atw 2018-04v6


atw Vol. 63 (2018) | Issue 4 ı April

| | Fig. 4.

HTHL TRACE Nodalization.

the development of RELAP starting

with next year.

TRACE has been designed to perform

best-estimate analyses of loss- ofcoolant

accidents (LOCAs), operational

transients, and other accident

scenarios in pressurized light-water

reactors (PWRs) and boiling lightwater

reactors (BWRs). It can also

model phenomena occurring in

experimental facilities designed to

simulate transients in reactor systems.

Models used include multidimensional

two-phase flow, none quilibrium

thermo-dynamics, generalized heat

transfer, reflood, level tracking, and

reactor kinetics. In addition, TRACE is

able to simulate several other coolants

such as helium and water in subcooled

condition and atmospheric pressure

(LVR-15 conditions). [7], [8]

For this reason, TRACE code was

selected and used for the simulation in

the Helium at 7 MPa with a temperature

rise from 200 °C up to 900 °C

(nominal parameters for HTHL). The

correlation adopted for simulating the

heat transfer from heat structures to

the helium coolant and vice versa

implemented in TRACE are Gnielinsky

and El Genk [7-9].

3.3 Codes assessment

The code assessment was done by

benchmarking of the codes with

available experimental results done in

different facilities around the world.

One of the most important steps

was selecting the code that can

perform the heat transfer calculation

under the high temperature He or

SCW conditions along with adequate

correlations [10], [11]. In the case of

ATHLET, the code was carefully assed

and benchmarked with experimental

results of a project coordinated by

IAEA [6] for steady state and with

Chinese SWAMUP facility [12] for

| | Fig. 5.

SCWL ATHLET Nodalization.

the transition from supercritical to

subcritical condition.

The aim of this analyses was to

simulate the deterioration phenomenon

[9] of heat transfer with fluid

transiting between subcritical and

supercritical condition. According to

Ref. [6], Mokry, Gupta and Watts-

Chou correlations show acceptable

prediction capabilities of the Heat

Transfer Coefficient (HTC). Both our

analyses and IAEA CRP program

concluded that an uncertainty for

calculating HTC is about ±25% while

the calculating wall temperature was

between ±10 to 15 %. As a result of

this exercise, the code certification

was obtained from SONS (State of

Office for Nuclear Safety) in March

2017 for using the code in simulating


The TRACE assessment was done

with the data available from the

project GoFastR [13] financed by the

EC in the Framework Program 7, in

particular with data related to the

HE-FUS3 facility [14], [15]. The

facility operational parameters are

similar to the HTHL.

The TRACE HE-FUS3 thermal hydraulic

model was developed and

compared with experimental data

from steady state loop operation and

selected transients. The comparison

showed that the TRACE T/H model

can simulate the helium temperatures

as well as the piping wall temperatures

along the different sections

of the facility accurately. After a sensitivity

analysis, the electrical heater

power has been lowered to 10.76 kW.

The certification for TRACE code was

obtained from SONS in December

2016 by CVŘ for simulating water in

PWR condition, sub-cooled water at

atmospheric pressure (such as LVR-15

operational condition) and helium

behaviour in the range of 7 MPa for a

temperature range between 200 to

900 °C. [16]

3.4 Model description for


The HTHL and SCWL are similar

experimental facilities characterized

by 2 steps upward and downward

flows, although some major differences

exist in the design. In particular,

the HTHL active channel contains

all necessary components for heat

transfer inside except of the compressor

and the main compensator, which

are located in the chemical control

system. The Figure 4 shows the

TRACE nodalization containing simulated


The SCWL is different in such way

that it needs some extra components

larger than the HTHL to help the sub

critical water to become gas. For this

reason additional axillary facilities,

such as a recuperator, cooler, pump,

compensator and other 4 sections of

electrical heater are located in a

different building along with the

chemical control system.

The ATHET SCWL loop model

shown in Figure 5 is focused mainly

on the active channel from inlet to

outlet, although all the previous

components are also simulated as a

part of the primary and the secondary

circuits. In addition to the primary

and the secondary circuits of the

SCWL, there is the third open loop

representing the active channel position

into the LVR-15 core and providing

additional heat transfer between

active channel and reactor coolant.

3.5 Analysed Scenarios

The planned in-pile operation of both

loops requires an amendment of the

LVR-15 Final Safety Report providing

thermohydraulic and structural integrity

analyses during normal operation


Operation and New Build

Experimental and Analytical Tools for Safety Research of GEN IV Reactors ı G. Mazzini, M. Kyncl, Alis Musa and M. Ruscak

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