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ORNVP-719
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ATIES
DEC 7 1964
OAK RIDGE NATIONAL LABORATORY
OPERATED BY
"INION CARBIDE CORPORATION
NUCLEAR DIVISION
UNION.
CARBIDE
(Conf-6444203-))
POST OFFICE BOX X
OAK RIDGE, TENNESSER. :37831
November 12, 1964
MASTER
To:
Members, Reactor Decontamination Information Exchange Group
Subject: ORNL Decontamination Research to be Discussed at the Vallecitos
Meeting of December 3 and , 1964
Gentlemen:
Attached are reproductions of the decor.tamination research sections of the ORNL
Chemical Technology Division Section A Monthly Reports for January through
June, 1964. These are preliminary reports issued by R. G. Wymer and R. E. Leuze
to F. L. Culler, Jr. Although decontamination research at ORNL was discontinued
on July 1, we are still interested in the field, and we will maintain contact with
the RDIEG.
I expect to see you at Vallecitos next month.
Q. B. Messey
A. B. Meservey
Chemical Development Section A
Chemical Technology Division
ABM:atm

The repor
terton, wat we pro
J. A. Ayres, General Electric, Hanford
H. J. Blythe, United Kingdom Atomic Energy Authority
Dale Busch, General Atomic
Pierre Cerre, Centre d'Etudes Nucleaires de Saclay
A. B. Carlson, E. l. duPont, Savannah River Plant
Emile Mestre, Centre d'Etudes Nucleaires de Saclay
Norman Michael, General Electric, Vallecitos
O. T. Roth (Chairman), AEC, Washington
Lyle Perrigo, General Electric, Hanford
C. L. Robinson, Richland Operations Office, AEC
D. G. Sammarone, Westinghouse Electric Corporatio'r
G. R. Taylor, Westinghouse Electric Corporation
R. M. Watkins, General Atomic
L. C. Watson, Atomic Energy of Canada, Limited
awal na ploy
Etnia o
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.
ORNA-CF-64-2-70 (2-1464)
3.0 GCR DECONTAMINATION STUDIES (A. B. Meservey)
The broad goal of all decontamination research programs is to
develop and test reagents and methods for the rapid and efficient radio-
active decontamination of metallic and non-metallic surfaces, without

unduly damaging these surfaces. Prior art has featured decontamination
by soap and water or by surface dissolution in acids. Recent trends
in the field are toward noncorrosive methods tailored to specific ap-
".
.
-
....
..
- -
-
-
..
.
.

T
!
-
-
.
plications. Our group has been concerned primarily with the special
s
7
problem of decontaminating metal surfaces which have been exposed to
the coolant stream in gas-cooled nuclear reactors. This month was spent
in the development of a reagent for the simultaneous decontamination
of Zircaloy-2, carbon steel, and stainless steel, for use in gas-cooled
and water-cooled reactors.
An oxalate-peroxide-fluoride reagent for the simultaneous decontamina-
tion of carbon steed., stainless steel, and Zircaloy-2 is under development.
An outstanding feature of the reagent 18 that the dark oxide coating on
Zircaloy may be removed and the metal surface beneath may be uniformly
dissolved to any desired depth, while the steels remain substantially
unattackei. This is accomplished by only minor modifications of the
oxala'c-peroxide formula recommenåed for decorataminating carbon steel.
Expected uses include the decontamination of Zircaloy-2 in mixed piping
systems of gas-cooled and I'. quid-cooled reactors such as the Oak Ridge
EGCR, and the now Hanford reactors containing Zircaloy-2 tubes in the heat
exchangers.
3.1
Corrosion Rates of Zircaloy-2 in Oxalate-Peroxide Solutions
.
.
.
.
.
.-
In previous work, the standard solution recommended for the decon-
tamination of carbon steel at 95°C. was 0.4 M oxalate--0.16 M citrate--
0.34 M hydrogen peroxide at på 4.0, the only cation present being the
ammonium ion, NH, *. This solution is non-corrosive to Zircaloy-2
(<0.001 mil/hr). Fluoride added to the solutions attacks Zirçaloy
until enough zirconium has dissolved to complex the fluoride ion, the
rate diminishing as the fluoride is consumed. The presence of fluoride
requires that the concentration of hydrogen peroxide be raised in order
to prevent initial corrosive attack on carbon steel. The danger of
attack decreases as the fluoride ion is complexed by aluminum, and is
expected to decrease similarly when the complexing 18 done by zirconium.
In this report period, the corrosion rate of Zircaloy-2 was measured
as a function of ph in the standard oxalate-peroxide solution to which
>
2
- 16-
NAWR
,'
>
had been added 0.1 M NAF (Table 4). Rates at room temperature ranged
from 1.7 mil/kx at pH 1.5 to 0.13 mil/hr at på 5.0. At 95°c the cor-
responding rates were 8.5 to 0.97 mil/hr. Carbon steel was rapidly at-
tacked at pH li and below.
Initial complexing of the fluoride with aluminum ion in an attempt
to decrease the corrosion danger to carbon steel, with the hope of keeping
the fluoride available for the zirconium, resulted in decreasing the
Zircaloy-2 corrosion rate to such low levels that the dark coating on
It was not dissolved (Table 4). Maintaining passivity of the carbon
steel would therefore have to be done either by increasing the peroxide
concentration, lowering the fluoride, raising the pH, or lowering the
temperature. Higher på and lower temperature both result in less ef-
wy
fective decontamination of steel, and were not considered for this
application.
Increased peroxide and lowered fluoride in combination have resulted
in satisfactory corrosion rates on Zircaloy-2 and carbon steel, both
separately and when galvanically connected, as shown in Table 5. In
this table two other phenomena can be seen also. These are the decrease
in corrosion rates on both metals with time as the fluoride ion becomes
complexed, and the galvanic effect of raising the corrosion rate of the
steel and lowering that of the Zircaloy when the metals are connected.
The decrease in corrosion rate of the Zircaloy-2 with time did not
appear to be a result of the decreased roughness of the metal as etching
progressed. This was shown by the fairly uniform corrosion of a piece
of the metal in a series of five separate 20 mlaute immersions in fresh
solutions (Table 6). The 10 min rate was 0.72 + 0.16 mil/hr (95% L.E. ).
WAR
A
..
..
.
.

-17-
Tammt Anaaoi *
Table 4. Corrosion of Zircaloy-2 in Oxalate-Peroxide-Fluoride Solutions
(0.4 M oxalate-0.16 M citrate-0.1 M fluoride, H2O2 and A1*** as shown)
Conditions
Corrosion,
H2°2M
AIFF, M Room Temp.
9500
1.7
8.5
8.3
0.73
5.7
0.52
3.3
1.5
6.5,8.3*
0.53
2.7,6.4
0.84
3.9,2.9
0.13
4.0
11
0.34
0.1
0.009
0.55
0.34
0.1
0.009
0.017
1.0
0.1
0.006
oóóóóóóório
ನನನನನನನ
0.97
A corrosion peak may occur here.
Table 5. Corrosion Rates of Zircaloy-2 and Type A-109 Carbon Steel
in 0.4 M oxalate-0.16 M citrate-0.8 M HC-0.05 M fluoride at pH 4.0,95°C
Electrical
Corrosion rate, mils hr
Metal
Connection 30 min
90 min
180 min
0.28
NO
Zircaloy-2
Carbon Steel
Zircaloy-2
Carbon Steel
0.47
0.009
0.24
0.07
0.004
0.21
0.03
0.09
0.003
0.07
0.018
Yes
Table 6. Corrosion Rates of Single Specimen of Zircaloy-2 During 10
min Intervals in Fresh Solutions (0.4 M oxalate-0.16 M citrate-
0.8 M 1202-0.05 M fluoride at pH 4.0, 9500
Solution
Corrosion Rate, mils/hr
0.55
0.84
0.65.
0.77
0.77
Average 0.72 + 0.16 (95% L.E.).
.
24
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.
.
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- 18-
ENT
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The decrease in rate with time in a single solution (Table 5) is due
1
primarily to the complexing of the fluoride and the rise in pH, and 18
of course dependent on the surface area exposed and on the volume of
solution which contacts it.
TA
4.
3
.-
.
3.2 Decontamination of Zircaloy-2
In initial tests, the new fluoride solution described above was
superior to fluoride-free oxalate-peroxide by factors of 3 to 10 in
decontamination effectiveness on Zircaloy-2. In practice on reactor-
contaminated specimens, instead of our laboratory-contaminated ones,
we expect the factor to be much larger, since the fluoride solution
dissolves at least one type of dark coating on the metal and the non-
fluoride solution does not. Table 7 shows the comparison between the
two solutions on Zirca loy-2 specimens that had been dipped in 23-No 95
solution, air dried, rinsed in hot water, and then baked in air at
200°, 40c°, and 600°C. Decontamination treatment was for 30 and 60 min
at 95°C, initial pH 4.0.
.
LAS
..
TE
wa
.
Table 7. Decontamination Factors (DF) of Zircaloy-2 from Er-Nos
in Non-fluoride vs. Fluoride Oxalate-Peroxide Solutions
Coupon
Baking
Non-fluoride
Oxalate-peroxide
DF, 30 min DF, 60 min
.
Temp, oc
Fluoride-containing
oxalate-peroxide.
DF, 60 min
1.0 x 103
5.8 x 203
79
148
*
200
205
.
.
.
30
400
600
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-19-
3.3 Life Testing of Fluoride-Containing Solutions
Initial life-testing and "Pail-safe" properties of fluoride-con-
taining oxalate-peroxide solutions appear satisfactory for Zircaloy-2
and carbon steel comblrations. This testing is still in progress.
:owian.co....
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64-3- 48 (3-13-64)
3.0 GCR DECONTAMINATION STUDIES - (A. B. Meservey)
7.montiert
-
T
rf
.
'
A
The broad goal of all decontamination research programs is to develop and test
reagents and methods for the rapid and efficient radioactive decontamination of
metallic and nonmetallic surfaces, without unduly damaging these surfaces. Prior art
.
CS
has featured' decontamination by soap and water or by surface dissolution in acids.
Recent trends in the field are toward noncorrosive methods tailored to specific appli-
cations. Our group has been concerned primarily with the special problem of decon-
taminating metal surfaces which have been exposed to the coolant stream in gas-cooled
lin .
..
H
.
.
TI
.
.
*
n
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1N14
airesanan dan sentiment es
.
rouclear reactors. This month was spent in continuing the development of a reagent for
,!.*
-
:
-
the simultaneous decontamination of Zircaloy-2, carbon steel, and stainless steel for
4
i
.
use in gas-cooled and water-cooled reactors..
St.
TT
preparat pentin
"
"
.

WA
ARM
AGEN
LAW
LL
.
•17.
Life tests on the fluoride-containing oxalate-peroxide solution for the simultane-
ous decontamination of Zircaloy-2, carbon steel, and stainless steel were satisfactory.
When these three metals were contaminated with Ru-Rh 106, Zr-Nb95, Ce-Pp144, and
Cs "37, and then held at 500°C for 30 min in helium, subsequent decontamination
factors in 1 hr at 95°C in the reagent were very encouraging.
3.1 Life Testing of Fluoride Solution
The useful life of a decontamination solution may be defined as the period of
use during which the solution continues to perform its function, and in addition does
.
5
not develop unwanted properties such as causing increased corrosion rates. Mixtures
of oxalate, citrate, and hydrogen peroxide decompose in time;' the pH gradually rising,
and the peroxide concentration falling until desirable traits are lost (ORNL-3308,
December 14, 1962). The fluoride-containing Zircaloy-2 decontamination solution
described last month had a useful life in glass vessels of about 15 hr at 95°C, with or
IT,
LTU
without Zircaloy present. It will be necessary to recheck some of these tests using
-
..
steel vessels because of a fluoride concentration. decrease which could have been due
.
.
1
to reaction with the glass, even at pH 4 to 5.
· Hot
Accelerated decomposition life tests were also made by adding 100 ppm Fe
to the solutions to simulate iron pickup from large surface areas during decontamina-
tion. The useful life of solutions containing metal surfaces of Zircaloy-2 and carbon
steel was about 5 hr at 95°C. The initial corrosion rates of the Zircaloy and carbon
ZA
steel were 0.5 mil/hr and 0.09 mil/hr, respectively, in 0.4 M oxalate-0.16 M citrate-
0.05 M fluoride-0.8 M peroxide at pH 4.0-4.3, 95°C. These corrosion rates decreased
(
7.
with time. The stability and corrosiveness of the solution under these accelerated
H
decomposition conditions would not seem to preclude usage for large scale decontami-
IL
.
-
nation purposes.
1.
TU
!
M
-18-
3.2 Decontamination of Metal Specimens Heated in Helium at 500°C
Coupons of Zircaloy-2, carbon steel, and type 302 stainless steel were satis-
factorily decontaminated from several fission products in the ſtvoride-containing
oxalate-peroxide solution (Table 4). The contamination technique, designed to coat
the metais as tenaciously as possible with fission products, featured dipping the coupons
into carrier-free solutions of the separate contaminants at pH 5, air drying, rinsing
thoroughly in hot water, and heating in helium at 500°C for 30 min. The effect of a
slight coating of oxide was studied in the first test with a trace of oxygen in the helium,
and the other tests were made on bright metal surfaces after heating in purified helium.
The cooled coupons were gamma counted in the well of a scintillation counter, then
agitated with the decontamination solution ai 95 +1°C for 30 min, rinsed, dried, and
again counted for the 30 min decontamination factor (DF). The coupons were then re-
turned to the solution for a second half hour. The total DF on the clean coupons was
102-104 for Mircaloy-2 and carbon steel, and usually below 10% on the stainless steel.
Zirconium-niobium-95, considered by Campbell to be the most tenaceous fission
product, was easily removed. Ruthenium was the most difficult contaminant to remove,
as shown in the table.
.
ā
.
.
.
PM
Table 4. Oxalate-Peroxide-Fluoride Decontamination of Metal Specimens Heated
in Helium at 500°C
DF, 30 min
Cs
302 55
27-
2
DF, 60 min
C
302 55
*Ru-R}"O6
Ru-Rh 106
Zr-2
il
52
25
471
Run
5
709
18
42
3.3x104
113
442
312
1.9x104
7x103
1.9x104
5.2x 104 · 1.9x104
134
Coop,144
88.
2.2x10
2.8x103
168
258
8.8x103
1.4x104
130
*Slight coating of oxide in first Ru-Rh 106 test.

JIN'
S
OK
MINY
"
R
64.4.80 (4-17064)
3.0 GCR DECONTAMINATION STUDIES - (A. B. Meservey)
The broad goal of all decontamination research programs 18 to develop
and test reagents and methods for the rapid and efficient radioactive
decontamination of metallic and nonmetallic surfaces, without unduly
damaging these surfaces. Prior art has featured decontamination by soap
and water or by surface dissolution in acids. Recent trends in the field
are toward noncorrosive methods tailored to specific applications. Our
group has been concerned primarily with the special problem of decontaminat-
ing metal surfaces which have been exposed to the coolant stream in gas.
"
cooled nuclear reactors.
This month, a special problem in Zirflex process
decontamination was also undertaken, and more information was gathered
on the Zircaloy-2 decontamination process previously described.
The only gamma-emitting fission products of long half-life deposited
from spiked acid flucride Zirflex solution onto stainless steels were those
of ruthenium-rhodium, from the neutral modified Zirflex process only cerium-
praseodymium, and from dilute nitric acid only zirconium-niobium and
ruthenium-rhodium. Oxalate-peroxide reagents were effective decontaminants
for all of these deposits. In GCR work, it became clear that bot cell
contamination was still a dominating factor in fission product deposition
studies. The Zircaloy-2 decontamination reagent discussed last month was
-14
found to "fail-safe" from a consumption of both acid and fluoride, but
the amount of zirconium dissolved was in considerable excess over that
required to form known fluoride complexes.
3.2 Contamination and Decontamination in STR and Modified Zirflex Processes:
the scintillation ropectrometer
A striking demonstration of the value of using:
in decontamination research was displayed in an investigation of the types of
1188ion products deposited on stainless steels, and the effects of different
decontamination reagents in the STR and modified Zirflex fuel dissolution
processes. In the STR process ENOZ-IT 18 used to dissolve Zircaloy-2-
uranium fuel elements, and in the modified Zirflex process the dissolution
18 accomplished with NHLF + NH4NO2 + very small amounts of Hºz: In the
investigation, 3 mc of mixed 118sion product solution, showing prominent y
peaks from 144ce-Pr, 206Ru-Rh, 95zr-No, and 137c8, were added to simulated
STR and modified Zirflex solutions and to £ 2 M ANO, solution as a control,
Strips of types 304 and 347 stainless steels were placed in each solution
for 1 hr at 60°C and then left in at room temperature overnight. The strips
were thoroughly rinsed in hot water and then gamma scanned. The acidic
fluoride STR steel strips displayed prominent y peaks only from ruthenium,
the neutral fluoride. Zirflex strips only cerium, and the 2 M HNO, strips
only zirconium-niobium and ruthenium, the latter with considerably lowe::
y activities than strips from the two fluoride solutions (Table 3);
Decontamination results on the three types of fission product deposits
were equally interesting (Table 4). In one test series, coupons were first
treated for 30 min in 3 M HNO, at 95°C, and then for 30 min in noncorrosive
2 M 1,6204 + 0.2 MH,02 at 95°C. The nitric acid easily removed cerium
(DF 28 x 103) but did relatively poorly on ruthenium and Zr-No (DF -8-18).
The subsequent oxalic acid-H2º2 treatment did well on the tenaceous ruthenium
-15-
Table 3. Fission Product Deposition from Aqueous Solutions
Scint. y/min Plateout
(1 in. x 1/4 in. coupons)
304L
347
Stainless Stainle88.
Steel . Steel
~7.0 x 203 8.5 * 20
Solution
y Peaks
103, 106RU
STR, acid fluoride
Modified Zirflex,
neutral fluoride
HNOZ, 2M .
144ce-PY
w2.0 x 10°
w3.0 x 104
1.0 x 106
3.0 x 104
9528-No, 103, 106Ru
Table 4. Gamma Decontamination Factors in Various Solutions
(Each test 30 min at 95°C with duplicate coupons)
Decontaminating
Solution
STR Coupons (Ru).
3041 .347
Modified Zirflex 2 M HNO, Coupons
Coupons (Ce) (Zr-NB, Ru)
304L
304L347304L 347
Test 1
HNOJ, 3 M
H2C2O4 + H2O2
Total DF
16.5
7.25
220
18.7
11.9
335 .
8.0x103
1.92
1.5x104
7.5x203
1.43
1.1x204
21.7
2.65
31
7.95
5.3
42
Test 2
Ox-cit-Hºg, pH 4.0
First 30 min 499
Second 30 min 2.0
Total DF 1.0x103
1.34x103
2.2
3.0x203
2.35x103
2.27
5.3x203
2.99x103
2.11
6.3x203
5.65
2.04
12
23.2.
2.30
53
--------...
(additional DF 7-12). A second test series on other coupons demonstrated
the effectiveness of the mild reagent 0.4 M ammonium oxalate-0.16 M ax-
monium citrate-0.34 M 420at pa 4.0, 95°C. The first 30 min DF was 500
to 1.3 x 103 on the STR-Deposited Ru and 2.3 x 103 to 3.0 x 103 on cerium.
23
:
-
.
.
..
...
..
.
.
.
......
..
...
..
.
-16-
-
-
-
-
.
:
After two treatments, the total DF on the STR ruthenium was superior to
that from the acidic test series, and the Zirflex cerium and nitric acid
deposited Zr-Ru DF's were almost as good. These results, together with
reproductions of the scintillation samme charts, will be reported in more
detail in a separate paper by Harrington, Nowman, and Meservey.
11
3.2 Hot Cell Contamination in F188ion Product Deposition Test:
A very extensive and detailed compilation of 1188ion product deposi-
tion test data from ORR loop 2 and lattic tests, 11sted in detail in
the forthcoming GCR semiannual report, showed the deposition level from
graphite-clad fuel elements to be so low that contamination during hot
cell handling usually exceeded f188ion product deposition. The deposition
level calculated as disintegrations (not counts) per minute per square
inch at loop shutdown time was of the order of only 103 per nuclide.
Better data will be secured when we can obtain deposition samples which
have not been in the hot cell.
3.3 Zircaloy-2 Dissolution in Fluoride-Containing Oxalete-Peroxide
In planning corrosion tests on Zircaloy-2 in oxalic acid-fluoride-
..
..
peroxide mixtures we thought that dissolution would stop after sufficient
zirconium had d18solved to form the stable complex ZrF2; however, in
this mixture reaction did not cease until considerably more than the ex-
pected amount of metal had been dissolved. In one test, dissolution dia
not stop until the Zr/F ratio was 4/3. The dissolution rate and the
total amount dissolved were affected both by the acidity of the solution
and by the fluoriide content, so that the depth of the metal layer removed
could be controlled by suitably limiting either or both factors.
-.
-.
-
•
•
.
•
..
4
..
•
-
.
-
-
.
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.
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.
-17-
*
2
-
In three room temperature dissolution tests of Zircaloy-2 in oxalic
acid-fluoride-peroxide solutions and one in nitric acid-fluoride-peroxide,
the dissolution rate resembled a first order reaction, since it was propor-
tional at any given time to the total amount dissolved at equilibrium
minus the amount dissolved at the given time. When a 5.5 in.? specimen
was suspended for 24 hr in 300 m2 of stirred solution containing 0.10
mole H2C2O4 0.02 mole NaF, and 0.30 mole H2O2, and the weight loss fol-
lowed gravimetrically, 0.0771 moles of Zr dissolved, with a hall-time of
2.8 hr. Dissolution had virtur.lly ceased after 24 hr, with a 2x/F ratio
of 4/3. The pH was 1.06, and about 0.20 moles of H,02 remained in solu-
tion. When a second 0.02 mole NaF was added, the dissolution rate became
high again, but not as high as before, and the reaction was again ap-
parently first order, with a half-time of 4.3 hr. In 23 hr, an additional
0.0056 mole of 2r dissolved, which was only one-fifth the amount in the
first test. Adding a second 0.10 mole H,C204however, again sharply
increased the dissolution rate. When the specimen was suspended in 0.30
mole of HNO, (instead of 0.10 mole H,C202) with 0.02 mole Naf and 0.30
mole H, s, in order to observe the effect of an acid which does not
complex zirconium as oxalic acid does, the reaction was still first
-
order, with a half-time of 2.8 hr. The amount dissolved in 2.5 days
.
CA
.
was only 0.016 mole, or 59% of that dissolved in 0.2 mole of oxalic acid.
It should be noted that all of the Zircaloy-2 dissolutions
... '
in the presence of ~1 M H2O2, in either oxalic ur nitric acid, were fume- '
.
less, giving off no hydrogen and no oxides of nitrogen. Fimeless dissolu-
tion seems to be a characteristic of acidic hydrogen peroxide attack on
ti
many metals.
.
2
21
.
t
.
-13-
64-5-65(50)4-64)
3.0 GCR GECONTAMINATION STUDIES - (A. B. Meservey)
.......
.
.
.
.
.
...env io
The broad goal of all decontamination research programs is to develop and
test recgents and methods for the rapid and efficient radioactive decontamination
of metallic and nonmetallic surfaces, without unduly damaging these surfaces.
Prior art has foatured decontamination by soap and water or by surface dissolution
in acids. Recent trends in the field are toward noncorrosive methods tailored to
specific applications. Our group has been concerned primarily with the special
problem of decontaminating metal surfaces which have been exposed to the coolant
stream in gas-cooled nuclear reactors.
..
Further life tests and corrosion tests on a reagent for the simultaneous de-
contamination of Zircaloy-2 and carbon steel confirmed its feasibility. The
electrode potential behavior of Zircaloy-2 in the reagent is unusual and may
deserve further study. The room temperature oxalic acid-peroxide method for
the decontamination of carbon steel continued to look good. The containment
vessel of the Nuclear Safety Pilot Plant was successfully decontaminated from
vaporized UO2 by an oxalate-peroxide reagent. Turco Products, Inc., is working
on an oxalate-peroxide reagent, and Hanford is obtaining patents on modified
formulas.
3.1 Useful Life of Oxalate-Peroxide-Fluoride Solutions
In the February report, the useful life of the decontaminating solution for
mixed Zircaloy-2 and carbon steel was reported as about 15 hr at 95°C, but the
use of glass vessels obscured the results because of reaction with the fluoride ion.
A recheck in polyethylene vessels under reflux. substantiated the results, however.
The useful life of the solution (0.4 M oxalate-0.16 M citrate-0.05 M NaF-0.8 M
H, Og, 95°C, pH 4-5) was slightly longer and the corrosion rates less than in glass,
but this was probably because the solutions were not stirred in the second test.
Results are shown in Table 6.
3.2 Electrode Potential of Zircaloy-2
In contrast to steel, Zircaloy-2 electrode potentials which were negative,
showing that the metal was active in the peroxide-fluoride decontamination
al
MY
•
•
....
Table 6. Aging of Three Oxalate-Fluoride-Peroxido Solutions at 95°C in Polyethylene Containers, and
Corrosion Rates on Zircaloy-2 and Carbon Steel
1
Time
Solution 1
Corrosion Rate
H,O2, M (mil/hr)
Soluiion 2
Corrosion Rate
pH H2O2. M (mil/hr)
Solution 3
Corrosion Rate
H2O2, M . (mil/hr)
thr)
pH
pH
4.50
0.80
5.00
, 0.80
.0
i
- 4.00
4.12
0.80
.
0.43 (Zr-2)
0.012 (steel)
0.03 (Zr-2)
0.006 (steel)
0.015 (Zr-2)
0.003 (steel)
5.5
7.5
4.68
4.95
0.71
0.70
4.53 :
4.97 0.67
5.13 0.65
4.92
5.25
5.38
-
0.65
0.64
-14-
19.5
5.72
0.54
5.91
0.43
0.000 (Zr-2)
0.003 (steol)
0.000 (Zr-2)
0.000 (steel)
0.000 (Zr-2)
0.000 (steel)
6.38
0.06 (Zr~2)
0.000 (stoel)
0.003 (Zr-2)
0.000 (steel)
0.000 (Zr-2)
0.000 (steel)
0.000 (Zr-2)
*0.13 (steel)
0.37
0.003 (Zr-2)
0.003 (steel)
0.000 (Zr-2)
0.000 (steel)
0.000 (Zr-2)
0.000 (stcel)
26.5
7.21
0.365
7.43
0.29
7.50
0.24
58
-8.02
0.008
61
-
-
:
**7.05
0.025
0.000 (Zr-2)
0.000 (steel)
** 7.44
0.02
0.000 (Zr-2)
*0.22 (steel)
*Loss of passivity
**Lower pH due to loss of NH, by volatilization above pH 7.
*
......
...
.......
..
.........
......
.
.
1
.
-
-
-
.
....
...
.
-15-
.
.
..
.
..
...
solution described in Section 3.1, did not become positive (showing passivity) at
higher pH or lower temperature. At the highest pH tested (6.5), the potential be-
came positive at 95°C (+130 mv) and then negative again as the temperature was
lowereó (-425 mv). At 25°C the potential was -62 mv. The potential was lower
at pH 3.2 than at pH 2.2 (-555 vs -455 at 25°C). This anomalous behavior would
be studied further before any large scale decontamination of Zircaloy-2 would be
attempted.
..
.
..
...
.
.
.
.
3.2 Room Temperature Decontamination of Carbon Steel
.
. .
.
.
.
.
.
.
.
.
.
.
.
Work was reopened on a previously announced simple and low-cost method
for the room temperature decontamination of carbon steel. The 2-step method
features immersion in very dilute oxalic acid (0.02 M) for a few minutes to dissolve
any slight oxide layer (with some decontamination) and activate the surface, fol-
lowed by the addition of hydrogen peroxide until 0.05-0.06 M is reached. The
peroxide brightens the surface and causes one to two orders of magnitude further
decontamination in a few more minutes. One of the latest tests measured re deposition
from prolonging the first decontamination step (oxalic acid). It was found that on
fission product-contaminated carbon steel initially baked in air at 200°C, the first
step DF was 37 in 1 min, 67 in 2 min, and 118 in 2 hr, with no signs of redeposition.
Since the surface of the steel becomes undesirably etched upon prolonged treatment
in the oxalic acid, and extending the time from 2 min to 2 hr merely doubles the DF,
it is evident that limiting the first step to a 2-min treatment is preferable. Diluting
the acid even further may be optimum for some applications. Heavily oxidized steel
surfaces baked at 500°C in air are resistant to scale removal by dilute oxalic acid,
but such surfaces would not normally be encountered in gas-cooled reactor decon-
tamination.
3.3 Decontamination in the Nuclear Safety Pilot Plant
L. F. Parsly achieved complete decontamination from vaporized cold UO, in
the stainless steel containment vessel of the NSPP by spraying with our oxalate-
acetate-peroxide formula at pH 2.5, 60°C. He will change to our oxalate-
citrate-peroxide formula next time, to avoid carbon-steel rusting caused by vapors
of acetic acid.
............
.
.
.
-16-
3.4 Applications of Turco and Hanford
Turco Products, Inc. is attempting to develop a dry, packaged oxalate-
peroxide decontamination reagent using urea peroxide as the H, O, source when
dissolved in water. R. D. Weed at Hanford is obtaining patents on cxalate-
peroxide solutions using acetate instead of citrate as a buffer. This type of solu-
tion was used in the decontamination of the PRTR.
.
.
-9.
64-6-53 (6-18-64)
3.0 GOR DECONTA:IVATION STUDTES - (A. B. Meservey)
The broad goal of all decortamination research programs 8 to dev:lop
and test reagents and methods for the rapid and efficient radioactive de-
contamination of metallic and nosmetallic surfaces, withuut unduly damag-
ing these surfaces. Prior art has featured decontaminatica by soap and
water om by surface dissolution In acids. Recent trends in the field are
toward noncorrosive methods tailored to specific applicatioas. Oir group
has been concerned primarily with the special problem of decontaninating
metal surfaces which have been exposed to tige coolant stream in gas-coole.
nuclear reactors.
Exploration of 10W-concentration oxalate-peroxide decontamination
reagents for carbon steel was continued. We found l.gat coatings of rust
to be soluble in room temperature or heated oxalate-citrate solutions at
a pä as high as 4.5. After the rust was dissolved, decontamination was
effected by the addition of hydrogen peroxide. Corrosion rates are still
sigher than desired (up to 1 mil/ar). The tests so far are on a labora-
toxy scale.
3.1
Low-Concentration Oxalate-Peroxide Decontaminat on Reagents
Carbon steel decontaminatio2 by means of a room temperature two-step
process (surface conditioning with 0.02 M oxalic acid for about 2 min fol-
lowed by adding H,0to a concentration of 0.06 M and circulating for 5
to 15 min) continued to give excellent results. Resulting surfaces were
clean and bright. When extreme heat conditions in the ECCR were sim.lated
by baking clean carbon steel in oxygen-free helium at 500°C, time steel
did not need a surface conditioning treatment in oräer to be attacked by
the oxalate-peroxide solution. The corrosion rate was 0.8-1.0 mil./hr.
Bakea coupons which had acquired a slight coating of oxide from standing
room ait for a day, and lission-product contazinated coupons which
were stained from being baked did require the surface conditioning treat-
ment, however. (The decontamination factor for a stained baked-coupon
aiter 15 min in the oxalate-peroxide solutions, without the surface con-
ditioning, was 1.2 compared to a decortamination factor of 900 when the
coupon was initially conditioned for 2 min in 0.02 M oxalic acid.)
-10-
When a contaminated coupon was heavily scaled by heating in air for
30 min at 600°C, the scale was not dissolved in 1 hr in 0.02 N. 1,2,3 at
room temperature but was partly removed in 3 hr at 75°C. When peroxide
was then added (to 0.c6 M), there was some further scale removal, followed
by renewed rusting. The decontamination factor (DF) wes 44. Rust, also
formed on an unstained contaminated coupon baked in hellum at 500°C when
It was decontaminated by immersion or 25 min in oxalic acid-peroxide at
60-70°C without surface conditiorlag (DF = 100). The coupon was not at-
tacked by the cold solution.
Quite surprisingly, it was found that carbon steel could be surface-
conditioned by dilute oxalate or oxalate-citrate solutions at på 3 to 4
even at room temperature, and then decontaminated by tire addition of per-
oxide. Room temperature surface conditioning, consisting of the dissolving
of most of the rust formed also at room temperature, took about 15 min in
0.02 M ammonium oxalate or 0.02 M oxalate-0.01 M citrate at PA 3. Rust .
dissolution took place in only 2 min at a boil. Table + shows the results
of conditioning air-baked and rusted contaminated coupons in boiling 0.02
M oxalic acid-0.038 M ammonium citrate (pa of mixture - 4.0), followed by
final decontamination in fresh oxalate-citrate-0.06 M EO, at 50°c. water-
soluble contamination had been rinsed off in hot water before baking. De-
contanination in the pH 4 sclution was complete, but the metal pitted some-
what with a corrosion rate of 0.7 mil/hr. No rust removal and a DF of only
2 occurred when a 400°C-baked coupon without surface conditioning was
bolled for 5 riin in the peroxide solution.
Solutions of the same composition as the above were evaluated at
lower temperatures in order to decrease the corrosion rate. At 25°C,
after a I min activation period, the rate was 0.4 mils/nr; and at 50°C
£t was 0.6 mils/hr. The concentrat109 wes then dropped to 0.01 M oxalate-
0.019 M citrate-0.035 M H, O, at p/ 4.26, which gave a room temperature
corrosion rate of about 0.17 mil/hr. At 50°C, the rate was 0.46 mil/n.
Wher the ps of the 0.02 M oxalate solution was raised to 4.5 by the use
of 0.09 M citrate, rust was still dissolved in about 20 min at room tem-
perature, but at 50°C the corrosion rate with 0.095 M EO, added to adjust
the millivolt potential to the polishing range was too high (1 mil/hr).
.
.
VIA
lui
* R
:1
UNA:
W
.
tid
2
A
2
.4
V
.
L
WILL
M
X
f
LR
de
HL
WWW
ww
ll.
Table 4.. Decortemination of Rusted Carbon Steel Coupons in Boiling
0.02 Oxalate-0.038 M Citrate at på 4 (solution 1) Pollcwed by
Similar solution (Solution 2) Combining 0.06 M 1,0, at 50°c.
Time required
for rust
removal, sec
Total y DF
after 5 min
in solution 2
Total y DF,
in solution 1
Coupon Baking
2.
l min
3 min
270
200°C in air
300°C 1. air
400°C in air
500°C 10 He
The corrosion rate was lowered to 0.26 mil/ar at 50°C by using only 0.01 M
citrate with 0.02 M oxalate and adjusting the pH to 4.0 with armonia.
We need to work out simple optimum formulas for maximum decontamina-
tion with minimum corrosion in several temperature and concentration
ranges, to suit varied needs in the decontamination of carbon steel.
Pa
3.
.
311
47
w
wir
hy
.
well
LI
AN
AL
..
:
T
64-7-43 (4-14-64)
3.0 GCR DECONTAMINATION STUDIES - (A. B. Meservey)
The broad goal of all decontamination research programs is to develop and test
reagents and methods for the rapid and efficient radioactive decontaminotion of
A
1
ICE
LEX
cameraman
metallic and nonmetallic surfaces, without unduly damaging these surfaces. Prior art
has featured decontamination by soap and water or by surface dissolution in acids.
Recent trends in the field are toward noncorrosive methods tailored to specific appli-
cations. Our group has been concerned primarily with the special problem of decon-
taminating metal surfaces which have been exposed to the coolant stream in gas-cooled
nuclear reactors. Because funding of this program has been discontinued, this is the
last report in the series.
The investigation of very dilute oxalate-peroxide solutions for the decontami-
nation of carbon steel was continued. Decontamination factors of 100 were achieved
from baked-on mixed fission products, using the solutions at elevated temperatures.
At room temperature and pH 4.0 the prediction is also for good decontamination, either
in the dilute solution or in the previously proposed concentrated solution, when the
hydrogen peroxide addition is suitably regulated.
3.1 Carbon Steel Decontamination
In further exploration of low concentration oxalate-peroxide decontamination
reagents for carbon steel, a decontamination factor (DF) of over 1 x 10° was obtained
in a 2-step process with a corrosion rate of only 0.15-0.25 mil/hr. The steel had been
contaminated by dipping in a mixed fission product solution at pH 5, drying at room
temperature, rinsing in hot water, redrying, and heating to about 300°C in air untii
blue. The oxide was then removed, along with most of the fission products, by boiiing
for 1 min in 0.02 M ammonium oxalate-0.01 Mammonium citrate at pit 4.0. The re-
maining gamma activity was measured in a gamma scintillation counter. The DF in this
step was 336. The coupon was then resensitized by re-immersing in the same solution
at 50°C for a few seconds, and then brightened and further decontaminated to back-
ground in 15 min by the addition of hydrogen peroxide to a concentration of 0.03 M.
Another coupon heated to 500°C in helium containing enough oxygen impurity to dis-
color the steel was similurly decontaminated (DF> 1 x 10°). There was no pitting of
the metal. The use of citrate with the oxalate resulted in a better scale and rust re-
moval than with oxalate alone.
3.2 Corrosion rates and Passiviry at Room Temperature
Ordinary light rust on carbon steel was largely dissolved in a few minutes at
room temperature in a mixture of 0.02 M ammonium oxalate and 0.08 M citric acid,
0.006M
VA
1.
1
1
1
WWW
CV
M
17
arch
Mil
WA
.
which had o pH of 4.02 without aci ustment. The corrosion rate was 0.034 mil/hr,
ot á millivolt potential of -635. The corrosion rate was increased to 0.15 mil/hir
ct -295 mv when 0.012 M H, was added to simulate decontamination conditions.
At 0.023 M H, Og, freshly added steel remcined passive, and active steel already
in solution went passive when touched by the passive steel. The corrosion rate in
the passive condition was less than 0.0!4 mil/month.
3.3 Room Temperature Corrosivity of High Concentration Oxalate-Peroxide Solutions
The standard decontamination solution which has been recommended for the
decontamination of carbon steel and the simultaneous dissolution of uranium oxides
in the GCR program is 0.4 M ammonium oxclate-0.16 M ammonium citrate-0.34
MH, O, at pH 4.0, and used at 90-95°C. The corrosion rate is less than 0.01 mil/hr.
li only about 0.1 MH, O, is used in the formula, however, the peroxide becomes a
corrosion promoter, and the rate is 2 to 3 mil/hi. The corrosive action of 0.012 M
HO, in room temperature solutions of 0.02 M oxalate at pH 4.0 (see section 3.2)
led to a detailed investigation of the corrosivity of the standard 0.4 M solution at
room temperature with peroxide concentrations less than 0.7 M. The corrosion rate
was 0.0!8 mil/hr without peroxide, but it rose rapidly as H, O, was added, to a
maximum of 1.6 mil/hr at 0.08 M H20, with moderate agitation. The corrosion rate
was cependent on the stirring rate. For example, at 0.04 M H, O, with no agitation
the corrosion rate was only 0.17 mil/hr, but with rapid stirring the corrosion was
higher by a factor of 8.2 (1.4 mil/hr). Between 0.04 and 0.08 M H, Og, steels were
passive in the solution unless activated by corrosive pretreatment or by sanding. At
0.08 MH, Og, the steel remained passive even when freshly sanded.
One cdvantage foreseen for room temperature decontamination with oxalata-
peroxide solutions is that, unlike the case at 90-95°C, no appreciable reaction takes
place between the peroxide and the oxalate or citrate. Within the error of experiment,
the only peroxide reaction found experimentally was that of oxidizing iron, as follows:
* 2Fe + 3H202 + 6H* > 2Fe+++ 6H,0 .
It is thus probable that suitable adjustment of peroxide and acidity can be made such
that corrosion will take place only to a calculated depth in a decontamination opera-
tion, and then cease. This would mean a high degree of safety against unwanted cor-
rosion.

DATE FILMED
| 2 / 23 165
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*
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END
de
k'