with the inconstant nature of the source by either storing energy or having other sources available to produce energy at night.

Q. - So you believe we need to increase our reliance on nuclear power?

Motta - My personal opinion is yes. Nuclear energy doesn't contribute to global warming the way fossil fuels do. Compared in context with other energy producers, the risks are low and more manageable. If you look through the technical reports, most every production technology has caused many deaths - people are scalded in coal plants, dams break and kill people - but there have been no deaths in U.S. nuclear production due to radiation.

We have, in fact, been increasing the percentage of nuclear electricity in this country through increases in its efficiency (capacity factor). This was accomplished by increasing the fuel cycle (time between outages for refueling) and decreasing outage time. From 1980 to today the capacity factor in the U.S. has increased from about 70% to above 90%, the equivalent of building 22 new nuclear plants. To help accomplish this we are trying to increase fuel burnup: by increasing fuel enrichment we can produce twice as much energy from a given fuel rod and, as a result, generate half the volume of the nuclear waste. This means, however, that the fuel has to stay longer in the reactor, at higher temperatures, and in a more aggressive chemical environment. So, we are pushing the fuel harder and longer and requiring less failure, which requires improvement in cladding performance.

Q. - You work with zirconium alloys. Tell us about your research.

Motta - My research focuses on the degradation of the Zircaloy cladding, why it happens, and how we can use better materials to safely arrive at higher burnups. In the reactor, the nuclear reaction is produced by slow neutrons that collide with Uranium-235 atoms in the fuel. The collision causes the U235 atom to split into two large chunks (the fission products), plus an additional two or three neutrons that will each cause, on average, one other atom to split. That's the controlled chain reaction that releases the energy produced in nuclear power. The uranium dioxide fuel is clad in a zirconium alloy tube and surrounded by water. Zirconium is used because it has long been known to be transparent to neutrons, allowing nuclear fission to proceed without too much neutron loss.

The cooling water, heated to 360 degrees Celsius by the energy released, creates steam to power the electric turbines. However, the cooling water can corrode the Zircaloy cladding tube. This corrosion is accompanied by hydrogen ingress, which can make the cladding brittle. The longer the fuel is in the reactor, the more brittle the cladding becomes; so, if we want to use the cladding longer, we have to improve its corrosion resistance. The interesting thing about zirconium is that a small addition of alloy makes a large difference in behavior. To make stainless steel, for instance, you need to add 15 to 20 percent chromium to the iron. To change the corrosion properties of zirconium, you only need a few tenths of a percent of alloying additions. We are trying to understand how these alloying additions improve corrosion performance by studying the nature of the protective oxide film.

To achieve this, we are using the recently developed technique of microbeam synchrotron radiation diffraction and fluorescence to study how the oxide that forms on the surface of new alloys can create a barrier to further degradation. At Argonne National Laboratory in Chicago, we use a beam line at the Advanced Photon Source, which is unique in the world in its ability to focus an x-ray beam onto a spot 0.2 microns in size, just 1/5 of a thousandth of a millimeter. The beam puts lots of photons in a very small space, which allows us to analyze the crystal structure and physics of an oxide layer in great detail and with fine spatial resolution. We use x-ray fluorescence spectroscopy to determine the distribution of alloying elements in the oxide layer. By using x-ray diffraction we can study the oxide crystal structure, grain size, and phases present within the oxide sub-layers and understand how the oxides grow in each alloy.

Q. - How will this work affect future nuclear reactors?

Motta - Penn State is currently leading an international research consortium with Korean Atomic Energy Research Institute in collaboration with Westinghouse and the University of Michigan on this corrosion program. We are testing materials in conditions relevant to current light water reactors, but we are also testing materials for a new supercritical water reactor that will operate at temperatures in excess of 500 degrees Celsius. This reactor concept is one of the Generation IV concepts currently being studied by the Department of Energy for deployment by 2025 or 2030. These reactors will use much higher temperatures to improve thermal efficiency and, as a result, cause correspondingly tougher materials challenges.

Q. - How can we make nuclear energy more acceptable to the public?

Motta - That won't be easy. People's feelings are already set in place on nuclear power, like the Red State/Blue State division. I'd be happy to have my family live near a nuclear facility, but I live and work with this subject, and I understand the reluctance of people that are less familiar with the subject to accept an expansion of nuclear power. I think part of the problem is that we promised too much when nuclear energy was introduced for peaceful uses in the fifties. There were ads with pictures of housewives sweeping with atomic vacuum cleaners with nuclear warning labels on the side. The public was told that energy would be "too cheap to meter." People were set up for disappointment.

However, because of the increased concern over global warming we are seeing, if not a sea change, then at least a "lake" change in the attitudes of environmental groups. For example, the former head of the Sierra Club is now suggesting we reconsider nuclear power. There are still powerful advocates against building more nuclear plants. I might be called an advocate for the other side. Ultimately, the public has every right to choose what form of energy it wants to support for electricity production. What needs to be understood is that every form of energy production, including renewables, will have some environmental impact, especially if produced at the high rates necessary for our energy-hungry society. We have to make the right choices to minimize environmental impact of energy production, but, unfortunately, no free lunch exists.