Skip to main content

Multiple failures exposed Diablo Canyon to higher risk

Steven Weissman, associate director, Center for Law, Energy and the Environment | March 21, 2011

It is a coincidence that the Union of Concerned Scientists has released  a new report on nuclear power plant safety while the Japanese nuclear crisis continues to unfold. Yet, the heightened awareness that many people now have of the importance of nuclear plant cooling systems may put us in a better position to understand the significance of the UCS findings.

Diablo Canyon nuclear power plantThe report highlights 14 “near misses” at U.S. nuclear plants in 2010, including one at California’s Diablo Canyon Nuclear Plant, where valves that provide emergency cooling water to the Unit 2 reactor core and containment vessel had been stuck in the closed position for 18 months without anyone knowing about it.  According to UCS, “that meant operators would be unable to provide cooling water to the reactor core and containment vessel at a key point during an accident.”

As plant operators tend to do, the managing utility attempted to minimize the apparent significance of this mistake.  The company points out that the plant’s operators could still have kept the reactor cool by opening the valves manually.  Besides, says Pacific Gas & Electric Company spokesperson Kory Raftery, “the potential is very small for the type of situation where we’d need this system in the first place.”

PG&E seems to be hoping that we will forget the importance of redundant protections in further reducing the risk of a catastrophic failure.  In a commentary related to the Japanese crisis, Harvard Kennedy School Associate Professor Matthew Bunn reminds all of us of the “huge importance of taking redundant safety systems seriously.”  The company’s observation that the odds of a meltdown are small, intended to offer reassurance to the public, can actually have the opposite effect.  It suggests that the plant operators are willing to forgive themselves for a major safety breach.

The Union of Concerned Scientists focuses on the Federal Nuclear Regulatory Commission’s inspection process, notes that NRC devotes about 6,300 person-hours of oversight to each plant each year, and wonders how diligent analysts could have missed this problem for 18 months.  UCS also points out that the NRC only looks at 5% of each plant’s records.  For every problem like this that the inspectors identify, there may be 19 more.  This fact, perhaps more than any other, underscores the importance of figuring out what went wrong in the one instance that the inspectors uncovered. Closer examination suggests that this situation is the result of a multitude of failures:

1. The initial mistake

With something as important as valves controlling cooling water, a mistake like this should never happen in the first place. Anticipating the potential for human error, there should be redundant visual cues that would make it obvious when a valve is improperly set.  Either such cues were not in place, or the plant operators ignored them.

2. Inadequate quality control at the plant

The second line of defense should be in the form of inspections occurring after any adjustment of critical safety equipment in the plant.  According to UCS, the NRC did eventually impose sanctions on the utility for this particular failure.  Yet, beyond the first inspections, it is unthinkable that this kind of mistake could go unnoticed for 18 months.  Shouldn’t safety equipment be examined daily — or at least weekly or monthly?  Again, either the inspections never happened, inspectors repeatedly missed the problem, or there was a subsequent failure to report or to act.

3. Inaction by Diablo’s Independent Safety Committee

When construction of Diablo Canyon was completed, a study of the design and construction process uncovered so many errors that the company risked losing billions of dollars in imprudent costs.  To avoid this, the company negotiated an arrangement under which it would be paid by ratepayers based on the plant’s output, rather than on the basis of reasonable construction cost.  In order to protect against the utility therefore pushing the plant too hard, regulators established an Independent Safety Committee to keep a sharp eye on the plant. Apparently the Committee was not looking for this kind of mistake, either, or it could have brought it to the attention of the operators and regulators much earlier.

4. A slow response from the NRC

In the 1980’s, when the NRC discovered that Diablo’s engineers had made serious design errors, the regulators lost confidence in the integrity of the plant.  In response, the NRC undertook copious inspections and ordered a complete design review.  Here, the NRC has looked at 5% of the plant’s records, uncovered a significant safety problem and even penalized the company for its failure to find the problem sooner.  Yet, where is the call for more thorough inspections, and a demonstration by the plant operators that the other 95% of the facilities and their operations are sound?  And how could 6300 hours of annual regulatory oversight not uncover such a basic problem or the lack of adequate post-repair inspections?

There are reasons for a loss of confidence in the safety of nuclear power plants.  That distrust can only grow if plant operators, inspectors, and regulators fail to make the extra effort to uncover and respond to significant problems.


Comments to “Multiple failures exposed Diablo Canyon to higher risk

  1. It is my sincerest hope that when Diablo Canyon finally pops, every single person responsible for its construction, from lobbyists to politicians, goes to jail for life. Who could possibly look at that area, its beautiful coastline, agricultural bounty, Mediterranean splendor, and allow for the potentiality of the despoilment and poisoning of that area for hundreds of years or perhaps longer? An absolute shame.

    I pray and hope the initiative to keep that plant running gives out before the inevitable 8.0 quake hits. What a shame! A huge reason I commute to SLO, where I work, rather than living there. I will not subject myself to the inanity of an energy-industrial complex, and energy-gobbling citizenry, that allowed that plant to be built.

  2. If we were living on a planet with intelligent live, we should principally build many forms of un-contaminating, inexhaustible and non-polluting energy like active solar energy, magnetic motors, wind energy and other sources that nature offers to us freely.

    When I speak about “intelligent life”, I intend to refer to a group of living beings that abide by the rules of nature and live positively according to their type and quality. On the other hand, a destructive species that is ravages their “home” (their planet), making life more and more impossible for themselves and for the other “fellow creatures” can, in my opinion, hardly be called “intelligent”.I believe more home owners need to look into alternatives such as building your own solar panels and or magnetic generators to power our homes.We do not have to depend on nuclear generation for electricity.

  3. If concerned scientists spent 6400 person hours at Diablo Canyon each yea, how did they miss the reversed valve?

  4. For a big picture view of nuclear reactor hazards read:


    There are 2 big reasons why not many nuclear plants will be built in the USA in the future:
    1) there isn’t enough uranium left to power the world’s existing plants unless fusion or fission is finally figured out after over 70 years of trying
    2) investors aren’t going to fund new plants because
    a) there’s too many years of waiting for a return on investment.
    b) the EROI (energy returned on energy invested) may not be positive or high enough to justify an investment — a huge amount of cement and steel are required — which is a LOT of energy upfront, perhaps more than will be generated when all the costs are factored in (the electric grid, backup generators, etc are part of the cost as well).
    c) the liabilities are too high in the event of a failure.

  5. Recently I saw a truck from our local water company and two men doing something underground at an intersection near my house. I was curious enough to stop and ask them what they were doing. The answer was that they were checking that the valves in the system were not frozen in place. Evidently the company has a practice of turning these valves once every six months. If my local water company can find the time and money to perform these checks on the system, should not a nuclear company be a hundred times more imaginative and industrious? If not, why not?

    • Patrica, et al.,
      As you may be aware when these reactors are shut down for service the utilities are forced to buy from other more expensive sources, mostly out of state. There is a huge economic benefit to keeping these plants running, and running safely. No operator wants issues like these for two reasons; they lose money and they lose face value and confinence with the public who are powerful enough to shut them down regardless of any regulatory agency.

      That being said, the Nuclear Regulatory Commission along with the industry and dozens of independent standards committees have created requirements for in-service inspection and testing (testing while the plant is operating) and out-of-service and preventative maintenance plans. These activities are approved by several organizations before a plant is allowed to use them. The particular valves in question cannot be tested without shutting down the plant, so they are tested only during outages (during plant refueling or other unplanned outages). The intervals in which they are tested are based on hundreds of thousands of dollars of calculations and independent consultant reviews and data from decades of testing of these valves.

      These companies spend an overwhelming amount of time and money trying to determine how often to test. Sometimes things fail prematurely and as a result the entire industry in the US responds and these testing programs are changed to account for these failures and testing becomes more rigorous. Also, these valves are provided in the plant redundantly; meaning that if one fails, 2 or 3 are still operating that provide the same capability.

      Plants make every effort to remain operating, safely and economically. Sometimes the economical incentive is higher which is why we have regulatory agencies keeping everything in check. So far, the nuclear system has worked. And if everyone spends time to read about all the improvements being made in safety technology and improvements being made in the nuclear regulatory commission I think everyone should feel better. These plants are becoming safer than the day they were built.

  6. Thank you for this article. You articulate some of my concerns very well.

    I am so tired of hearing “it’s not the nuclear plant’s fault,” which I’ve heard a thousand times in the last 10 days (“it was a 9.0 eq, it was a tsunami, but the plant did just fine!”) or spokespersons for utilities always reverting back to: “the potential is very small for the type of situation …” blah blah blah, as if we didn’t just witness with our own eyes the unleashed, jaw-dropping power of ‘potential.’

    Nobody can predict the future and what some of these statistics are based on is less than 200 years of recently recorded history, the tiny length of an atom compared Earth’s history of growing pains. The least the NRC and utility companies can do is make sure safety promises are kept.

    18 months? Give me a break. Did the inspector at least win immunity?

    If any good comes out of this nightmare in Japan it is that people have been rudely awakened by a thump in the night, encouraged to get involved in the way the world works.

    I congratulate you on your admirable choice of vocation.

  7. Regardless of how sound the design is, what are the security and safety measures and how these measures work, the fact is that there is no safe nuclear technology. All is just a small part of much bigger money and power game going on in our country and worldwide. We were told for years and years that off-shore drilling is completely safe now! Technology is so advanced that there are absolutely no risks involved! Then what happened in Gulf? Same is the case with nuclear power plants. We were told time and time again that nuclear energy is now totally safe and with advanced technology, there are no risks involved. So, comes the Japan disaster. Truth is that the media and politicians are sold out to big corporations and their lobbies.

Leave a Reply


Security Question *