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Explanation of some nuclear terms.

  1. Apr 29, 2013 #1
    Hi everyone,
    I was reading the report about the Fukushima incident and I do not understand some concepts because of my limited understanding. Could you please help me?

    Combustible Gas Control. <----- can you explain this concept in simpler language
    The NRC regulations in 10 CFR 50.44, “Combustible Gas Control for Nuclear Power Reactors,” require reactors either to operate with their containment atmosphere inerted, resulting in the lack of oxygen to support combustion, or to have the capability for controlling combustible gas generated from a metal-water reaction involving approximately three-quarters of the fuel cladding so that there is no impact on the containment structural integrity. RG 1.7, “Control of Combustible Gas Concentrations In Containment,” provides further guidance on regulatory expectations for combustible gas control. pg 42

    What happened fukushima

    Information available at the time of this report indicates that, during the days following the Fukushima prolonged SBO event, Units 1, 3, and 4 experienced explosions, causing significant damage to the reactor buildings for those units. It is believed that the explosions in Units 1 and 3 resulted from hydrogen gas that was liberated inside the drywell during high-temperature zirconium fuel cladding reactions with water and that hydrogen gas migrated to the reactor building. The migration route of the hydrogen gas from the primary containment to reactor building has not yet been determined definitively; however, the failure to prevent, through containment venting, the primary containment pressure from significantly exceeding the design pressure likely contributed to the transport of hydrogen gas. It is believed that the explosion in the Unit 4 reactor building also resulted from hydrogen gas, but the source of the gas in Unit 4 is not yet clear. Unit 2 may also have experienced a hydrogen explosion in its suppression pool inside containment. However, the mechanism for suppression pool failure remains unclear. pg. 42

    2. Containment Overpressure Protection pg.39 <----- could you explain this in simpler language?
    can you explain what happened at fukushima pg. 40

    3. Spent Fuel Pool Safety pg 43. <------ could you explain this in simpler language?
    Can you explain what happened at fukushima pg. 45


    Thank you very much,
  2. jcsd
  3. Apr 30, 2013 #2

    Simon Bridge

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    They mean pretty much what they say - perhaps if you explained which bits you didn't understand?
  4. Apr 30, 2013 #3

    jim hardy

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  5. Apr 30, 2013 #4


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    "controlling combustible gas generated from a metal-water reaction involving approximately three-quarters of the fuel cladding so that there is no impact on the containment structural integrity," applies in the case of a loss-of-coolant-accident (LOCA) in which the primary coolant system is compromised. With loss of coolant, there is a risk of loss of cooling of the fuel, which generates a fair amount of heat following shutdown, although the heat generation (decay heat) diminishes rapidly following shutdown.

    If the coolant is not circulated, the coolant will heat up, and possibly change to steam, which has poor heat transfer. As the coolant and fuel temperature (specifically the cladding) increase, there is a potential for cladding oxidation. In the case of Zr alloys, Zr + 2 H2O => ZrO2 + 2H2 is the primary concern.

    At Fukushima, they had LOCAs in the cores, or at least that is the current understanding. At the very least, there was insuffiicient cooling, or once the sea water was introduced, it reacted chemically, with the fuel which apparently disintegrated, hence the large release of fission products.
    Last edited: Apr 30, 2013
  6. Apr 30, 2013 #5
    Hi everyone,
    I am very sorry for not being clear about my question. When I read the report, I learn the main concern of a nuclear plant is station blackout, SBO. SBO leads to the following issues:
    1/ Prolonged Loss of Alternating Current Power
    2/ Containment Overpressure Protection
    3/ Combustible Gas Control
    4/ Spent Fuel Pool Safety
    5/ Onsite Emergency Actions
    Thank you very much, Astronuc for explaining the concept of combustible gas control. What have changed (regulations ....) to the above issues after the Fukushima incident?

    I am writing a research paper on nuclear energy and I am so confused by the sea of information on the internet. Here is my research outline:

    Topic: Whether or not a moratorium on nuclear energy should exist

    1. If U.S. nuclear plants can sustain an incident like the Fukushima accident, US nuclear plants should be continued.
    2. If new forms of safety regulation can insure the safety of civilians, us nuclear plants should be continued
    3. If the current nuclear plants are outdated and the cost of retrofitting is inefficient, a moratorium should be considered
    4. If all the negative opinion on nuclear energy are true and scientifically correct, a moratorium should be considered.
    5. If the insurers of these plants insure the safety of us civilians and be responsible with any nuclear accidents, us nuclear plants should be continued.

    I have trouble with number 5 because I have no knowledge of the insurers of these plants. Could anyone provide me some scholarly sources about the insurers? Is there any problem with the insurers?

    I have a few questions and I would very much appreciate if anyone could answer them and provide reliable sources?

    1. What new rulings have been made by the us courts regarding nuclear energy regulation (post-fukushima)?
    2. How do new regulations insure that it is safe to continue nuclear energy? What are the new regulations (I know SBO regulation is one of them)
    3. Are the negative views on us nuclear energy industry pessimistic or realistic?
    4. Is there a need to retrofit current plants? what are the costs? will it be dangerous to not replace current nuclear plants?
    5. Can the fukushima incident happen to us nuclear plants? why? Can us nuclear plants sustain a accident like fukushima? because some in the forum said that people have confirmed that there is no problem with our nuclear plants so a moratorium did not exist. Could you provide me some sources regarding this?
    6. How are nuclear plants safe enough to be relied on as a source of energy?
    7. What are the insurers? What do they do? Are there any problem with them?

    Here are the sources I have found: (however, I couldn't find all the info I need because of my poor research skill)
    NRC.gov, Tepco, Nytimes (provide news on nuclear energy)
    Thanks Jim for the website!
    -sorry for my bad grammar.

  7. Apr 30, 2013 #6

    jim hardy

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    wow. Quite a topic yoou picked.

    I worked in a plant for decades so am probably not without my bias.
    Nuclear power is like any other human undertaking, do it well or not at all. Beware of hubris and dont take short cuts.

    Here's a good introductory manual for BWR's, in case you hadn't already found it:
    be back later - i'm away from home , wife is getting a new hip and we gotta go now to physical therapy....

    old jim
    Last edited: Apr 30, 2013
  8. Apr 30, 2013 #7
    Hi xholic.

    Looking down your questions. With regards to a Fukushima like accident, it depends on what you make your assumptions to be. The US NRC has issued (http://www.nrc.gov/reading-rm/doc-collections/news/2012/12-097.pdf) executive orders requiring modifications which do three things. First is to add hardened reliable venting, which will help improve management of post-accident conditions. The second is improved spent fuel pool instrumentation (safety grade and remote). The third is to have N+1 portable equipment and procedures available both on site and offsite, with the ability to FULLY maintain critical safety functions (water injections/heat removal) indefinitely. The third option requires manual connections of portable equipment, and other than the portable connection hookups and engineering analysis, does not involve installed automatic protection systems. Some people say, because the portable equipment requires human actions to be installed, that this is nothing more than "Safety theater", I personally think that a reader should look into this, and the industry's FLEX program, to make their own determination. (note: I work in the industry, and FLEX is an industry program which is driven by NEI, which means a lot of the material could be considered biased).

    The FLEX program involves installing portable connections, procedures, doing the engineering analysis, purchasing onsite and offsite portable equipment, to extend cooling conditions indefinitely. The first phase of FLEX is post accident where a beyond design basis event occurs. The event is assumed to be (basically) a total and extended loss of all permanently installed AC power equipment, AC powered emergency pumps, any resources (water tanks/fuel tanks) that do not meet very specific criteria, and gross damage of the facility caused through natural or man made (security threat) means. In Phase 1, on-site equipment that is DC powered, or that meets very specific criteria, is assumed to be used for the first few hours of core cooling. In Phase 2, on-site portable equipment is installed to hold the plant over for at least 24 hours. In Phase 3, the off-site portable equipment is brought on-site to extend these safety functions indefinitely. The goal is to prevent core damage. The US nuclear industry has built 2 off-site regional response centers, where there is enough portable equipment for 5-6 units at each site, and they can get all of their equipment to any site in the country within 24 hours.

    So the answer to #1 is basically, the US NRC has found that all US nuclear plants are safe, and that the orders being introduced are enhancements to support lessons learned and defense in depth of nuclear power facilities to withstand severe post accident conditions.

    (I think I inadvertently answered #2 as well).

    For #3, it depends on what your requirements are. If you are someone who feels that fully passive cooling systems NEED to be installed on nuclear plants (such as the opinion of former NRC chairman Jazcko), then all current nuclear plants should be shut down immediately, as there is NO cost benefit to doing so for existing plants. It is virtually impossible to install long term passive cooling systems, you need to design the plant around using them. The new generation 3+ reactors (AP1000/ESBWR) and small modular reactors DO have passive cooling systems for at least 72 hours, so there should be no moratorium on licensing of new plant designs (in my opinion).

    4: There is a lot of positive opinion too on nuclear energy, with many polls showing that a majority of the US supports nuclear power, with a majority showing that they would even support new reactors at existing sites. I'm not familiar with how the numbers were generated, but there are polls out there. Like any other political issue, its not a one sided issue.

    5: With regards to insurance in the US, look up the "Price Anderson" act. The act requires each plant to have its own initial insurance pool, along with a full industry combined pool. The total liability is something like 12.6 billion dollars. There are people who say the act is a government subsidy (it kind of is from one point of view), and that a full on nuclear accident would cost drastically more than that. Supporters of the act claim that by having this shared pool, the total insurance cost is far more than any private insurance would ever be able to provide.

    (I was looking at your hypotehsis, and just running down the items in order, I think i ultimately answered all your questions though)

    Anyways good luck in your research.
  9. Apr 30, 2013 #8
    Thank you very much everyone!
    My research paper is around 3000 words, which is nothing compared to the reports you guys do on the daily basis, but it is a huge deal for a high school student like me.
    Thank you very much for helping me out!

  10. Apr 30, 2013 #9
    Jim: Which sections should I read that will directly help me with the research?
    Take care, Jim

  11. Apr 30, 2013 #10
  12. Apr 30, 2013 #11

    When I said biased, I was really referring to all the NEI PR material about it. The program itself is fair game. Search for NEI 12-06, which is the FLEX program document, and what all plants will eventually incorporate into their operating license conditions. http://pbadupws.nrc.gov/docs/ML1214/ML12143A232.pdf Here is a link to the NEI document about the FLEX program. http://pbadupws.nrc.gov/docs/ML1213/ML12132A009.pdf Here is a link to a power point about the program.

    This document (NEI 12-06) is the actual description of the FLEX program, so its not "subjective" like all the PR material is. I was just cautioning you about basing a paper on the PR material.
  13. Apr 30, 2013 #12
    I see. Thank you very much.

  14. Apr 30, 2013 #13

    jim hardy

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    Ahhhh yes this is a research paper not a career (yet).
    You might want to use that BWRmanual as a backup source for details.

    Here's a much shorter introduction that would probably be of better use to you. I hope you get to give a talk on your paper and can use some of the graphics.

    The sections on decay heat removal, emergency core cooling systems and containment describe the systems that were made unavailable when the electrical rooms and diesel generators got flooded.
    Look at page 3-18, it shows where the electrical room is - key 18. It got flooded by saltwater so no electricity was available to run emergency equipment.

    Now imagine for a minute that you worked at that plant in some lowly position.
    When you found out there were geophysicicist's reports that a forty foot tidal wave was a possibility, and you knew your electrical room could only survive a third of that, what would you do?
    I have to believe that if TEPCO executives had been made personally aware they were sitting ducks they'd have taken action. And i do think it is proper for a lowly employee to raise such a concern.
    Are US plants safe from loss of all AC power? That depends on how well they keep their electrical gear and diesels in shape and protected from natural phenomena. Ours were sacred to us.
    Observe that the Fukushima units whose generators stayed high and dry came through just fine.

    I want to think a while on your questions.

    Camper's post is first i've heard of "Flex". We started some of those things in 1990's because they seemed prudent and i'm sure others did also. That's progress.

    i'll watch a while...

    old jim
  15. Apr 30, 2013 #14
    Thank you, Jim.

    I think your hypothetical situation is great to be noted in my paper because it can give another perspective about the fukushima incident. Although the tsunami was a beyond-design-basis event, the aftermath would have been better if they took action in response to the coming tsunami.

  16. Apr 30, 2013 #15
    Can somebody please verify whether I can use these polls?
    http://www.nei.org/resourcesandstats/publicationsandmedia/newslettersandreports/perspectivesonpublicopinion [Broken]

    Last edited by a moderator: May 6, 2017
  17. Apr 30, 2013 #16


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    During operation, the plant systems draw electrical power from the power being produced by the reactor, actually from the generator, which is driven by the turbine, which receives steam from the directly from the reactor in a BWR, or indirectly via a steam generator in a PWR. When the reactor is shutdown, the plant draws power from the grid - just reverse from supplying the grid.

    SBO is a concern when the reactor does not produce power (it had to shutdown), nor receives power, because the grid is down - as was the case in Fukushima. In that event, emergency diesel generators must provide the electricity to run the controls and instrumentation, and the pumps to cool the fuel in the reactor and the fuel stored in the spent fuel pool.

    A reactor/NPP designer must comply with a number of federal regulations that ensure that a reactor can be safely shutdown, remains shutdown, and is coolable, such that the fuel integrity is not compromised. If the fuel does become compromised, the primary system and containment must be designed to contain the release of fission products. In the worst case, if those systems fail, then it would be necessary to control the release such that any dose does not exceed limits. Clearly that process failed at Fukushima.

    As an engineer/designer, I'd go for a design that precludes the challenge to containment.

    The Commandments (Bible) of nuclear plant design is - Appendix A to Part 50—General Design Criteria for Nuclear Power Plants. http://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-appa.html

    Everything else follows from that. The other sections support that, as to the Regulatory Guides and other requirements.

    Then there is - Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition (NUREG-0800, Formerly issued as NUREG-75/087)


    Now there is Regulatory Guide 1.181 - Content of the Updated Final Safety Analysis Report in Accordance with 10 CFR 50.71(e)

    Some background - http://www-ferp.ucsd.edu/ARIES/DOCS/Hoffer9505/NRClicensing.pdf
    Last edited: Apr 30, 2013
  18. Apr 30, 2013 #17
    Thank you very much, sir!
    Is the subsidy the only problem of the Price Anderson Act?
    Are there any other problems about nuclear insurance (the insurers .. etc)
    Price Anderson
  19. Apr 30, 2013 #18


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    Price Anderson may not be adequate in all cases. It probably wouldn't be adequate for those who have been forced from their homes or businesses in Fukushima.

    As a engineer/designer, I'd be more interested on ensuring the plant systems are in place to preclude the need for an insurance program. That comes from being a proficient engineer with an fundamental understanding of the physics of the system (and components) and proper application of the theory.
  20. Apr 30, 2013 #19
    I see. Thank you, sir.
  21. May 1, 2013 #20
    I would like to ask whether the American Nuclear Insurers (ANI) is an interest group? Is there anything significant about the ANI?
    Also, what do you think about this quote?
    "The insurance industry considers the nuclear industry an unsafe bet. As a result, the nuclear industry must self-insure, with help from the government. My view on nuclear is that when it becomes safe enough for commercial insurers, I'll seriously consider it. But even then, only if the shareholders, investors, and executives who stand to benefit are confident enough in the safety that they are willing to keep the spent nuclear waste from the plants in their own basements." No Impact Man

    Could you provide me some sources in response to this quote?

    Last edited: May 1, 2013
  22. May 2, 2013 #21
    hi xholicwriter !
    You have many good questions, I hope you remain interested and take the time to find answers. Here's a little advice on your paper -- 3000 words probably sounds like a lot to you, but it really isn't. You might want to pick just one of these questions as your subject, rather than trying to answer so much in a single paper. For example, you could write pages and pages about insurance and the Price-Anderson act. Or about the US nuclear industry response to Fukushima, or about what actually happened at Fukushima... Or why hydrogen is even a concern (where does it come from and what does it do). If you pick one of these and focus on it, your paper will probably be more interesting and get a better grade. You can always write more papers on the other questions later (even if you do them just for yourself).
  23. May 2, 2013 #22
    The insurance question is used as a standard whip by the anti-nuclear crowd. Their statements (like your quote) seem on the surface very reasonable, "it must not be safe if the insurance companies won't sell insurance at any cost..." But is this really true? Is there really "no insurance" on the nuclear plants? Are nuclear plants the only facilities like this? Who insures Hoover dam?

    How much has the US government paid out since Price-Anderson started back in the 1950s? How much did they pay at Three Mile Island?
  24. May 2, 2013 #23


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  25. May 2, 2013 #24
    Thank very much everyone,

    The NRC says "Price-Anderson does not require coverage for spent fuel or nuclear waste stored at interim storage facilities, transportation of nuclear fuel or waste that is not either to or from a nuclear reactor, or acts of theft or sabotage occurring after planned transportation has ended."
    Do we have insurance coverage for these accidents?

    Sorry I'm in a hurry. I'll respond to the comments when I get home.

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