What if a nuclear power plant loses outside electricity?

  1. Nuclear power plants as well as power plants in general are not self-sufficient in terms of electricity. If a nuclear power plant loses outside electrical power, the plant must then be powered with emergency diesel generators which typically have about 10-12 hours worth of fuel, and then emergency batteries. When the batteries lose power, and they still haven't gotten electricity going back to the plant, the cooling systems for the reactors won't work because of no electricity, and then the reactors will overheat and melt. Inevitably resulting in a total meltdown.

    This is precisely what happened at the Fukashima NPP in Japan. The earthquake knocked out power, and then precisely what I described in the above paragraph occurred. But also many of the important systems at the plant were flooded, destroyed, or severely damaged by the tsunami.

    This is a very real danger facing nuclear power facilities. Have electrical engineers figured out a fool-proof way designing the electric grid in a manner where nuclear power stations will have electricity regardless of power outages/damage to the local grid from things like severe storms, earthquakes, tornadoes, and other natural disasters?
     
  2. jcsd
  3. etudiant

    etudiant 902
    Gold Member

    The issue you point to is quite central to most nuclear emergency plans.
    The diesel fuel supply is much greater than just 12 hours. At Fukushime, the pictures of the tsunami effects included some of the diesel tanks, big refinery sized units holding maybe 50,000 tons of fuel. Their problem was not fuel supply, but a washed out switchboard and flooded diesels.
     
  4. I sincerely hope fuel reserves are vastly larger than what you say.

    This might be true for many of today's reactors, but it doesn't have to be this way. Adequate totally passive cooling systems can be designed and built. I hope all new NPPs ever built will have them.
     
  5. tsutsuji

    tsutsuji 1,220
    Gold Member

    The Tokyo Electric Power Company plans to publish later this year the results of its findings concerning why the power lines collapsed despite being "designed with some margin against the seismic design guideline (JEAG5003) issued by the private sector". See: https://www.physicsforums.com/showpost.php?p=3457680&postcount=10952 and https://www.physicsforums.com/showpost.php?p=3460338&postcount=10979 .
     
  6. At least here in Finland, loss of external grid is considered an anticipated operational occurrence, with frequency of the order of once per year. All equipment related to the external grid are non-safety classified, and therefore they are not credited in the plant safety analyses (even though there are arrangements to attempt transferring to the alternative external grid and to island operation from plant's own generator, if the primary external connection is lost). Since loss of external grid is a relatively common occurrence caused by loss on non-safety classified components, it must not have any consequences on plant safety.

    In the European approach, especially the newer plants are very dependent on the A/C supply (no steam driven emergency cooling pumps, isolation condensors or such, with the possible exception of capability to use firefighting or other diesel powered pumps to provide cooling water for the reactor/steam generator), and therefore a very high emphasis is on the reliability of the emergency diesel generators. In the Finnish plants, there are 4 EDGs per plant unit (+ some additional diesel-driven pumps in lower-safety classified systems). One specific design feature up here is the potential common-cause failure of a heavy snowstorm cutting off the external grid and blocking the air intake of the diesels simultaneously, which has required some modifications on the design of air intake systems.

    Diesel generators have so called "day tanks" that contain enough fuel for some 10 - 20 hours, but they can be refilled when necessary from the larger storage tanks on site. After a couple of days, the decay heat has diminished to such a level that the cooling systems are not needed to run on full capacity, and therefore the fuel consumption of the EDGs is smalled that just after the shutdown.
     
  7. Astronuc

    Staff: Mentor

    From US NRC Regulatory Guide 1.009

    http://www.nrc.gov/reading-rm/doc-collections/reg-guides/power-reactors/rg/01-009/01-009.pdf
     
  8. jim hardy

    jim hardy 4,512
    Science Advisor
    Gold Member
    2014 Award

    my plant kept thirty days supply onsite.
    Gov't emergency managers are well aware of eletric grid's status and needs. Fuel delivery will get high priority.

    In theory a nuke plant could "island" and provide its own house power but we never did. There was one morning when all outgoing power lines went down because of unusual weather and were left as a local island with an adjacent fossil plant. Our house load amounted to around 20% of Mr Fossil's capacity so like '3 men in a tub' we just waited for system to reconnect us to grid.
    Nuke plant didn't experience a loss of offsite power because of the fossil unit next door and shared switchyard.
    There's a lot to be said for diversity.
     
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