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View Diary: The Nuclear Regulatory Commission and Fukishima (154 comments)

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  •  Running at 70% power isn't any safer then (7+ / 0-)

    running at 100% power.

    There are 3 basic failure modes in a nuclear reactor
    1) Loss of coolant,
    2) Accidental Transient
    3) Station Blackout.

    The reality is running at 8% power can still createa transient or if you look at Fukushima unit 4, they were powered down and disassembled and they went into Blackout and exploded.

    I will let you work out loss of coolant.

    The issue at SONGS 1, is the heat exchanger is vibrating and cracking tubes. They are hoping that the lower power setting won't crack the tubes.  I think it's a false hope.

    i suspect the extended operations at a bad condition so damaged the heat exchanger as to bust it a long time ago.

    •  I think the Chernobyl disaster was caused (1+ / 0-)
      Recommended by:

      buy tests where the reactor was being run at very low power levels.

      "If the young are not initiated into the village, they will burn it down just to feel its warmth." African Proverb (-6.00,-7.03)

      by Foreign Devil on Thu Apr 04, 2013 at 11:49:34 AM PDT

      [ Parent ]

      •  Exactly right. They created a massive (1+ / 0-)
        Recommended by:

        water hammer and it ruptured the main steam lead.

        Dr. Isaac Asimov: "The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!' but 'That's funny ...'"

        by davidwalters on Thu Apr 04, 2013 at 12:19:57 PM PDT

        [ Parent ]

        •  the way wikipedia states it (0+ / 0-)

          The increased coolant flow rate through the reactor produced an increase in the inlet coolant temperature of the reactor core, which now more closely approached the nucleate boiling temperature of water, reducing the safety margin.
          The flow exceeded the allowed limit at 01:19. At the same time, the extra water flow lowered the overall core temperature and reduced the existing steam voids in the core.[30] Since water also absorbs neutrons (and the higher density of liquid water makes it a better absorber than steam), turning on additional pumps decreased the reactor power further still. This prompted the operators to remove the manual control rods further to maintain power.[31]
          All these actions led to an extremely unstable reactor configuration. Nearly all of the control rods were removed, which would limit the value of the safety rods when initially inserted in a SCRAM condition. Further, the reactor coolant had reduced boiling, but had limited margin to boiling, so any power excursion would produce boiling, reducing neutron absorption by the water. The reactor was in an unstable configuration that was clearly outside the safe operating envelope established by the designers.


          Because of the positive void coefficient of the RBMK reactor at low reactor power levels, it was now primed to embark on a positive feedback loop, in which the formation of steam voids reduced the ability of the liquid water coolant to absorb neutrons, which in turn increased the reactor's power output. This caused yet more water to flash into steam, giving yet a further power increase. However, during almost the entire period of the experiment the automatic control system successfully counteracted this positive feedback, continuously inserting control rods into the reactor core to limit the power rise.

          (THey were on the edge of nucleate boiling in the reactor, and the control rod design would briefly increase power by pushing water out of the channels, which led to positive void coefficient which leads to a massive run up in power)

      •  Initially yes, (0+ / 0-)

        but the severe design flaws and operator errors made the power spike at the bottom of the vessel precisely when they were trying to shut it down with control rods.  The startup phase is typically the most dangerous when it comes to reactivity accidents because you're not in a stable-state configuration where anomalies are easily detected.

        Running at low power doesn't imporove the basic safety features, but it does prevent heat imbalances.  In the reactors I work on you also get "Xenon poisining", whereby a noble gas accumulates and slows the reaction even more.

    •  read the diary again (0+ / 0-)

      70% refers to the percent of procedures and safeguards in place, not the power levels.  

      Hay hombres que luchan un dia, y son buenos Hay otros que luchan un año, y son mejores Hay quienes luchan muchos años, y son muy buenos. Pero hay los que luchan toda la vida. Esos son los imprescindibles.

      by Mindful Nature on Thu Apr 04, 2013 at 01:10:55 PM PDT

      [ Parent ]

      •  Uh, no (0+ / 0-)

        We're talking about operating at 70% power and so is the diarist.  No plant I know of counts numbers of procedures and safeguards as a measure of realiability.

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