ML19221A616
| ML19221A616 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/13/1979 |
| From: | Dietrich INDUSTRY ADVISORY GROUP |
| To: | |
| References | |
| OLS-790413, TASK 6B, TASK-6B, NUDOCS 7905230440 | |
| Download: ML19221A616 (3) | |
Text
,
i TASK CLOSE OUT DOCUMENT o
Task Scope
(*
v1e nh a s s c s1 m * & c> S Cc<<
slodus s sc~~a J
.,~k L
To:
M. Levenson S. Levy E. Zebroski Ta s k No.
lo h Date Complete 4 l,a f 7 9 i
Reason felt task is cernplete:
Memoers of Comittee D.y Lic L i <. d,w/
-/(
.~, t mie d < '
T.- L...., t-Comittee Leader D,,n k :0 166 003 7 905 23 P VFO pg
COMMENTS ON HISTORY OF CORE DAMAGE J. R. Dietrich C
4/12/79 The question has been asked whether there was additional uncovering and damage to the core after the sequence of events that lasted fran about 100 minutes to 200 minutes after the reactor trip.
The behavior of the source range neutron detectors during the 100-200 minute time span 1: qualitatively consistent with the other evidence of core damage during that period.
It appears that these detectors continued to be able to see the source for at least 17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br /> after the reactor trip (Mr. Ball believes these BF3 counters r : certe-c are counting neutrons, and this certainly seems reasonable).
If the core were again uncovered during the 17-hour period after reactor trip we should expect to see evider on these counters canparable to that which they exhibited during the 100-200 minute period.
Only two subsequent blips appear after that period, and they are very much smaller than the events recorded during the 100-200 minute period when we know there was core damage.
One of these blips occurs at about 585 minutes and the other at about 865 minutes.
The first of these two does occur near a minimum in the RCS pressure (at-500 psig) and while the That is still off scale.
Either or both of the blips could correspond to some additional core damage, or possibly a shift of the damaced fuel, but hardly an uncovering of the core.
The same remarks could apply to the readings of the intennediate range ion chambers during the 100-200 minute duration of the known damage event.
- However, Mr. Ball thinks they are reading.gamas, and they are off scale in the low direction except during the period of core uncovery.
Consequently one does not know whether they would come back on scale during a subsequent core uncovery if
)
one occurred, since the gama level is decaying.
e Mr. Kaufman's qualitative analysis of events, which takes into account the g]
nuclear detectors, seems to me toLbe ' worthy of an attempt at quantitative confirmation if we want to get more understanding of just what happened. There are some aspects of the quantitative nuclear instrument behcvior which seem surprising to me, and of course there are some parts of Mr. Kaufman's interpretation for which he had to resort to conjecture.
Gne of the things difficult for me to understand is the very rapid decrease in readings of the in:truments which occur at certain points during the period in question (100-200 minutes after reactor trip).
It is hard for me to see how changes in the water density or configuration could produce such large changes so rapidly.
I am also puzzled by the flat top of the high-level reading recorded by the intermediate range ion chambers -- if they were indeed reading gammar.
In the event of a core uncovery one would expect a relatively flat top on the high-level reading of a neutron = detector. As the water level decreased below the top of the core one would not expect to see an increase in neutron source would be confined pretty much to that portion of the core containing water. The gamma situation should, however, be quite different:
one would expect a continuing increase in ganna reading as more and more of the core was uncovered. Of course the flat top could correspond to a constant water level below the top of the core but it seems unlikely that a constant level would be maintained for some 40 minutes as indicated by the tracts.
Mr. Kaufman appears to give more emphasis to steam fonmation within the cc-than to actual uncovery of the core. This point needs to be looked inta quan ti ta tively.
I believe that a quantitative analysis of the data would take a man-week or more of uninterrupted effort, and could best be done at one of the home offices rather than here at the site, although there would no doubt be a requirement for gathering additional information that may not be available elsewhere.
I also wonder whether such an analysis may be already under way by others outside the Industry Advisory Group.
-