PWR

Directorate-General For Translation European Commission

Description

Nuclear energy and safety

Sujets

• Nuclear safety
• Plutonium

Informations

• Publié par: EUROPEAN-COMMISSION
• Nombre de lectures: 24
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

Commission of the European Communities
nuclear science and technology
MULTIDIMENSIONAL FAILURE ANALYSIS
FOR LWR WITH PLUTONIUM FUEL
Part I: PWR
Report
EUR 7449/1 EN
Blow-up from microfiche original Commission of the European Communities
nuclear science and technology
MULTIDIMENSIONAL FAILURE ANALYSIS
FOR LWR WITH PLUTONIUM FUEL
Part I: PWR
(SYNTHESIS REPORT)
RESEARCH AND DEVELOPMENT PROGRAMME
ON PLUTONIUM RECYCLING IN LWRS
Contract between
The European Atomic Energy Community
and
Kraftwerk Union Aktiengesellschaft
Contract no 008-77-1 RPU D
1981 EUR 7449/I EN Abstract
The equilibrium cycles of three cores containing different
numbers of Plutonium fuel assemblies (0 %, 37 %, 100 % MOX-FA)
are used to perform multidimensional failure analysis. Two
failures are investigated:
- The rupture of a main steam line during stationary full
power operation at end of cycle.
A higher number of MOX-FA will lead to a higher core power
after return to criticality. However, no intolerable high
fuel and cladding temperatures occur during the incident.
- The ejection of a fully inserted control rod at full power.
Only small excursions of temperatures were seen during the
incident. Therefore, no cladding or'fuel failure is being
expected.
The consequences of the investigated failures are influenced
trifling by the number of loaded MOX-FA. Much smaller conse­
quences are to be expected using more realistic boundary
conditions.
Zusammenfassung
Die Gleichgewichtszyklen von drei Kernen, beladen mit unter­
schiedlicher Anzahl Plutoniumbrennelementen (0 %, 37 %, 100 %
MOX-BE), sind Ausgangspunkt für mehrdimensionale Störfallana­
lysen:
- zu einem Frischdampfleitungsbruch am Zyklusende bei Vollast.
Beir Beladung mit mehr Pu-Elementen wird nach dem Wie-
derkritischwerden eine höhere Leistung erreicht. Die Brenn­
stoff- und Hüllrohrtemperaturen führen jedoch nicht zu­
stabschäden.
- zum Auswurf eines ganz eingefahrenen Steuerelements bei
Vollast.
Es sind keine Brennstabschaden zu erwarten.
Die Auswirkungen der untersuchten Fehler werden nur wenig von
der Anzahl MOX-BE beeinflußt. Bei Verwendung weniger konser­
vativer Handbedingungen verringern sich die Störfallauswirkun-
gen weiter. - 1 -
Table of Contents Page
1 Introduction 3
2 Short Description of the Model Plant 4
3 Description of the Computer Codes 5
3.1 One-dimensional Spectral Code FASER
3.2 Multidimensional Burnup Code MEDIUM
3.3 Space-Time Kinetics Code IQSBOX 6
3.4 Summary on the BRUSEK-Code
3.5 Verification of the Used Computational 7
Methods
4 Cores and Fuel Assemblies to be Considered 9
4.1 Fuel Assembly Design 9
4.1.1l Assemblies for the U-Core
4.1.2 Fuels for the Recycling Core
4.1.3l Assemblies for the Pu-Burner 10
4.2 Core Description 1
5 Reactivity Worths from2
Stationary 2D-Calculations
5.1 Control Rod Worth
5.2 Reactivity Coefficients3
5-3y Balance
6 Three-dimensional Failure Analysis 15
with the Kinetics Code IQSBOX
6.1 Preparatory Calculations 1- 2 -
Page
6.2 Main Steam Line Rupture at Stationary Full 16
Power Conditions
6.2.1 Time Sequence of the Failure 1
6.2.2 Description of the Plants Behaviour During 17
a Main Steam Line Rupture at Full Power
with Aid of BRUSEK
6.2.3 Transient Computations8
6.3 Rod Ejection at Stationary Full Power 20
Operation
6.3.1 Assumed Sequence of Events 2
6.3.2 Description of the Incident by IQSBOX1
6.3.3 Effects of the Incident at the Uranium- 22
and Plutonium Core
7 Discussion of Computational Uncertainties 24
and Conservative Assumptions
8 References 26 - 3 -
1 Introduction
This report describes the influence of plutonium recycling on the
accident behaviour of KWU-PWRs. The following accidents were eval­
uated for that purpose :
a) Main steam line rupture during stationary full power operation
at the end of an equilibrium cycle
b) Rod ejection during stationary full power operation at the end
of an equilibrium cycle -
These investigations were conducted under the auspices of the'EG-
programme "Control and Safety" (Contract No. 008-77-1 RPU D). - 4 -
2 Short Description of the Model Plant
Biblis-B is being used as a model plant for the hazards analysis.
Its core consists of 193 fuel assemblies (Fig. 1) delivering 3765 MW
on thermal power. 236 fuel pins are arraied symmetrically within
a fuel assembly in a 16x16 lattice together with 20 control rod
guide thimbles (Fig. 2). Control and shut down of the reactor are
performed by 61 control assemblies. Each consisting of 20 elastic
control rods being inserted in above mentioned guide thimbles and
being supported by a control rod spider. Each control assembly
is being positioned by an electro magnetic jack and rabbit type
drive mechanism mounted on top of the pressure vessel.
Boric acid is being added to the coolant for additional reactivi­
ty control. That facilitates a reduction in control assemblies.
Special attention is being paid to the reactivity coefficients
during core lay out. One attempts to achieve self-stabilizing ope­
rating conditions following operational and accidental changes.
The coolant is transported by four main pumps through four heat
exchangers. Within the latter heat is being transferred and steam
being produced in the secondary loop. Four main steam lines lead
through the reactor containment into the power plant and to the
turbine (Fig. 3) with its main control and shut down valves. All
four main steam lines are connected into a main steam plenum serv­
ing for pressure equalization. The sensores for the main steam
pressure measurement are positioned within that plenum. The shut­
down valves are contained in separate compartments for avoiding
any unwanted perturbations during hazard conditions.
Table 1 contains operational data of this model-plant. A more de­
tailed description may be found in Ref. /I/.