PRELIMINARY TRANSIENT ANALYSIS FOR THE IRIS REACTOR PRESSURIZER
WITH RELAP5/Mod3.3 CODE
Sabundjian1, G.; Andrade1, D. A. de; Baptista Filho1, Benedito Dias; Palmieri2, E. T.
1CEN/IPEN - Travessa R, 400 – Cidade Universitária
CEP 05508-900 – São Paulo – SP – Brazil
Phone: +55-11-3816 9165 ext. 259/263/262, Fax: +55-11-3816 9423, E-mail: gdjian@ipen.br
2CNEN/CDTN - R. Prof. Mário Werneck, S/N
Cidade Universitária – Pampulha
Caixa Postal 941 – Belo Horizonte – MG – Brazil
Phone: +55-11-499 3125, E-mail: etp@cdtn.br
Abstract - The International Reactor Innovative and
Secure (IRIS) concept is being developed by an
international consortium led by Westinghouse Electric
Company. The pressurizer design and transient
analysis are under the responsibility of Brazil as part
of an agreement established with Westinghouse. The
IRIS pressurizer is housed within the vessel head. Its
configuration is quite different from that of
conventional pressurizers. A specific nodalization for
RELAP5/Mod3.3 code was developed to reproduce the
main phenomena involved within this component. The
objective of this work is to check the control logic
actuation as well as to describe the nodalization
scheme proposed for the thermal-hydraulics analyses
of the IRIS pressurizer. Few results are presented.
Only the model of the pressurizer is considered.
Boundary conditions as well as controls are supplied.
The analyses performed provided relevant
information to the project task. Although the
nodalization is still in development, the results showed
to be very consistent.
I. INTRODUCTION
One of the most notable characteristics of IRIS, the
International Reactor Innovative and Secure [Grgic et. al.,
2002], is the integrated design of the primary system, with
eight steam generators, eight spool pumps and pressurizer
located inside the vessel, thus without any large vessel
penetration. The IRIS concept is being developed by an
international consortium led by Westinghouse Electric
Company.
The IRIS pressurizer is housed within the vessel head. Its
saturated water layer is separated from the reactor water
by a plate that resembles an “inverted hat.” Its
configuration is quite different from that of conventional
pressurizers and a specific nodalization for
RELAP5/Mod3.3 code [NUREG/CR-5535 Report, 1995]
had to be developed to reproduce the main phenomena
involved within this component. This work has the
objective of describing one of the nodalization schemes
proposed for the thermal-hydraulics analyses of the IRIS
pressurizer.
The positioning of the steam generators in a peripheral
annulus for easy maintenance and for core refueling
without first removing the steam generators results in a
comparatively large diameter and tall reactor vessel. The
reactor vessel, the automatic depressurization system and
suppression pools are within a spherical containment. The
power rating for the reactor ranges from 100 MW (e) to
300 MW (e). The IRIS has been projected with two types
of fuel: the first uses uranium oxide with enrichment 5%
and the second uses MOX – mix uranium and plutonium
oxides. This integral reactor vessel makes it possible to
reduce containment size. Making the IRIS cost more
competitive. IRIS is being designed to enhance reactor
safety, and therefore a key aspect of the IRIS program is
the development of the safety and containment systems.
These systems are being designed to maximize
containment integrity, prevent uncover core following
postulated accidents, minimize the probability and
consequences of severe accidents, and provide a
significant simplification. Figure 1 illustrates this concept.
II. IRIS PRESSURIZER NODALIZATION
In order to study some transients involving the pressurizer
a detailed nodalization of the pressurizer [Andrade et. al.,
2003] was developed for RELAP5/Mod3.3 code, as
shown in Figure 2 and Table I. Pressurizer was divided
into two axial parts to better represent the flow path (up
and down). Heaters are located in the lower part.
Pressurizer is composed by components 131, 132, 133,
134 and 135. Component type and divisions are presented
in Figure 2. Calculation was based on 37 guide rods, 90
heater rods and 48 instrumentation rods. In present
version the diameter of the guide tubes is 0.1143 m,
heaters diameter is 0.0316 m and instrumentation diameter
is 0.0381 m. There are 10 heat structures in the model
including 2 heater groups. The head of the vessel is
assumed with constant thickness of 0.133 m. It is insulated
on the outer side as well as on all other outer parts of the
vessel.
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