ML19221A601
| ML19221A601 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 05/02/1979 |
| From: | Richings H Office of Nuclear Reactor Regulation |
| To: | Kniel K Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7905230296 | |
| Download: ML19221A601 (2) | |
Text
.
?
Q'
~?
e Kf 2 1979
(
MEMORANDUM FOR:
K. Kniel, Chief, Core Performance 3 ranch, DSS FR0?l:
H. Richings, Reactor Physics Section, CPB,.'SS
SUBJECT:
THI2 STARTUP RANGE COUNTS FR0tt D(y, m)
This is a brief note to estimate the possibility that the apparently abcomally high count rate obt..ved on the TII2 startup range excore neutron detectors (BF3 proportional counters) may come in part from D(y, m) rcecfre/ pin fle downcomer region rather than from the "nomal" source multiplication in the core.
A possibility that the count rate could originate from such a source was (in part) suggested by the observation (f t. A. Schultz) that there may be a 12 day half life correlation to the count rate, which could indicate Bal40, LA140 decay, with the La140 2.53 MeV gappa providing a neutron source from interactions with the D ) (need at least 2.3 2
MeV gama). This note provides a partial numerical estimate for that possibility.
Assuming the neutron source cones only from Lal40, the 4/11/79 primary coolant sample analysis indicated a tal40 concentration of about 150 microcuries per cm3, or about 5 x 106 disantegrations per second per cm3 Since tne y, m cross section is about-10-3 times the (primary energy loss at 2.5 MeV) Compton cross section, in an infinite D medium there will be about one neutron for 1000 garrnas.
Since in the 2 MeV range the Compton tross section is proportional to mass, in a D20 medium there will be about 4 oxygen Comotio reactions for every D noaction, thus the neatron reactions are reduced by 1/5. The D/H ratio 0.00015 also reduces the reaction rate.
l40 Only about 3*. of the La decays produces a 2.53 MeV garma.
Combined we have 5 x 106 x 10-3 x 1/5 x 0.00015 x :si, or about 5 x 10-3 neutrons /second/cm3-(on~ April 11).
~
- jf jjf27C
/o OFFICE >
.u
. =
- o.Ta >
Nic PORM 313 (9-76).*0tCM 0240 D w. * *
- v a * * *' * * * * * 'a m' * * * * ' c a ' ' ' ' e - a..., e.
GJ $
gj 2
~~
MAY 2 1979 K. Kniel,
in the downcomer region there should be a region about 12 feed high, 5 feet wide and 10 inches thick.in which neutrons which are boron (at about 103 eV) can be expected to reach the detector with any use-tul degree of probability. There are about 7000 neutrons per second produced in that region.
If there are to be the order of 10 counts /
second in the detector then one cut of 700 of the neutrons must reach and be absorbed in the detector. Geomitric view factors are about 1/70, so that means about one in ten neutrons must also be appropriately slowed down in the downcomer or shield and absorbed in the BF. This would appear to be a rather high probability for 3
this latter process, but perhaps not totally out of the question.
Thus it is possible that y-m neutrons from the downconer region are contributing to the startup range detector count rate, but this estimate does not conclusively demonstrate it.
o,.irJ i,. a: !rx N. I. [ilsiildSS Howard Richings "3
Reactor Physics Section Core Performance Branch Division of Systems Safety
' l RR READING
.CPB READING 165 274 DSS /CPBJh DSS /CPPg ome s,
HRichings:cc DFieno "
_ 5///79 5/1/79 y....... -....... -..............
-c--,.._