Table Of ContentExtraction ' 84
Symposium on Liquid - Liquid Extraction Science
Organised by the Institution of Chemical Engineers and the Dounreay Nuclear
Power Development Establishment and held at Dounreay, Scotland, 27-29
November 1984.
Organising Committee
Mr C. McArthur Chairman, Scottish Branch, I Chem E
Dr LR. Weatherley Secretary, Scottish Branch, I Chem E
Professor J D Thornton Consultant
Mr D.W. Harris DNPDE
Dr W. Batey DNPDE
THE INSTITUTION OF CHEMICAL ENGINEERS
SYMPOSIUM SERIES No. 88
ISBN 0 85295 182 5
i
PUBLISHED BY THE INSTITUTION OF CHEMICAL ENGINEERS
Copyright © 1984 The Institution of Chemical Engineers
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British Library Cataloguing in Publication Data
Extraction '84: Symposium on Liquid-Liquid
Extraction Science. - (Institution of Chemical Engineers Symposium series;
no. 88) .
1. Extraction (Chemistry)
I. Title II. McArthur, C. III. Institution of Chemical Engineers IV. Dounreay
Nuclear Power Development Establishment V. Series 660.2'84248 TP156.E8
ISBN (W)8-031439-2
Library.of Congress Cataloguing in Publication Data
Symposium on Liquid-Liquid Extraction Science (1984: Dounreay, Caithness)
Extraction '84. (Institution of Chemical Engineers symposium series; no. 88)
1. Extraction (Chemistry) — Congresses. I. Institution of Chemical Engineers
(Great Britain) II. Dounreay Nuclear Power Development Establishment. III.
Title. IV. Title: Extraction eighty-four. V. Series: Symposium series (Institution
of Chemical Engineers (Great Britain)); no.88. TP156.E8589 1984 660.2'84248
84-26560 ISBN 0-08-031439-2
ii
Foreword
This Conference maintains the tradition of previous Liquid-Liquid Extraction
conferences held at the University of Newcastle upon Tyne under the aegis of
the Institution of Chemical Engineers. The aim has always been to provide a
UK forum for the exchange of current ideas relating to the science as well as
the engineering aspects of extraction operations. The 1984 meeting continues
this pattern and the Conference has been divided into a number of sessions
covering extraction processes, contactor performance and design as well as
fundamental aspects of mass transport in liquid-liquid systems.
In previous years, meetings were held at irregular intervals as the need arose.
Within the last decade however, the impetus has increased and new extraction
techniques have been developed which could be relevant to a range of industrial
problems. It is felt that this now calls for a more formal approach to future
meetings and that this Conference should become an established feature of the
Chemical Engineering calendar. The Scottish Branch of the Institution of Chemi-
cal Engineers is therefore proposing to hold future Conferences at three yearly
intervals and the next meeting, "Extraction '87" will once again be held at the
Dounreay Nuclear Power Development Establishment. The Scottish Branch has a
close association with DNPDE and we are fortunate in being able to hold future
conferences at this centre which is in the forefront of fast reactor and fuel
reprocessing developments.
It is always a difficult task to acknowledge all the help that the organisers
have received in setting up a conference of this nature and it becomes all the
more invidious lest any names be omitted from what must be a long list. Never-
theless, I must place on record the fact that this Conference would not have
been possible without the considerable help and encouragement that the organi-
sing committee has received from Mr CW. Blumfield, Director, Dounreay
Nuclear Power Development Establishment, and Mr C. McArthur, Chairman of
the Scottish Branch of the Institution of Chemical Engineers. Thanks are also
due to Mrs Gillian Nelson of the Institution of Chemical Engineers who so ably
handles all the hundred and one detailed arrangements associated with "Ex-
traction '84".
J.D. THORNTON
iii
A FIVE YEARS EXPERIENCE OF PULSE COLUMNS EXTRACTION CYCLES FOR THE REPROCES-
SING OF FAST BREEDER REACTOR FUELS AT THE MARCOULE PILOT PLANT (SAP)
MM. CHARVILLAT - FABRE - LE BOUHELLEC - HENRY
The reprocessing of Phenix fast breeder reactor started at
the MARCOULE PILOT PLANT in 1977 with the enriched UO2 first
core (2.3 tons U) followed by several campaigns of UO2-P11O2
Phenix-core II (6.5 tons U-Pu).
After a short description of the Pilot Plant, characteristics
of the pulse columns extraction flow-sheets are presented.
Pulse columns are used for extraction and scrubbing of uranium
and plutonium and for uranium backwashing whilst plutonium
stripping and U-Pu partition are carried out in mixer settlers
with HAN and in-line electrolytic U IV generation. Performances
of pulsed columns including recovery yields and decontamination
factors are discussed : they show a good B y decontamination
can be reached with two cycles and partition carried out at the
second cycle.
INTRODUCTION
The Marcoule spent fuel reprocessing pilot plant was built in 1960-61
for extended testing of various fuel reprocessing methods under
conditions approximating those of actual production facilities.
The initial line, designed for reprocessing natural uranium base
metallic fuels, was modified and upgraded on several occasions, notably
for MTR fuel (U-A1, Pu-A1) reprocessing and neptunium recovery. In 1973
it was adapted to handle oxide fuels, especially those from fast
breeder reactors.
After several reprocessing campaigns with oxide fuels from the Rapsodie
an KNK reactors between 1974 and 1977, systematic reprocessing began
for the Phenix fast breeder reactor core charge. A total of 2.6 metric
tons were reprocessed from the first Phenix enriched uranium core
(26 % 235u after irradiation), followed by 6.6 metric tons from the
second core load, containing approximately 25 %plutonium (core II).
After mechanical treatment and disolution, solvent extraction is carried
out in 3 cycles for uranium and 2 cycles for plutonium, with partitio-
ning in the second cycle.
All of the extraction steps use pulse columns except for the partition
and for solvent treatments specific to each cycle, which are carried
out in batteries of mixer-settlers (30 % TBP). This report covers five
years of extraction cycle experience in reprocessing the second Phenix
core charge.
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I.CHEM.E. SYMPOSIUM SERIES No. 88
EXTRACTION CYCLES : DESCRIPTION, THROUGHPUT CAPACITY AND PROCESS FLOWSHEETS
The following three extraction cycles are used continuously with no
intercycle concentration (Figure 1).
FUNCTION EQUIPMENT
Extraction & decontamination of 1 extraction column
1st CYCLE solvent solutions (after NO 1 scrubbing column
reduction of PuVI formed)
U + Pu coextraction 2 backwashing columns
Solvent treatment 4 mixer-settler stages
Additional U+Pu extraction & 1 extraction column
decontamination 1 scrubbing column
U/Pu partition and Pu scrubbing Battery of mixer-settlers
10 Pu backwashing stages
4 Pu scrubbing stages
2nd CYCLE
Diluent scrubbing of PuIII 1 diluent scrubbing column
solutions
Pu concentration to 250 g.l~1 1 evaporator
Solvent treatment 4 mixer-settler stages
U extraction (after reduction of 1 extraction column
residual Pu with HAN-N2H4) 1 scrubbing column
U backwashing 1 backwashing column
3rd CYCLE
Solvent scrubbing of backwashed U 1 solvent scrubbing column
(uranium)
Uranium concentration to 400 g.l~1 1 evaporator
Solvent treatment 3 mixer-settler stages
A third plutonium purification cycle is implemented only in exceptional
cases to process substandard plutonium batches. It comprises two pulse
extraction & scrubbing columns and banks of mixer-settlers for pluto-
nium backwashing (16 stages), solvent scrubbing of the backwashed
plutonium (6 stages) and diluent scrubbing (4 stages).
The extraction throughput capacity is 1500 g.h"^ of U+Pu under
equilibrium conditions, and is reached gradually because of the weekend
shutdowns. Maximum capacity operation is achieved for no more than
3 days a week, limiting the weekly throughput to 120 kg maximum.
The process layout has remained virtually constant throughout the
different campaigns. Figure 2 details the most recent campaign,
on fuel with the highest burnup values.
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I.CHEM.E. SYMPOSIUM SERIES No. 88
Notable points include the following :
-1 7
- specific pulse column flowrates ranging from 0.7 to 2.2 l.h ,cm"c
in continuous aqueous phase except for the 1st cycle extraction and
scrubbing and the diluent scrubbers,
- the absence of any intercycle concentration steps,
- the use of specific solvents for each cycle.
FUEL REPROCESSING CAMPAIGNS
The second Phenix reactor core charge is a U0o-Pu02 mixed oxide fuel
containing natural uranium. Each fuel pin includes a fertile portion
(the integral axial blanket) that is dissolved together with the
fissionable core ; as a result, the Pu/U+Pu ratio is between 18 an 20 %.
The specified burnups correspond to the fissionable portion : the^burnup
values increased form 37 000 to 80 000 MWd.mt-1 with cooling times
ranging from 14 months to 3.5 years.
A number of experimental sub-assemblies were reprocessed, including
one irradiated to 100 000 MWd.mt-1 and two others containij^rplutonium
already submitted to two irradiation-reprocessing cycles.
Table I summarizes the data for the campaigns completed between 1979
and 1983.
PULSE COLUMN CHARACTERISTICS
Major pulse column specifications are shown in table II.
Continuous Organic Phase Pulse Columns
These columns have a separate lower settler : an airlift raises the
dispersion into this unit from which the solvent is recycled to the
bottom of the column. The recycled solvent flowrate is held constant
as a setpoint for regulating the emulsion airlift.
These columns are equipped with plates supporting 3.5 mm diameter
nozzles on a 50 mm pitch with 18 % transparency. The 1st cycle extraction
and scrubbing columns have been in use since 1974.
Continuous Aqueous Phase Pulse Columns
These columns are equipped with a pressure pot letdown system :
the pressure is slaved to the interphase level in the upper settler,
allowing the letdown flowrate to be regulated bu controlled siphoning.
These columns are fitted with conventional perforated plates (3 mm
holes on a 50 mm pitch with 23 % free-area.
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I.CHEM.E. SYMPOSIUM SERIES No. 88
The first cycle columns were commissioned in 1974, the 2nd cycle columns
in 1976 and the third uranium cycle units replaced the centrifugal
extractors in 1979 when an additional 2nd cycle extraction column was
also installed.
RESULTS
Hydraulic Operation
Throughput Variations in Continuous Aqueous Phase Pulse Columns
Despite relatively long experience in operating pulse columns since
1964, no change in their throughput capacity was noted during the
pilot campaigns, lasting from 1 to 4 months. The phenomenon was only
detected during the extended campaigns of 1976 (1.6 metric tons of
KNK fuel) and the Phenix uranium core campaign or 1977-78 (2.6 metric
tons), and subsequently reproduced in non-radioactive facilities :
in order to maintain a constant flowrate it was necessary to modify
the column pulse conditions on several occasions by reducing the
amplitude to prevent fouling.
Several conclusions were drawn from the experience of multiple
campaigns :
- the phenomenon stabilizes before the amplitudes are reduced below
a value incompatible with proper pulse column operation, and the
column efficiency remains satisfactory,
- initial conditions can be restored, although only temporarily,
simply by flushing the columns with a 1-2 N NaOH solution,
- the capacity variations are not identical in all columns, but are
observed after 2 or 3 months of operation, especially in the first
and second cycles.
Studies on non-radioactive solutions showed that the phenomenon
involves gradual clogging of the plates by the organic phase which
reverses the wetting properties of the perforated plates used in
columns operated in continuous aqueous phase.
The final treatments were carried out after flushing the columns
with a soda solution only between campaigns. The throughput capacity
decreases stabilized at values that did not require revision of the
extraction flow-sheets as the column efficiency was unaffected by
the decreased amplitudes.
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I.CHEM.E. SYMPOSIUM SERIES No. 88
Column Shutdown and Restart Conditions
During operation, for brief shutdowns such as over weekends the columns
are depleted of fissionable material to a few milligrams of plutonium
per liter, and left filled with their continuous phase. For longer
shutdowns, the columns are filled with 3-4N nitric acid.
Restarts are conducted step bu step after first obtaining stable
hydraulic operation by simultating the feed solution with an equivalent
flowrate of acid.
Plutonium and Uranium Recovery
Refined material losses into the backwashed solvents and evaporation
distillates are totally negligible under equilibrium conditions, and
correspond to recovery yields exceeding 99.98 % in every case.
In actual operation, because of the weekend shutdowns, the overall
losses are somewhat higher, but remain fully acceptable. Table III
shows the overall losses (in grams) recorded in the first six months
of 1983 during which 1 644.5 kg of uranium and 307.6 kg of plutonium
were reprocessed.
The principal source of plutonium losses is the 2nd cycle refined
solutions, but the total amount of the extraction losses is less
than tose incurred during high-level laboratory analyses.
$ y Emitter Decontamination
Feed Solution Composition
As a result of the wide diversity of irradiation conditions and
especially the highly variable cooling times for the spent fuels
reprocessed, the composition of the 1st cycle feed solutions has
varied in considerable proportions. The $ activity limits (as
measured by gamma spectrometry and thus excluding pure 3 emitteurs
such as 90$r) have ranged from 30 to 250 Ci.l"1 as shown in Table IV.
Decontamination Factors
Table V showsan example of determinations corresponding to a general
sampling carried out after 50 to 70 operating hours. This duration
certainly does not correspond to the achievement of a stable physico-
chemical equilibrium, hence the relative dispersion of the values
indicated in the table. From the whole results, the following remarks
can be made :
- irrespective of the 3 activity of the 1st cycle feed solutions,
the activity of the co-backwashed U+Pu solutions remains virtually
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I.CHEM.E. SYMPOSIUM SERIES No. 88
constant at between 0.2 an 1 mCi.l"1 for most of the values recor-
ded (U+Pu = 60 g.H),
- similarly, the activity of the uranyl nitrate produced by the
2 nd cycle (U = 30 g.1-1) generally is less than 10 uCi.1-1,
i.e. near the finished product specification of 100 uCi.kg-1
of uranium. This clearly shows the limited decontamination role
of the 3rd cycle in ensuring the required 3Y activity value,
- with regard to plutonium, the dispersion of the a activity
after partitioning is greater, generally ranging from 0.01 to
0.2 mCi.1-1 for a mean plutonium concentration of 13 g.1-1.
This activity is essentially attributable to Zr-Nb and Ru-Rh
pairs, and varies independently of the 2nd cycle feed solution
activity. These variations may be due to interphase fouling or
precipitates related to solvent decomposition products in the
electrolytic partition units. This contamination is also due
to weekly work schedule of the reprocessing facility : at
equilibrium during the middle of the week, specification values
are routinely obtained.
Nevertheless, the residual contamination is still compatible
with the decontamination factors obtained during oxalic conver-
sion : all of the oxide batches produced by the plant have met
the specified 1 uCi.g-1 Pu limit required to permit reutilization
of the plutonium for fuel fabrication.
Uranium-Plutonium Separation
The fundamental operation of uranium-plutonium separation is carried
out in 10 mixer-settler stages (5 to 14), six of which are equipped
with electrolysers to reduce a fraction of the uranium to valence 4.
Stages 1 through 4 are used for plutonium scrubbing by fresh solvent
to extract trace amounts of uranium IV or VI entrained with the
plutonium.
While the UO2 fuels were reprocessed using only electrolytic reduc-
tion, the high plutonium content of the Phenix fuels justified
combining electrolytic reduction with reduction by hydroxylamine
nitrate. The uranium IV makes it possible to ensure partial reduc-
tion of the plutonium in the organic phase, and thus complete the
partition.
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I.CHEM.E. SYMPOSIUM SERIES No. 88
Uranium Removal from the Plutonium
Despite the relative dispersion of the results due to the importance
of the transient conditions arising from the semi-continuous opera-
ting schedule, the mean residual plutonium contamination in the
uranium at the mixer-settler outlet is 0.25 ppm corresponding to
a mean decontamination factor of 10^, while values of 0.05 ppm are
reached under equilibrium conditions. The process without electro-
lysers is not efficient enough for the 3rd cycle to eliminate the
residual plutonium, for which the contamination in the purified
uranium must not exceed 0.04 ppm (i.e. 10 000 disintegrations per
minute (dpm) per gram of uranium).
This specification is almost met after partition, and is ensured
in the 3rd cycle by adding a reducing agent (HAN 0.05 M + N2H4
0.03 M) to the feed solution before acid adjustment ; this proce-
dure permits an additional plutonium decontamination by a factor
of 10 to 20.
Plutonium Removal from the Uranium
The uranium decontamination factor obtained during oxalic acid
conversion of the plutonium is sufficient to ensure that the
MARCOULE plant (UP1) entry specification of 15 000 ppm of uranium
in the plutonium batches can be easily reached.
The residual contamination level routinely observed at the outlet
of the partition unit is about 300 ppm, which is Pu O2 specifica-
tion, while the batches transferred to the plant have had contami-
nation levels of between 1 000 and 6 000 ppm (due once again to
the discontinuous pilot operating conditions).
Neptunium Behavior (Table VI)
In the high level solutions, the neptunium concentration of the
first cycle feed solutions was calculated, unlike the medium level
solutions which were analyzed.
The dissolution solutions, which should contain Np VI after prolon-
ged boiling, are treated with NO before feeding in order to reduce
the PuVI. The neptunium should therefore be present at several
valences. In any event, 90 % of the theoretical quantity
(17-25 mg.1-1 for a 150 g.1-1 U+Pu feed solution) is extracted
with the uranium and plutonium during the first cycle, while
about 1,5 mg.1-1 remain with the fission product solution.
During the second cycle the acidity is raised from 0.6N to 3.5N,
and extraction occurs about 5 hours after the end of the 1st cycle.
The neptunium extraction results are highly scattered, ranging
from 35 to 80 % ; this would seem to indicate considerable variation
in the valence distribution. Thus, out of a total of about 9 mg.1-1
in the 2d cycle feed solution, from 1 to 3.2 mg.1-1 of Np pass into
the refined solution. The presence of two reducing agents with
7
