Radiolytic Gas Generation in Chemically-bonded Iron Phosphate Ceramic Forms used for Immobilization of Plutonium Ash Res
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1207 Mat. Res. Soc. Symp. Proc. Vol. 556 ©1999 Materials Research Society
concentration in the ash. For radioactive samples prepared according to Method IPC- 1, the estimated amount of 238Pu(NO3 )4 in nitric acid was added into the silica and cerium oxide mixture. To remove free nitric acid, distilled water was added into the mixture to be dried under the infrared lamp. This procedure was repeated three times. Table I. Composition of iron phosphate ceramic samples FeO
FeO,
Solid: Liquid
Simulated Ash HPOG, 70%
FeO
wt.%
g
wt.%
g
wt.%
g
wt.%
g
wt.%
g
g/g
0.72
0.43
7.15
4.29
6.4
3.85
33.3
20.00
52.4
31.43
1:1.1
In Method IPC-1, simulated ash containing
23 8
Pu as nitrate, was mixed with the remainder
of the ash and iron oxides powder. Orthophosphoric acid was added into the mixture to result in a specific activity of 1.91 mCi/g. Due to a rapid increase of the viscosity of the mixture, mixing was conducted for four minutes and then the paste was poured into the molds. The sample size for the radiolysis test was 28.7 g. The IPC-1 samples are estimated to contain 15.7 wt.% of added water In Method IPC-2, simulated ash containing 238Pu as nitrate was calcined at 800'C for 60 minutes. The brownish color of the powder indicated generation of plutonium oxide. The powder was mixed with orthophosphoric acid solution, and the remainder of the ash was added over a duration of 15 minutes. Iron oxides were added, mixed with the paste for 4 minutes and the mixture was poured into the molds. The sample size for the radiolysis test was 51.66 g. Iron oxides included Fe20 3 as hematite, Fe 30 4 as magnetite, and FeO as wustite. The composition of simulated Rocky Flats incinerator ash is shown in Table II. B20 3 and Na20 were added into the system as Na 2B40 7, while P20 5 and K20 were added as KH 2PO4 . Other elements were taken as oxides. Table II. Composition of simulated rocky flats incinerator ash waste Component Concentration, Wt.% Component Concentration, Wt.%
A10Nd20 3 B)0 3
BaO
CaO Cr20 3 CuO Fe20
K0
MgO
4.0
6.6
0.8
4.5
C
SiO 2
CeO 2
18.9
41.9
11.2
3.0
0.1
0.8
1.0
1.0
Na2O
NiO
P)0
PbO
SnO Nb,05 TiO 2
0.7
0.3
1.2
0.7
0.1
0.3
1.6 1.3
X-Ray diffraction analysis (XRD) of the IPC samples was performed with a diffractometer DRON-1.5 with Cu Ku radiation. The operational mode was 32 KV, 16 mA, with the counter rotation of 2°/minute. Differential Thermal Analysis (DTA) of the IPC samples was performed with Derivatograph MOM-1. The heating rate was 10°/minute. Leaching of the IPC samples was performed according to ANSI/ANS-16.1 (American National Standard Institute/American Nuclear Society, 1986) at 20'C in distilled water with sample surface (S, cm2) to water volume ratio S/V = 0.1 cm'. The amount of the non-radioactive elements in the leachate was identified by inductively-coupled plasma atomic emission (ICP) and massspectrometric methods. The activity of the leachates was measured using an ultra pure
1208
germanium detector with Schiumberger EGPC 20P1 A # 4175, with
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