Station Blackout: Q&A on Causes and Effects

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In summary: Ref: 10 CFR 50.2 - http://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-0002.html%E2%80%93 10 CFR 50.24 - http://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-0024.html%E2%80%93 NUREG/CR-6890 In summary, station blackout means the complete loss of alternating current (ac) electric power to the essential and nonessential switchgear buses in a nuclear power plant (i.e., loss of offsite electric power system concurrent with turbine trip and un
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matt222
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I have Q regarding station blackout, the causes of it complete loss of Onsite and offsite power. However if there is no make up what is happening exactly before core damage by steps
 
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matt222 said:
I have Q regarding station blackout, the causes of it complete loss of Onsite and offsite power. However if there is no make up what is happening exactly before core damage by steps
That would largely depend on what event precipitated the SBO.

Station blackout means the complete loss of alternating current (ac) electric power to the essential and nonessential switchgear buses in a nuclear power plant (i.e., loss of offsite electric power system concurrent with turbine trip and unavailability of the onsite emergency ac power system). Station blackout does not include the loss of available ac power to buses fed by station batteries through inverters or by alternate ac sources as defined in this section, nor does it assume a concurrent single failure or design basis accident. At single unit sites, any emergency ac power source(s) in excess of the number required to meet minimum redundancy requirements (i.e., single failure) for safe shutdown (non-DBA) is assumed to be available and may be designated as an alternate power source(s) provided the applicable requirements are met. At multi-unit sites, where the combination of emergency ac power sources exceeds the minimum redundancy requirements for safe shutdown (non-DBA) of all units, the remaining emergency ac power sources may be used as alternate ac power sources provided they meet the applicable requirements. If these criteria are not met, station blackout must be assumed on all the units.
Ref: 10 CFR 50.2 - http://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-0002.html

See also - http://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-0063.html

Reevaluation of Station Blackout Risk at Nuclear Power Plants (NUREG/CR-6890)
http://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr6890/

The concern with a SBO or loss of critical AC power would the effect on core coolability, basically the loss of decay heat removal. The progression to core damage would depend on the how decay heat removal is impaired and for how long.

If the RCS is intact, there is a chance that some cooling will occur. In PWRs, it's possible to get some natural convection, but the steam generators would also need some circulation on the secondary side.

Basically, as cladding temperature increases the oxidation rate increases. Under normal operation, cladding oxidation is very slow - less than 0.1 microns per day, and preferably less than half that or < 0.05 microns per day. Once that cladding temperature increases by more than 100°C above normal operating temperature, the oxidation rate increases. The concern then is that the cladding would breach and release fission gases Xe, Kr and volatiles, I, Cs. Ingress of steam would allow oxidation of the ceramic fuel and more fission products. The oxidation of Zr-alloys produces hydrogen gas, which is combustible. Ignition of hydrogen could lead to containment overpressure and failure.

In the worse case, e.g., Fukushima, the core could experience near adiabatic conditions, in which case, the fuel would reach melting temperatures, or at least severe chemically reactions. If fuel melts, then there is an increase risk of damage to the reactor pressure vessel or loss of integrity.
 
  • #3
Hi there,

Station blackout is a very serious event that can occur in a nuclear power plant. It is defined as a complete loss of both onsite and offsite power, which means that the plant is no longer able to generate electricity or receive it from external sources.

The causes of station blackout can vary, but they usually involve a combination of equipment failures, natural disasters, or human error. For example, a severe storm or earthquake could damage the power lines that supply electricity to the plant, while a malfunction in the plant's own systems could result in a loss of onsite power.

When a station blackout occurs, the first step is for the plant's emergency diesel generators to kick in and provide backup power. However, if these generators fail or are unable to provide enough power, the plant will start to shut down. This is because the reactor needs a constant supply of electricity to keep it cool and prevent a meltdown.

If there is no backup power available, the plant will eventually enter a state known as "cold shutdown," where the reactor is no longer producing heat. However, without any cooling systems, the residual heat from the fuel rods can still cause them to overheat and potentially melt, leading to a core damage.

In summary, before core damage occurs in a station blackout, there are several steps that take place, including the loss of backup power and the plant entering a cold shutdown state. It is crucial for power plants to have robust backup systems in place to prevent a station blackout from escalating into a more severe event. I hope this helps answer your question.

 

1. What is a "Station Blackout"?

A Station Blackout is an event in which the entire electrical power supply to a nuclear power plant is lost. This results in the loss of power to essential systems and can lead to a loss of cooling capability and potential release of radioactive material.

2. What are the common causes of a Station Blackout?

The most common causes of a Station Blackout include natural disasters such as earthquakes, hurricanes, or severe weather conditions. Other causes can include equipment failures, human error, or cybersecurity attacks.

3. What are the potential effects of a Station Blackout?

The potential effects of a Station Blackout can include a loss of control of the nuclear reactor, a release of radioactive material into the environment, and damage to equipment and infrastructure. It can also lead to long-term power outages and disruption of essential services.

4. How can a Station Blackout be prevented?

Nuclear power plants have various safety systems in place to prevent a Station Blackout, such as backup power sources, redundant cooling systems, and emergency procedures. Regular maintenance and training also help to prevent equipment failures and human error.

5. What are the emergency protocols in place for a Station Blackout?

In the event of a Station Blackout, emergency protocols include activating backup power sources, implementing cooling measures, and monitoring for any potential release of radioactive material. Communication and coordination with local authorities and the public are also crucial in these situations.

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