Keeping Reactor Electric Systems in Phase

Jake Zimmerman
Electrical Engineering Branch Chief
Office of Nuclear Reactor Regulation

Nuclear power plants generate electricity, but their systems need power from the grid to operate. That electricity is delivered through three lines, or “phases.” If one phase is lost, or “open,” that can challenge a plant’s ability to safely shut down. The NRC and U.S. nuclear power plants are working to ensure “open phase conditions” are resolved safely.

CalvertCliffs_DSC2302Losing one or two phases coming from the grid to a transformer can unbalance the voltage on the side of the transformer connected to plant safety equipment. Voltage problems can automatically trigger the plant to disconnect from the affected power line, but sometimes they don’t. In that case, the plant’s safety systems might not get switched to backup power sources and may lack enough power to function properly. An “open phase” can happen at all but one U.S. commercial reactor (Seabrook).

The issue got our attention in 2012, when the Byron plant in Illinois shut down safely after an “open phase” event. The plant didn’t automatically switch from the affected power line, but control room operators diagnosed the problem in eight minutes and manually swapped power sources.

The NRC examined the issue and determined a handful of plants had dealt with open phase situations that never challenged plant safety. The agency’s response included sending all U.S. nuclear power plants a Bulletin to confirm they could meet electric power system requirements.

Every affected U.S. nuclear power plant has temporary measures in place to reduce the risk associated with an open phase condition. These measures include ensuring control room operators are aware of the issue and are trained to respond, and modifying power source switching procedures to ensure plants have emergency power if needed. The NRC staff reviewed and agreed with the temporary measures, and regional inspectors plan to inspect the measures.

The nuclear industry’s proposed permanent fix would provide alarms to alert operators to the issue and start an automatic swap of power sources. The NRC staff has laid out four goals that plants should meet when they install the proposed fix. We’ve also developed objective guidelines for our reviewers to consider when examining the plants’ implementation, which the NRC expects will be done by January 2019.

The NRC recently received an enforcement petition on the open phase condition. The petitioners asked the NRC to require either immediate corrective actions or shutdown of operating nuclear power plants. While the agency concluded the plants’ temporary measures eliminate the need for additional immediate action, the petition was accepted for further review.

Author: Moderator

Public Affairs Officer for the U.S. Nuclear Regulatory Commission

33 thoughts on “Keeping Reactor Electric Systems in Phase”

  1. Scott,

    Thanks. You said: “The NRC staff’s determination was based on engineering judgment and qualitative reviews of the Byron Unit 2 event and plant-specific accident analysis performed by the licensee.”

    What is the track record of “engineering judgment?”

    Is it as reliable as “knowledge-based performance?”

  2. Your reference cited here (ML14120A203) has this statement:
    “The staff determined that a design-basis event concurrent with an OPC would likely have resulted in the plant exceeding criteria specified in 10 CFR50.46, “Acceptance criteria for emergency core cooling systems for light-water nuclear power reactors.””

    What does this mean in plain English?
    Minor fuel damage?
    Major fuel damage?
    Complete meltdown?

    The quotation above is just one more example of NRC obfuscation, bafflegab, spin-meistering, and deliberate lack of transparency.

  3. The NRC staff’s determination was based on engineering judgment and qualitative reviews of the Byron Unit 2 event and plant-specific accident analysis performed by the licensee. The operating event at Byron Unit 2 revealed a significant design vulnerability where an OPC in the plant’s offsite power supply caused a loss of certain safety functions powered by the site’s alternating current electric power system. As a consequence, neither the onsite emergency diesel generators nor the offsite electric power system was able to perform its intended safety functions in accordance with NRC requirements.

    In this case, the OPC was unrecognized by the operators for almost 8 minutes. The accident analysis for Byron Unit 2, as described in Chapter 15 of the Updated Final Safety Analysis Report, discusses postulated design basis loss-of-coolant accident (LOCA) scenarios, which are unlikely, and demonstrates that the plant is designed to meet the regulatory acceptance criteria for both large-break and small-break LOCAs. As part of the analysis sequence of events, tables provided the expected times when various actions occur. For example, in a large-break LOCA sequence of events, pumped safety injection is expected to occur at 46 seconds and the resulting peak clad temperature would occur at 96 seconds. For a small-break LOCA analysis, pumped safety injection is expected to occur as early as 54.3 seconds and the peak clad temperature would occur as early as 889 seconds. The availability of pumped safety injection depends on power from either the emergency diesel generators or offsite power. It is the NRC staff’s engineering judgment, and reasonable to assume that, had a design-basis large break LOCA occurred concurrent with the unrecognized OPC that occurred at Byron, it likely would have resulted in the plant exceeding the emergency core cooling systems acceptance criteria due to the delay in pumped safety injection.

    Scott Burnell

  4. Which one?

    The one hiddencamper works at: “For my plant, this was easy, because we are one of the few who actually have the ability to detect when this condition occurs.”  This was all in references given to you previously.

    How come?

    Go ask him, he’s the subject-matter expert.

    Did this one know it was the first?

    Go ask him.

    How come no others got it right?

    That’s been quite adequately detailed in text that I’ve seen referenced here but you aren’t reading closely enough:  it was an underestimation of the event likelihood and magnitude of consequences.  Now that operators are watching for this problem in particular the likelihood of any adverse consequences are about nil.

    Compared to the certainty and magnitude of consequences from the fossil backups required for “alternative energy”, we should be welcoming a Three Mile Island every decade as a very tolerable price to avoid them.

  5. What is the increase in Core Damage Frequency (CDF) for a plant vulnerable to Open Phase Fault as compared to a similar plant that is not vulnerable?

  6. An inescapable fact is that when a design flaw is revealed by an actual event there are corresponding flaws in the design processes, the design review processes, and, usually, other processes that were expected to have prevented and/or revealed the flaw.

    Observation: The Open Phase Fault episode reveals fundamental weaknesses in the nuclear power design and licensing processes.

    Observation: Fixing a design flaw is just one step in fixing what is unacceptable.

  7. It is not in the public interest to have design flaws manifested by real events.

    In a good safety culture design flaws are revealed by design reviews or by testing.

    Positive control is when what happens is what is supposed to happen and that’s all that happens.

  8. Engineer-Poet,

    Which one?
    How come?
    Did this one know it was the first?
    How come no others got it right?
    Perhaps there’s a great story behind this.

  9. I am not for shutting the plants down.

    I am for the following:

    ONE: Fix the problem.
    TWO: Fix the extents of the problem.
    THREE: Fix the systems involved in creating the problem.
    FOUR: Fix the systems that should have identified the problem earlier.
    FIVE: Fix the harmful conditions, behaviors, actions, and inactions that resulted in the nature, the magnitude, the location, and the timing of the problem.
    SIX: Fix the harmful conditions, behaviors, actions, and inactions that resulted in the nature, the magnitude, the location, and the timing of the system problems.
    SEVEN: Fix the extents of those harmful conditions, behaviors, actions, and inactions.
    EIGHT: Fix the other harmful effects of the systems problems.

  10. Please keep in mind our guidelines specify that comments must be related to the post on which they are submitted. This comment is straying away from the topic. You can use the open forum for further discussion of this matter.

    NRC Moderator

  11. Gary – Thank you for the substantive technical background information so that the rest of us can better understand the issue rather than relying on opinion.

  12. I would greatly appreciate an answer from the moderator or any member:

    [Moderator note: Some verbiage here was removed to adhere to our comment policy.]

    What were the harmful conditions, behaviors, actions, and/or inactions that resulted in there being a serious flaw in every design basis, every safety analysis report, every regulatory review, and every probabilistic safety analysis that were left to be revealed by actual events?

    Speaking as an electrical engineer, I will bet that the possibility of a broken wire that does not reach the ground and cause a ground fault was considered to be very rare.  The fact that the equipment continued to run during this open-phase condition, albeit at degraded performance, suggests that the designers were almost correct in dismissing it.  Speaking as a double-E, I would not be surprised if the proper configuration of phase-shifting capacitors could step in for the open phase (which would have to be properly breaker-isolated first) and allow equipment to run at full capacity on the remaining two phases.  This is how 3φ power is generated from 1φ sources for e.g. small machine shops.

    One fact you’re doing your best to bury through obfuscation is that the entire industry has been aware of this problem for years now and is designing the fixes.  Operators are also very much aware of it and how to respond to it if they detect it.  Last, the worst possible outcome of an undetected problem was on the order of a fraction of a TMI, which had exactly zero fatalities and zero injuries.

    Another fact that you’re trying to bury is that any shutdown of nuclear plants immediately increases the demand for natural gas, which is about as damaging as coal through GHG emissions and has substantial damaging health effects through leakage of toxics.  The Aliso Canyon fiasco has caused more harm to human health than the entire commercial power industry of the USA.

  13. Let’s apply the same vague, FUD-derived criteria to “renewables” (specifically, wind and solar) as a “fix” for GHG emissions and criteria pollutants.

    ONE:  Fix the problem (of inability to provide reliable power without nearly 100% fossil-fired backup).

    This is the termination condition.  Nobody has done so, nobody has a serious proposal to demonstrate the capability, and the energy cost of the batteries and such required to do it even in theory suggest that it is impossible.  Ergo, “renewables” almost certainly cannot solve the problem and no “plan” based on them should be taken the least bit seriously.  Further, given the utmost seriousness of the problem, no proven solution should be taken off the table.

    But taking that solution off the table is the FIRST thing on your agenda.

  14. …there was one US BWR that already had such conditions taken care of in its design and operational specs.

    Moderator Note: Some verbiage was removed to adhere to the comment policy.

  15. No doubt what you say is true. Radiation is a silent killer much worse than CO. Those that are not educated do fear it. But I was raised on it, Rickover’s nuclear power program + over 30 years in a commercial nuke plant, & I fear it as well. There is just no such thing as a safe nuke.

  16. The Open Phase Condition as revealed by actual events points to fundamental flaws in the NRC license application review process affecting the integrity of all light water reactor licenses. What is being done to investigate this?

  17. Because most of the people are not educated for the structure of Nuclear Power Plant. How process works? How safe it is?

    The worst most of them are always rely on media not by research.

  18. If there were a good safety culture what would be fixed?

    ONE: Fix the problem.
    TWO: Fix the extents of the problem.
    THREE: Fix the systems involved in creating the problem.
    FOUR: Fix the systems that should have identified the problem earlier.
    FIVE: Fix the harmful conditions, behaviors, actions, and inactions that resulted in the nature, the magnitude, the location, and the timing of the problem.
    SIX: Fix the harmful conditions, behaviors, actions, and inactions that resulted in the nature, the magnitude, the location, and the timing of the system problems.
    SEVEN: Fix the extents of those harmful conditions, behaviors, actions, and inactions.
    EIGHT: Fix the other harmful effects of the systems problems.

    What has been fixed?

  19. You cannot fix stupid or nuclear power plants. It is just like trying to sugar-coat…!

    Moderator Note: Some verbiage removed to adhere to blog comment guidelines.

  20. “Fix it and move on” is not good nuclear safety culture.

    It is more pruning the poison ivy.

  21. I would greatly appreciate an answer from the moderator or any member:

    What were the harmful conditions, behaviors, actions, and/or inactions that resulted in there being a serious flaw in every design basis, every safety analysis report, every regulatory review, and every probabilistic safety analysis that were left to be revealed by actual events?

  22. One of the most important lessons to be learned is that there was a serious flaw in every design basis, every safety analysis report, every regulatory review, and every probabilistic safety analysis and it was revealed by actual events.

    What are the other flaws?

    Can we find them before the events?

  23. Sorry, I was wrong EP. Even us trolls can make a mistake. Besides a wise man can change his mind, a fool never!

  24. The hysterical claims here show that this forum is primarily used by anti-nuclear propagandists to spread their FUD to a naïve public.

    Look at it.  The last time this came up on the NRC blog, I posted links to an insider’s view of the issue which shows that the industry has already put measures in place well ahead of the rule-making process (part 1, part 2), and there is no danger to plants any more, let alone the public.  (The industry wants to keep unnecessary expenses down, and equipment that breaks due to undetected open-phase conditions is certainly one of those.)  Most of what’s going on now is getting experience with the new systems so they can be calibrated correctly and the NRC’s rulemaking finalized so everyone can certify compliance.

    ALL of the FUD was refuted the last time around, but what do you see if you come here today?  “NRC’s failure to correct a long standing ‘open phase’ problem”!  “Seven engineers within the NRC decided to take action because the open phase condition was not being given the necessary emphasis for 4 years, thus compromising public safety.”!  “To me this speaks to NRC safety culture features that include negligence, willful misconduct, and reckless gambling with public safety.”!  Everything that refuted the propaganda narrative fell on deaf ears; the propagandists are completely shameless.

    I submit that IT IS NOT IN THE PUBLIC INTEREST for the NRC to operate a forum which is primarily used to spread disinformation about its particular area of expertise, disinformation which in most cases is completely contradicted by authoritative sources on this very NRC site.  Moderators should either not approve such propaganda, or attach notes to it stating that it is in error (preferably with links to authoritative sources).

  25. Dear Anonymous,
    I too once thought that nuclear power was safe. But I have believed for some time now that the term “safe nuke” is an oxymoron like “limited nuclear war” or “congressional wisdom”. Bitter experience & lax regulation has completely changed my mind. Thankfully nukes are becoming a thing of the past because they are just too expensive to build, operate, or maintain. They can no longer compete in the energy marketplace. In fact the NRC needs to be renamed the Nuclear Retirement Commission.

  26. Safe nuclear power can bring prosperity peace modernization education to the world these tools can be used to combat terrorism poverty and help promote environment and good health

  27. Excellent comments all. Shameful performance by an agency that is no longer our watchdog but a lapdog for the nuclear industry.

  28. The NRC, FEMA, MEMA and the owners of Pilgrim Nuclear Power Station in Plymouth, MA have known about Pilgrim’s switch yard vulnerability to ground fault during severe winter weather conditions (Nor’easters, blizzards, ice storms, etc) yet allowed the plant to roll the dice in the face of NOAA Blizzard warnings gambling with public safety knowing that evacuation would be impossible (sometimes for days) during these kind of winter storms. Since the Blizzard of “78” Pilgrim’s switch yard has “flashed over” and ground faulted eight times and gone uncorrected. It was only public pressure after Nor’easter/Blizzard Juno January 27, 2015 switch yard failure accompanied by multiple additional safety equipment failures during the Scram that the owner/operator, the NRC and MEMA initiated preemptive precautionary shutdowns (all be it discretionary) in advance of NOAA winter weather warnings for the Plymouth, MA area.

    To me this speaks to NRC safety culture features that include negligence, willful misconduct, and reckless gambling with public safety. These suspicions are only strengthened by how this phase loss design oversight and weakness was only acknowledged by the NRC due to a 2.206 petition filed by seven NRC employees as citizens because their concerns expressed in the professional workplace were being systemically ignored by the NRC.

  29. Mr. Jake Zimmerman,
    Your reference cited here (ML14120A203) has this statement:
    “The staff determined that a design-basis event concurrent with an OPC would likely have resulted in the plant exceeding criteria specified in 10 CFR50.46, “Acceptance criteria for emergency core cooling systems for light-water nuclear power reactors.””
    I have a straight forward question. How exactly did you “determine” this event would “likely” exceed the requirements of 10CRF50.46? Did you actually run the Safety Analysis transient using the actual known conditions at Byron2 at the time of the event, or are you guessing based on the science fiction world of Safety Analysis transients? I don’t even like the use of the word “likely.” This is not something that needs a guess, run it with ACTUAL known conditions at Byron2 at the time of the event. Then make a simple English statement (clear communications) about “the actual analysis shows, using known plant conditions at the time of the event…Does it or doesn’t it show exceeding the requirements of 10CFR50.46”?
    I understand Safety Analysis transients, and why they are run. They can use input assumptions that can be actual mutually exclusive conditions, forcing conservative inputs all in the worst direction all at the same time. But those results may have nothing to do with the results of an analysis of the actual plant event using actual plant conditions at the time of the event.
    My issue is not about whether the OPC condition should be fixed or not; it should as it might put an operating team in a challenging position. My issue is about a “perception” created by the above quote. The LER Supplement for the above Byron2 event states the OPC condition combined with a DBA (LOCA) would have cleared the ESF buses on UV and started the EDGs, but with only about a 1 minute time delay (over the delay assumed in Safety Analysis).
    So is this an actual real problem, with respect to the Acceptance Criteria of 10CFR50.46, or an imaginary problem? It is quite a statement to claim this is a real 10CRF50.46 problem, without understanding how this conclusion was reached.

  30. Yet another of a seemingly endless number of threats to nuclear plant & public safety. This industry is well over a half century old & still new threats to safety are revealed all the time! The only “phase” the NRC should be looking at is “phasing” themselves out of business!

  31. This is a long standing issue identified by your staff, which some of them had to go public in order to bring attention to the ‘open phase’ issue. It appears, NRC officials at the executive level have decided to support the nuclear industry instead of public safety.

    Contradictions? – Quote – “The NRC examined the issue and determined a handful of plants had dealt with open phase situations that never challenged plant safety.” But, before that you say, referring to ‘open phase condition’ issues, “…the plant’s safety systems might not get switched to backup power sources and may lack enough power to function properly.” Seven engineers within the NRC decided to take action because the open phase condition was not being given the necessary emphasis for 4 years, thus compromising public safety. That is a serious issue of which executive decision making at the NRC seems to have become compromised. Now the issue is attempting to be downplayed as evidenced by the lack of complete information within this article. It is appreciated that the NRC is allowing public input on this issue.

    The problem – “This paper discussed that how and why standard or traditional protection elements cannot always detect an open phase in transformers…” http://www.cce.umn.edu/documents/cpe-conferences/mipsycon-papers/2013/openphaseconditionsintransformersanalysisandprotectionalgorithm.pdf

    Questions and a resolution via devices and equipment? – Description of damage that may occur to electrical components in an open phase condition. http://www.elongo.com/pdfs/voltages.PDF Questions – Have “special sensing devices” been installed on all components where an ‘open phase’ condition would compromise the safe operation of a nuclear facility? Have “automatic voltage regulators” been installed on all critical components?

    The NRC’s failure to correct a long standing ‘open phase’ problem and executive staff covering up the problem is indicative of an upper echelon Human Reliability failure of our nuclear regulator. Bravo to the 7 who came forward and shame on those officials who have ignored this long standing problem.

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