Data acquisition and control system for a heavy waterdetritiation plant

Iuliana Stefan *, Carmen Retevoi, L. Stefan, O. Balteanu

Institute of Cryogenics and Isotopic Technologies, P.O. Box 10-4, Rm. 1000, Valcea, Romania

Abstract

The importance of detritiation of heavy water from CANDU-type reactors is well known, as is the implications of

detritiation in fusion processes and installations. The nature of the fluids that are processed in detritiation requires the

operation of the plant in maximum security conditions in order to protect the working staff and environment. The

paper presents how the data acquisition and control system could be made for an experimental heavy water detritiation

plant. The plant must be designed to be operated without any working staff in the technological space. The purpose of

the security and control system is to ensure for the population an irradiation risk below the prescription limits. The

radiological risk is the tritium leakage that can be gas, vapor or liquid.

# 2003 Elsevier Science B.V. All rights reserved.

Keywords: Data acquisition; Control system; Detritiation; Tritium separation

1. Introduction

The scope of the experimental plant for tritium

and deuterium separation is to extract tritium

from heavy water. Heavy water is used as mod-

erator in CANDU-type nuclear reactor and after a

period of operation, an accumulation of tritium

appears. The high concentration of tritium creates

some problems for safety operations of the plant

and also for the population and environment.

Solving these problems means that a heavy

water detritiation plant must be built and linked

to the moderator circuits of the CANDU power

plant. This type of plant can be assimilated as a

nuclear facility, involving special regulation and

safety systems, respecting the nuclear laws of

Romania, EU and International Safety Regula-

tions, including IAEA Vienna specifications. Like

any nuclear facility, a special safety system is

provided, with special hardware and software

that supervise the technological process and safety

equipment.

The tritiated heavy water is received from the

nuclear power plant and introduced into the

process. The output result is a low concentration

* Corresponding author. Tel.: �/40-250-732744/736979; fax:

�/40-250-732746.

E-mail address: istefan@icsi.ro (I. Stefan).

Fusion Engineering and Design 66�/68 (2003) 931�/934

www.elsevier.com/locate/fusengdes

0920-3796/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.

doi:10.1016/S0920-3796(03)00378-8

of tritium in the heavy water. This water is

returned to the moderator circuits, and so the

safety regarding the concentration level of tritium

in the heavy water is re-established [1,2]. At thesame time, this plant can constitute the basis for

obtaining high-purity tritium that can be used in

future fusion reactors or other laboratory re-

search.

2. System description

Under normal operating condition of the detri-

tiation plant, no operating personnel is allowed to

enter in the technological area. Therefore, the

monitoring, analysis and control systems must

use remote-controlled equipment. The plant build-

ing must include a control room and a data

acquisition chamber which contains, respectively,the monitoring and control computers, and the

sensors and control equipment. In the control

room, digital computers are used for status

monitoring, plant control and alarm annunciation.

The digital computers communicate and manage

all the other components of the system using

software applications (LabView platform) with a

friendly interface [1,2].

The measured values generated by process

variables are converted into electrical or pneu-

matic signals, which are then transmitted to

subsidiary units used for indication, control and

protection functions. Before transmission, sensor

signals are usually converted to standard signal

levels (e.g. 4�/20 mA or 0�/10 V). For remote

transmission of signals, the 4�/20 mA current

signal is more common because of its higher noise

immunity. Voltage signals (such as 0�/10 V) are

generally used within the control room for recor-

ders and indicators [3].

During operation, the data acquisition can be

done by a digital computer that provides signals

from a network interface module of type Field-

Point which connects an RS-485 network to I/O

modules and manages communications between

the host computer and the I/O modules with a rate

of 115.2 kb/s [4] (see Fig. 1).

The input modules receive signals from trans-

mitters (flow, pressure, level), push buttons, con-

tacts and limit switches. The measured values of

the parameters are recorded and displayed in the

control room for a continuous indication of the

Fig. 1. Architecture of acquisition and control system.

I. Stefan et al. / Fusion Engineering and Design 66�/68 (2003) 931�/934932

parameters and give a systematic view of the

control status. These data are compared with

predefined limits and if one parameter is out of

these limits, a visual and acoustic alarm will be

actuated. The software that controls inputs and

outputs contains a logical structure based on

control analysis of the technological process.

Using implemented logic and signals from the

technological process, a decision is taken and an

output command is sent to execution. This action

can be corrective (for technological process) or

preventive (safety of the plant).

For cryogenic temperature measurement (e.g.

temperatures from a cryogenic distillation column

at about 23 K), carbon resistance temperature

sensors can be used. In order to measure variation

of the sensor resistance with temperature, a four-

wire measurement method can be used, which

offers the best accuracy. For higher temperatures

(e.g. temperature from the isotopic exchange

column), type J thermocouples can be used [1,2]

(see Fig. 2).

The parameter display computer assists control

room personnel in evaluating the control status of

Fig. 2. Example of status monitoring using LabView platform.

I. Stefan et al. / Fusion Engineering and Design 66�/68 (2003) 931�/934 933

the plant by providing a continuous indication ofthe parameters or derived variables that are

representative of that status.

It is important to consider the experimental

nature of the plant, and therefore all data equip-

ment is flexible and easy to adapt to the techno-

logical process.

This type of data acquisition system can be used

as the basis for the measurements that are neededin most tritium experiments. In the case of

industrial plant, dedicated equipment must be

considered.

The control system provides the following func-

tions:

�/ Ensures that all controlled parameters in the

experimental plant remain within prescribed

limits during all operational modes;

�/ Enables changes in set points to be made

without excessive transients;�/ Allows operation of remote equipment under

automatic and manual control.

The main advantages of such a system are the

continuous surveillance of the plant status with a

display of main plant parameters, and making

corrective and safety decisions regarding the

technological process [3].

3. Conclusions

The system is flexible, easy to use and the

improvements needed by any technological pro-

cess experiment could be done in a short time and

with low costs. Such a system can replace dedi-

cated hardware and software for industrial pro-

cess, especially regarding the experimental

character of this plant. Information on the plant

state is also essential in the dynamic prioritization

and conditioning of alarm messages. The basis of

the software design is to assure a good interface

between hardware and software with high-speed

connection.

References

[1] Reference technical project of tritium separation plant,

Internal Report, ICIT, Romania, 2001, pp. 68�/77.

[2] Security final report of tritium separation plant, Internal

Report, ICIT, Romania, 2002, pp. 50�/58.

[3] Modern Instrumentation and Control for Nuclear Power

Plants: A Guidebook, International Atomic Energy Agency,

Vienna, 1999, pp. 142�/147.

[4] FP 1000/1001 User Manual, National Instruments Corpora-

tion, April 1999, pp. 2�/10.

I. Stefan et al. / Fusion Engineering and Design 66�/68 (2003) 931�/934934