Although it is not generally known, all nuclear power stations make radioactive xenon nuclides while they are generating power, and it eventually goes up in the atmosphere by way of the otherwise inexplicable “smokestack” on site. Gaseous fission products find their way into the primary cooling loop, and they are drawn off in the water makeup system, located in the auxiliary building. Scavenged gases are compressed and stored in the “decay tank.” When the decay tank gets full, a worker turns on a valve, and up the stack it goes. This is routine. The instant it scrammed, TMI-2 stopped making radioactive xenon. The zirconium fuel pins try to keep any gas from getting away, and a lot of it decays in the fuel without escaping, but xenon is good at finding its way into the coolant. The only reason that TMI-2 released a big slug of xenon was that the fuel pins had disintegrated, so the normal hindrances were gone.
The decay tank was purged at 8:00 a.m. on Friday, March 30. A helicopter directly over the stack measured a 1.2-rem-per-hour dose rate at 130 feet over the plant, and the reading immediately tailed off as the gas dissipated. It eventually made a narrow but diluted plume, 16 miles long. All off-site radiation measurements, peaking at about 0.007 rem per hour, were probably due to the xenon gas. In general, nuclear workers are allowed to absorb 5 rem per year, and civilians are allowed 0.5 rem per year. A population group, such as the citizens of Harrisburg, is allowed a collective 0.170 rem per year. Standing at the fence around the Three Mile Island plant for a year, an individual would have received 0.005 rem.
On April 7, 1979, at 2:03 P.M., Three Mile Island Unit 2 achieved cold shutdown. TMI-2 would never again generate any electricity. In the history of the world, it had been the worst industrial disaster in which not one person was harmed. Over the next 20 years, there were certainly cancers among some people who were downwind of the plant, as happens in any group of people over time, but it was difficult to correlate these illnesses with any aspect of the reactor meltdown at Three Mile Island.[241] The most popular T-shirt slogan was “I survived Three Mile Island … I think.”
Many changes in nuclear power training, control-room instrumentation, and pressure-relief valves came down from the NRC in the following years. “PORV” now means “Power Operated Relief Valve,” and not “Pilot Operated Relief Valve.” Dresser Industries, maker of the PORV in TMI-2, put a full-page ad in the New York Times, with Dr. Edward Teller claiming that he was not afraid of nuclear power, but he was terrified of Jane Fonda.
The thorough cleanup operation, costing $1 billion, was completed in 1993. $18 million of the cost was contributed by the government of Japan, with the provision that we include Japanese workers to have experience in a nuclear power cleanup. The final report concluded that 35 to 40 percent of the fuel had melted, while 70 percent of the core structure had collapsed. A surprise to everyone was that there was never a chance of melted uranium oxide burning through the bottom of the reactor vessel. The melt-down had, in fact, formed an insulating layer of ceramic material, a durable mixture of zirconium and uranium oxides, at the bottom of the vessel, and it was impervious to extreme temperature.
TMI-1, the other reactor sitting next to TMI-2, has been quietly generating power and making money for its owner, the Exelon Corporation of Chicago, ever since 1985, when it was allowed to resume operation. Its operating license runs out in 2034. B&W never received another order for a full-sized civilian power reactor. They are now developing a small modular power reactor called mPower.
Could TMI-2 have been cleaned up, refurbished, and restarted? Economically, no. The entire inside of the containment building and every tank, pipe, valve, and piece of equipment inside was hosed down with radioactive fission products having a complex, ever-changing array of half-lives and radiation types, actively breaking down for thousands of years, and it had soaked into the fairly new concrete. It would have been cheaper to have bulldozed the plant into the ground and started from scratch, if only it had been legal to do so.
In the years afterward, there was an eerie quiet in the world of nuclear power. It was as though the worst had happened. Nature and probability seemed to have nothing else up their sleeves, and all was still.[242] Then, early in the morning of April 26, 1986, all hell broke loose in an ancient town in Ukraine named Chernobyl.
In 1986, Ukraine was a close member of the Russia-based Union of Soviet Socialist Republics (USSR), a large conglomeration of geographically connected countries making up Eastern Europe. The government, Communism, was a 20th-century invention being beta-tested, and there was a big ongoing contest with “the West,” which was basically Western Europe and the United States, to find which experimental government system, soviet communism or a democratic republic, could develop the stronger, more dominant economic system. The USSR was still in its pre-war mode, implemented by Communist Party Head Joseph Stalin, to win the competition by having the larger population percentage of engineers, technicians, and scientists, thus advancing more rapidly in a world where technology seemed important. The West was not quite as tightly organized but was giving the USSR a lot of heat. To meet its goal of economic domination and modernization, the USSR saw fit to construct big, powerful nuclear power plants as quickly as possible, while building a vast inventory of nuclear drop-weapons and warheads.
Both goals, electricity and bombs, are met simultaneously using the RBMK reactor concept, a design that was original to the Soviet Union and not, as were some other mechanical motifs, a copy of Western machinery.[243] The RBMK uses blocks of solid graphite as the neutron moderator and water as the coolant, boiling in metal tubes running vertically through the reactor core. It therefore suffers from the worst characteristic of two reactor concepts, the possibilities of a graphite fire plus a steam explosion in the same machine, and it thus wins the prize for the most dangerous method for making power using fission. The advantage of it is the fact that it can be used both for power production and for plutonium-239 conversion. The neutron-energy spectrum produced by the use of graphite plus the fact that it can use natural uranium as fuel made it optimum for plutonium production, and the fuel assemblies can be swapped out while the plant is running at full power.[244] Timely, selective removal of the fuel, as opposed to changing it out during a refueling shutdown, means that the disadvantageous production of plutonium-240 can be minimized. It was designed in the 1950s, when a commercial power reactor in the United States made 60 megawatts of electricity. An RBMK was designed to make a gigantic 1,500 megawatts of electricity, under the belief that overwhelming size would be a factor in winning the global economic contest.
There were some serious design flaws. The reactor core is big — a graphite cylinder 46 feet in diameter by 23 feet high. Each fuel assembly is 12 feet long, and the machine that automatically pulls one out and exchanges it for another requires a space 114 feet high over the top of the reactor. There was no practical way to construct a sealed containment building over this tall machine, so the world is protected from fission products in the reactor by a single barrier, a round, concrete lid, eight feet thick, held by gravity in the reactor room floor. A sheet-metal roof keeps rain off the equipment.
Western reactors use the “scram” system to rush all the controls into a reactor and shut it down as quickly as possible. It takes about three seconds to complete the scram on a General Electric BWR power reactor, from the instant of hitting the big red button to having the controls top out in the reactor core. The equivalent Soviet system is the AZ, or “Rapid Emergency Defense.” Push the big red AZ button, and it takes 20 seconds for the control rods to be completely in.[245] A lot can happen in 20 seconds, but that is not the worst characteristic of a Soviet-style scram.
241
Immediately after the incident was declared over, hundreds of people in the area reported a metallic taste in the mouth, nausea, skin rashes, and hair loss, the symptoms of having stood atop a reactor as its power spiked way above design limits. There were rumors of cancer, sudden infant deaths, and stillbirths. These reports did not correlate with any measured radioactivity. The only thing that was able to escape the containment building was some radioactive gas, and it was gone within hours. Radiation-induced cancer has a latent period of about 20 years. The TMI-2 accident did cause illness, but it was most likely psychological and not radiological.
242
It was relatively still, at least. In September 1982, the No. 1 RBMK reactor at the Chernobyl Nuclear Power Plant experienced a partial core meltdown. Such minor incidents were not brought to the attention of the greater world of nuclear power, as the Soviet government was very careful not to release any information unless they had no other choice.
243
RBMK (Реактор Большой Мощности Канальный) means “high-power channel-type reactor.” Although it was considered obsolete even in Russia by the 1970s, there were RBMK power plants under construction as late as 1993. There were 26 RBMK reactors planned, eight were cancelled in the middle of construction, and 12 are still operating.
244
Natural uranium fuel was a goal, but very low, two-percent enriched fuel was usually used in RBMK power plants. This was still cheaper than the higher enrichment used in the PWR and BWR reactors which were so popular in the West. After the Chernobyl disaster, the RBMK fuel enrichment was increased to 2.4 percent to compensate for revisions in the control-rod design.
245
There is not one AZ button for an RBMK; there are five. By choosing a low-numbered AZ button, an operator can gently shut down the reactor with a minimum amount of inserted negative reactivity without shocking the system too badly. Hitting button AZ-5 throws everything in at once, giving a rapid, absolute shutdown. Unlike most Western reactors, the control rods are not hastened into the core using hydraulic cylinders, but are driven in by the electric servo motors that are normally used to position them, running at maximum speed.