ML20247B837
| ML20247B837 | |
| Person / Time | |
|---|---|
| Site: | 07000754 |
| Issue date: | 04/29/1998 |
| From: | Stimmell G GENERAL ELECTRIC CO. |
| To: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| References | |
| 70-0754-97-02, 70-0754-98-01, 70-754-97-2, 70-754-98-1, NUDOCS 9805110061 | |
| Download: ML20247B837 (8) | |
Text
- - _ _ -
rk 4 3 M,/
/
GENuclear nergy c-ame c com uh a nas Nada Cc%a eawaw warausnw 3
fiPa5d'dUQ CA SRibG l
- e lS99
[,
5li:
~
U.S. Nuclear. Regulatory Commission
..l Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, Texas 76011-8064 1
1 Attention:
Director, Division of Nuclear Materials Safety l
Subject:
Reply to Open Item 70-754/9702-01," Review Sampic Results of ImhofTTank Sludge" l
l
References:
- 1) License SNM-960, Docket 70-754.
- 2) NRC Inspection Report 70-754/98-01; March 24,1998.
I
Dear Director:
During a routine inspection conducted by NRC personnel from Region IV, it was noted that laboratory analyses ofliquid samples of the sludge from the sanitary waste "Imhoft" tank detected the presence of alpha and beta radioactivity. Since the sludge is removed periodically from the tank for disposal by a licensed septic disposal contractor, the need to identify the composition of the radioactivity was necessary.
The attached report discusses the details of the sampling and analysis process and confirms that the measured alpha and beta radioactivity is due to naturally occurring radionuclides. It is concluded that the radioactivity did not originate from any licensed activities at the GE Vallecitos Nuclear Center (GE VNC).
l l
Analyses methods and procedures are documented and available for review at GE VNC. If there are further questions on the presented material, please contact B. M. Murray at (925) 862-4455.
/
Sincerely,
[
,n n C&==a\\
n G. L. Stimmell, Manager l
Vallecitos and Morris Operation f
cc:
Walnut Creek Field Office, Region IV y
hev U.S. Nuclear Regulatory Commission 1450 Maria Lane Walnut Creek, CA 94596
(
9005110061 990429 PDR ADOCK 07000754 ~
C PDR j
i 04/29/98 l
i Response to NRC Inspection of SNM-960 Open Item
~
Reference:
NRC Inspection Report 70-754/98-01; February 24-26,1998. Open Item
)
70-754/9702-01," Review sample results ofImhoff tank sludge."
Summary of NRC Concern:
l 1
" Review oflicensee's sample analysis of sludge from the sanitary waste 'Imhoff' tank.
On October 21,1997, the licensee had taken a sample of 6,000 gallons of sludge removed 1
from the tank for off site disposal and had not received the vendor's laboratory analysis as of the time of the inspection (NRC Inspection Report 70-754-97-02). The inspectors noted that the subsequent vendor analysis (Appendix A) indicated a gross alpha activity of 22.8 pCi/g and a gross beta activity of 24.6 pCi/g. A subsequent sample of the sludge remaining in the tank was taken on December 21,1997, and indicated a gross alpha activity of 27.6 pCi/g and a gross beta activity of 33.2 pCi/g. Although the sample data j
indicate the presence of radioactive material, without an isotopic analysis, the licensee j
could not explain the source of radioactivity (i.e., naturally occurring or radionuclides associated with NRC or state licensed activities).. "
Backaround and D:scussion:
Vallecitos Nuclear Center sanitary wastes are concentrated, separated, and digested in an l
Imhoff tank before the liquid component undergoes sand filtration, disinfection, and collection in a 50,000-gallon holding basin. After the basin is sampled and tested for pII and radioactivity, it is then discharged onto VNC property via a sprinkler system. Liquid with suspended solids (referred to as sludge in the NRC report) from the Imhoff tank is collected periodically (approximately annually) by a contractor and disposed of to an off-site treatment plant.
During the December 1997 NRC inspection of SNM-960 activities, the NRC inspector questioned why the sample results for the site outfall Weir box were reported in units of pCi/l rather than pCi/gm, as they are reported normally. The answer to this question was found to be due to a typographical error in the vendor laboratory report, combined with misidentification of another sample, the Imhoff tank sample, also labeled as a " Weir" box sample. A sample had been taken of both the outfall Weir box (the sample result questioned) and the sanitary system Imhoff tank (also mistakenly identified as a " Weir" box sample) during the same month. The results reported for the " Weir" box sample in question were, in fact, the results for the Weir box sediment sample. Ilowever, due to the misidentification, the questioned sample results were initially thought to be from the Imhoff tank liquid. Following an intemal review, query of the employees who took the samples, and comparison of the sample dates, the confusion about the sample identity was clarified. The Imhoff tank sample had not been sent to Davi Labs, the vendor laboratory, for analysis because the gross alpha and beta activity results, as performed by the GEVNC counting room, were below the limits for liquid effluent release. A call to 1
l 04/29/98 the vendor laboratory verified that the Weir box sample results were reported incorrectly
', in udits of pCi/l instead of the normal pCi/g units.
An archived sample (number 143,2) from the Imhoff tank, which was taken when the tank was emptied in October, and a subsequent sample (number 150,3) taken during the NRC inspection in December,1997, were sent to Davi Labs for analysis. Again, gross alpha and beta count results, as performed by the GEVNC counting room, on sample 150,3 were below limits for liquid effluent release. The initial gross alpha and beta count results (Appendix A) from Davi Labs for samples 143,2 and 150,3 were reported in units of pCi/g of an evaporated dry sample. These results were prepared and calculated to determine the specific activity in the small amount of dry solids recovered from the one-liter liquid samples. This preparation and reporting method gives a misleading activity per unit volume of sample, in that the small amount of natural activity in the sample is concentrated into a very small quantity of dry material suspended in the sample.
When the detected beta and alpha activities are reported in units of activity per unit volume ofliquid sample, they are similar to the results obtained from the GEVNC count room. For example, ifit is assumed that one gram of solid resulted from the evaporation of the one-liter sample, then 33.2 pCi/g is equivalent to approximately 3.32x10-8 pCi/ml, which is less than the VNC counting room detection limit of 5x10-8 Ci/ml.
During the February 1998 NRC inspection of SNM-960 activities, the NRC inspector reviewed the Davi Labs results and requested that VNC establish an isotopic profile for any radioactive materials which may be present in the Imhoff tank. Another six-liter homogenized sample (number 110,5) of the Imhoff tank liquid with suspended solids was taken in March of 1998. Two 1-liter aliquots were sent to the GEVNC analytical laboratory for a qualitative isotopic profile analysis using a gamma spectroscopy system (high-purity germanium detector) and a gross alpha / beta count by a gas proportional counter (Model LB5100). An isotopic profile was established from the spectrograph aliquot. The profile showed trace levels of radioactive materials from natural background isotopes (uranium and thorium daughters). The results of the spectrometer analysis are reported in Appendix B. No waste stream constituents were identified as being above detection levels or background count levels for individual isotopes identified. The gross alpha and beta analyses of the second aliquot indicate levels less than the detection limits of <2x 10'8 pCi/ml alpha and <5xiO-8 Ci/ml beta, which are the site release limits for liquid effluents.
Two 1-liter aliquots of sample 110,5 were sent to Davi Laboratories for an independent quantitative analysis of gamma-emitting isotopes which may be present in the Imhoff tank. It was discovered that in performing the analysis on one of the two samples of the Imhoff tank liquid, with suspended solids, Davi Laboratories had aliquoted the 1-liter sainple, dried it by evaporation, and measured the activity in the dry sample. The yield of dry material from a 1-liter liquid sample was approximately I gram of sample. As stated earlier, the results reported for samples I43,2 and 150,3 also were reported in units of pCi/gm of dry weight material instead of the units of pCi/l (or pCi/ml) of the original 2
04/29/98 1-liter sample. This method of calculation provided misleading results and did not reflect
. the actual concentration of radioactive material present in the Imhoff tank. GEVNC requested that Davi Labs reevaluate the results frem sample 110,5 basing concentrations of radioactive material on the total sample volume. The results of the gamma count on l
the second 110,5 sample showed no specific isotopes (Co", Cs'", K", Gross Alpha, and Gross Beta) above the Davi Labs detection limit (Appendix C).
The results of the analyses of these Imhoff tank samples are summarized in the following table:
VNC Counting Lab Davi Labs Sample No.
Date Sampled Gross Beta Gross Alpha Gamma Isotopes Gross Beta Gross Alpha Gamma Isotopes 143,2 10/14/97
<5e-8 pCi/ml <2e-8 pCi/ml n/a n/a n/a n/a 14 3,2 10/14/97 n/a n/a n/a 24.6 pCi/g 22.8 pCi/g n/a 15 0,3 12/10/97
<5e-8 pCi/ml <5e-8 pCi/mi n/a 33.2 pCi/g 27.6 pCi/g n/a 110,5 3/6/98
<5e-8 Ci/ml <5e-8 pCi/mi n/a O pCilg 0 pCi/g n/a llo,5 3/6/98 n/a n/a (See Appendix A) n'a n/a 0.299 pCi/g*
(Gamma)
- The reported gamma activity is an approximate conversion of the gross count rate in the total gamma spectrum, above a background spectrum, which includes any naturally occurring isotopes and scattered spectra. The accuracy and significance of this activity value is minimal, since the counting efficiency is a function of the gamma photon energy.
==
Conclusion:==
Based on both the GE and the vendor analyses, it is concluded that any measured gross alpha or beta radioactivity in the contents of the Imhoff tank are the result of naturally occurring radioisotopes. The " standard" water analysis used for determining the releasability of the VNC effluents can be applied to the Imhoff tank liquid with suspended solids. The VNC counting lab detection limits for the " standard" water analysis are <2x10~8 pCi/mi alpha and <5x10-8 pCi/ml beta.
The gamma photon peaks above background which were identified at VNC by a long count time, high-sensitivity gamma spectrograph of a sample of the Imhoff tank liquid were all daughter products of the uranium and thorium decay chains: Th-230, Ra-226, Pb-214, Pb-211, Bi-214, and Ac-228. The count rates at the energy ranges corresponding 3
04/29/98 to the photons from the by-product isotopes Co-60 and Cs-137 were either at or below
,backigound.
Future samples of the Imhoff tank liquid with suspended solids will be analyzed at GEVNC for gross alpha and gross beta concentrations and will be considered acceptable for free release to a licensed septic disposal contractor if the concentrations are <2x10-8 Ci/ml alpha and <5x10 Ci/ml beta.
i 4
Appendix A DAVI LABORATORIES, ENVIRONMENTAL ASSOCIATES 701 "B" Belmont Way. Pinole, CA 94564. (510) 724-9450. Fax (510) 724 9174 GENERAL ELECTRIC COMPANY Vcliecitos Nuclear Center Pleasanton, CA 94566 Aftn: Mr. Mike Rogers l
Results reported on 971215 S M LE Cust # ISOTO RESULT COUNTING OVERALL ANALYSIS SAMPLE Moisturr TYPE ERROR Sigma SIZE DATE TIME Percent.
ERROR T.
Sludge 14 3, 2 Alpha 2.2 8 E+01 pCi/g 1.7 5 E-01 5.2 E+00 1E-01 971021(1440 99.99 Beta 2.4 6 E+01 pCi/g 4.4 3 E-01 3.1 E+00 1E-01 971021(1440 99.99 l
l Sludge 15 0, 3 Alpha 2.7 6 E+01 pCi/g 1.8 5 E-01 5.5E+00 1.0 E-01 971210(0800 99.78 Beto 3.32E+01 pCi/g 5.19 E-01 3.6 E+00 1.0 E- 01 971210(0800 99.78 Somple 150. 3 was processes by on alternate EPA Method 7110C for QA purposes. The results of Gross Beto do not include K40 and are as follows:
i Sludge 150,3 A!pho 1.80E+01 pCi/g 2.3 9 E-01 7.1 E+0 0 SE-01 971210(0800 99.78 l Beto 1.4 3 E + 01 pCi/g 8.6 6 E-01 6.1 E+00 SE-01 971210(0800 99.7 E l l
n
\\.
I g
p (grx Patricio Davi e'
OA/0C Manager
5 Appendix B GE Nuclear Energy Vallecitos Nuclear Center Materials Technology l
l l
Copy: DRF A00-2971-9 i
April 27,1998 i
To:
Ben Murray Regulatory Compliance l
Subject:
Imhoff Tank Analysis (Gamma Emitters)
On 3/10/98 a liquid sample from the VNC Imhoff tank was analyzed for gamma activity using a 100-cc Ge(Li) detector and a Nuclear Data 6700 gamma spectrometer system. The count time was 23 hours2.662037e-4 days <br />0.00639 hours <br />3.80291e-5 weeks <br />8.7515e-6 months <br />. For maximum sensitivity, the sample was counted in a Marinelli Beaker, which allows the sample solution to surround the Ge(Li) detector. A "long count" (63 hour7.291667e-4 days <br />0.0175 hours <br />1.041667e-4 weeks <br />2.39715e-5 months <br />) background count was also performed on the empty Marinelli Beaker.
The only gamma peaks found to exceed the detection limits (based on the empty beaker background count) were peaks associated with naturally-occuring uranium and/or thorium and their daughters. Absolute quantities were not determined.
R. D. Reager Materials Technology RDPA27 L._._____._
__m___.
______m
- o Appendix C DAVI LABORATORIES, ENVIRONMENTAL ASSOCIATES 701 "B" Belmont Way. Pinole, CA 94564. (510) 724-9450. Fax (510) 724-9174 3.7
.p., sin.. '.
- e.
q e.
+.cp. 7 *.
i -
c.
.g
.. v i
'/c eeltes Nx ee' Ce'.te'
- u Ecosa'to', CA 94566 alt, W. We Roge :
I ke0' 'is "t$0#t?d $1 E4 b C dC 7 e_e. m.._
w w.> g ;
.cq cer a..r e. w.,
r v v w y r. s, e..J
- n..,r_,p e i
% i m e c..e e.. o. _:_
u.n pa.,t vuv c
y v.
T' E
~RROR Sl ^* 3 E T.,
M TE Tu? ?e ce*i Q
- r. R
_s Q
3
.n$'3 v.avitvo
- e. l - Q 3..*, n -st sc n
e.,,-
p.,
en
.ne n~
n
-er,n e e -
D '_d 4
'In l.n e -v v.ta v 3.v" al Q 90a3vb-S S.d 6 a
v,
.6.
q O r r.t. n a
(
a. n G. r _.6 4
Ire.; Ann
-. O r. _r j
_.. l.,
z G. a c : n q G G.. G c.
a, a.w s-Ja
.a w.w s JJ w.
a ww-w.
v
~e e nn
.no m en -
n.
,en-.nm
- e. -
e -en ne
-e e.b.Da v.JJ'TJV Ol Q
. J 3 *. ~ J l 2. v u *. T J 'J i. C '. 'h' e n Q
0C0:02
- Y m g Ju i
3. e.s -a a *. + e r 7. g '~ + e n Q
dcu3a6 dd.d
.. s 1 3,
- v. val +wu b, I Q
.s 3. r l
,3
,, re-en s ew-
~.
e mene
.- e e 7 u
as
... sa
..'.].,
- P. _17.
"., j
.%.6. q 7_4_,9_
4740_m' y
Q " r_. _T. q E G. " G r.,
_1"
^ o n_ ; 4 0. 0 6
m r _
Oase a es u'. shh[_O i g **
'g 8
Ya er
.vJ
=J a.Jo T'Ju Q
s w a' s a sg s.
.s s
4
..' a a
g a l y...
au
_'If3 $ 9 l..
yl;37,j,3 79, 7,-
$j g,}.j 9 l7- {
4 9 3
Y f l
1 gA' 1
l l
6 i
I
- o..,. m...,,I w
e d
Y
'j i 2.".
- t. !O
- 3 g e r