Join
Search

Fission Stories #145: When Good News Causes Bad News

Bookmark and Share

Figure 1.  (click to enlarge)

The defense-in-depth approach to nuclear power safety employs multiple barriers between radioactive materials and the environment. While no single barrier is 100 percent reliable, multiple barriers reduce the chances that all fail to prevent radioactive materials from reaching the environment.

One such barrier is the hollow metal rods containing fuel pellets inside the reactor core of a nuclear power plant. These fuel rods, when intact, prevent the radioactive particles and gases formed as a byproduct of fissioning atoms from escaping into the reactor cooling water.

The good news is that fewer nuclear power plants are operating with defective fuel rods (see Figure 1). Where 20 to 30 percent of the plants had defective fuel rods just five years ago, fewer than 5 percent operated with fuel defects last year.

This trend is certainly good news. Fewer defective fuel rods put less radioactive particles and gases into the reactor cooling water. Less contaminated water means lower radiation doses to workers performing maintenance and testing on plant equipment. And more of the radioactive particles and gases being retained in the fuel rods mean less being discharged to the air and water.

But there was bad news associated with this good news. The owner of the Oconee nuclear plant in South Carolina informed the NRC that the improved fuel rod reliability had a safety side effect. The plant’s operating license contained a requirement that a leak of one gallon per minute of reactor cooling water into containment be detected within an hour. This requirement stemmed from the leak-before-break concept: a pending rupture of a large pipe connected to the reactor vessel would be preceded by a small leak. The plant’s operating license also contained a complementary requirement that the reactor be promptly shut down if a small leak was identified.

There are many tanks and pipes containing water inside containment. For example, there are large tanks of borated water standing ready to inject this volume into the reactor vessel in event a pipe breaks and drains cooling water. And there are air conditioning units inside containment supplied with cooling water.

To differentiate between a puddle on the containment floor caused from a leaking a borated water tank or from the cooling water supply pipe to an air conditioner, the instrument used to monitor the reactor cooling water leak rate relied on the fact that this water would be radioactively contaminated. In other words, the monitoring instrument was not tracking drops of water as much as it tracked the amount of radioactivity that would be within the reactor cooling water.

But improving fuel reliability meant less amount of radioactivity in the reactor cooling water. The instrument was not re-calibrated to retain its ability to detect a one gallon per minute leak rate within one hour. It would either require a larger leak rate (e.g., 10 gallons per minute) or a longer time period (e.g., 4 hours) for the instrument to indicate a problem.

Workers at Oconee re-calibrated the instrument to restore the required sensitivity and revised procedures to use the amount of radioactivity actually present in the reactor cooling water in future calibrations.

Our Takeaway

No one could possibly have anticipated that improving fuel reliability would have adverse implications on the ability to detect leaks of reactor cooling water inside containment.

Unless of course one read the August 3, 2005 warning issued by the NRC on this very matter.

In that warning, the NRC cautioned owners that fuel reliability improvements had reduced the amount of radioactivity within the reactor cooling water with the result that instruments used to detect leakage inside containment “may not be able to detect a 1 gallon-per-minute (1-gpm) leak within 1 hour.”

The NRC based this warning on information it received May 2, 2005 from the owner of the McGuire nuclear plant. That owner informed the NRC it became aware on December 19, 2004, of industry operating experience about other nuclear plant in the US having problems detecting reactor coolant system leakage inside containment and took corrective actions at McGuire after determining it shared the problem.

But the owner of the McGuire nuclear plant also owns the Oconee nuclear plant. Why did it take 8 more years for workers at Oconee to learn (and fix) what workers at McGuire leaned?

More importantly, why does the NRC put up with this nonsense?

The NRC warned Oconee’s owner – in writing – back in August 2005 about a safety problem detected at one of this owner’s other nuclear plants. But the owner essentially ignored both the NRC’s warning and the lessons learnable from McGuire to let the three reactors at Oconee operate for 8 more years with the same problem.

The NRC’s 2005 warning, in theory, should take away this owner’s “get out of jail free” card. The NRC warned the owner, in writing, about this problem. The owner cannot claim ignorance about it in 2013.

But it would do little good for the NRC to throw the book at this owner for violating this safety requirement. If this owner cannot be bothered to read the NRC’s three page warning letter, it likely won’t read the book whizzing by either. Maybe the NRC should consider doing more to get this owner’s attention – like causing the plant to be shut down for awhile as the agency has been doing at Fort Calhoun in Nebraska. Now that the NRC has that owner’s attention, all kinds of longstanding safety problems are now being found and fixed. Oconee’s owner seems to be begging the NRC for this same kind of healing treatment.

NRC – heal that wayward owner before it’s too late.

 

“Fission Stories” is a weekly feature by Dave Lochbaum. For more information on nuclear power safety, see the nuclear safety section of UCS’s website and our interactive map, the Nuclear Power Information Tracker.

Posted in: fission stories Tags: , , ,

About the author: Mr. Lochbaum received a BS in Nuclear Engineering from the University of Tennessee in 1979 and worked as a nuclear engineer in nuclear power plants for 17 years. In 1992, he and a colleague identified a safety problem in a plant where they were working. When their concerns were ignored by the plant manager, the utility, and the Nuclear Regulatory Commission (NRC), they took the issue to Congress. The problem was eventually corrected at the original plant and at plants across the country. Lochbaum joined UCS in 1996 to work on nuclear power safety. He spent a year in 2009-10 working at the NRC Training Center in Tennessee. Areas of expertise: Nuclear power safety, nuclear technology and plant design, regulatory oversight, plant license renewal and decommissioning

Support from UCS members make work like this possible. Will you join us? Help UCS advance independent science for a healthy environment and a safer world.

  • Richard Solomon

    Thanks for, once again, pointing out the NRC’s failure to follow up on plant owners who ignore its warnings.

    When, if ever, will the NRC realize that plant owners do not take its warnings seriously until some consequences are attached?!? HELLO, out there at the NRC……

  • Sean McKinnon

    When did Oconee’s fuel rod reliability Improve so dramatically? You insinuate that it took them 8 years to identify this problem but as you stated im the first paragraph 20 to 30% of plants had defective fuel rods 5 years ago? Why did you not clearly indicate how long Oconee ran in this condition? You make it seem like they just noticed this but according to the LER this issue was noticed in 2006 and 2011 and corrective actions taken. I think it is disingenuous to insinuate that it took them 8 years to notice.

  • David Gaeddert

    Mr. Lochbaum, thank you for explaining fuel rods all leak to some extent. With gases as Xenon evolved, some leakage would have to happen, or rods would rupture. Makes cooling water control important.

    Btw, most recent report on website of Omaha Public Power District reports that 11 of 36 safety items are “closed or almost closed”, whatever that means, “22 are showing progress”, no comment on 3 items remaining, for Fort Calhoun reactor restart. Who will give me a bet that reactor never actually restarts? Thanking you all again for helping this concerned citizen stay as informed as possible.

  • Joyce Agresta

    More importantly, why does the NRC put up with this nonsense?

    You might ask the NRC as to why. As you know its unlikely to receive a straight answer from this agency. I’ve taken notice the pre approved scripted replies seldom address the inquiry. The puppeteer is more offensive than are the puppets.

    I’ve given the same question some thought over the year’s watching the NRC website and daily incident reports.

    Anyhow the best we can do with out a straight answer is guess. Anyone’s best guess would do. Yours mine the fool on the hill whom ever.

    Without any assumption of being correct we may guess to be more thorough we may even second guess. Such is the nature of the Nuclear Industry. The very foundations of all Nuclear Reactors are based on guesses.
    One might venture a guess that a better scenario would be for the eventuality of severe Nuclear Reactors accidents to happen sooner rather than later. The powers that be only take pause when there is a severe nuclear accident. Accidents happen as long as Nuclear Power Reactors are in operation there will be Nuclear Power Reactor accidents. Long after they are decommissioned there will be waste storage accidents and all such things that come from the spent fuel. As we all know accidents happen. There was a pause after the severe accident at Three Mile Island . There are only a few Nuclear reactors in the Western Alliance States (states west of the Mississippi.). Many thought after the accident at Three Mile Island all Nuclear power plants would have been decommissioned. The world would be such a different place if it had. Instead the nuclear industry used the best guess method to create the Fukushima Daiichi nuclear disaster .

    Guessing again perhaps the good people at the NRC educated in such matters are purposely allowing the reckless operators to cause more severe accidents sooner rather than latter. Based on track record it’s a safe guess that there will be more severe accidents. Based on track record it’s a safe guess the powers that be will try to revive the Nuclear industry.
    Based on science it’s a safe guess if the industry grows. It will hinder human existence With out a more logical way around it perhaps the good folks at the NRC want to let the industry kill itself. Instead of us. Just guessing. The Nuclear industry at its best is a guessing game.