Safety in United States Nuclear Power Plants
The question of how safe are nuclear power plants in the Unite States against the threat of terrorism or catastrophic accidents, can be broken down into three parts:
· The ability to prevent entry by unauthorized personnel
· Limiting the consequences of human actions (accidental or deliberate)
· Preventing the release of radiation to the public
To address the first concern it would be helpful to describe the layout of a typical nuclear facility and specifically the two in Virginia located in Surry and Louisa Counties; Surry Nuclear Power Station and North Anna Nuclear Power Station.
Entrance to a nuclear plant is by an access road, which has staggered concrete barriers like those used to separate opposing traffic on highways. This forces vehicles to reduce speed as they approach a guard post manned by armed personnel. Since 9/11 the preferred weapon has been an assault rifle. I am not inclined to go into much detail about security measures beyond this point but what is common knowledge or what can be seen from a distance, I will mention. There are elevated concrete guard towers with bulletproof glass on the perimeter of the plant. There are roving patrols throughout the plant, both inside and out of buildings, all armed with assault rifles or side arms. There are untold numbers of remotely controlled security cameras, some of which are hidden. All these security personnel are not Rent-a-Cops but are plant employees.
In order to pass the first security check point, a photo ID badge issued by the Utility, must be presented. Badged workers have had their fingerprints checked by the FBI to uncover criminal records. They have passed tests searching for drug or alcohol use. They have gone through a psychological evaluation. They have passed tests determining their proficiency in their professed craft and must demonstrate their knowledge of radiation, (its source, effects and control) and knowledge of the plant’s layout, and location of emergency measures and devices and the proper use of them.
Having gotten this far they are now on plant property. In order to enter the plant proper they must pass through a double row of concrete barriers filled with gravel, which protects a double row of chain link fence from vehicles attempting to crash through. The fence is anchored in concrete and topped by barbed wire. In addition there are multiple runs of concertina razor wire from top to bottom. Between the two rows of fencing are motion sensors, infrared cameras and other devices.
Access is only through the Security Building. An entrant must pass through a metal detector and an explosives sniffer. All hand carried material is x-rayed. A key card is then passed through a reader, which corroborates the bearer’s identity and permission to enter only those parts of the plant that to which authorization has been given. Further corroboration is supplied by ‘hand geometry’, which is the matching of a previous scan of the entrant’s right hand with the present reading. When all this is successfully completed, the lock on a turnstile releases, allowing entrance.
In addition all badged personnel are subject to random drug testing and must report legal proceedings as minor as convictions for traffic offences. Periods of unemployment must be verified by state agencies. One man I know was denied access because he was in arrears in his child support payments. Our credit history is checked; I can only guess that it is to identify those who may be amenable to a bribe.
Addressing the second point it should be understood that nuclear workers are constantly aware that the uninformed (not unintelligent) public has a ‘not in my backyard’ mentality about nuclear plants. We protect our jobs by self-checking each other’s work and work habits. We have so many rules for safety and security that some workers quit in frustration. We don’t mind seeing them go; they are the ones who would take short cuts or falsify documentation. Nobody works by themselves; everyone’s work is checked by his peers and by a quality control specialist. On the most critical systems the layers of inspection and documentation are double and triple.
Having laid that groundwork it would be foolish to think that even in the most stringent environment, accidents and mistakes do not occur. As for deliberate acts of vandalism or sabotage, I have never heard of a single incidence in the ten years that I have done this work. It is a federal crime to knowingly damage or disrupt a nuclear power plant. Supervisors receive training to help them spot potential personality disorders. One engineer that I worked for who became vocally abusive when some work was done in a different manner than he had specified (he also threw some things around) was led away by a security guard. He returned to work three days later after a re-evaluation of his ‘fitness for duty.’ He was reprimanded for aberrant behavior. I have never met a ‘disgruntled’ employee in a nuclear plant.
When accidents happen or mistakes are made the whole nuclear industry hears about it. Such things are regularly and freely circulated among all plant operators in this country. We want to learn from other’s experiences beside our own. Each event is analyzed to find the root cause and to insure that a re-occurrence will not take place. Most are minor and do not affect plant operations but the occasional major event is usually followed by a nationwide mandate by the Nuclear Regulatory Commission to change procedure, modify equipment or retrain personnel to preclude similar events elsewhere.
Personnel cited for violations of safety or security measures are coached to prevent a re-occurrence and the crew that they work with is advised concerning their role in maintaining group safety. Repeat violators are fired.
In a worst case scenario where a berserker runs amok with a sledge hammer or an oxy-acetylene torch, the damage could run into the millions but the public would still be safe. This will fall into context in the next heading.
Now for the third concern. Some people who live near a nuclear plant have a fear that one day they will see a bright flash on the horizon, milliseconds before they vaporize. It will never happen! The nuclear fuel used in a commercial reactor is of such a low concentration that it can never reach a ‘critical mass’, which is required to produce a thermonuclear explosion. This country’s worst nuclear accident at Three Mile Island produced only a partial meltdown of the reactor core. This means that it got hot enough to melt the metal cladding surrounding the fuel rods thus fusing part of the reactor into one large radioactive glob and still it did not explode.
When this situation began there was a loss of coolant. If it continued, the safety systems would have shut down the reactor but the operators failed to see some indicator lights, which would have told them how to correct the situation. They tried one thing after another in an effort to keep the plant on line. When the reactor started to melt on the third day they had run out of ideas and gave up their attempt to fix the problem. The safety systems kicked in and shut down the reactor. Confidence in nuclear power was shaken so badly by this event that no operator since would dare rely on his own expertise in this type of situation. If it can be proven that an operator ignored warning indicators or alarms he can be held both criminally and civilly liable.
To borrow a computer term, the default condition of a nuclear reactor in the United States is ‘shut down.’ The words ‘safety related’ are much used in the industry. It refers to those systems and controls that are essential to bring the reactor to its default condition. More emphasis is placed on safe shut down than safe operation. There are literally thousands of pieces of equipment, controls, gauges, sensors and instruments that must function correctly in order for the plant to run and if any one of them does not, a shut down will occur.
Some devices are so sensitive that signs are placed near them warning that bumping them could trigger a shut down. The whole plant is equipped with seismic restraints so that if an earthquake happened the plant would shut down safely without damage. I spoke to some knowledgeable people and asked if the reactor building could withstand the impact of a 767. Their honest answer was that it was not designed with that in mind but at the very least it would feel like an earthquake and the seismic sensors would shut down the reactors without a breach of integrity before the first piece of concrete could fall from the dome.
I would like to make a comparison between US plants and Chernobyl. The reactor in the USSR exploded because the operators lost control of the rate of fission. When fission is self perpetuating it is called a chain reaction and it works like this: atoms of Uranium are subject to natural decay, giving off neutrons and heat. Each neutron released strikes other Uranium atoms, which then fission (split into other elements) and give off neutrons and heat. In nature, the Uranium atoms in ore are so far apart that no chain reaction occurs and there is no discernable heat given off. The refined ore, in the concentration used for fuel, allows a chain reaction to be controlled with precision, not so with a nuclear bomb where the concentration is much higher.
By absorbing stray neutrons before they strike other Uranium atoms, the fission can be slowed down thus reducing the heat output. The Soviet reactors accomplish this with graphite (a form of Carbon), which is combustible. American reactors use an alloy of Silver, Cadmium and Indium, which is a bit more expensive but is not combustible. When the reactor in Chernobyl overheated the resulting explosion was a combination of superheated water turning instantly to steam and the graphite rods burning. The force blew the roof off the building, which highlights another major difference between Soviet and American nuclear plants.
In the United States the structure housing the reactor is called the Containment Building. It is constructed with two and a quarter inch diameter steel reinforcement rods encased in concrete walls that are four and a half feet thick at the base and reduce to two feet at the top of the dome. In addition there is a secondary wall inside Containment that is of similar construction and two feet thick and rises to the base of the dome. The dome itself is mostly empty space, housing a crane, which is used to service the reactor. The top of the reactor is below ground level and extends downward into solid rock for sixty feet. Every reactor in the US is located near a source of water, lots of water. Surry is on the James River and North Anna on Lake Anna, a thirty-mile long lake.
In a worst case scenario, in which there would also be a loss of electric power, the control rods would drop into the reactor in the time that gravity could pull them down fourteen feet and the Containment would fill with cooling water, which was also gravity fed (that’s why they are underground). The building is designed to contain all the radiation that normal operation produces, plus any unforeseen malfunction. The incident at Three Mile Island was contained within the building except for some gases that were allowed to vent into the atmosphere. The radioactivity that was released was within limits set by the Nuclear Regulatory Commission.
The containment building at Chernobyl was basically made of sheet metal on a steel skeleton. Its design was meant to contain radioactive particles and gasses, not to withstand the force of a tornado or a jet engine falling off an aircraft like US plants, and especially not an explosion of the type that occurred. If Chernobyl had an American type containment, children in Lapland would not be drinking radioactive reindeer milk. Periodically containment buildings in US plants are vacuum tested to discover leaks. They are not permitted to operate unless they can hold the vacuum. Some plants in the US enclose their Containment buildings with a metal-sided structure for aesthetic reasons but there is still a concrete dome beneath it.
Nothing comes out of an American containment building unless it has been monitored for radioactivity; this includes personnel. On one occasion every stitch of clothing I was wearing was confiscated, boots included, and I almost had to have my head shaved because of radioactive contamination on me. I had to shampoo and shower until I was rid of it. Even our internal organs are scanned for anything we may have inhaled, ingested or absorbed.
The last item of concern that has gained some public attention is nuclear waste. Low-level waste such as my clothing, cloths used for cleaning and monitoring, floor sweeping and the like, go in sealed containers to Barnwell, SC. I don’t know what happens to it after it gets there. The really nasty stuff like spent fuel never leaves the site. It is put into steel and concrete casks that weigh upward of 300,000 pounds, which are stored on concrete pads in a high security area that is patrolled and scanned by remote cameras. After a steel lid is welded to seal the cask, it is filled with Helium to preclude corrosion and remote sensors are connected to monitor heat and radiation.
I don’t believe that I have been at risk because of my work. I don’t believe that anyone living near a nuclear plant should be afraid of being exposed to radiation. My exposure total for ten years was about 3000 millirems; 95% of which was during outages when my duties required me to enter the Containment Building. The lifetime exposure limit set by the Nuclear Regulatory Commission is 40,000. This country has an excellent record of nuclear safety, Three Mile Island notwithstanding.
Phillip R. Varady Sr.