Dismantling and decontamination of the tube bundle of a feedwater preheater of the Garigliano BWR

European Commission Directorate-General For The Information Society And Media Directorate-General For Research And Innovation

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Nuclear energy and safety

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• Publié par: EUROPEAN-COMMISSION-DIRECTORATE-GENERAL-FOR-THE-INFORMATION-SOCIETY-AND-MEDIA-DI
• Nombre de lectures: 34
• Langue: English
• Poids de l'ouvrage: 3 Mo

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Commission of the European Communities
Dismantling and decontamination
of the tube bundle of a feedwater
preheater of the Garigliano BWR
■ff:,:i's{£&ffmîŞgf2eiMmigaa' Commission of the European Communities
Dismantling and decontamination
of the tube bundle of a feedwater
preheater of the Garigliano BWR
F Bregani,1 A. Garofalo2
1 Ente Nazionale per l'Energia Elettrica
Direzione Studi e Ricerche
Centro di Ricerca Termica e Nucleare
Via R. Rubattino, 54
1­20134 Milano
2 Ente Nazionale per l'Energia Elettrica
Direzione della Produzione e Trasmissione
Gruppo Impianti Nucleotermoelettrici del Garigliano
Casella Postale, 60
I­04023 Scauri (LT)
Contract No FI1D­0023
Report
This work was performed in the framework of the European Communities' research programme 'Decom­
missioning of nuclear installations', Section C 'Testing of new techniques under real conditions'
Directorate­General
Science, Research and Development UL .
1991 IFI IR 13?fifiFM[
/νκνοί^ 5^ Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Telecommunications, Information Industries and Innovation
L-2920 Luxembourg
LEGAL NOTICE
Neither the Commission of the European Communities nor any person
acting on behalf of the Commission is responsible for the use which might
be made of the following information
Cataloguing data can be found at the end of this publication
Luxembourg: Office for Official Publications of the European Communities, 1991
ISBN 92-826-0509-4 Catalogue number: CD-NA-13255-EN-C
© ECSC-EEC-EAEC, Brussels · Luxembourg, 1991
Printed in Luxembourg ABSTRACT
The report deals with dismantling and decontamination of the tube bundle of
a feedwater preheater of Garigliano-BWR.
Decontamination is a common practice in decommissioning works and it
can be used both for reducing radiation exposures, in order to save man-
rem, and for the unrestricted release of materials. In this latter field
the decontamination of tube bundle is a particular case because of their
large contaminated surfaces and relatively low weight; at the moment no
decon technique was available on the market to decontaminate up to the un­
restricted release the materials of tube bundles.
In this context an innovative decon technique using aggressive chemi­
cals together with ultrasounds in a tank, was developed by several labo­
ratories and assessed with in-scale testings. A decon procedure considering
two phases: first with ultrasounds applied in water at 60°C, and second
with ultrasounds applied in a solution of HF/HNO acids at 60-70°C, was
qualified.
The demonstration of the performances of the new technique under real
conditions was made by performing ten "full-scale demo tests", each one on
an assembly of 100 straight tubes, 1 m long each, for a total of 1000
meters.
The demo programme showed that the new decon process is able to decon­
taminate the tubes of the tube bundle lower than 0.3 Bq/g (as measured
directly by Nal gamma detectors).
During the demo works about 2.3·10 man-Sv were spent of which
-3 -4
1.95*10 man-Sv for dismantling activities and 3.5*10 man-Sv for decon
works.
About 2100 litres of contaminated aggressive solutions were generated,
with about 9 m of contaminated waters. It was estimated that by treating
these solutions about 300 litres of dry sludges would be generated.
An approximative cost of about 6 ECUs per kg of decontaminated mate­
rial was also estimated.
Finally the demo programme showed that the realisation of proper fa­
cilities for performing the decontamination is a critical point; in fact
the performances of a special ultrasonic machine were not satisfactory. CONTENTS
Page
ABSTRACT 111
1. INTRODUCTION 1
2. GARIGLIANO-BWR POWER STATION 2
2.1 Operative Data
2.2 Dismantling and Decontamination of the Turbine Building:
a Feasibility Study
3. THE FEEDWATER PREHEATERS 7
3.1 The Selection of the Preheater to be Decontaminated 7
3.2 Characterization of Test Materials 11
4. PRELIMINARY LABORATORY TESTING5
5. IN-SCALE TESTING 20
5.1 The Ultrasonic Machine
5.2e Radiometric Measurement System
5.3 Description of the First in-Scale Testing 27
5.4n of the Secondeg 3
6. OUTLINES OF THE DEMONSTRATION PROGRAMME 4
7. DISASSEMBLING THE PREHEATER FOR SAMPLING 1 m LONG TUBES 4
7.1 Selection of the Cutting Techniques1
7.2 Description of the Disassembling and Cutting Works 42
8. FULL SCALE TESTINGS 46
8.1 The Ultrasonic Machine
8.2e Radiometric Measurements Systems 53
8.3 Description of the Demo Testings
9. EVALUATION OF THE SECONDARY WASTES ARISING FROM
THE PROCESS 62
10.N OF THE OCCUPATIONAL DOSES 6
11. COST EVALUATION5
12. CONCLUSIONS7
13. ACKNOWLEDGEMENTS8
14. REFERENCES
- V -1. INTRODUCTION
The decontamination for decommissioning purposes has not yet been applied
extensively for the total cleaning of large components.
For heat­exchanger decontamination, only soft chemicals have been
applied on large scale, and unrestricted release levels have never been
obtained. Many problems are connected to the tube bundles; in fact they
have very large surfaces and in some cases they are contaminated both
inside and outside.
The scope of this work was to demonstrate the feasibility of decon­
tamination of a large heat­exchanger coming from a first generation BWR
(Garigliano). Experience gained in other plants were taken into account, in
the sense that the decontamination of the shell, and probably of the tube­
sheet, may be carried out by electrochemical way; so this study was mainly
focused on the decontamination of tube­bundles.
The tube­bundles of feedwater preheaters of BWRs are characterized by
large contaminated surfaces (both ID and OD) and relatively low weights. As
a consequence of this high surface/weight ratio, direct melting without
decontamination could be considered only for disposal and not for
uncontrolled release.
Among decontamination techniques the use of aggressive chemicals could
meet the objective of unrestricted release. Nevertheless direct in situ
chemical n needed too large solution volumes. Therefore chem­
ical decontamination in a tank, after dismantling the tube­bundle, was con­
sidered.
Taking into account the geometric features of the bundle pin­tubes and
2
previous results from aggressive chemical decontamination experiments, the
use of ultrasounds in connection with chemicals was considered in order to
enhance the effectiveness of the decontamination.
In this context, an experimental research programme, was outlined as
follows:
­ laboratory tests on ρin­tube specimens in order to select operative con­
ditions;
­ in­scale testing on small assemblies of tubes;
­ selection of procedures for residual radioactivity measurements;
­ dismantling and decontamination on real scale.
These activities were performed in joint collaboration between the
Special Unit for Decommissioning (USD of ENEL G & Τ Division) and the Ther­
1 ­mal and Nuclear Research Centre (CRTN of ENEL R&D Division), with some
CISE laboratory support.
2. GARIGLIANO-BWR POWER STATION
2.1 Operating Data
The Garigliano-BWR nuclear plant is equipped with a boiling water forced
circulating system reactor, dual cycle, with a turbo-nuclear unit of 160
MWe.
Basically the plant consists of a "nuclear section", enclosed in a
large spherical container in which are set the reactor, the two secondary
steam generators and the auxiliary systems of the nuclear section, and of
the "conventional section" installed in a separate building containing the
turbo-alternator, the condenser, the feed-water condensate cycle and the
auxiliary services of the plant.
The plant, constructed by IGEOSA, was put into commercial operation in
q
April, 1964; it was operated by ENEL and produced 12.5Ί0 kWh with an
utilization factor equal to 687o, until August, 1978, when it was closed
3
down because of a breakdown in a secondary steam generator.
Altogether the reactor functioned for 87850 hours, equivalent to 3250
days at full power and the turbine ran for 86020 hrs. In March, 1982, the
Board of Directors of ENEL declared the plant definitely out of operation.
A subsequent resolution of the Board approved the "Plan of action" prepared
by the Generation and Transmission Division, setting in motion the deacti­
vation of the plant and its subsequent shut­down; arrangements were made
for its conservation in absolute security for at least 30 years.
This decision was impelled both by the high number of man­Rem which
would have been necessary in the case of an immediate total dismantling and
by the current lack in Italy of an appropriate area to stock the thousands
of tons of activated and/or contaminated material deriving from the
dismantling.
2.2 Dismantling and Decontamination of the Turbine Building:
a Feasibility