New TEPCO video- November 30, 2011

Now available at the APR YouTube Channel is the opening of the third series of "Explanatory Videos" produced by Tokyo Electric Power Company which cover the recovery from the Fukushima Daiichi accident.

This video covers many of the basics of radiation - how it's produced, what some basic terms and measurements are, and some thumb rules. The video is actually very interesting (even if not all the captions and illustrations have been redone in English) and it would be good viewing for anyone who has basic questions on radiation or radioactivity.

Click here to get to the APR YouTube Channel.

2:51 PM Eastern Wednesday November 30, 2011
ATOMIC POWER REVIEW

Read More

TEPCO reporting on vessel failure

NHK has carried the distilled result of information it has obtained from TEPCO regarding the possible amount of fuel damage, and melt, and vessel failure, and fuel melt into the dry well at Fukushima Daiichi No. 1.

To summarize the report (and we should note this is all preliminary) TEPCO feels that the melted core material that exited the pressure vessel may in the worst case, or in other words if the worst postulated case exists, have eaten about 2/3 of the way into the bottom structure of the dry well.

No exit of the material from the dry well structure is supposed.

TEPCO does not feel the material could have gotten below the structure, or into the actual basement, or come in contact with the floor or the ground. The material is not in the earth below the plant. Such reports as this are circulating, leading to a widely hysterical supposition on one site of a "hydrovolcanic explosion." That is about the worst - and certainly the least intelligent - hyperbole this author has ever read. I only mention it here because TEPCO's initial analysis released to NHK today (and about which I'm sure we'll see more) is timely in relation to that story.

Readers of this blog are all too well aware of this likelihood. In fact, let's take a look at a post from way back -- below is a link to a post I made on May 14th, 2011 when details were still far from clear about the plant conditions.

Fukushima Daiichi No. 1: Core melt / exit of pressure vessel speculated by TEPCO, NISA (post from May 14, 2011)

Readers may recall, a couple of months back, repeated attempts by TEPCO to indirectly assess the conditions of the lower vessel heads at the three reactor plants. None of these was successful - no useful data was obtained. What was clear though was that the electrical equipment in the lower head area was very heavily deranged, and not just in one zone or area, it appeared. TEPCO would like very much to get a handle on the actual condition and location of core material at each plant (and each is different in this respect) but so far has been really unable to directly assess this. The new study results that NHK is quoting come from a variety of data TEPCO has accumulated which don't require direct vision or detection. This is probably the best we'll have for a while.

Sharp readers also may recall the days in which the JAIF was continuously posting updates; that organization's last given estimate of core damage at No. 1 plant was, I believe, 70%. I should add though that all the data JAIF was using to attempt to estimate core damage percentages was very rough and some of JAIF's revisions of core damage percentages were taken directly from TEPCO. (Of course, all of JAIF's news items now are from NHK -- it has stopped making its own statements or assessments, at least in public.)

When TEPCO releases the full detail of this report, I'll put those details here.

9:15 AM Eastern Wednesday November 30, 2011
ATOMIC POWER REVIEW

ADDITIONAL MATERIAL / 9:35 AM

The NHK report indicates a melt depth of about 2.1 feet. The distance to the ground is roughly eighteen times this depth from the dry well interior floor to grade. Below is a drawing from WASH-1082 which I've marked to show the distance from the dry well floor to the grade outside, which on the particular plant shown is 39' 0". I do not presently know the exact measurement at Fukushima Daiichi No. 1 but it is likely within ten percent of this measurement... meaning that in the worst case that TEPCO is describing, by its own data, the core material may have melted only about as much as 5% of the distance to the grade.

Read More

Details of nitrogen injection at Fukushima Daiichi

I have made several posts on Twitter and on the FB page for APRA as developments on the nitrogen purge have become, but it's time for a roundup here.

Since the discovery that hydrogen gas was trapped in the upper part of the reactor vessel at Fukushima Daiichi No. 2, TEPCO decided that even though the concentration was not high enough to be dangerous (2.9% was found, while hydrogen concentration must be above 4% depending on humidity to be combustible) it was high enough to consider and then implement a nitrogen purge directly to the reactor pressure vessels themselves.

In order to make sure all of our readers (and we get new ones all the time) are clear on what is going on, let's look at some illustrations we've used before on this site but which have some new captions.

Below is a view of what the reactor plants at Fukushima Daiichi look like. By that I mean BWR/3 and BWR/4 reactors, installed in Mk I containments.


Below is a view of the drywell assembly, inside of which is the reactor vessel. The drywell is the primary containment.


We know that the reactor cores have been seriously damaged; in fact, they are in all likelihood nearly completely damaged or destroyed by melting due to overheating. This can be expected to cause the fuel elements to collapse. That is the reason that I have used, and continue to prefer, the term "demolished" for the cores in these plants. So first we know that the cores are not in their expected locations, but are in all likelihood fallen to the bottoms of the pressure vessels.

However, we also know (and knew very early on) that the cooling water being injected to the reactors was getting into the reactor buildings. The best guess of course as to how it was getting out of the reactor vessels is that the core melt caused damage to the lower ends of the vessels. It seems unlikely that the entire cores have fallen out of the vessels, into the dry well area, according to TEPCO and NISA. But damage to the many various openings at the lower vessel head area is probable in part, and there may even be direct melt openings in the vessel lower heads.

The hydrogen gas we are talking about in these plants came from two sources during the accident: Hydrogen liberated by the energetic zirconium-water reaction which is expected in a serious core melt accident, and also by more normal radiolytic decomposition. Presently the generation of hydrogen, which is very slight, is only by the latter process. However, because there has been no gas flow in the upper ends of the reactor vessels, some hydrogen has probably been trapped there a long time and any new hydrogen may congregate there. To mitigate this, TEPCO has now added nitrogen feed to the reactor vessels instead of to only the primary containments (dry wells.) TEPCO has jumpered in, if you will, the nitrogen feed to the top core spray line (normally used for cooling water) to push the hydrogen through the vessels and into the drywells. Knowing that hydrogen will be flushed, TEPCO has almost doubled the nitrogen feed rate to the drywells from the previous rate.

Below, you can see the top spray line I'm talking about at the very top of the illustration. Click all illustrations on this page to enlarge them.


Below is an illustration I've made for this post. It is very large, but must be blown up to see the detail.


These are the details at the moment. Updates will appear on the APRA FB page, and/or on Twitter (see the Twitter news feed at the right of this page) until another post here is required.

8:30 AM Eastern Wednesday November 30, 2011
ATOMIC POWER REVIEW

Read More

Erroneous readings at Fukushima Daiichi No. 2

TEPCO has reported some spikes in gas temperature readings and air conditioner (primary containment) temperature readings at Fukushima Daiichi No. 2 plant. These readings show some sharp increases, or in the case of the A/C plant a "stair step" increase. Some alarm may be generated in the public (and the press) if these are not properly interpreted.

-TEPCO has begun lowering the feed rates at all three plants in order to INCREASE the temperature of the reactor cores and thus the volume of cooling water in contact with them. This is being done to increase the amount of steam extant inside the pressure vessels to ensure that hydrogen trapped there cannot burn.

-The desire to lower the chance of hydrogen burn follows the discovery that hydrogen gas was indeed trapped inside the reactor vessel of No. 2 plant, with a maximum reading of 2.9%. TEPCO is altering its nitrogen feed plan at all three plants to give direct nitrogen purge to the pressure vessels, not just the primary containments. This new nitrogen feed is to be at twice the present rate.

-Given the lowering of feed rate to increase temperature and thus steam it follows that damaged cables / wires may be further damaged by the increase in moisture. Given this fact, TEPCO is investigating to determine the failure mode of the equipment that is giving errant readings. To be clear, there are other detectors that are NOT showing the same temperature increases, but rather are showing the expected gradual increase.

This set of facts is very likely to be misinterpreted by the press and deliberately misinterpreted by the anti-nuclear crowd. That's why I'm posting this explanation about the temperature increases, which are deliberate, and the reasons for this. Keep in mind that the APR Twitter feed noted the beginning of this operation as soon as it was announced; watch the Twitter feed for further updates.

4:28 PM Eastern Sunday November 27, 2011
ATOMIC POWER REVIEW

Read More

Carnival 80 online now

The rotating Carnival of Nuclear Bloggers is up (very early this Sunday morning) over at Brian Wang's site "Next Big Future." This rotating feature travels around the nuclear blog sites and features the very best of the nuclear blogging world. I highly suggest that anyone interested in nuclear power check it out every time it appears (which is weekly) to get a wide scope of opinions on a wider scope of topics.

Click here for CARNIVAL 80.

As a final note, Atomic Power Review does in fact have a contribution this week; the article on PRA and transmittal of risk data to the public.

5:40 AM Eastern Sunday November 27, 2011
ATOMIC POWER REVIEW

Read More

PRA and Public Knowledge: WASH-740/1250/1400

All of us with any interest in nuclear energy have spent the better part of this year locked in a struggle with the realities of the Fukushima Daiichi nuclear accident. While many of us had known about the (remote) chances of such an occurrence prior to the March, 2011 earthquake and resulting tsunami that triggered the accident, it's likely that few placed a high enough chance of actual occurrence on such an event to cause worry. What is most unfortunate is that now, having had to watch, analyze, write about and sometimes defend actions by TEPCO, NISA and the Japanese government on and off site, the chances of any other such event are still as low as they were before the event .. and that no one will realize this fact. We might actually blame the US Government for this, in reality.

This line of thought was recently brought up in this writer's mind when the NRC published a brief historical perspective of the PRA or Probabilistic Risk Analysis technique that was used in WASH-1400, known as "The Reactor Safety Study." You can see this piece at the NRC blog by clicking here. It has long been my concern that such a document pushes away the general public because of its complexity. For background and support, I'll give a brief additional history to that found in the NRC piece.

Even in the earliest days of nuclear energy in this country (both military and commercial) it was recognized that any accident that caused harm to the general public or damage to citizens' property must be avoided at all cost and plants were designed with so much conservatism overall at the beginning that today we might be surprised. As the best example, the first commercial nuclear power plant, the Shippingport Atomic Power Station, was constructed with all of its primary components below grade in massive reinforced cylindrical or spherical (for the reactor) vessels.

I could go on for days about early plant design, but that isn't the focus. What's important is that even with the conservative designs, many still wanted some sort of study performed that could augur the real risks to the public from nuclear power plants were there to be an accident. This desire resulted in the first watershed safety study to be performed; this was an Atomic Energy Commission study titled "Theoretical Possibilities and Consequences of Major Accidents in Large Nuclear Power Plants." This study was completed in March, 1957 and received the AEC publication number WASH-740. This study has often been named as the first such of its kind, and often been cited as having been far too unrealistic in its assumption of what would actually occur if an accident took place. For example, WASH-740 indicated that if a 500 MWt reactor plant were to melt down and the containment were to fail, this might result in 3400 dead and 43000 injured. We can see clearly from the multiple reactor accident in Japan recently, the Chernobyl accident in Russia and can surmise from other accidents (this many years later, I must note) that this study was way over the top in its estimations.

Because of the increase in plant size over the years, there was pressure to re-perform the analysis taking into account the larger source terms that more powerful reactors would generate and, as a result, the study was revised in 1967.

This analysis did not appear in public, and was kept within the AEC. However, there was a clear need for a document for the public which would be more readable, more reassuring, more descriptive and more thorough than WASH-740 and another effort was begun. This effort resulted in a document frequently quoted ONLY on Atomic Power Review and little remembered today for it was never widely published and only appeared in draft forms. This document is something that I consider to be vastly superior in content to either WASH-740 or the later and more famous WASH-1400 made to stand on WASH-740's shoulders because it's written for the general person and contains a great deal of basic information about nuclear energy in general. This document was titled "The Safety of Nuclear Power Reactors (Light Water-Cooled) and Related Facilities." The publication number was WASH-1250, and I have one of few copies here.


There has been but little information made available concerning the fate of this document. However, the transcript of a speech given by Joseph M. Hendrie in 1986 (see DOE database, document BNL-36253) and which was titled "A Probabilistic Commentary: The Rise, Fall, and Rise Again, of Risk Assessment" and in part on which the recent NRC blog post may be based does mention this obscure WASH-1250 document. Unfortunately (according to Hendrie's speech) Senator Pastore, a ranking member of the JCAE did not feel that WASH-1250 was what was needed to get at actual risk to the public. Although 1250 was ready in preliminary draft form in 1972 the JCAE commissioned essentially a full revision of the WASH-740 study with new PRA techniques using fault tree analysis, as a totally separate effort, and the final draft (shown above) of WASH-1250 which was prepared in July 1973 never really saw the light of day.

This is where the problem with public assessment of nuclear power risk and benefit begins. The decision to make the sole effort essentially a "new math" exercise made almost sure that the information would be daunting to the average man on the street. In point of fact, the formal debut of WASH-1400 in 1975 was accompanied by the launch of a training course for NRC personnel titled "System Safety and Reliability Analysis" to help with understanding the analytical method; this ripened into the development and publication of NUREG-0492, the "Fault Tree Handbook," to make a text for such a course generally available.

Joe Average doesn't want to have to take an advanced math course to be able to understand what his relative risk from nuclear power is. Even then, he won't want to take the time to find out why this or that fault tree branches off at "relief valve fails to reseat / no operator action" and then assess a percentage risk in terms of reactor-years for core melt.

WASH-1250 was in my opinion the right way to go for persons outside the industry, while WASH-1400 was the right way to go for persons inside of it. I am left to wonder whether the voluminously informative 1250 was lost in the dust of the splitting up of the AEC; surely, the new, almost anti-nuclear NRC would not attempt to publish a document like 1250 because of its almost clear but always implied support for the capability of the industry, the owner-operators, the regulator and anyone else involved. WASH-1250 in fact admits a slight pro-nuclear bias, right on page ii of the prologue... "By and large, however, it is a summary and discussion of a large body of published information pertinent to nuclear safety, as interpreted by AEC staff. The reader will, therefore, understand that a certain degree of pro-nuclear power bias is probably inherent in the discussion, although staff has tried to make the presentation as simple, factual, and objective as possible."

The simple fact is that after the publication of the final draft of WASH-1250 there has been exactly one nuclear accident at any US commercial plant (which is only what this volume is intended to discuss -- nuclear plants built to US practice, inside the United States) at which no one was killed or even injured. Thus, at least in terms of integrity of this report, there is no damage in so far as no major accident has occurred at any US plant to contradict it. While the previous may seem defensive to those either undecided or anti-nuclear, it is simply meant to indicate that such a report -- which does not augur disasters and then calculate their average chance of occurrence and resulting damage, but rather which attempts to clearly explain safety in design, construction and operation -- is not inherently pro-nuclear but actually inherently, simply explanatory.

The authors of WASH-1250 clearly knew that their approach was under fire. One wonders if the quoted statement in the preface was original to the first draft; one also wonders if the following description, found on page 6-40 of WASH-1250, was included in the first version either. This section follows some discussion about risk probability which had not used any sort of fault tree analysis:

6.4.8 A Current AEC Study

"... It is a fair presumption that knowledge and techniques will be improved in proportion to the future effort devoted to such studies. In this connection, the AEC has recently undertaken a quantitative, probabilistic study to try to reach some meaningful conclusions about the risks of accidents from nuclear power plants currently in service."

The above refers of course to the launch in 1972 of what became WASH-1400 which apparently, we now realize, suppressed WASH-1250. I must add that, at the end of this section of WASH-1250 the last sentence is as follows:

"It is possible to conclude from the order of ranking currently perceived that nuclear power presents one of the smallest man-made risks (mortality) to which mankind is exposed."

One could get that assumption from any number of places, but when one reads only PRA for nuclear accidents, one gets locked into the thinking that surely one of these or another, or something not exactly predicted but nevertheless dangerous (as TMI was, exactly) is bound to happen. It might, but the death toll from nuclear accidents since WASH-1250 in the United States is still zero, so that even if something predicted by PRA does happen, or something almost predicted does happen, the risk is still incredibly small to plant operators or the public when compared with almost any other risk.

What I am really talking about here, of course, is slant. Publication of loads of PRA work to indicate risk of every conceivable failure and operator fault is actually necessary but indicative only of the negative side of things, as it were, to the average man. Such a volume as WASH-1250 was, which includes a vast amount of detail on plant construction, fuel processing, spent fuel handling, dose rates and effects, regulatory responsibility (and also many complete federal codes) might seem overly on the positive side in terms of simply stating what the industry and AEC were doing to ensure safety, should be considered necessary too since nuclear energy is a major portion of our energy generating capacity in this country. I again wonder if this report were just a bit too pro-nuclear for the new anti-nuclear NRC to allow, and regret that fact if it is true.

6:35 PM Eastern Friday November 25, 2011
ATOMIC POWER REVIEW

Read More

Hydrogen gas / Fukushima Daiichi

TEPCO has detected a higher than previously recorded level of hydrogen gas at its Fukushima Daiichi No. 2 plant. This hydrogen, according to TEPCO, was probably located high in the reactor pressure vessel and primary containment until this time, and was flushed out when TEPCO placed its (improvised) gas handling system into operation. This new gas system changed the flowpaths for gas and is able to purge more of the previously mentioned volumes.

The highest hydrogen concentration noted thus far was 2.9%. The concentration has dropped. Roughly 4% is combustible, vapor concentration notwithstanding.

TEPCO has made a few alterations to its plans in order to mitigate the possible effect of this hydrogen; it plans to alter the nitrogen purge system feed flow path to inject nitrogen directly into the pressure vessel, instead of into the primary containment. This will take some time. In order to mitigate possible deleterious effects from hydrogen until such time as the new nitrogen feed is available, TEPCO plans to alter the feed injection rate to the No. 2 plant (this means cooling water) to make certain that there is enough steam present to make whatever hydrogen is available not flammable. Upon restart of nitrogen injection to the RPV, the nitrogen flowrate will be doubled. This procedure should flush the hydrogen and prevent any risk of burn.

Finally, TEPCO made a reference in a press handout to not beginning alternate water injection to Unit 1 until that unit, also, has direct nitrogen feed to the pressure vessel; I assume this means the addition of the core spray line to the feed line. (Number 1 plant is the only one of the three only using the feed line and not both the feed line and core spray line.)

5:30 AM Eastern Friday November 25, 2011
ATOMIC POWER REVIEW

Read More