atw 2018-09v3

inforum

atw Vol. 63 (2018) | Issue 8/9 ı August/September

pictured. Typically, four control rods

are required for reactivity control in

TRIGA reactors with thermal power

levels of less than 1 MW [IAEA2016B].

Further, graphite elements are at the

outer positions. For MTR research

reactors, there are often empty places

at the centre of the core grid for

radiation samples. If the input number

of fuel assemblies or elements

does not match the number of grid

positions, the implemented algorithm

considers these typical core characteristics.

The assemblies or elements are

positioned in respect of this information.

Furthermore, the free flow path

is calculated as a function of total core

area and number of fuel assemblies,

elements and other components

inside the research reactor core.

3 Generated input decks

of exemplary MTR and

TRIGA reactors

In this part, first functionality of

the new modelling system is demonstrated

by generating an exemplary

MTR and TRIGA research reactor

model. For this purpose, two reference

research reactors were chosen.

Providing technical details in

[ABD2008A] and comparative data in

[ABD2008B], the ETRR-2 was identified

as a MTR reference facility. The

ETRR-2 is a multipurpose research

reactor located in Inshas, the Arab

Republic of Egypt. It corresponds to

the rightmost research reactor design

in Figure 2-1. The ETRR-2 reactor

consists of 29 fuel assemblies of MTR

type with 19 fuel plates each and has

22 MW nominal power. Further

description is presented in [ABD2008].

The main nodalisation of the generated

ETRR-2 model in ATHLET is

pictured in Figure 3-1. On the left

side, the coolant loop is presented

in bright blue. The reactor pool is

modelled with two pipes interconnected

by cross-connections. The

inner pool pipe is connected to the reactor

chimney, which is marked in

brown, by a single junction pipe. The

reactor core is modelled with two

representative assemblies. Each is

composed of 18 core cooling channels.

One assembly is representing 28

grouped average assemblies. The

other assembly considers a hot channel

factor on the 19 fuel plates plus

one extra penalised fuel plate. The

nodalisation of both assemblies is

identically and shown in Figure 3-2.

To check the capability of the

nodalisation to reproduce the thermal

hydraulic plant conditions, steady

state calculations were performed.

| | Fig. 2-5.

MTR core layout (left) and TRIGA core layout (right), generated by software for input deck generation.

| | Fig. 3-1.

Overview of whole Nodalisation of the ETRR-2 (left) and one fuel assembly (right) with 18 core channels generated by the software

for input deck generation.

Power

[MW]

Loop mass

flow

[kg/s]

The initial conditions of the experiment

and the calculated parameters

are compared in Table 3-1. The

experiment was performed at 9.5 MW

thermal power. There is good agreement

between the calculated and

experimental stationary data.

As an exemplary TRIGA research

reactor, the IPR-R1 was identified.

The IPR-R1 is a TRIGA Mark I model,

installed in Belo Horizonte in Brazil

and operated since 1960. Several

analytic and experimental studies

were performed and published. As

reference data, experimental results

in [REI2009] were used. The IPR-R1

corresponds to the leftmost research

reactor design in Figure 2-1. It is

operating at 250 kW and consists of

63 fuel elements of TRIGA type.

Further description is presented in

[REI2009]. The main nodalisation of

the generated IPR-R1 model in

ATHLET is shown in Figure 3-2. On

the left side, the coolant loop is

Core mass

flow

[kg/s]

Core outlet

temperature

[°C]

Core pressure

drop

[bar]

| | Tab. 3-1.

Overview of whole Nodalisation of the ETRR-2 (left) and one fuel assembly (right) with 18 core channels generated by the software

for input deck generation.

presented in bright blue. The reactor

pool is modelled with two pipes interconnected

by cross-connections. The

inner pool pipe is connected to the

core entrance and core outlet. 13 core

channels, interconnected by crossconnections,

with 63 fuel elements

represent the reactor core (see Figure

3-2 right). The core nodalisation

based on the nodalisation presented

in Figure 2-4.

The experiment was performed at

50 kW thermal power. In Table 3-2,

the calculated steady state results are

compared to measured core inlet and

outlet temperatures. At different

positions, measuring devices were

installed (see [REI2009]). There are

small deviations but overall the results

are consistent.

Further, the ATHLET simulation is

compared to published RELAP steady

state calculation in [REI2009], which

reaches steady state conditions after

about 2000 s simulation time.

Reference

pressure

[bar]

Calculation 9.5 309.24 302.86 35.01 0.42 2.2

Reference

[ABD2015]

9.4 309.24 302.87 34.9 0.31* 2.0

*in [ABD2015] core pressure drop of 3.1 bar is mentioned, but in /IAEA2005/ 0.6 bar pressure drop at 100 % core power is referred

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AMNT 2018 | YOUNG SCIENTISTS' WORKSHOP

AMNT 2018 | Young Scientists' Workshop

Heuristic Methods in Modelling Research Reactors for Deterministic Safety Analysis ı Vera Koppers and Marco K. Koch

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