Wednesday, November 19, 2008

Is Nuclear Power Safe?

With President-elect Obama looking to energy sources other than oil and gas, and threatening to bankrupt any new coal-fired power plant someone might attempt to build, nuclear power is sure to be part of what fuels America’s future. While his initial support for nuclear power was weak, he softened his position and even stated that he supported nuclear power. This is apt to bring about many questions and revive old fears.

Here, we offer you a thoughtful posting from a team of scientists who have spent their lives--long lives--working with nuclear power.

CARE was introduced to the Los Alamos Education Group (LAEG) through our efforts to support uranium mining. This is their first piece to be included in the CARE Blog--though it will probably not be the last. If you have specific questions about nuclear power, please post them here. The LAEG will be happy to provide answers for you that we’ll post here.

Reactor Safety
If you’ve ever wondered "Is there anyone out there willing and able to educate us about nuclear power in a balanced fashion?" you’ll want to read on.

Many people have expressed ill-defined fears about radiation, fission products, and the dreaded core, or nuclear meltdown, all of which derive one way or another from the use of nuclear weapons.

The Los Alamos Education Group has qualified members active in reactor and radiation safety. Many of us are retired WW II veterans that recall the entire postwar nuclear era, including knowledge of nuclear explosions.

One of the group was a member of the Atomic Energy Commission’s Committee on Reactor Safeguards for nine years and took part in the committee’s review of three fourths of the US reactors in operation. In 1979 he was appointed to the staff of the President’s Committee on the Accident at Three Mile Island (Kemeny Commission). The task of figuring out what happened in the core, e.g., what fraction melted, what happened to fission products and in particular why did iodine not escape, became tasks he was given.

With the help of consultants from other national laboratories, universities, and industry the problems were solved.

The report of the commission and working groups are in the public literature. These reports stimulated Nuclear Regulatory Commission studies that demonstrated the same conclusion: nuclear electric power plants are much safer than had been believed.

Another member has been and still is active in radiation studies, health physics, and associated activities. The LAEG provides factual answers--conclusions belong to the questioner. We contend that nuclear electric power is safe by any reasonable standard of safety and has a history of operational safety that far exceeds other comparable industrial activities.

Of the 104 commercial nuclear power stations now operating in the US all are pressurized or boiling light water reactors; most of the 339 reactors in 32 other countries are of a similar design. Exceptions include some pressurized heavy water of Canadian design, a very few sodium cooled plants, some old graphite moderated reactors (UK) scheduled for replacement and the Chernobyl design in Russia. The total reactor-years of operation world wide is over 3000 and increasing by 443 each year. The basic light water design concept was developed and chosen by the Naval Reactors organization on the basis of perceived safety superiority. About 500 reactors of the naval design have been used, each one for several years with no accident. The evolution for commercial operations led to the pressurized and boiling water reactors that we see all over the world. The commercial plants are larger physically and produce more electric power and with more safeguards to protect the public. No person has been harmed by radiation in all these reactor years of operation light water reactors.

To defend this assertion of safety of the light water reactor we must discuss the accident at Three Mile Island, the Davis Besse incident and the Chernobyl accident.

The accident at Three Mile Island in 1979 was, initially, a minor "scram." The reactor shutdown was caused by workers on a part of the cooling water system outside the reactor and containment. The reactor shut down properly, the control rods went in and stopped the production of power, the high pressure emergency cooling system turned on automatically (as was proper), and that should have been the end of the incident. However, the control panel erupted with a dozen alarms, confused the operators who turned off the emergency cooling. A slow leak in a valve in the high pressure system allowed water to slowly escape to the containment, but not to the environment. The containment was not challenged. Of all the actions they could have taken, this was the worst. It was turned on again, later, but too late to save the core of the reactor. Poor, inept press relations by the utility and the NRC and panic by the press did the rest. A great many people were unnecessarily frightened.

The problem of the control panel was recognized and has been redesigned. Simulators resembling airplane flight simulators permit operators practice all sorts of simulated emergencies--their realism is extraordinary.

Did fission products escape? Yes, the first search found some 5-day xenon-135, a harmless noble gas that is biologically inert, but no iodine-131 (half life 8 days), volatile and metabolically dangerous to the thyroid gland. Airborne search teams were activated very quickly, found the xenon, but could not find iodine-131 or cesium-137 that everyone expected. They went back to base, recalibrated instruments, searched diligently again and found traces that could have been as much as 18 curies, a negligible amount.

Essentially no radioactive iodine escaped! That was a puzzle because for twenty years, accepted doctrine had been that given an accident to the core, such as TMI, 50% of the iodine would escape to the containment, half of that would be deposited on surfaces and 25% would be available to escape to the environment.

This was the accepted assumption--it did not happen. Historically, this assumption, accepted without experimental evidence, had been the basis for the incredible consequences predicted by early "safety" studies. The studies subsequent to the Kemeny Commission report incorporated correct physics and chemistry assumptions.

The accident was not a public radiation event. No person was injured--not even a grasshopper received any measurable radiation dose and the measuring equipment is very sensitive. An extraordinary example of the near unbelievable sensitivity of modern radiation detection and chemistry occurred in the summer of 1979. A pike caught in the Susquehanna river showed evidence of cesium. Analyses, however, showed that because of the different decay rate of two isotopes, Cs-134 and Cs-137, the cesium was identified as originating in China, nine months earlier, during an atmospheric test!

The reactor was ruined and the damaged core was removed and shipped to a storage site in Idaho. During the removal of the damaged fuel, samples of the pressure vessel steel from beneath and containing the molten fuel were taken. The steel showed no damage--a big surprise and natural safety factor unrealized before. The event WAS a core meltdown, but natural phenomena intervened and prevented the accident from progressing into the imaginary and dreaded "China Syndrome"--in fact, the "China Syndrome" is an impossible event.

In 2002, the Davis-Besse pressurized water reactor near Toledo, Ohio was found to have a very severely corroded spot on the pressure vessel head or top piece. It was caused by boric acid (boron is a neutron poison used for control in the reactor) leaking at a control rod penetration. Inadequate inspection by staff was the basic problem. This could have been an accident comparable to TMI, but was caught by safety inspection, control panels were of a superior design, and operator training was much better. The importance of periodic inspections by different groups is obviously important. The power station was shut down for a considerable period, the utility fined severely, placed on a special "watch list" by the NRC and is now back in operation

These two events are the only serious ones in the US light water reactor industry. We assert that this reactor design is safe and may be manufactured and used with confidence. No person has been injured in a reactor accident by radiation. Production of electricity by nuclear power is actually much, much safer than by coal or natural gas. The usual industrial accidents, e.g. falls, steam burns, falling objects, etc. certainly will continue.

The Chernobyl accident was a bad one, the seriousness compounded by the incompetence of the USSR public relations organization. For days they would not even admit that anything had happened, and the worldwide panic was caused, again, by news media’s lack of good information, lack of understanding of radiation hazards, and by panicky exaggeration. It was bad--it did not need exaggeration.

Thirty "liquidators," first responders, were killed outright by radiation and/or thermal burns while fighting the fire. Later fatalities increased the total to 58, and some excess thyroid cancers, with three deaths, have appeared in young people in the area at the time of the accident. But because health records were inadequate in that area prior to the accident, convincing epidemiological evidence is difficult to derive.

The accident was triggered by an electrical engineering experiment that required the reactor to be in an unstable condition, unique to the design--it could not happen in a US-designed pressurized or boiling water reactor. A steam explosion blew off the top of the reactor, and the graphite moderator caught fire because it was operated at extremely high temperatures. THERE WAS NO CONTAINMENT. Because of the lack of containment and the steam explosion, some of the iodine and cesium probably escaped as a compound. Fission products were deposited in nearby areas, sufficient to cause extensive evacuation and prevailing winds carried detectable amounts into Europe, and, indeed, around the world.

Prior to the 1970s, France depended in large part on cheap mideast oil for their electrical power. The oil crises of the 1970s caused near panic---the Metro could not run, elevators would not operate and they were seriously worried about riots in the streets. The decision was made to make the electrical network depend on nuclear power. They did and the job was completed in the 1990’s (only 20 years) after construction of about 50 pressurized water reactors of uniform design. Now they export electricity to their neighbors. There has been NO accident and public attitude is supportive.

What now can we add about the new designs that would make them even safer? Adding something to make a nuclear power station even safer is not easy. However, the power station designers have the advantage of operating experience for the past 40 years. The new ones are designed for easier safety and operational maintenance, more components will be manufactured in the manufacturers’ shop where quality control is much better and designs will be optimized for easier safety and operational inspection. But the most important issue of which we are aware is emergency core cooling. Current designs depend on electrical power for activation, either offsite or emergency diesel power. The newer designs will also make use of gravity--a force that never fails, to provide immediate availability of water to the core and pressure vessel. Some of these new designs are under construction abroad. As with existing nuclear power plants, these will be operated with complete safety.

Finally, the safety of spent fuel is a legitimate question connected to reactor safety. Fuel (1/3 of the core) is changed in the light water reactors every year, year and a half, or two years depending on design. The fuel is removed by remote control to a "spent fuel storage pool" where the deep water provides both shielding and cooling and allows visual and instrumental inspection. The pool is essentially a large, deep swimming pool, temperature controlled and very clear. No accident has happened in this operation. After a few years the heat and radiation rate has decreased sufficiently that air cooling with shielding is adequate and can be safely located external to the immediate reactor area. The stuff is thermally too hot to handle and too heavy to steal without obvious lifting and hauling equipment. Another safety factor not generally realized is that volatile iodine-131, the most dangerous of the fission products, has a half life of only 8 days. After 10 half lives or 80 days, the activity is down by a factor of 1000 and is no longer significant. Nearly all other fission products are solids and do not readily become airborne even if fuel pins are damaged. There has been NO accident during transfer in or out of the spent fuel pool or during transportation to a different location. The operation is safe.

Why are we making such a fuss and spending so much money on Yucca mountain storage? The concept of permanent disposal of transuranics and depleted UF6 is viable only if stupidity or antinuclear activity is successful in terminating nuclear power production. Otherwise, recycled, it is worth close to a trillion dollars as fuel in sodium cooled reactors, and Yucca Mountain and WIPP would be adequate for permanent disposal of fission products far into the future.

This is a safe and satisfactory end point for spent fuel and reactor safety questions but a serious problem remains--the finite amount of uranium that can be mined even at a cost much higher than the current price. Estimates of years before we run out of uranium-235 vary from 50 to 100 but are finite. The oceans have enormous quantities of uranium but the cost to retrieve it is certainly high. The answer to problems of fuel availability, waste management, and sodium-cooled reactors is the subject of the next essay.

Bill Stratton has a PhD from the University of Minnesota. He is a retired reactor safety expert with extensive advisory service to the Nuclear Regulatory Commision. As a staff member of the President's Kemeny Commission, he was instrumental in explaining the minimal radiation release from Three Mile Island.

Don Petersen has a PhD from the University of Chicago. He is a retired radiation biologist involved with health effects of radiation, neutron dosimetry and effects of neutrons and alpha particles. He has had first hand experience with investigation, description and reporting of radiation accidents involving injury and fatality.

Both spent their entire careers at the Los Alamos National Laboratory.

1 comment:

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