ML20212Q802
| ML20212Q802 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/15/1987 |
| From: | NRC COMMISSION (OCM) |
| To: | |
| References | |
| REF-10CFR9.7 NUDOCS 8704240060 | |
| Download: ML20212Q802 (124) | |
Text
9 ORIGINAL c
UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION
Title:
Briefing by DOE on the TMI-2 Core Examination Program (Public Meeting) pd -
9 Location:
Washington, D. C.
Date:
Wednesday, April 15, 1987
(
Pages:
1 - 64 l
J Ann Riley & Associates Court Reporters 1625 i Street, N.W., Suite 921 Washington, D.C. 20006 (202) 293-3950 I!!R42?8888**2" PT9.7 PDR
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D i SCLA I MER 2
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This is an unofficial transcript of a meeting of the 7
United States Nuclear Regulatory Commission held on 3
4/15/87 In the Commission's office at 1717 H Street, 9
'I4. tJ., (Ja sh i ng t on,
D.C.
The meeting was open to public 10 attendance and observation.
This transcript has not been 11 reviewed, corrected, or edited, and it may contain 12 inaccuracies.
g 13 The transcript is intended solely for general 14 informational purposes.
As provided by 10 CFR 9.103, it is 15 not part of the formal or informal record of decision of the 16 matters discussed.
Expressions of opinion in this transcript 17 do not necessarily reflect final determination or beliefs.
No 18 pleading or other paper may be filed with the Commission in 19 any proceeding as the result of or addressed to any statement 20 or argument contained herein, except as the Commission may 21 authori=e.
22 23 e
24 25
o 1
UNITED STATES OF AMERICA 1
2 NUCLEAR REGULATORY COMMISSION 3
4 BRIEFING BY DOE ON THE 5
TMI-2 CORE EXAMINATION PROGRAM 6
7 PUBLIC MEETING 8
9 10 Nuclear Regulatory Commission 11 Room 1130 12 1717 H Street, Northwest 13 Washington, D.C.
14 15 April 15, 1987 16 17 The Commission met in open session, pursuant to 18 notice, at 2:02 p.m., the Honorable LANDO W.
ZECH, Chairman of 19 the Commission, presiding.
20 21 COMMISSIONERS PRESENT:
22 LANDO W.
- ZECH, Chairman of the Commission 23 THOMAS M. ROBERTS, Member of the Commission 24 JAMES K. ASSELSTINE, Member of the Commission 25 FREDERICK M. BERNTHAL, Member of the Commission
r 1
STAFF AND PRESENTERS 2
SEATED AT COMMISSION TABLE:
3 W.
PARLER 4
J. HOYLE 5
J. VAUGHAN 6
G.D. McPHERSON
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7 J.
BROUGHTON 8
D. McGOFF 9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
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3 1
PROCEEDINGS 2
CHAIRMAN ZECH:
Good afternoon, ladies and gentlemen.
3 This afternoon is a briefing by the Department of Ene'gy on the status of research related to the examination of 4
r 5
the reactor core at the Three Mile Island Unit 2 plant.
It is 6
my understanding that the briefing will cover research 7
highlights over the past year or so and provide a summary of 8
remaining research.
9 Mr. James Vaughan is Deputy Assistant Secretary for 10 Nuclear Energy at the Department of Energy, and Dr. G. Donald 11 McPherson, Program Manager for TMI-2 Accident Evaluation of 12 the Department of Energy, will provide the briefing.
Also 1
13 present, I understand, is Mr. David McGoff, Office of 14 Light-water Reactor Safety and Technology at the Department of 15 Energy, and Mr. James Broughton, Program Manager for TMI-2 16 Accident Evaluation at EG&G.
17 The examination of the damaged core at Three Mile 18 Island, Unit 2, is an important research activity.
The NRC is 19 very interested in the information from this program.
This 20 information will provide a better understanding of severe 21 accidents, source terms, and will help to resolve some of the 22 uncertainties in this area.
23 This is an information briefing this afternoon and 24 no formal Commission decisions are anticipated.
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25 Do any of my fellow commissioners have any opening
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1 comments to make?
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[No response.]
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If not, Mr. Vaughan will you begin, please?
4 MR. VAUGHAN:
We are pleased to be here again this 5
afternoon, Mr. Chairman and commissioners, to discuss with you 6
the progress and findings resulting from our R&D program at 7
Three Mile Island.'
By way of background, DOE's TMI R&D 8
program was authorized in 1981 to cover two main 9
areas: development of innovative technology to support the 10 cleanup of the damaged reactor, and second, research and 11 analysis on the accident itself, focusing primarily on where-12 did the fission products go.
13 As you are aware, the primary responsibilities for i
14 cleanup and removal of the damaged core rests with General 15 Public Utilities.
The Department of Energy, however, has 16 provided over $78 million in R&D support directly to GPU as 17 well as goods and services amounting to $29 million for direct 18 support of work at the TMI site, for a total of $107 million 19 in R&D cleanup support at the site.
i 20 That second number I used, the goods and services 21 and direct support, are sometimes misunderstood because they 22 are not typically listed in the charts, but, for example, the 23 core boring machine that you are going to see a lot of is part 24 of that direct support, where the monies were expended offsite i
1 25 but the work is directly relevant to the site activity.
1.
5 1
The balance of the $189 million DOE commitment to 2
this R&D effort supports the actual core examination and 3
related activities.
4 To date, about 40 tons, or 26 percent of the total 5
core debris, has been shipped to the Idaho National Engineering 6
Laboratory.
This has involved seven safe shipments, a total of 7
ten casks.
The status of the cleanup effort was presented to 8
the commission a few weeks ago by GPU, and therefore, I will 9
not try to repeat that in any detail.
However, since we met 10 with you last year on this same subject, there have been 11 several key developments related to the core exam, which I want 12 to summarize very briefly, and then my colleagues will present 13 in some detail.
~
14 For the highlights, you will recall that earlier 15 exams of the lower plenum of the reactor had given clear i
16 evidence that core material had melted and flowed down to that 2
17 region.
Recent core boring and mechanical probing results 1
18 show that the material sort of overflowed or broke through the 19 top of a cup-shaped crust which formed around the central and 20 hottest portion of the core as it melted.
21 Some of the molten material caused internal parts, 22 down to a point about nine inches above the lower head, to be 23 molten, and also we have observed that the molten core material 24 broke through what is called the core former wall or the wall
~
25 surrounding the core, and went into the bypass region inside
6 1
the core barrel.
2 We have got some video pictures to show you that 3
will give a good representation of that.
j 4
The examination of the core has continued actively 5
over the last year.
The samples of debris were obtained by 6
making ten bores through the core, and these bore materials 7
have been shipped to the Idaho National Engineering Laboratory 8
for exam, and analysis of these is the primary source of the 9
information that we are going to present.
10 Just as one aside, this core boring equipment that I 11 have mentioned that we developed in the R&D program for 12 obtaining the samples has also been extremely invaluable in i
13 enabling the utility to simply break up the core to facilitate 14 the defueling operation, so it has had a side' benefit beyond 15 its original purpose.
16 I think you would be interested to know that i
17 arrangements have been made for international involvement in 18 the nassie exam program.
Under the auspices of the CSNI, 19 Committee for the Safety of Nuclear Installations, which is l
20 part of the OECD Nuclear Energy Agency, debris samples will i
21 soon be shipped to Canada, the UK, Germany, France, 22 Switzerland, Sweden and the European Economic Community.
We 1
23 believe this will greatly augment our data base of fuel damage 24 information and provide an international hands-on understanding 25 of the material science of a severely damaged core.-
There is a y - __.._.,_-.. __.._ _ _
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lot of interest by our colleagues.in that subject.
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COMMISSIONER BERNTHAL:
If I may just interrupt a 3
moment, Jim, I want to congratulate you.
I realize it is 4
probably a customary and common practice at DOE to seek broad i
5 outside expert opinion on these things, but I think that is 2
6 exactly the right way to go.
7 MR. VAUGHAN:
Okay.
We appreciate'that.
I am not 8
sure we do it on everything, but this kind of effort is kind 9
of modeled after the international cooperation on the LOFT 10 program that we previously had.
In addition to those countries 11 I named, the understanding of the accident has progressed to 12 where we can have what is called typically in the scientific l
13 community a benchmark problem that can be analyzed by the 14 participating foreign countries.
15 So in addition to those countries I named, analysts i
16 from Japan, the Netherlands, Finland and Italy are involved in 17 the analysis as well as the actual examination of the core.
18 This should help us to disseminate the data and the accident 19 codes in these countries.
20 Before we proceed with the detailed presentation, 21 there are three or four qualitative observations in regard to
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i 22 the results that have been obtained to date.
These are kind j
23 of the punchlines.
24 The first observation relates to fission product 25 behavior.
Our analysis of the core debris has confirmed most l
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of our understanding of fission product behavior, but there 2
are a few cases we are going to highlight where there have 3
been some questions raised and others where there are new 1
understandings.
That is important, I think, to ongoing 5
technology.
6 The second key observation -- and we did a little 7
bit of this last year with you -- is thdt a little bit of i
8 water goes a long way.
Although the water level dropped to as 9
low as about one or two feet above the bottom of the core, 10 there was sufficient cooling to contain most of the fuel i
11 within the core region and to prevent the molten material
]
12 which flowed into the lower plenum from penetrating the 13 reactor vessel.
i 14 That is an important conclusion, and I guess that is 15 one of the principal lessons that is feeding back into our 16 advanced light-water reactor activities that we have discussed 17 with you separately where the more advanced designs will l
18 assure that in the event of a severe accident, water will be J
19 present or it can readily be made available.
20 Now, the third qualitative observation is tnat the 21 flow of a large quantity of molten core material into a pool 22 of water such as occurred at TMI-2 does not cause a steam 23 explosion in a high pressure system.
We think both of these 24 last two points are areas that can be factored into
~
25 probabilistic risk analyses to further reduce the risk to i
9 1
containment challenge during severe accidents.
2 COMMISSIONER BERNTHAL:
I hesitate to interrupt the 3
presentation, but I am wondering what is more efficient here, 4
to have our questions in while we are on the subject, or are 5
you going to c,ome back to some of these things?
6 MR. VAUGHAN:
Your choice.
I had one more comment I 7
wanted to make, and then we can discuss broad questions or you 8
may want to see the details and we will take it as you choose.
9 CHAIRMAN ZECH:
I think we can watch and see how it 10 goes, but I think it would be preferable to try to let them 11 complete if we can, and then ask our questions later.
12 MR. VAUGHAN:
My final observation was simply i
13 related to the implications of the results on the methodology 1
i 14 that is used by NRC and others to analyze severe accidents. We 15 think these results are proving to be both important and 16 valuable to the application of the data to understand l
'.7 postulated severe accidents in large plants, and as this l
j 18 understanding is modeled in the computer codes that are used 19 by NRC, industry and others and we can compare the analysis 20 from these codes with the actual results, we think we will l
l 21 have provided a better measure of the capability of the codes 22 to predict the consequences of severe accidents.
l 23 It would be our firm hope that through NRC, these 24 can be translated into technology-based standards and 25 regulations so that we, in fact, are not operating just on w
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1 some long-standing premises where the actual data is capable J
2 of updating our technical understanding and the application of 3
that through regulations.
4 Mr. Chairman, those were the key points I wanted to 5
cover to' introduce the subject.
Dr. McPherson and 6
Mr. Broughton are going to provide the detailed presentation 7
unless you want to interrupt for questions in advance.
It is 8
your choice.
9 CHAIRMAN ZECH:
I think you should go ahead with the 10 presentation, if you don't mind.
]
11 MR. VAUGHAN:
Let's go through this as crisply as we*
i 12 can.
It roughly should take us to the neighborhood of 3:00, 13 and then we had thought we would allow a half-hour for
>s 14 discussion per the schedule.
15 CHAIRMAN ZECH:
All right.
Let's proceed.
16
[ Slide) 17 MR. McPHERSON:
Mr. Chairman and Commissioners, I 18 will begin by recalling the program's goals and objectives.
I 19 will give you an update on the international partnership that 20 Mr. Vaughan referred to, and then I will get into the 1986-87 21 research highlights, provide you with a description of the 22 accident scenario as we now see it based on these more recent 23 results, and then summarize the impact of these observations 1
l 24 on issues which we believe relate to the Commission.
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j 25 Finally, I will sum up by showing you the research i
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which remains in our program.
2 (slide]
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3 The overriding goal of our program is to provide 4
evidence from the TMI-2 accident for realistic severe accident i
5 source terms.
6 (Slide]
7 In support of this goal, we must meet the following.
8 program objectives.
We must understand what happened during 9
the accident.
We must apply this understanding to a resolution 10 of severe accidents and source term issues and transfer these i
11 results to the government nuclear-industry and the public, both 12 domestic and internationally.
These are the identical 13 objectives which we presented to you last year at this time.
s 14 (Slide]
15 To meet those objectives, we need the following 16 basic information from our research.
From on-line 17 instrumentation, we need initial system configuration and 18 operator actions, and we need plant initial and boundary 19 conditions.
From the defueling information, which we will be 20 discussing at greater length today, we need the current 21 condition of all parts of the reactor, including damage to the
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22 core support assembly, instrument structures and the reactor 23 vessel lower head, and the core.
j 24 (Slide]
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25 In addition, we need detailed chemical, physical and J
- 12 1
metallurgical information on the and state and composition of
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2 the core materials, on' peak temperatures, materials 3
interactions, and the extent of the material oxidation.
We i
4 need to know the effect of the control rod and burnable poison 5
rods, and we need to know the retained fission products and 6
the chemical forms of those fission products.
7 Those are the things we are after in our program.
j 8
Before describing this year's research highlights, I 9
will present to you the status of the international component j
10 of our TMI program.
11 (Slide]
12 At our meeting last year, we informed you of an 13 offer made by the Department through the organization for 1
14 Economic Cooperation and Development for participation in our 15 program, and there were two components described to you at i
16 that time, one the analysis exercised, which at the time we 17 referred to as the standard problem, but given the context of l
18 this particular accident, we felt it was more appropriate to
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19 refer to it as an analysis exercise; and the other component 20 the examination of various samples which we have been obtaining 21 from the core.
22 (Slide) 23 We will discuss each of these components very 4
24 briefly.
25 As for the analysis exercise,Iit will provide an e
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assessment and a data base for best estimate severe accident i
2 codes and methodologies for a full-scale severe accident.
It 3
will also compara alternate severe accider.L analysis techniques 4
and methods.
4 f
5
[ Slide]
6 We have divided the accident into four phases for 7
this purpose that are shown on this slide.
I won't review 8
them but simply point out that the reason for doing this is to 9
distinguish various predominant phenomena which occur during 10 these four phases, and hence which relate to different models 11 and often different codes which are used in analyzing each of 12 the four phases.
i 13 At this time, during this current calendar year, we j
14 are proceeding with Phases 1 and 2 of the accident.
15 (Slide]
16 Participants in the analysis exercise include, 4
17 under the NRC funding, Battelle, Sandia, Los Alamos, and Idaho i
l 18 Engineering Lab.
Of the U.S. utilities, New Power Authority 1
i' 19
.is participating, and wiathin the CSNI membership, there are 1
20 the Euratoms Joint Research Center, the U.K., Italy, Japan, 21 Finland, Sweden, France, West Germany, Netherlands and J
22 Switzerland.
I 23 COMMISSIONER BERNTHAL:
Is core relocation the term 24 I am now supposed to use for core melt?
i 25 MR. McPHERSON:
No, not precisely, Mr. Commissioner.
l.
14 1
Rather the movement of the melted core is what we refer to as
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2 core relocation.
3 COMMISSIONER BERNTHAL:
Thanks.
4 (Slide) i 5
The sample examination program involves the 6
examination of various pieces of debris which have been 7
removed from the core and the pressure vessel.
The benefits 8
of this include the participation of international scientists 9
on the evaluation of the TMI-2 samples, thus achieving a q
10 worldwide consensus before publishing the results of the TMI-2 1
11 findings.
l l
12 Another benefit, of course, is the increased number j
13 of samples which we can now have examined and thereby reducing 14 the statistical uncertainty of the data.
15 (Slide]
16 The next slide shows the type of samples accepted by 17 each of the different participants, and I will not go through 18 it, of course, but simply point out that the left-hand column gives you an idea of the type of samples which have been sent, 19 20 which are being sent to each of the participants, and they j
21 really cover every important aspect of the samples we are 22 taking.
23 (Slide]
24 Now I will proceed to our current understehdi?g of 25 the end state core configuration.
You will.recal'. late: year i
l
15 1
that we presented our understanding of the core configuration 2
as shown on the screen, and you will recall also that the area 3
below the solid black line was that area where we had no 4
informaiton whatever within the core.
So we knew what was 5
above the line and what was below in the lower plenum.
We 6
provided information on those areas.
7
[ Slide]
8 However, the next slide shows what we now know on 9
the basis mainly of the core bores which Lxvc been taken this 10 year.
To cover the entire area, we have information on the 11 upper grid damage. We recall there was core void above an 12 upper debris bed, then a crust agglomerate whose nature I will 13 discuss in a second.
That crust was the upper part of a cup 14 which enclosed what was previously molten material, a more 15 homogeneous material, and then in the lower plenum we, of 16 course, found debris, which we discussed last time.
17 Something new we have discovered this year is the 18 previously molten material which ficwed down on the left-hand 19 side of this diagram and the failed instrument structure, 20 which was referred to by Mr. Vaughan earlier.
I am going now 21 to discuss the -- oh, I'm sorry, I missed one other point that 22 is on the left-hand side there -- it doesn't show up very well 23
-- the failed core former wall, which was recently discovered.
24 You will see that in a video we have to show in a few minutes.
25 Some material is in the core bypass area that has flowed out
16 1
from the cup area within the core.
2 COMMISSIONER BERNTHAL:
I am sorry.
Is that on my 3
drawing?
Oh, I see, right here.
4 MR. McPHERSON:
A little dotted section.
That is of 5
a core bypass area between the core former wall and the core 6
barrel.
7 Next I am going to give some information on the 8
debris taken from the upper debris bed and the lower plenum.
9 (Slide) 10 In the picture shown on the screen at this time you 11 will see quite a mess of odds and ends which have been taken 12 out of the upper debris, and in that is -- I will try and give c
13 you the description of the various components.
It is a
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14 heterogeneous form of debris exhibiting a broad range of 15 oxidation and material interactions, but it is well mixed.
It 16 is composed of fuel pieces, which Jim Broughton is pointing 17 out, cladding fragments, and the rest of the material is 18 previously molten material, both fuel and metallic.
19 The average temperature of these materials is 20 approximately 2200 K. or 3400 Fahrenheit.
The previously 21 molten ceramic pieces exhibit significant fracture toughness, 22 and 90 percent of these pieces fall in the range of one to 23 five millimeters in size.
On the other hand, the materials in 24 the lower plenum fall in a range of one to 200 millimeters,
~
25 generally, therefore, of a larger diameter.. The piece you see
17 1
here is about 50 millimeters across.
2 These particles appear to be ceramic fuel and can be i
3 homogeneous and very porous.
The average peak temperature 4
reached by these materials is in the range of 2800 to 3100 5
K. or 5100 degrees F.,
which is the melting temperature of 6
UO-2.
Samples which are not otherwise laced with fracture 7
lines exhibit significant fracture toughness.
Probably these d
)
8 fracture lines cccurred during cooling.
9 There is a uniform fission product concentration 4
10 across these samples.
11 (Slide]
12 Now I am going to summarize the fission product 13 retention information relating to both these types of samples 14 from the upper debris and the lower plenum.
15 COMMISSIONER BERNTHAL:
Let me ask a question about 16 that picture of debris on the previous slide.
Do I take it to 17 mean, both from the appearance of that as an outgassed 18 lava-like appearance and the comment that the average peak 19 temperature was between 2800 and 3100, that you sort of see 20 these as having been chunks that dropped into the water and 21 were quenched?
What do you mean by that?
22 MR. McPHERSON:
There appears to be a period of l
23 abov' 18 to 30 seconds during which there was core relocation 24 that you asked about earlier, that is, a flow of molten core
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25 from above to the lower plenum, and whether.it was a constant J
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flow or chunks, we don't know.
But it got down there as a rs 2
liquid, clearly, because some of these chunks could not have 3
flowed down through.
We have seen from instrumentation I will 4
refer to later that this all occurred during a very short 5
interval, so very likely it was a flow, and it seemed to have 6
flowed out the top of that cup down inside of the reactor and 7
across the lower plenum.
8 COMMISSIONER BERNTRAL:
And then quenched in the 9
bottom.
10 MR. McPHERSON:
And then quenched over a long period 11 of time,, clearly.
12
[ Slide) 13 The nature of the fission product retention in both 14 the upper debris and the debris from the lower plenum can be
/
15 summrized very briefly as follows.
More details of these 16 quantitatively are provided in the following piece in the 17 handout, but I will not show them.
4 18 There has been a significant retention of iodine 129 1
j and cesium 137 in the high temperature core debris and in the 19 20 previously molten core materials.
There has also been a 21 significant amount of ruthenium released from the fuel with 22 retention in the metallic structures.
Bothofthesepiecesofinformationhavenots'bwn 23 24 up in the small scale experiments that we have done r1avious
/
25 to this accident, or following this accident, for that matter.
19 1
1 The impact of this information is that the iodine i 'f 2
and cesium present in the molten core materials are probably i
3 available for direct release to containment in the event of a 4
reactor pressure vessel failure, and second, the ruthenium 5
must be properly accounted for or tracked in order to estimate i
6 the source term.
That is, we know that it moves from the fuel i
7 into, subtracted by and adsorbed by metals, and therefore, one i
8 must model that in modeling the releases.
COMMISSIONER BERNTHAL:
One of the interesting 9
10 points about the ruthenium I am sure you are aware of is that 11 at Chernobyl the radiation is very small, but the very small 12 levels of radiation that they measure, like 10 microcuries per 13 day or something like that, at the surface of the sarcophagus 14
-- for reasons that I don't understand and, as far as I know, 4
15 Richard Wilson from Harvard who learned this piece of j
16 information doesn't understand -- seems to be ruthenium or 17 predominantly ruthenium.
Nobody that I have talked to so far j
18 understands that.
Maybe you do.
l 19 MR. McPHERSON:
I had heard the same information, i
20 and my understanding is that ruthenium in highly oxidizing I
l 21 atmosphere, which this is because there is air passing through 22 all the time, tends to form ruthenium oxide, which is volatile j
l 23 and is picked up by the filters.
My understanding is that is 24 where it is showing up, in the filters.
25-COMMISSIONER BERNTHAL:
I see.
So it is a volatile r
1
20 JL oxide.
(
2 MR. VAUGHAN:
We were not going to mention Chernobyl 3
in this briefing.
I think it would be useful for the 4
Commissioners to know, just by way of the people, that we are 5
really indebted to Dr. McPherson, as is the whole nuclear 6
community.
He has been one of our principal people with 7
knowledge of the Chernobyl-type plants and their control 1
8 system that contributed to what DOE was able to put together 9
and contribute to the NRC report on gathering knowledge on the 10 whole Chernobyl event.
In fact, he predicted for me within 24 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br /> of the event -- he had 80 percent of the punchlines just 12 based on what he knew about the system.
So he has been a big 13 asset to the country in helping us in that regard.
14 COMMISSIONER BERNTHAL:
That is an important point.
15 You are suggesting that the reason behind the statement of 16 ruthenium is that that, in fact, is what they were picking up 17 in this air cooling system in the filters associated with 18 that, so they just predominantly filter that material out.
19 MR. McPHERSON:
That is correct, Commissioner 20 Bernthal, yes.
21 (Slide) 22 Very briefly, and I will not go into this again, but 23 last year, you will recall, we showed you this diagram of the 24 core boring machine and how it is mounted on the reactor.
I 25 just wanted to refresh your memories.
I will say no more on
- = -...
21 1
it but go on to the next slide.
2
[ Slide) 3 This shows the locations at which the core bores 1
4 were made, and you will see by the distribution that we were l
5 able from these core bores to provide sectional information, i
4 6
cross-sectional information, both east-west and north-south, t
l 7
both north-south central and peripheral, and also a diagonal.
i 8
This core boring operation provided not just the 9
materials which we took from the core but, in addition, visual 1
i 10 observations via video camera which could be put down the 11 bores, surface contour information, and the core l
12 cross-sectional structural information.
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(Slide) 13 14 Now I am going to show photographs of four of 15 these core bores after that material was taken out.
This is t'
16 the material that we saw, and following that I will show one
]
17 vertical cross-section that we made from this information.
1 18 Now, you will probably best look at the handouts you 19 have to see what I will refer to here, but going from left to 20 right, we are moving from the bottom of the core towards the i
i 21 top of the top crust.
As you will see in the upper core bore, i
l 22 D-8, a stand of about four feet of standing rods.
They are i
23 twisted because as the core boring machine went in it caused f
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l 24 them to twist, but we believe that they were standing vertical i
j 25 upright before we bored through them.
_ _ -. _. _. _ _ _ - ~ _ _. _. _.
22
-1 At the 4 foot level, just above that you will see 2
rather a solid chunk, some pieces and then another solid 3
chunk.
There are a lot of the pieces in between those two*
4 solid chunks which we were not able to trap in the core borer 5
machine, and that is the case all through all of the core x
6 borer operation.
These were very brittle and tended to break 7
out and not be captured within the drill.
8 The first one, then, is the core borer taken on the 9
edge or periphery of the core, so we have about four feet of 10 standing rods.
The next one, G-8, was taken near the center 11 of the core, and you will see only about two feet of standing' 12 rods, followed by the debris, and right at the top, one of the 13 pieces of the crust.
L 14 The next one, G-12, is back to the edge, and there 15 we are back close to four feet of standing rods and the same 16 kind of debris at the top.
The core bore showing the lowest 17 stand of fuel rods is shown in K-9, where they only reach to 18 about 20 inches above the core, and from there on is the 19 agglomerate and homogeneous melted materials.
20
[ Slide]
i 21 In the next slide I will show you the piece that is 22 in the second -- before I go on, the second core bore to the 23 right, you will see right at the top a piece which has some 24 shininess to it, and the next photograph is that same piece 25 enlarged now.
~
9 s
.m-
.,4 n
23 1
You ill sep that the shiny pieces we have identified 2
are metallic materials which are laced through, holding this 3
brittle material together.
Just to the left lower part of the 4
photograph is a piece of ceramic melt, homogeneous melt which 5
was then underneath within the crust enclosed in the cup.
So 6
that is the kind of material that formed the homogeneous melt.
7 There is another piece taken from the periphery in 8
the following photograph, a piece of the agglomerate or crust 9
material, again showing the metallic lacing holding the 10 ceramic together.
11
[ Slide]
12 The regio: below the top, hard crust consists of two 13 distinct structures that I have alluded to already.
One is 14 the standing fuel rods that go up anywhere from two feet in 15 the middle to about four feet around the periphery, and then 16 above that is the previously molten core materials, one type 17 being the homogeneous structure which fills the cup formed by 18 the agglomerate material. That agglomerate material is made up 19 of the previously molten material which surrounded material 20 which didn't melt and which is solidified within that melt.
21 Of the solid materials which can still be seen there 22 are in some cases axially stacked pellets, and in other cases, 23 randomly oriented pellets.
24 COMMISSIONER BERNTHAL:
I am sorry.
You didn't say 25 what the metallic material was on that.' Do you have an
24 1
analysis on that yet?
2 MR. BROUGHTON:
We are in the process of doing 3
that.
We have identified some silver and we believe it is 4
probably silver or unoxidized zircalloy and possibly some 5
steel.
6
[ Slide]
7 MR. McPHERSON:
From this information that I have 8
just shown you and from mechanical probing data, we have 9
developed information which, put together, form contour maps.
10 These contour maps show the upper surface of the solid 11 structure, that is, the crust, and the bottom surface of that 12 crust.
/
13
[ Slide]
14 We have, in fact, cross-sections now covering the 15 entire reactor right from periphery to center and out to 16 the edge again, both north-south, east-west directions, but I
'am only showing you one to show you an example, to give you a 17 18 good picture of what the whole central core area looks like.
19 You will see the cross-section is cut through G in the 20 north-south direction.
21 To start right at the center, we have the homogeneous 22 ceramic material, and that is surrounded by this cup-shaped 23 agglomerate, the half-hatched area, or yellow in the slide, and 24 then we have discovered a large metallic segregate shown there
~
25 in one piece, but we expect that would be the same all the way
25 1
through.
We simply haven't got all the pieces out yet, but 2
that appears to be typical.
And then all the way down, the G-8 3
core bore, we found these metal veins, again probably silver or 4
steel.
5 The standing rods then stand below that cup, and l
6 there is a discoloration on the cladding in the region close 1
7 to the cup.
And then, of course, above the upper crust is the 8
upper debris bed and the void on top.
~
9 Two of the core bores plus some camera information 10 provided an estimate of the debris bed height.
4 11
[ Slide) 12 We see three heights shown in the lower plenum, 18 13 inches, 30 inches and 12 inches.
of the two core bores, the 14 two attempts to make a core bore that went.down into that 15 lower plenum, neither succeeded in acquiring any material.
It 16 appears to be too loose to be captured by the coring machine.
17 We will next look in the next Vu-graph inside this 18 flow distributor, the core support assembly.
First we will,be 19 looking in the volune between the fuel assembly grid and the 20 flow distributor plate, then we will be looking in the next l
21 volume below that, between the flow distributor plate and the 22 core grid forging, and then in the area between the forging 23 and the elliptical flow distributor.
1 24 We will see the materials which we have discovered 4
25 in those areas.
~
.,-m-,--
v
26 1
[ SLIDE.]
l 2
MR. McFHERSON:
To begin at the top, we see the 3
curtains of material clearly, previously molten material that 4
has been flowing down just solidified in that area and then 5
just below in the second volume down, we see some more curtain 6
material which appears to be a continuation of those flows in 7
' general and those flows have shown up even in the third volume 8
just above the elliptical flow distributor.
9 In addition, we have just recently, this past two 10 months, discovered some materials over on the west side, 11 northwest side, which indicate there has been a flow down on 12 that side.
13
[ SLIDE.]
1 i 14 MR. McPHERSON:
Now I would like to summarize what 15 we think has become of the core mass.
This next slide in hand 16 and in the handout, I am only gcing to cover the left and i
17 right hand columns to show of the original core mass, the 100 18 percent, there is 23 percent accounted for in the upper core 19 debris and 42 percent in the standing rods.
20 Those then are the portion of the core which did not l
21 melt or was not molten.
Then the molten zone which is found i
R within the core constitutes about 19 percent of the mass and 22 l
23 the material in the lower plenum constitutes 16 percent.
24 This is the sum up before we made the discovery of
~
25 the material located in the by-pass volume and these sum ups
27 1
may change slightly as a result but we don't think they will 2
be that much within the degree of error we already have, they 3
probably are not going to change that much.
4 (SLIDE.]
1 5
MR. McPHERSON:
Therefore, we go on to the 6
significant results which we have derived from this i
7-information; namely, approximately 35 percent of the core was 8
in a molten stage.
This indicates that core melting is 9
possible with limited damage to the reactor vessel internals.
10 We don't know yet how limited that is but clearly a great deal 11 of the core support assembly is in good shape as we saw last 12 year.
13
[ SLIDE.]
14 MR. McPHERSON:
Now I will summarize the information 15 we have on fission product distribution.
There is a 16 significant retentien of noble gas products in the undamaged 17 fuel assemblies and the ro'd stubs expected.
We don't know 18 this for sure because we are not in a molten state, we expect 19 that much of the noble gas contained that fuel is still there.
20 We believe that iodine and cesium which was released 21 was dissolved in the coolant water and that is consistent with 22 cesium iodine and cesium hydroxide behavior.
The ruthenium 23 and antimony which are associated with the metallic material I
24 but essentially these have remained completely within the
~
i 1.________,.
28 1
This is unanticipated from our small scale 2
experiments and it should be included, therefore, in the l
3 analytical models used in severe accident analysis.
4 Finally, the lanthanides are retained with the fuel 5
materials which confirms our current understanding.
You will 6
see that there is a variety of things that we do understand, 7
we thought we understood and we confirmed that, other things 8
which there is some surprise about and other things which we i
9 now know we have to modify our analysis on.
10 COMMISSIONER BERNTHAL:
I guess I don't understand 11 the statement on ruthenium.
In fact, I didn't understand it 12 when you showed us the table because the table indicates a 13 percent of ruthenium, 106, at least, retained and in the lower 14 plenum and upper debris, it was four to nine, and in the first 15 case 35 to 86.
There is large room for error there, I guess, 16 in the upper debris.
17 How is that consistent with saying that they 18 essentially remained completely within the pressure vessel.
19 MR. McPHERSON:
By the fact that they have not been 20 detected outside.
21 COMMISSIONER BERNTHAL:
You didn't see them outside 22 the pressure vessel.
i 23 MR. McPHERSON:
Correct.
9 24 COMMISSIONER BERNTHAL:
So you are assuming they are 25 coded on the walls --
~
w-9 m
w
_.,__c
~, _ -,
._m.__,.,__,,,..m.,
4 l
29
-l 1
MR. McPHERSON:
On the metals.
,~
2 COMMISSIONER BERNTHAL:
-- of the reactor metal.
3 MR. McPHERSON:
That's true.
4 MR. BROUGHTON:
We are actually'seeing increased 5
ruthenium concentrations in these metallic structures within 6
the metal but we are just getting those pieces to-look at.
7 COMMISSIONER BERNtHAL:
I see.
8 MR. BROUGHTON:
The analysis is preliminary at this 9
point but we are finding what appears to be the higher 10 concentrations or a concentration of ruthenium in those 11 metallic structures.
12 MR. McPHERSON:
More quantitative information is in 13 the following tables but I will not discuss that.
- x 14 (SLIDE.]
)
15 MR. McPHERSON:
I wanted to show you next the.
16 current core configuration from the point of view of its 17 actual physical configuration as of this date showing the 18 material having been removed above the lower crust.
I 19 There is really nothing more to say but clearly you I
20 can see that this 26 percent of the core that has been shipped t
21 and a little more has been removed, it shows up by this 22 viewgraph.
l 23 Now we are going to continue with a seven-minute i
24 video which has been taken during this past two months so this 25 is the newest information that Mr. Vaughan alluded to earlier.
~
30 1
MR. BROUGHTON:
These tapes are courtesy of GPU.
2 Most of the material was acquired during the February video 3
inspection and there are some tapes from earlier inspections j
4 for comparison purposes.
5 (Whereupon, at this point in the proceedings, a 6
video presentation was made.)
]
7 MR. BROUGHTON:
The first is a look at the damage to 8
the core former wall.
The camera swings back and forth here.
9 This is the debris bed itself and the camera will swing back.
10 This is the core former wall and this is the break in.the core 11 former wall.
We have a freeze frame on that in just a minute.
j 12 There is the freeze frame.
This is the break.
Fuel 13 rods are actually sticking through the break in the core 14 former wall.
This is a lap joint that we shouldn't be able to 15 see indicating that that wall has been pushed out or deformed 16 at a high temperature.
17 The wall thickness on the core former wall is one 18 inch and this is the primary location right now that we see 19 where material would have flowed from the core into the 20 by-pass region.
l 21 We will next look at the large rocks that GPU has 22 been trying to break up that are now resting on the debris 23 bed.-
This is a probe that was being used on this particular j
24 day to try to break up the debris bed or these large rocks.
i 25 This is one of the rocks.
~
i i
31 1-These are fuel rod segments.
Here is a much bigger f
^
2 rock and they have just glanced off the sdge of it.
Another 3
rock here, I believe the biggest rock has been estimated to 1
4 weigh about 1,500 pounds.
It is on th'e order of four or five 5,
feet long, a foot in one dimension and a foot and a half in l
6 another dimension.
'x i
7 COMMISSIONER BERNTHAL:
This is all lying in the i
8 bottom now?
9 MR. BROUGHTON:
This is material that is lying on 10 the surface of the debris bed.
11 COMMISSIONER BERNTHAL:
I see.
12 MR. BROUGHTON:
Now we will see a slide hammer.
13 Basically it is a 300 pound hammer up on the working platform 14 that is being slid down and impacting a collar on this steel 15 rod and they are trying to break this ledge off this large 16 rock here and you can see that not only did the rock not move, 17 but the ledge itschf wasn't deformed and there are a couple l
18 more.
19 I think this very graphically illustrates how tough 20 some of these pieces are. I believe that basically-previously i
21 molten metals that have frozen in place and now been exposed l
22 by the swiss-cheesing operation.
23 Now look at the inside surface, this surface right i
24 here, that exists now as a result of the swiss-cheesing i
i 25 operation and the removal of material and you can see fuel
~
32 1
rods with previously molten material surrounding or in the 2
coolant by-pass.
3 We will now look at the lower plenum itself over 4
here on the north side and the first view is what the condition 5
looked like in December of 1985 prior to any of the core boring 6
operation and you will see pristine like lava flows.
7 This is an instrument guide tube.
This is ihe 8
debris that was down there and you will see it right-herc 9
where it has flowed around one of the penetration tubes.
Now 10 you will see what it looks like in 1987 after the 1
11 swiss-cheesing operation.
1 12 GPU has estimated that somewhere between five and 13 ten tons of material has sifted down into the lower plenum.
14 It looks like a snow field and all of that structure that was 15 previously visible is now covered by this very fine particulate 16 material that has settled in place.
17 The next view looks up inside the elliptical flow i
18 distributor into this region here on the north side, the i
19 northeast side, and that is when GPU first saw the material 20 frozen in place that Don alluded to in this region right here 21 between the elliptical flow distributor and the instrument i
22 support plate.
It came back.
There it is.
i 23 I had forgotten, these are the welds on the 24 penetration nozzles.
We do come back to that, the penetration i
25 nozzle coming up.
This was obviously in 19.85 before the 1
-..,... ~ _ -.,,
.,m-...
. _.. _.,,..,, - - -.... ~ _. -. -'
t 33 1
swiss-cheesing operation.
This is another view of that.
(
2 This is just debris resting on the stainless steel i
3 liner.
The lines here are the weld lines where the stainless 4
steel is welded to the~ carbon steel and this is looking up 5
into this space here and, in fact, what you are seeing is the 6
instrument support plate and the grid forging.
7 So in this particular location, everything was clean 8
and pristine.
These wholes are six inches in diameter and 9
this is one of the pieces, a quick shot, that was material I
10 that was hanging down in this region right over here on the j
11 north side.
I I
12 Now we will look at the east region in the lower 13 half.
This is one of those flow holes in the elliptical flow j
14 distributor and as you can see, it is very difficult to see 15 the outline of the hole.
Here is one of them right~here.
16 This one is completely clogged with material and, in fact, the 17 sharp edge of the hole is obscured.
There may be some melt 18 interaction there but all of these holes are plugged above.
19 MR. VAUGHAN:
This is after the break-up operation.
20 MR. BROUGHTON:
Yes, this is after the break-up 21 operation.
22 This is the melted instrument structure in the lower 4
23 plenum, number 45, right over here.
It is about 12 inches off i
24 of the lower head.
This is the top of the melt region.
The 25 structure is about four and a half inch'es in diameter.
GPU
34 1
right now in this view is vacuuming the debris away from
(-
l 2
around that structure to get a better look at the melted zone 3
and that is what is coming into view right here.
4 This is the face that has been melted away.
This is
~
i 5
the instrument penetrat, ion nozzle, the very top of it.
The 6
wall thickness of.the guide tube right here is about 0.8 j
7 inches.
The total diameter of that structure is about four 4
8 inches.
You can see that there has been some significant 9
melting.
1 10 It is the melting of this structure here and the 11 melting on the core former wall is our first hard evidence of 12 melting of reactor vessel structures?
j 13 COMMISSIONER BERNTHAL:
Why dim. ' t that tube fail or I
14 would you say it was close to failure, that penetration?
15 MR. BROUGHTON:
I wouldn't.
That view that you 16 looked at there was about ten to 12 inches off the surface of J
17 the lower head.
The weld or seal joint is right at the lower l
18 head.
i 19 COMMISSIONER BERNTHAL:
Right.
i i
20 MR. BROUGHTON:
It is intimately coupled thermally i
21 to the lower head itself and I believe it was that thermal 4
22 coupling and the fact that it was right at the surface of the 23 lower head that saved that seal joint and I think GPU has done 24 an analysis on that and the analysis indicates that there was j
25 no metallurgical changes or temperatures didn't increase high t
---,-.m---4,---,.,-y,
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x
.%m7...._-,,,,,__._,-.,,...._,w--,_--
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35 1
enough to cause metallurgical changes in that weld joint.
'2 It is obvious that some of these structures down i
3 here at least above the surface have been melted.
4 We are continuing to do more analysis on that in 5
preparation for what we will find as GPU details the lower
)
6 plenum.
7 COMMISSIONER BERNTHAL:
The melt only came in 8
physical contact with the upper part of that?
9 MR. BROUGHTON:
Commissioner, there is a layer of 10 non-radioactive material down here on the bottom and that l
l 11 could be silver or metallic zircalloy or stainless steel 12 structures that flows down with the ceramic materials, because 13 they are immiscible, they separated, at if they came down at j
14 that time the temperatures of this molten metallic structure 15 would be very high, on the order of 2,800 Kelvin, that 16 interface then might have approached the melting point of the 17 steel, but we won't know until GPU gets the details and we get 18 a chance to look at it.
I 19 COMMISSIONER ZECH:
But that's a very important I
i 20 finding to try to determine exactly what happened in that part 21 of the vessel.
22 MR. BROUGHTON:
I believe it is.
+
23 CHAIRMAN ZECH:
When are we going to find that out?
24 MR. BROUGHTON:
We won't have the opportunity to 25 find it out until de-fueling of this re"gion is completed and t
36 1
we have access into this region.
2 CHAIRMAN ZECH:
But we are planning to do that, I 3
presume.
4 MR. VAUGHAN:
We don't know whether that is going to 5
be able to be put in the current plan or not because it's 6
beyond the scope of what we planned to do.
I'm not sure l
7 whether we are going to have frankly the money or the time to l
8 do it, that's well beyond the scope of what we envisioned.
9 I would say that if NRC thinks that is an important, l
10 you know, potential finding, that we'd like to work with you 4
11 on how important it might be and if it's going to take extra
]
12 funding, maybe we could share in doing some of that with some 13 NRC contribution, if it seems to be, you know, a really 14 important finding.
I 15 It's beyond the scope of where do the fission 16 products go, which is where we started this effort out.
We 17 never anticipated finding out all of the stuff at the bottom.
18 COMMISSIONER BERNTHAL:
Is there any reason to think i
19 it's not important, that we understand exactly how hot it was i
20 on the bottom, what the molten materia 1 was that came in l
21 contact with the bottom and how close we came to failing 22 instrument tubes at the bottom?
23 MR. VAUGHAN:
No.
I don't think there is questions 24 that it is not important.
It gets into the very practical i
~
j 25 matter, you know, of how much R&D you can do on this vis-a-vis l
I
,.~.,,_.., - ---,-. -
---a,--
37 1
complete the clean-up, and it's been a constant balance as we 2
have gone through this, as you might imagine.
3 I don't think there is technically any question, you 4
know, that it is important.
I think it becomes a practical 5
matter and what's the use of the results.
T 6
CHAIRMAN ZECH:
It seems like it is very important 7
to me that we pursue this and not let perhaps previous 8
decisions that were made without benefit of the knowledge that 9
we now have stop us from going ahead.
It seems to me that to 10 find out more about the bottom part of the head where the 11 molten material meets perhaps the bottom of the vessel itself' 12 is extremely important information to have.
I would hope that 13 DOE could continue to fund this part of the evolution, but in f
J
(
14 any case, it seems to me that we should work together to try 15 to get this information which it seems to me would be extremely 16 valuable.
17 MR. VAUGHAN:
I am sure you probably heard 18 Dr. McPherson describe how we tried to get the existing 19 machine, which is tricky.
This whole think is tricky 20 technology you are looking at, never been done before, and how 21 we tried to get the existing machine to go through the bottom I
22 and it just won't go.
l 23 My guess is you are talking $2 to $5 million just to 24 go get that last piece of data.
You might have to do it by 25 going through the wall of the vessel somehow and it's going to i,
38 1
be tricky.
(
2 CHAIRMAN ZECH:
I would certainly agree it's tricky 3
and it's certainly an unique operation but you know, I would l
4 hope that we could -- we have gotten this far and come this 5
far, it seems to me this is extremely valuable information and 6
it is right in front of us and we simply should figure out a 7
way to get that kind of valuable information, it seems to 8
me.
I would certainly like to hear from others who perhaps 9
are more knowledgeable than I am, but it does seem to me from 10 a common sense standpoint, if we are this close to what could 11 be very valuable information, that we should certainly not 12 stop now and find a way to proceed.
13 p
I would like to say at the moment, while I have 14 interrupted you, that I think DOE has done a commendable job 15 and so has GPU.
This is a very tricky and very difficult 16 operation.
I certainly appreciate and respect that.
I really 17 do commend all of you who are involved in it, GPU and DOE and 18 others, too.
19 But we have an opportunity here to get extremely 20 valuable information and I think we have an obligation to 21 figure out some way to get it.
That's just my personal view.
22 COMMISSIONER BERNTHAL:
I couldn't agree more.
I 23 think it's essential that we get that information.
I cannot 24 imagine that with an one of a kind accident, that we would not
~
25 learn everything we possibly can on the progression and the
.~. -.
39 1
circumstances surrounding that accident, how close we may have 2
come to breaching the bottom of the vessel, the integrity of l
3 the design of the instrument tube penetrations and what not.
]
4 Mr. Chairman, as far as I'm concerned, if we have to i
j 5
go to the Congress, I'm personally prepared to do that, if we 6
have to make this case ourselves, the commission, based on the i
7 judgment of others that you suggest that we should consult, at 8
this point, I would want to be convinced that it is not j
9 necessary to do that and if it is worthwhile doing it, there 10 just has to be a way to get the money to.do it.
1 11 CHAIRMAN ZECH:
I agree with that.
Before we go to 3
12 Congress, it seems to me we certainly ought to be able to i
!g 13 continue our efforts with DOE to find a solution to this x
14 matter.
I think that's our responsibility jointly, frankly.
15 COMMISSIONER BERNTHAL:
I agree.
16 MR. VAUGHAN:
We would like to work with you to do i
17 that.
Frankly, the bottom line is that we are just absolutely 18 short of money and I know you are well aware, there are great T
19 pressures not to exceed the total planned program.
20 CHAIRMAN ZECH:
Let me just say this; from the NRC's 21 standpoint, we don't have money to spare either but I would i
22 certainly hope that DOE in their responsibilities for research, 23 this is your responsibility, as far as I'm concerned.
I'd like I
24 to start from that approach anyway and ask you to continue the
\\
efforts you have made in this program, 'but certainly we will l
25
?
l 4
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-,,_m_,..,mm--,,m
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40 1
work with you.
I don't think we should not pursue this issue.
2 I would request that DOE try to find the money from a much 3
largsr amount than NRC has.
4 But no matter what happens, we simply must find a 5
way to solve this problem in my judgment.
6 MR. McGOFF:
Mr. Chairman, if it is helpful, I would 7
observe that NRC is already involved in funding portions, 8
although a small portion, of the TMI core examination.
9 CHAIRMAN ZECH:
I'm well aware of that.
10 MR. McGOFF:
It's not a matter of principle.
3 11 CHAIRMAN ZECH:
We are not talking about a lot of 12 money from a relative standpoint.
Let's try to find a 13 solution, as far as I'm concerned, to continue this very 14 unique opportunity.
I don't know if I am speaking for all my 15 fellow Commissioners.
I would think I was speaking for some 16 of them.
17 COMMISSIONER ASSELSTINE:
I certainly agree with 4
18 that as well.
Jim, could you give us an understanding of 1
19 where your effort cut's off and for what the difficulties are 20 in doing the kind of examination that the Chairman and Fred 21 are talking about?
For example, is part of the problem that 22 you have to look at that stuff before it is disturbed?
All of 23 that eventually has to come out.
Where is the difficulty in 24 continuing the examination effort?
25 MR. McGOFF:
Dr. McPherson wil'1 be. describing what
~
41 l
1 we plan to do in the next year in the core examination.
Maybe
- (
2 we can take it from that point.
COMMISSION'R ASSELSTINE:
Fine.
3 E
4 CHAIRMAN ZECH:
Let's go ahead with that.
5 (SLIDE.]
l 6
MR. McPHERSON:
I will try to accelerate my presentation to leave some time for discussion.
7 i
i 8
We have seen the pressure history of the accident.
9 I'll jump ahead and not go into details on this but I wanted i
10 to point out on this slide, we are going to show configurations 11 of the cores as we see them in the scenario at the point just -
i 12 before the pump transient occurred, 173 minutes, at the point i
I.
13 just before the core relocated, and just after the core
(
14 relocated, so that we have an idea of the important events 15 which took place involving movement of fuel.
i 16 Before moving on, it's important to note one 17 particular pressure pulse here, I referred to earlier.
During i
core relocation at'224 minutes, you can see the pressure 18
)
19 increased of about 300 psi which took place over about 18 j
20 seconds and lasted several minutes before it came down again.
21 That is an indication of the steam generated by the core, the 22 liquid core falling down into the lower plenum.
Of course, 23 there would be a great deal of steam produced at that time and i
I 24 that caused the pressure to pulse.
i
{
25 COMMISSIONER ASSELSTINE:
Are'you going to talk l
9 42 1
about the characteristics of that relocation?
Whether it
(-
2 dribbled down in a small little stream, whether it dropped as 3
a big block or what you think occurred?
4 MR. McPHERSON:
Commissicner Asselstine, I'll show 5
you what we believe happened but I can't get into that much 6
detail.
It would be just purely conjecture.
7 COMMISSIONER ASSELSTINE:
Fine.
8 (SLIDE.)
}
9 MR. McPHERSON:
From that particular pressure pulse, 10 I do want to give one bottom line here.
There was no j
11 significant steam explosion and that's terribly important, I 1
12 think, given this type of core melt or full core relocation i
13 into water, indicating a low probability of steam explosions 14 at a high system pressure.
15 (SLIDE.]
16 MR. McPHERSON:
I will go on to show those three 17 configurations I mentioned at different times during the 18 accident.
I showed this last year so there is nothing very 4
19 new.
You will recall, I think, all of the characteristics of 20 the core, the upper grid damage at this particular time.
I f
21 (SLIDE.]
i i
22 MR. McPHERSON:
After the pump was turned on for a l
23 few minutes, that caused the shattering of the oxidized fuel, 24 zircalloy, towards the top of the reactor, which led us to the
~
25 core debris sitting on top of this, probably melt front moving 1
l
)
l
____.._,_._.__._,._,__.__.._,__._,.._____._.,_,.___.,,____,..__.,__,f_,.__i
i I
43 1
upwards into that debris as it heated up and melted more and 2
more of the debris into it.
1 3
This is the situation we think existed just before 4
the relocation.
That leads us -- the core relocation we 5'
deduce from the following information shown on instruments I
l 6
which showed this particular information at 224 minutes, 7
namely the reactor core system pressure increased to 300 pai, 8
as shown earlier.
There was an indication by the source range i
9 monitor both on the east and west side of the core which 10 increased by a factor of two.
These are very sensitive 11 monitors showing,some movement of the core was taking place at 4
12 that time.
There was an increase in the cold-leg temperature 1
~
13 which means some steam was being generated and there was an f
14 alarm on the SPND's showing a pattern of movement of core i
1 I
15 across the lower plenum.
j i
16 COMMISSIONER ASSELSTINE:
Did any of the plant j
17 personnel at the time take note of these changes?
Were these i
l 18 things that were available based upon the instrumentation they
\\
i i
19 had and did any of them pick up on them?
l 1
20 MR. McPHERSON:
The cold-leg temperature increase l
4 1
1 21 and the system pressure would be the two that would have 22 access to and I'm not sure.
23 MR. BROUGHTON:
I don't believe they did.
i j;
24 COMMISSIONER ASSELSTINE:
Didn't pick up on them or i
25 recognize they were occurring?
~
w i
C _ _ _._ __, _ _ _ _. _ _ _ _ _ _ __. _ _.. _ _.. _. _ _ _ _ _ _ _ _. _ _.__
2
44 i
1 MR. BROUGHTON:. I don't believe so.
I believe they 7
2 were watching the pressurized liquid level at the tire i
3 primarily and monitoring the system with that.'
4 COMMISSIONER ASSELSTINE:
Okay.
l 5
MR. McPHERSON:
Rather newer information has l
l 6
indicated in our observation study of the source range monitor f
7
.that at the east side, there was a continued rise of that i
8 monitor over a period of about 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> which we think relates 9
to this movement of core into the bypass area.
This is very i
10 new information and we are not certain of it but we are still 11 continuing to study it to determine if this is the situation.-
4 12 That would mean not only was there a movement at 224 13 during the short period but probably for a longer period into j f
! \\
l 14 the bypass area.
15 COMMISSIONER ASSELSTINE:
I'm sorry.
You said they i
j 16 were focusing on pressurizer.
I take it from that this was at i
i 17 a time when they thought they were providing adequate cooling
?
i 18 for the core because of the level in the pressurizer?
Is that j
19 right?
i j
20 MR. McPHERSON:
Yes.
j 21 COMMISSIONER ASSELSTINE:
Despite these indications i
l 22 of what was actually going on in the vessel, particularly the j
23 increase in pressure?
1 24 MR. McPHERSON:
Yes, sir.
25 MR. BROUGHTON:
I believe so.
~
i 1
1
45
~
l COMMISSIONER ASSELSTINE:
Okay.
(,
~
2 (SLIDE.]
3 MR. McPHERSON:
Now, the next viewgraph is a cross 4
section through one particular area where we have discovered 5
this very low level in the upper crust.
You will note there 6
that is where we believe the core relocation took place and it 7
is consistent with the other information that we have already 8
discussed.
9 We will move right on and show you what we think 10 happened at the 226 minutes, that is following relocation, we 11 were left with -- we are now looking in from the northeast 12 direction, we are seeing a flow of liquid core down the left 13 hand side of this figure into the lower plenum, which is 14 consistent with all that information I just gave you, and then 15 a secondary flow into the bypass area.
16 You will note there is some showing up on the other 17 side which would indicate that flow went through the small 18 holes in the bypass plates, the baffle plates, which are 19 horizontal, and down into that lower level and flowed right 20 around.
21 We don't know how much is there.
We have just 22 detected it by probes going in from the top.
We know the 23 upper level.
We don't know the total quantity.
24 COMMISSIONER ASSELSTINE:
There's the water level;
~
25 okay.
.=.
+
46 4
1 MR. McPHERSON:
Although there is certainly -- I i
f 2
don't know how large the uncertainty is, but at least 2-3 s
3 feet.
}\\
l 4
COMMISSIONER ASSELSTINE:
What you think is pouring
'5 out of this cup directly into the water?
t 6
MR. McPHERSON:
Yes; that's correct.
7 COMMISSIONER ASSELSTINE:
There was water in that 8
lower core area.
i 9
MR. McPHERSON:
Yes.
l 10 (Slide.)
j 11 MR. McPHERSON:
This significant result from this is.
4
]
12 that the molten debris in the lower plenum was coolable, and 13 there was water in the reactor vessel, which terminated the f
i 14 progression of the accident.
i 15 (Slide.)
16 Going next to the major areas of uncertainty where 17 we think we can focus on.
These lists of uncertainties here 18 are taken from your NUREG-0956, and you will see on tl?e i
19 righthand column that we believe that the information comir.g j
20 from TMI impacts on the natural circulation, the steam 21 explosion, the coremelt progression and hydrogen generation, i
22 and then the fission product release and transport of iodine, I
23 the iodine and the chemical form of the iodine, and fission i
24 product revaporization.
25 (Slide.)
E. - u
47 1
The next Vu-graph I will probably skip over now, 2
because what this does is summarize all of the bottom lines 3
that I have listed through my presentation.
I have just H
4 reiterated them all in one table for your benefit, so there is 5
no need to repeat them again for the sake of time.
6s These, then, are what Jim Vaughan summarized very 7-briefly in his opening remarks.
~
8 (slide.]
N 9
Now I'll go on to the planned research.
This is the s
10 last item in my presentation.
11 In this Vu-graph those items which are shown in 12 green on the screen or hatched on your handouts are those 13 areas that we have already done work in or are doing work on.
14 You'll see that we're looking at the lead screws right at the 15 top in the upper plenum.
We have looked -- we have samples 16 taken from the upper end fittings, control rod spiders, the 17 peripheral fuel rods, the upper debris bed, the core, the 18 homogeneous previously molten materials and then the crust 19 materials.
We believe -- well, we will be getting samples 20 from GPU's -- if they use their good offices to provide it for l
21 us.
We haven't identified funding for it, but they have 22 promised to provide us some of the core material that's found 23 in the bypass area.
24 We have already plans for getting the materials 25 from the instrument structure and the d'amage to the instrument
(
48 1
structure in the lower plenug.
You know we have already l t j
2 gotten the lower plenum debris materials, the fuel rod stubs, u
3 and that covers pretty well everything.
i 4
We have got the work yet to be done in the sample 1
l 5
acquisition.
Part of our program includes core bore sample, 6
control rod, fuel rods, and lower planum debris examinations, i
j 7
interaction zone between the lower plenum in instrument 8
structure and the molten material, and not show here on this i
9 Vu-graph are debris from the steam generator upper tube sheets
}
10 and the pressurizar, and then we cover backing plates.
11 That's all the program that we'll be doing over the l
12 next two, three years.
Those are detailed in much, much t
13 greater length in the next five or six slides of the handout.
j 14 (Slide.)
i l
15 That leads us to the most recent defueling l
16 observations, and you've already seen them, we've already 17' discussed them, so I needn't go into them, but the impacts, i
18 you've already discussed in your questioning, so there's no 19 need to do a -- repeat that.
l 20 (Slido.)
21 The conclusions of my presentations are that the i
l 22 results of the TMI research will have significant impact on I
23 resolving existing uncertainties identified in NUREG-0956 24 related to core damage progression, to steam explosions, and l
25 the fission product release and transpo'rt..
i i
i
49 l
1 As a result of this, the risk assessment can now be 2
based on more realistic understanding of severe accidents and 3
fission product behavior.
Furthermore, accident management 4
procedures can be based on the actual mitigation of a severe 5
accident.
6 Thank you gentlemen.
7 CHAIRMAN ZECH:
Thank you very much.
Questions from 8
my fellow Commissioners?
i 9
Mr. Roberts?
10 COMMISSIONER ROBERTS:
I think this is fascinating.
11 CHAIRMAN ZECH:
Commissioner Asselstine?
3 j{
12 COMMISSIONER ASSELSTINE:
Maybe just two quick ones.
1
{
,e 13 Jim, you mentioned a number in terms of what it l
14 might cost to do the things that we were talking about 15 earlier.
Is that a fairly well-thought-out number, the $5 16 million or somewhere in that ballpark, or how much uncertainty 17 is assoc'iated with that?
18 Is that something that we could really target on, i
19 finding a specific amount of noney that would be needed to i
20 really do that lower head examination and do it right?
21 MR. VAUGHAN:
I'm going to let Mr. McGoff speak to i
22 the estimate.
23 MR. McGOFF:
Commissioner, that's really a best-guess l
24 estimate.
We have estimates which came in about the $2 million l
25 range, but looking at the realism of do'ing.the job and
a 50 1
collecting the samples, we took $5 million as a sophisticated 2
guess.
3 COMMISSIONER ASSELSTINE:
Okay.
And I take it what i
4 you have to do is figure out some way to get at that material 1
5 before -- you just can't work down from the top, right, and 6
just wait for everything else to be settled out?
l 7,
MR. McGOFF:.Well, we've got to wait until all the 1
8 fuel is removed.
There still remains the problem, then, of
)
9 what condition GPU wishes to leave the vessel in.
They may 10 wish to leave the vessel in as a pressure boundary, which 11 makes the task even more difficulty.
12 COMMISSIONER ASSELSTINE:
Yes.
You can't cut a I
13 chunk out of it, for sure.
14 My last question:
Do you have a basis now, assuming 4
for the moment that you aren't going to be able to do that 15 16 research, for trying to estimate how much -- whether if the 17 accident had not been arrested, and if the additional cooling 18 had not been provided, when you would have gotten to the point 19 of vessel meltthrough?
20 MR. McGOFF:
There have been several analyses that 21 have addressed thet one, and at this peint in time, there's 22 still only guesstimates.
23 MR. BROUGHTON:
We have done some preliminary 24 analyses in that area, and with the amount of material that is 25 on the lower head, it would take severa1 tens of minutes, l
S,
, _ _ _ -. _., ~
i l
51 o
1 maybe as much as an hour, to heat the lower head 'to the point 2
where one could expect to start creep, and that's a gross type 3
of analysis, not taking into account the individual 4
peculiarities associated with failure of instrument 5
6 So to answer your question, the answer is not 7
complate', but I believe that does give a round figure for the 8
type of heating that was taking place in the event that the 9
water had not been added to the system.
10 MR. VAUGHAN:
Of course, even if it starts to creep, 11 that's just the start of creep, and that does not necessarily.
12 mean it will penetrate.
13 COMMISSIONER ASSELSTINE:
Yes, okay, thanks.
That's 1
i 14 all I have.
15 CHAIRMAN ZECH:
Commissioner Bernthal?
16 COMMISSIONER BEENTHAL:
Gee, I thought you would all 17 figure out where to get the $5 million while I was out of the 18 room, Mr. Chairman.
J 19
[ Laughter.]
j 20 COMMISSIONER ASSELSTINE:
Well, the Chairman had a 21 suggestion that sounded good to me.
22
[ Laughter.)
1 23 CHAIRMAN ZECH:
DOE is going to start looking first.
24
[ Laughter.]
25 CHAIRMAN ZECH:
Did you have a~nyth,ing?
52 1
MR. VAUGHAN:
We have previously invited the NRC to
("
and we have not had the most 2
contribute more to this effort, 3
vigorous of responses.
4 CHAIRMAN ZECH:
Well, we've got to find a way.
5 That's all there is to it.
6 Commissioner Bernthal?
7 COMMISSIONER BERNTHAL:
I think they're assuming, 8
because we didn't get our budget cut this year, that we've got 9
the deep pockets, and that's not true, unfortunately.
10 I had one earlier question, and if I understood ws11 11 my note to myself, I probably could ask it more intelligently 12 at this point.
But let me ask it anyway, and maybe you can 13 figure out what I meant.
14 I was wondering about the cooling mechanism when you 15 had this two feet of water left in the bottom of the vessel.
16 Do you have a good picture of the thermal hydraulics, if you 17 can call two feet of water that, actually -- there must have 18 been crucial cooling that was occurring, even with that small l
19 amount of water.
20 Do you have a sense of what the mechanism was at 21 that point?
22 MR. BROUGHTON:
There was water continually being 23 added, but at a relatively low rate, from the high-pressure i
24 injection system, and the net effect was' a liquid level that 25 was -- which appears to have been fairly stable from about 150
53 1
minutes out to 175 minutes at this one to two-foot elevation.
}
2 As the core damage progressed, molten material l
3 gradually got down to this two-foot elevaticn and started to i
4 block the core.
The.n as the water is boiled off, that steam 5
rises around that blockage, and the convective heat transfer 6
tends to cool the next material as it's coming d wn at a 7
higher elevation, with the result that you don't have a flat 8
plane across the core of solid material, but a funnel or cup 9
shape, because as it's gradually blocked, the velocity of the 10 cooling steam rises, increasing the convective heat transfer, 11 resulting in freezing of the material at a higher elevation.
4 12 So it appears to have been boiling and convective 13 heat transfer as the steam rose around it.
14 COMMISSIONER BERNTHAL:
And then this molten material 15 that flowed down the side, I guess maintained -- well, there's 16 two questions here -- one is how homogeneous was that 17 material?
It was apparently coolable at some level, and 18 yet was homogeneous enough or at least moving enough as a 19 single mass such that it could have presented an immediate and 20 direct threat to the instrument tubing penetrations, I gather.
21 MR. BROUGHTON:
When you look at the alarming of the 22 instrument strings at 224 minutes, it starts -- the first 23 alarm is near the failed instrument string that we saw in the 1
24 video, and they fail from the -- it would be the southeast 25 side across to the northwest side in a general pattern.
And I
54 1
believe that that failing would indicate that these instrument
~
2 strings have been raised to high temperatures by the molten 3
materials that flowed across.
4 We know from the NRC experiments at Battelle 5
Northwest Labs that the viscosity of this material, the 6
ceramic material at 3100 Kelvin is very.much like water.
So 7
- as it first started to flow, it woqld move very rapidly, but 8
it also starts to cool, because there's water in the system.
9 So it may have formed a pipe that allowed the 10 material to relocate all the way down.
We'll know much more 11 as GPU continues its defueling operations, and we get this 12 gross structure from -- during the normal course of defueling.
13 COMMISSIONER BERNTHAL:
Okay.
That brings the 14 question of the heterogeneity or lack thereof in the molten 15 regions and elsewhere in the destroyed core region.
16 I recently spend some time out at the Sandia 17 Laboratory and listened to their concerns, a very capsulized 18 presentation of their concerns about the direct heating 19 phenomenon and the experiments that they are planning.
20 One of the things that struck me, though, is that 21 believing in that phenomenon -- and not everybody believes in 22 it -- requires, it seems to me, at least, a certain assumption 23 that you will have a relatively homogeneous melt material.
If 24 it really gets lumpy, the the phenomenon' becomes rather 25 difficult to imagine.
-n
55 1
Although you didn't have an X in the box by that to 2
indicate you' thought we would learn much about it, I wonder, 3
is there something to be learned here about the likely 4
characteristics of melt material, and from that, something t
5 about the direct heating phenomenon?
6 MR. BROUGHTON:
I believe in a real sense what is in 7
the lower plenum at TM repres.ents the initial conditions for 8
that melt prior to failure of the lower head.
9 COMMISSIONER BERNTHAL:
One would think so, yes.
j 10 MR. BROUGHTON:
And from that point, my staff and I i
11 discussed this question, does an X belong there, and we 12 decided, no, it doesn't, because if TMI is going to impact
]
13 that question, it will impact it through the melt progression 14 question and the mechanisms and eventual mechanisms that 2
15 control failure of the lower head.
16 That's where, I think, TMI can have the biggest 17 impact on that basic issue.
And the question comes down to, -
18 do the instrument penetrations fail, or does the head fail in 19 a more general sense, allowing less dispersal of those 20 materials around the containment and thus reducing the direct 21 containment heating?
22 COMMISSIONER BERNTHAL:
And yet this is the very.
23 area that you're telling us here is about to run out of money, 24 is it not?
Generally what's gone on down in the very bottom 25 of the vessel.
e y
y y
._,,-y,..
56 1
MR. BROUGHTON:
Well, our program focused first on 2
understanding'the fission products, their release, and their 3
transport.
And what we have -- you know, what we have learned 4
about the core damage progression provides us the basic 5
information for understanding the release and transport of the 6
fission products.
And we will complete the fission product 7
inventory in the current program.
8 The condition of the lower heat is and was outside 9
the scope of that program, although it's, I think, without a 10 doubt, a question of great interest, and I think that TMI can 11 make a unique contribution.
12 COMMISSIONER BERNTHAL:
I'm sure it's not outside 13 the scope of your personal program, and it's certainly not 14 outside the scope of my program, and I hope we're able to do 15 something about that.
16 One other question:
Is there any sense from what 17 you've learned now about the accident that would point to the 18 relative desirabilities in an accident situation of simply 19 sticking to the maxim of getting maximum water flow into the 20 core in any possible way, or can the conclusion at this point 21 be drawn that it might be better to have some sort of 22 preprogrammed limited flow rate under an accident condition?
23 MR. BROUGHTON:
In my mind, there have been some 24 unique pieces of knowledge that have come out of the research, 25 specifically in this area.
57 1
First, it shows that if a core does get in this f
2 condition, wh' ether it's been significant melting and it's held 3
in place, the fact that you continue to add water doesn't 4
immediately terminate the progression of the accident.
5 We believe that relocation into the-core, into the 6
lower plenum, occurred after the reactor vessel was nearly i
7 refilled with water.
We believe that water was above the 8
upper surface of the solid structure, and yet the containing 9
crucible failed and allowed material to relocate into the 10 lower plenum.
But we believe it was the presence of the water 11 in the lower plenum and the interaction of this material with 12 the water and the structures down there that resulted in it 13 being cooled.
14 We have done some preliminary analysis on the steam 15 generation that would be necessary to repressurize the system 16 by 300 psi.
It indicates that there was significant heat 17 transfer from this molten material to the steam or to the 18 water during this time period, and there was substantial 19 reduction in stored energy during that time.
20 So we think that the presence of water is critical, 21 and then the continued addition of water.
So it's a 22 combination of having water present and continuing to add 23 water, but water did not prevent it from going into the lower 24 plenum.
25 COMMISSIONER BERNTHAL:
But the question of whether,
, 58 1
I don't know quite how to put this, an appropriate ration of 2
water versus 'get all the water in you can all the time.
3 MR. VAUGHAN:
It depends on when you are talking 4
because just to keep this in context, his answer, 5
Mr. Broughton's answer was if the core gets into this condition 3
6 nothing should supercede lesson number one which is to keep it 7
cool and keep water in there from the beginning so it nev,er 8
gets in that condition.
9 COMMISSIONER BERNTHAL:
Exactly.
10 MR. VAUGHAN:
So we need to listen to his complex 11 technical answer is context.
Lesson number one is keep the 12 water in there and keep it flowing and keep it cool so you 13 never get there.
r 14 COMMISSIONER BERNTHAL:
But once you are in this 15 condition, then you --
16 MR. BROUGHTON:
You want to continue to add water 17 but that won't necessary prevent --
18 COMMISSIONER BERNTHAL:
Sort of a hope and a prayer.
19 MR. BROUGHTON:
Yes, that won't necessarily prevent 20 the core from reaching the lower plenum but I think TMI 21 demonstrates that that is not necessarily the first step or 22 that does not automatically lead to failure of the lower head, 23 that you can have significant relocation and still have the
-24 lower head maintain its. pressure integrity and I think that is 25 a key lesson.
9
59 1
COMMISSIONER BERNTHAL:
But that was not just
'(
^
2 because of ths steam cooling either as I understand or the 3
water cooling, well, ultimately the water cooling but I 4
understand that these internals also made possible a lot of 5
conductive cooling.
6 MR. BROUGHTON:
The lower head represents a very 7
substantial heat sink and the combination of the water in the 8
vessel, the large heat sink represented by the lower head 9
resulted in maintaining vessel integrity.
10 COMMISSIONER BERNTHAL:
But what about the plate 11 itself, for example?
12 MR. BROUGHTON:
We don't know yet.
13 COMMISSIONER BERNTHAL:
For example,j as I understand 14 it from previous briefings, it looked like you were squeezing 15 molten material that would nominally have been above the 16 melting point of some of that stainless steel and yet 17 apparently the conductive cooling effect was sufficient that 18 it didn't appear to melt in those cases.
19 MR. BROUGHTON:
Again, the answer to your question 20 is not intuitively obvious because of the differences in 21 temperature.
22 COMMISSIONER BERNTHAL:
I see.
23 MR. BROUGHTON:
The material that comes down is 24 primarily ceramic with a low thermal con'ductivity.
As a 25 result for these large structures, the interface temperature i
,,,e
-- ~
60 1
is below the melting point of the stainless.
~
2 COMNIISSIONER BERNTHAL:
I see.
3 MR. BROUGHTON:
And for the large structures with 4
the large thermal capacitance, it takes a long time to heat 5
that interface temperature up to the melting point of the 6
stainless steel structure.
7 If it is molten metallic coming down'at tho'se 8
temperatures, the interface temperature is above the melting 9
point.
It is a different story.
10 COMMISSIONER BERNTHAL:
Right.
11 MR. BROUGHTON:
That is why this question of what is 12 that bottom layer of material on the lower head, why is it 13 important.
14 COMMISSIONER BERNTHAL:
One last rather technical 15 question.
Have we learned much yet about the temperatures 16 which some of the piping, the primary piping, for example, 17 achieved and whether we were ever close to failing some of 18 those primary penetrations of the vessel?
19 MR. BROUGHTON:
I think I can say with confidence 4
20 that we were never close to it.
The evidence we have from the 21 two lead screws we have examined from the upper plenum shows 22 peak temperatures at the bottom to have reached 1,200 Kelvin, 23 at the top to only have reached 700 Kelvin and the hot-let 24 RDT's indicate temperatures went up to around saturation but 25 never do we believe those structures got hot enough to approach I
61 1
failure of the penetration joints.
p..
2 COMM'ISSIONER BERNTHAL:
All right.
Why don't I let 3
someone ask some questions here.
Thank you very much.
It 4
really is invaluable information it seems to me and I hope we 5
see all we can from it.
6 CHAIRMAN ZECH:
I certainly agree.
Let me just say 7
first of all, I would again like to thank the DOE people, all 8
of you here, who are involved in this very important activity 9
for not only a very fine presentation but for your continued 10 efforts to get as much information from this important 11 undertaking as we possibly can.
12 I believe the examination of the damaged core at 13 Three Mile Island is extremely important.
I think also that 14 the additional information that we could.get from the samples 15 and the activity is extremely important.
It seems to me that 16 the vessel bottom layer information really is important.
17 I would like to say, too, that I think we ought to 18 not only get as much information as we can on core melt 19 progression, but again perhaps we can gain information on the 20 likelihood of the pressure vessel failure and, to me, that 21 would be extremely important information to have.
22 I would hope that DOE can complete this program in 23 an orderly manner.
The information is extremely valuable.
I 24 see Mr. Ed Kintner-in the audience and know he is from GPU 25 Nuclear with particular responsibilities in this area and I i
7.
w
62 1
would just like to thank him for his real dedication to a 2
very, very di'fficult task as I see him here today.
3 COMMISSIONER BERNTHAL:
Ask him if he has five 4
million dollars.
5
[ Laughter.]
6 MR. VAUGHAN:
Mr. Chairman, if I could, let me say 7
that the Department of Energy has appreciated the cooperation 8
of GPU and Mr. Kintner in working carefully with us to obtain 9
the results with minimum interference of their program to get 10 it cleaned up and as I noted, it is a careful balancing act 11 and it has been a good example of cooperative effort.
12 COMMISSIONER BERNTHAL:
I agree with that and from 13 my understanding of the program, that is certainly accurate.
1 14 Let me just say, too, that some way or another, we have to 15 find the funds.
I certainly hope that DOE could find them.
16 I would like to ask our Office of Research to work 17 with the Department of Energy to see how we can find the 18 solution and to get back to the Commission with a 19 recommendation and some kind of a proposed solution.
20 We simply, in my judgement, must finish this very 21 important activity.
Do my fellow Commissioners have any 22 additional comments or questions?
23 COMMISSIONER BERNTHAL:
May I ask one small 24 question?
You indicated that apparentiy steam explosions 25 were not a realistic scenario at least -under these conditions i
i
63 1
at high pressure.
I think-those were the words you used.
I
/
2 understand why they wouldn't be at high pressure.
J What is the rest of the story?
You have a number of 4
qualifiers or at least implied qualifiers there.
Can you 5
imagine circumstances in any reasonable accident progression 6
of this type where steam explosions now l'ook to be a reasonable 7
possibility?
8 MR. BROUGHTON:
In attempting to answer your I
9 question, Commissioner, let me first make the statement that I 1
10 am not a qualified steam explosion expert'.
11 COMMISSIONER BERNTHAL:
I am not sure there are any, 12 but go ahead.
13 MR. BROUGHTON:
In my understanding of steam 14 explosions in a controlling phenomenon, first it is required 15 that the high temperature material be it liquid or solid must 16 first be broken up into very fine particles.
I don't believe 17 we have evidence of that occurring to any extent in TMI.
18 Secondly, it appears that this material in TMI did 1
19 come down very rapidly.
As Don indicated the system pressure 20 went up in 18 seconds; the source range monitor increased by a l
21 factor of two in less than a minute.
So we believe in a few 22 tenths of seconds, it all came down.
23 In doing that, it had to come down through rod 24 stubs, this very complex large core support assembly and once 25 it got through that it only had a foot or two feet of free 1
64 1
space before it hit the lower head and it is very difficult 2
for me to env'ision anywhere in that process how that material 3
could be broken up into large or small pieces, large volumes 4
of very small pieces, that would be homogeneously mixed with 5
the water so that you would have the heat transfer.
6 It may be at the high system pressures, that a 7
process couldn't occur and it could occur at low system 8
pressures but if that is the case, I am unaware of it.
So in 9
my mind, I don't see how it could occur but I qualify that 10 because it is a personal opinion and I certainly am not the 11 qualified expert.
12 COMMISSIONER BERNTHAL:
That is very well stated and 4
( ~
13 by the way, the entire presentation was very well done and we 14 are sort of laymen here in these areas and I certainly got a 15 great deal out of it.
Thank you very much.
16 CHAIRMAN ZECH:
All right.
Thank you all very 17 much.
We stand adjourned.
18
[Whereupon, at 3:41 o' clock p.m., the meeting of the 19 Commission was adjourned to reconvene at the Call of the 20 Chair.]
21 22 23 1
24 25
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1 2
REPORTER'S CERTIFICATE 3
4 This is to certify that the attached events of a 5
meeting of the U.S. Nuclear Regulatory Commission entitled:
6 7
TITLE OF MEETING:
Briefing by DOE on the TMI-2 Core Examination Program 8
PLACE OF MEETING:
Washington, D.C.
9 DATE OF MEETING:
10 11 were held as herein appears, and that this is the original 12 transcript thereof for the file of the Commission taken
{^
13 stenographically by me, thereafter reduced to typewriting by 14 me or under the direction of the court reporting company, and 15 that the transcript is a true and accurate record of the 16 foregoing events.
17 18 2 4 d'0 1 = =-'\\"23 EC 4:.------
Marilynn Nations 19 20 21 22 Ann Riley & Associates, Ltd.
23 24 25 y
y
i i
l l
TMI-2 Accident Evaluation
~
Program 1986-87 l
ENTbp 4
g D '%p 8
Presented by:
G. D. McPherson a
April 15,1987 f
Outline
~
Program goals and objectives NRC and CSNI partnership 1986-87 research highlights Accident scenario i
impact on issues
=
l Remaining research l
1 l
I PSSO 87-0231-02 l
k.
^
1 d
i
~
Program Goal I
Provide evidence from'TMI-2 for realistic severe accident source terms-i i
b PSSO ST-0331-08
Program Objectives Understand what happened during accident Apply understanding to resolution of severe accident and source term technical issues Transfer results of program to government nuclear industry and public - domestic and internationally
~
e PS90 ST-0231-04 l
a
)
i Basic Information Required from TMI-2 Research System configuration and operator actions Plant initial and boundary conditions Damage to core support assembly, instrument structures to the RV lower head Current core configuration P300 ST-0231-05 i
4
l i
Basic Information Required from TMI-2 Research (continued)
- End state and composition of core materials
- Peak temperatures, materials interactions,
.i and extent of material oxidation
- Effect of control and burnable poison rods
- Retained fission products and chemical form i
I PSSO ST-0231-04 i
I
i i
l NRC/OrDanization of Economic Cooperation and i
Development (OECD/CSNI) Participation in the t
TMI-2 Accident Evaluation Program l
- Analysis exercise (standard problem)
- Sample examinations I
PSSO ST-0231-07 i
l TMI Analysis Exercise Provide an assessment and data base for best-estimate severe accident analysis codes and methodologies from a full-scale severe accident i
Compare alternate severe accident analysis techniques and methods
+
I PSSO ST-0331-04 1
4
i i
Phases of the TMI-2 Accident l
Phase 1:
(0-100 min) Small break LOCA, operational transient i
Phase 2:
(100-174 min) Core boil-off and initial core heatup and damage Phase 3:
(174-200 min) Pump transient and continued heatup Phase 4:
(200-300 min? HPI and core relocation to core bypass and lower plenum areas 4
I PSSO ST-0281-00
{
i i
l l
Analysis Exercise Participants
- NRC:
- Battelle Columbus Lab., Sandia National Lab /Los l
Alamos National Lab., Idaho National Engineering Lab
- U.S. Utilities:
- New York Power Authority l
l
- CSNI:
- Euratoms Joint Research Center, United Kingdom, Italy, Japan, Finland, Sweden, France, West Germany, Netherlands and Switzerland PS90 ST-0231-10
l NRC/CSNI-2 Participation in TMI-2 $ ample Examination Program f
includes international scientists in the evaluation
)
a of TMI-2 samples Achieves world-wide consensus before publishing results of TMI-2 findings i
increases number of samples examined and thereby reduces statistical uncertainty of data 1
'l i
P300 ST-0231-11 I
J I
I
- l 1
CSNI/NRC Sample Examinations Switzer-United I
)
Samnia lSC/ANL-E Franea Germany Canada JCB Sweden land Kingdom Core bores X
X X
X X
X X
Fuel rod X
X X
X segments (Peripheral)
Fuel assembly X
X X
X rod seamente end control rode (ct)
Upper core X
X X
X X
Icose debris l
Lower core X
X X
loose debris i
Burnable poleon X
rod spider, upper end boxes, and ll springs
.i
)
P300 ST-0281-12 i
I.
i
/
End-State Core Configuration 7
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Summary of Upper Debris l
Examinations Debris is heterogeneous exhibiting a broad range of oxidation and material interactions, but well mixed It is composed of fuel pieces, cladding fragments and j
i previously molten material - both fuel and metallic Average peak temperature of debris bed estimated'to be about 2200 K Previously molten ceramic pieces exhibit significant fracture toughness 90% of particles between 1 and 5 mm P900 ST-0331-13 i
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Summary of Lower Plenum i
Debris Examinations
\\
l l
- Particles appear to be ceramic (UO or (U,Zr)O ),
2 2
j can be homogeneous and very porous l
- Particles are from 1 to 200 mm
- Average peak temperature of debris between 2800 K i
and 3100 K (UO2 melting)
- Samples exhibit significant fracture toughness - otherwise l:
laced with fracture lines
~
i l
- Uniform fission product concentration across samples l
P300 ST-0231-14 4
I Fission Product Retention
= Significant retention of 12sI and s7Cs in the i
high temperature core debris and previously molten core materials Significant ruthenium released from fuel a
with retention in metallic structures Impact:
- lodine and cesium present in molten core materials are available for direct release to containment in the event of RPV failure t
- Ruthenium must be properly accounted for to correctly estimate the source term i
P900 87-0291-15 l
Measured Flssion Product Retention Percent of inventory retained
- l Lower Plenum Upoer Debris Radionuclide Average Range Average Range 129 { **
2 0-10 22 10-28 137Cs 16 9-22 21 6-32 12sSb 5
3-10 28 18-38
' 'Ru 7
4-9 55 35-86 4
l 8 Sr
~100 40-160 93 79-102 "Eu 85 75-94 90 60-108 i
"Ce 114 106-124 114 90-130
~
l
- Compared with whole core average ORIGEN-2 analysis (.Ci/gU) and average uranium content
" Radionuchde content based on the average of a number 1
of small (6-40 mg) particle analyses P390 ST-0281-14 l
I s'
l l
Core Boring Machine Drilling machine l
I bOperator
[l M platform Transfer 2
cask roller platform eg H
339.f t. elevation ii Interface 3
Defueling platform Ut' work platform MI f Fuel 331 f t,6 in. elevation drrM canister
~ " '
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mast 327 f t,6-in. elevation Shielded l Underwater
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l i
Visual observations l
l Surface contours i
l Core cross-sectional structures i
l PS90 ST-0231-17 1
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l l
t Region Below Hard Crust Consists of Two Distinct Structures l
- Standing fuel rods J
l
- Previously molten core materials l
- Homogeneous structure
- Agglomerated material - previously molten l
material surrounding fuel pellets / rods
~
- Axially stacked pellets
- Randomly oriented pellets PS90 ST-0231-18 i
l i
r i
~
Contour Maps l
l
- Upper surface of solid structure l
- Bottom surface of solid structure i
i P300 ST-0231-19 i;
l I
o Core Cross Section Column G
_^ _ _ _ _
9140 i
i iiiiiiiiii i
'l U 130 -
i 5
Void
'd ii e 120 i, 10 g 110 -j o
o 8
7 B 100 3
o.
S 90
-i Upper Debris Bed i
in G-12 C-8 T
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-i 1
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E I AIBIClDlElf! lHlKIL IMlt410lPlRI
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[ 40
@ Ceramic.
2nd 8 Agglomerate
=
30 X oiscolored E Large metal segregations 20 1st
.g cladding al VeN b Bottom of fuel r,ods,
,Stqnding fpel Rodg O 1514131211109 8 7 6 54 3 2 1 Fuel Rod Assembly Row 3
P313 ST-197-248
}
Estimated Debris Bed Height i
f f
4 Core 4
l 1
Fuel assembly grid g-
/
-=
l P ate wwwwwwww 4
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g sssssssssssssss j
i Elliptical flow distributor
' ' instrument i
support i
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30 in.
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4 i
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Regi'ons in CSA Containirig Previously Molten Fuel
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Core Support j
Assembiy I1 i
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1 Estimated Core V sumes and Masses 1
j i
j i
Estir ted Estimated i-V.. me Mass Solid 8
8 i
Region
- (ft )
(10 lbs)
Mass i
Original core 1182 285 100 l
i Void volume 325 i
l Upper core debris 236 68 23 Molten zone 122 53 19 l
Standing rods 499 120 42 i
Lower plenum debris 106 46 16 PSSO ST-0231-40 I
1
Significant Results i
Approximately 5% of core melted j
Indicates core 1elting possible with l
=
limited damag to reactor vessel internals 4
e i
PSSO ST-0231-22 l
l l
t j
N Summary of Fission Product Distribution
- Significant retention of noble gas fission products in undamaged fuel assemblies and rod stubs is expected lodine and cesium dissolved in coolant water -
a consistant with Csl and CsOH behavior Ruthenium and antimony associated with metallic materials but essentially remain completely within the RPV - unanticipated from small scale experiments -
should be included in analytical models Lanthanides are retained within fuel materials -
basically confirms current understanding P300 ST-0231-23
]
l l
Ex-Core Fission Product Distribution (%)
i I
Noble
]l Gases I
Cs Sr Sb R_u Ce
~
Reactor building basement j
and tanks 47 21 42 2
0.3 0.5
.01 i
1 1
0.1 ND NM l
Auxiliary building 1
2 5
0.2 0.3 NM NM l
Decontamination resins NM NM 5
0.1 ND ND NM 1
.)
Total outside core 48 25 53 3
0.7 0.5 Nil NM = Not measured l
ND = Not detected PSSO ST-0231-24
{
i
l l
l
\\
l In-Vessel Fission Product Distribution (%)
4 Fractia.:
(
l cf Core Noble 1
)
Mass (%) Gases I
Cs Sr Sb R_u Ce g
Intact rods 42 5
Upper debris bed 23 I
5 5
21 5
113 26 Consolidated mass 19 3,
i s
i-Lower plenum 16 I
0.3 3
(14) 0.8 1
18 1
i Projected in-vessel retention (from i
ex-core data) 52 75 47 97 99
>99 (100) i i - in proc...
NM = Not measured j
- = Samples not yet avallable A
4 P300 ST-0231-25 k
i 1
Current Core Configuration
' [
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1 TMI-2 Accident Scenario i
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a P890 ST-0281-24 l
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O 100 200 Time (mitiutes) esso sr-onsi-ar 1
I j
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Significant Results l
l There was no energetic steam exposion j
= -Indicates ow probability of steam explosions l
at high system pressure
\\
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l l
Hypothesized Core Damage Configuration at 173 Minutes
-=&:= = = r h h b b
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us m
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Hypothesized Core Damage Configuration (224 Minutes) diW= tam %
=a55y@
=
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m w
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t Instrument Response at 224 Minutes RCS pressure increase (300 psi?
- 2. Source range monitor
- 3. Cod-eg temperature increase
- 4. SPND alarm data pattern
~
P300 ST-0231-20 l
I
Core Croas Section-Row 6 914 0 i
i i
iiiiiii ii E
I 1
0130 Void r5 12 0
'f I110 f
j i
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~
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, bl,0nding fuel rods E
ottgm pf fpelr,ods, O A BCDEFGH K L MNOPR Fuel Rod Assembly Column P390 ST-231-308
Hypothesized Core Damage Configuration (226 Minutes)
.-re :
m
=
x
=
=
=
- =s
'= = = = 5 5 5 5 =
i
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,/
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s I'l "//,[ff-
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tu Crust failure E.'
2
.......y near
,,lf
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){
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g
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- h. c
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periphery i
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'(' h, j l
=h M
7 relocation
./
- )
Lower pienum route '''P C
y,'
g -9
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- _ ->j@g6
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.h N-Failed instrument structure
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71245
[
t Significant Results l
l Moten debris in lower plenum was coolabe Water in reactor vessel (and continued HPl>
terminated the accident I
P390 ST-0231-31
(
.j.-
?.
'l l
Major Areas of Uncertainty NUREG-0958 TMI-2 Information Area of Uncertainty l
x Natural circulation in RCS Core melt progression and hydrogen x
generation x
Steam explosions High-pressure melt ejection Core-concrete interactions Hydrogen combustion lodine chemical form
( Fission product x
Fission product revaporization ) release and transport P900 87-0291-31 t
i
)
~
~
Significant Results and Impact t
impact Results in-core liquid level detector developed
- Core uncovered while pressurizer for improved accident management indicated full Indicates core molting possible with only
- Approximately 35% of core limited damage to the upper plenum and core melted support structures in presence of some water Water in reactor vessel (and continued HPI)
- Molten debris in lower plonum terminated the accident was eventually cooled Consistent with current belief of no steam
- There was no energetic steam explosion at high system presssure explosion I and Cs would be present in core debris
- Retention of I and Cs in core for direct release to containment during debris and molten materials was molten core-concrete interaction si0nificant J
Ru release from fuel should be properly
- Ru appears to be retained in accounted for in fission product release matallic debris and transport models rsoo sr-ossi-ss O
Reactor Sampling and Examination Status l/ / / A Adequately sampled and examined
~~
8=.6L 5 3 5 5 5 5's
=
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~
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/
o
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and control rod
~
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spiders
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,,.f ;',,4,;.,,'*s]
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molten core 7
s j.
materials Relocation
.,f.
d route c'%
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'N C i s
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q
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ii
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i i
Summary of Remaining Tasks l
i Sarnole Acouisition and Examinations FY-87:
- Complete radiological and metallurgical exams of:
- Distinct components (cy trol rods and fuel rods)l) Reports
- Core bores
- Core sample support:
- ORIGIN-2 confirmation
- Fission gas measurements completed
- Bulk oxidation state measured
~
1
- Microscanner analysis of lower vessel and core bore debris
- Complete upper debris bed draft report PS90 ST-0231-41 1
i 6
i
~
Summary of Remaining Tasks (cont'd)
Sample Acauisition and Examinations (cont'd)
FY-88:
- Complete exams on augmented co(e samples (D-
- Ex-RCS final concrete core bore report
= Lower vessel debris examination and report
~
= Reactor vesselinstrument. penetration exams and re P390 ST-0231-41
l Summary of Re Ining Tasks (cfnt' )
uction and Qualification Analysis Exercise and D4ta R
~
FY-87:
- Response to CSNIissues and questions
- Data Qualification Summsry Report
- Complete data basel structure and summary report
- Complete demonstration calculation to 300 minutes FY-88:
- Data base nianagement
- Analysis exercise! comparison report P390 ST-0231-43
l
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i
e Summary of Remaining Tasks (cont'd)
Accident Scenario Development (cont'd)
FY-87 (and beyond):
d to lower plenum
- Evaluate long-term thermal response of lower hea asses of
- Evaluate the release of fission products from large m debris t
lower
- Estimate fission product release during core relocation o molten core materials chemistry on
/
- Evaluate the effects of long-term leaching and aqueous plenum the fission product behavior
- Incorporate examination results and issue final report on accident scenario d
e
--M m
</
Summary of Remaining Tasks I
(cont'd)
Information and6n i
FY-87:
aminations and lower issue technical bulletins on core bore ex plenum examinations e
ti gs, CSNI Review ANS policy statementCoordinate pre workshops and JCWR meetings l Program Chairman
- ANS TMI-2 Topical Meeting - Technica FY-88/89:
- ANS Special Session - TMI-2 impact P900 ST-0331-44 l
l
1 Recent Defueling Observations and 4
PotentialImpact imp _esl i
Observation Realistic understanding of coreda Molten core materials have RPV structures caused limited melting of internal RPV structures Understand the processes control-Evidence of interactions between ling damage to the lower head molten core materials with lower head e
- S90 ST-OSS1-88,
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l placement in the Public Document Room. No other distribution is requested or
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