Application of Personal Computers to the Control System for the Liquid
Waste Treatment Station at the Dalat Nuclear Research Institute
T. H. Anh, N. N. Dien, T. D. Hai
Nuclear Research Institute, Dalat, Vietnam

Abstract

1 Radioactive liquid waste treatment station

The radioactive liquid waste treatment station of theNuclear Research Institute (NRI – Dalat) was establishedand put into operation in July 1984, four months after thecompletion of the Dalat nuclear research reactor′sreconstruction . The previous control system of this station
was designed and manufactured by the former Soviet
Union and had generally good reliability and had proven its
ability to ensure the operating regimes. However, due tousing discrete and low-level integrated electroniccomponents of 1970’s generation, the system′s technology
was somewhat obsolete. After ten years of operation, thesystem′s reliability was degraded because of ageing effects
on equipment and electronic components. In the frameworkof a national project on the nuclear research reactor generalinspection and refurbishment, of the renovation andmodernization tasks for the control system of theradioactive liquid waste treatment station was implemented
as part of the project.
The design and construction of a new PC-based control
system for the liquid waste treatment station of the NRI
were imperative for improving its reliability andmeasurement accuracy and for increasing the systemfunctions.
This paper describes the application of PC-based
electronic systems to the liquid waste treatment station′scontrol.
The level measurement system has the function ofmonitoring, measuring, displaying and storing information
on liquid radioactive waste level for 24 vessels andautomatically controlling valves and pumps when required.
The system was built upon add-on interface cards to aPC/AT computer.
The design and construction of the dosimetry systemwere performed. The electronic blocks of this system werealso built upon add-on cards to PC. The system is used formonitoring the radioactivity level at different positions in
the liquid waste treatment station. Information onradioactivity is displayed digitally and graphically on acomputer monitor and saved continuously on the PC′s harddisk. The system can also give warning signals (visual andaudial) whenever the radioactivity level at any observed
position exceeds the set limit.
Software programs for both level measurement anddosimetry systems were written in Turbo Pascal andAssembler languages.
The new control system for the liquid waste treatment
station was checked, commissioned and put into operationin May 1997.

The radioactive liquid waste treatment station is a part of
the radioactive waste management system [1]. The stationconsists of 4 storage tanks (5 m3 each) for waste collection
and precipitation; 6 ion-exchange and 2 mechanical filters;
4 sludge reservoirs; 6 storage tanks containing alkalineacid solution; 2 purified water tanks; electric pumps andvalves and other accessories. The diagram , Fig. 1, showsthe main part of the station. The designed capacity of thisstation is 5 m3 per day. Annually 100 – 150 m3 ofradioactive liquid waste can be treated by this station.
As the Dalat nuclear research reactor is used forradioisotope production, scientific research and training
purposes, the main waste sources collected by this station
are from reactor operation and radioisotope production
activities.
The most significant quantity of the collected waste is inliquid form. Every month, the Institute generates about 10 15 m3 of liquid waste. The quantity and radiochemicalcomposition of the waste greatly depends on the activitiesof the reactor and radioisotope production laboratories. The
produced radioisotopes are mainly those serving nuclear
medicine needs, industry applications, sedimentology andhydrology studies and other scientific research. Several
types of isotopes are produced, such as 32P in injectable
solution and applicator, 131I solution andcapsule, 99mTc
51
generator, Cr in injectable solution. Other isotopes suchas 60Co, 65Zn, 64Cu, 24Na, 86Rb, 46Sc, 192Ir, 71Ge, 55Fe, etc.
are produced in small amount when requested. The liquid
waste in the collection tanks consist principally of 131I, 51Cr,60Co, 139Ce, 134Cs, 54Mn with radioactivity between 3.7 - 37
KBq/l. The chemical and radiochemical composition ofwaste in these tanks are classified in two types. The firsttype, having ″simple″ composition, is the result of reactor
operation, and the second type, with more ″complicated″composition, is from radioisotope production laboratories.
2 Description of the control system
The control system for the liquid waste treatment stationconsists of 3 main parts:- System for measurement of technologicalparameters, such as liquid level in various tanks of thetreatment lines, the liquid waste′s pH and conductivity
values before and after treatment, flow rates of filtering
unit, etc.
- Dosimetry system for measurement of radioactivity
at various positions in the treatment station.
- Control panels and control console for installingelectronic equipment, indicators and others.

Fig. 1. overview of the radioactive liquid waste treatment station of the NRI
The most important renovation task was to re-design andconstruct a number of systems/blocks which might play akey role in enhancing the reliability of the whole control
system The main results obtained from the renovation andmodernization work are the following:- Replacement of the old system for technologicalparameter measurement with the new one. This system wasbuilt using a PC and advanced multi-purpose add-on cards.
The designed system allows the operators to measure
simultaneously various parameters of the treatment station.
Measured as well as alarm setting values are displayed on aPC monitor in digital and graphical modes.
- Redesign and construction of a new PC-based 8channel dosimetry system. The electronic part of thissystem was also built upon PC interface standard. The
information on the radioactivity level is displayed digitallyand graphically on the PC monitor. Data can be saved on
the PC′s hard disk.
- Redesign and rearrangement of the control panels
and the control console in the control room. Due to using
modern components and equipment, the size and number ofcontrol panels were significantly reduced: 4 out of 7 panels
were removed but all the control and monitoring functionsof the old system were kept unchanged.
As a consequence, the new control system contains
two separate PC systems for information acquisition andprocessing, data storage and display, as well as for sending
alarm signals in order to control automatically secondary
devices such as electric pumps and valves.

the storage tank to the PC interface card. The third part is acontrol driver and motor for moving a potentiometer
whenever the liquid level changes. The front-end electronic
blocks are installed on the outside of the storage tank, at a
distance of about 100 m from the control room, where thePC system with add-on interface cards is located. The
block diagram of the 8-channel add-on interface card isshown in Fig. 2. There are a total of 3 such interface cards
used in the designed system. The level measurement
system is used for monitoring, measuring and displaying
information from 24 storage tanks, as well as for sending
control commands to output devices. There are different
units in each card. In the address decoder unit, a switching
method with a digital comparator on IC 74LS688 is usedthat permits easy change using address range. Theswitching 8-channel 8-bit ADC type ADC0809 has enoughaccuracy for this purpose. The 24-bit digital I/O port on IC
8255 and other buffers are used for controlling the status ofthe interface and sending alarm signals on lower and upperlevels.
Application software of the system permits the operators
to display both in graphical and digital modes. The monitor
of the PC is divided into various windows. The main
window in the upper area is for displaying 24 liquid levelmeasurement channels both alphanumerically

2.1 PC-based level measurement system
In general, the storage tank′s liquid level has to bemonitored. In total, there are more than 20 measuring
channels for the storage tanks in the station. The front-end
electronic blocks of each channel consist of three parts. The
first one is the sensor unit based on either a float orcapacitance method. The second part consists of voltage
buffer or converter and some amplifier stages in order tosupply a voltage value in relation with the liquid level ofFig. 2. Block diagram of the interface card forlevel measurement systemand using vertical bar-graphs with separate columns. The
upper and lower level alarm set of each channel are also
indicated on the window. The alarm set values can bedefined by the operator from his PC keyboard whenneeded. When any level measurement value exceeds thepreset value, a visual alarm indication appears on thecorresponding column and at the same time a control signal
is sent to output devices for switching on or off an electric
pump and/or a valve. The remaining windows in the lower
area of the PC monitor are used to display pH andconductivity measurement values of the liquid waste before
and after treatment, flow rates of filters, etc.
alphanumercially and using horizontal bar-graphs.
2.2 PC-based dosimetry system
The multi-channel dosimetry system [2] for area
monitoring at the liquid waste treatment station is based ona set of individual measuring probes. The system is used
for detection and measurement of ambient gamma radiation
as well as for processing, displaying and storing
information on radioactivity level at 8 different positions inthe station where technological equipment is installed. The
hardware of the system consists essentially of three parts:
probes, central unit and alarm devices. As sensing
elements, 8 GM gamma counters with shaping circuits areused. The electronic blocks of the central unit including acounter/timer board using programmable timer/countertype I8253 were built upon 8-bit add-on standard interface
cards to PC through extension slots of the PC. An
intermediate relay board to control the alarm devices islocated in the same PC crate in order to access the power
supplies. The system has the following functions:- Continuously measuring radioactive level at 8 points- Displaying count rate/dose rate in digital and graphic
form on the PC monitor- Giving light and sound warning signals whenever theradioactive level exceeds the setting values- Recording information on count rate/dose rate into
PC hard disk.
In the counter/timer board of the central unit, three IC
I8253 are used to set up to 9 counting channels and one IC
I8253 is used as a programmable timer. Each counting
channel has maximum capacity of 216. 8 channels are
simultaneously counting from the ″Start command″ fromthe computer and stopped counting by the timer
interruption. In our case, a quartz generator 1 MHz is used,
therefore the interval range of the timer from 20 - 232 µs canbe set from the PC keyboard. The counter/timer board isconnected to the computer via add-on interface cards using
either an interrupt function (IRQ3) or a flag setting (DB0on the data bus of the PC).
Whenever the radioactive level at any monitoring
point exceeds a set level, the control programme from thePC sends a signal to the intermediate relay board to warn
by lamp and buzzer at the detector as well as in the control
room.
Application software permits the system to display bothin graphic and digital modes. For this purpose, the screenof the PC is divided into four windows where each one canFig. 3. Block diagram of the dosimetry system
display three channels but only one is visualized at eachtime. It means that, at any time, four channels arevisualized, but the operator can see any other channel bypressing a pre-assigned function key. In each window, thevertical axis indicates the signal amplitude calibrated incounter/dose rate and the time information is indicated on
the horizontal axis. As the trace displaying the current
radiation value reaches the extreme right end of thewindow, the display is reset for a fresh record. In the casethat the signal value of any of the radiological channels
exceeds the preset level, a visual alarm indication appearson the corresponding window. The alarm can be reset by
the operator but the visual indication remains as long as thealarm condition persists.
The smoothing technique used in the processing
programme is of digital count rate type. It is a combinationof the self-adapting and the floating mean techniques.
3 Conclusion
The renovation and modernization of the control system
for the liquid waste treatment station were carried out bystaff members of the NRI during the past two years. The
new system was checked and put into operation in May
1997. Until now the system has been working with highreliability, is convenient for the users and is easy to repair
and maintain.
In the past five years, a number of computer andmicroprocessor-based systems have been designed,
developed and used at the NRI for the liquid waste
treatment station control system, the reactor control andinstrumentation system and other systems for physics
experiments [3]. The main configuration of each system
contains sensor elements; functional electronic modules,
each having a specific application; central computer ormicroprocessor unit; and output devices. These
autonomous systems are working on their separate
hardware and software architectures. In the near future,they will be linked for system development, improvement
and more efficient utilization in the framework of a local
computer network system.
The use of personal computers as an operator aid has
been found in NRI to be highly beneficial for operation andmaintenance related tasks and has a potential for
application in many different areas.
References[1] Nguyen Thi Nang et al. Treatment and conditioning ofradioactive wastes at Dalat Nuclear Research Institute.
International Workshop on Waste Management.
Malaysia, October 1996.

[2Tran Khac An et al. PC-based data display anddosimetry systems. Conference on nuclear physics andrelated topics. Hanoi, 13-15 March 1994.
[3] Nguyen Nhi Dien et al. Application of personal
computers to the control system of the Dalat nuclear
research reactor. IWCSMSA’96 Workshop. KEK,
Tsukuba, Japan, 11-15 November 1996.