AECL-5997

ATOMIC ENERGY MS& L'ÉNERGIE ATOMIQUEOF CANADA LIMITED V f i j T DU CANADA LIMITÉE

DEVELOPMENT OF AN AUTOMATED SYSTEM FOR

CANDU SECONDARY COOLANT CIRCUIT CHEMISTRY CONTROL

PROGRAM SUMMARY AND CONCLUSIONS

by

J. R. Dean and R. B. Stewart

Whiteshell Nuclear Research Establishment

Pinawa, Manitoba, ROE 1LO

April 1978

ATOMIC ENERGY OF CANADA LIMITED

DEVELOPMENT OF AN AUTOMATED SYSTEM FOR

CANDU SECONDARY COOLANT CIRCUIT CHEMISTRY CONTROL

PROGRAM SUMMARY AND CONCLUSIONS

by

J.R. Dean and R.B. Stewart

Whiteshell'Nuclear Research EstablishmentPinawa, Manitoba, ROE 1LO

April 1978 AECL-5997

DEVELOPPEMENT D'UN SYSTEME AUTOMATISE

POUR LE CONTROLE DE LA CHIMIE DU

CALOPORTEUR SECONDAIRE DES REACTEURS CANDU

Sommaire du programme et conclusion

par

J.R. Dean et R.B. Stewart

RESUME

Ce rapport est un sommaire des travaux effectués pour développerun moyen de contrôle automatisé de la chimie du caloporteur secondaire desrpacteurs CANDU de 600 MW(e) utilisant des analyseurs et un mini-ordinateuren lisr.e. Les travaux de développement ont été effectués en coopération avecla Saskatchewan Power Corporation de Estevan. Les résultats et les conclusionsdu programme sont inclus ainsi que les recommandations pour un prototype dansun générateur de vapeur de réacteur CANDU canadien de 600 MW.

L'Energie Atomique du Canada, LimitéeEtablissement de Recherches Nucléaires de Whiteshell

Pinawa, Manitoba, ROE 1L0Avril 1978

EACL-5997

DEVELOPMENT OF AN AUTOMATED SYSTEM FOR

CANDU SECONDARY COOLANT CIRCUIT CHEMISTRY CONTROL

PROGRAM SUMMARY AND CONCLUSIONS

by

J.R. Dean and R.B. Stewart

ABSTRACT

This report is a summary of work done to develop a means forautomated control of the secondary coolant chemistry of CANDU 600 MW(e)power reactors using on-line analyzers and a minicomputer. The developmentwork was carried out in cooperation with Saskatchewan Power Corporationat Estevan. Results and conclusions of the program are included, as arerecommendations for a prototype installation in a domestic CANDU 600 MWsteam generator.

Atomic Energy of Canada LimitedWhiteshell Nuclear Research Establishment

Pinawa, Manitoba, ROE 1L0April 1978 AECL-5997

CONTENTS

Page

1. INTRODUCTION

1.1 GENERAL 11.2 BOILER-TUBE CORROSION 21.3 AECL APPROACH TO STEAM-GENERATOR CHEMISTRY CONTROL 31.4 CONGRUENT PHOSPHATE TREATMENT (CPT) 31.5 CHEMICAL SPECIFICATIONS FOR FEEDWATER AND BOILER WATER 4

DURING LEAKING AND NON-LEAKING CONDENSER CONDITIONS

2. PROGRAM FOR THE DEVELOPMENT OF AN AUTOMATED SYSTEM 6

3. THE EXPERIMENTAL PROGRAM 8

4. SUMMARY OF RESULTS OF THE DEVELOPMENT WORK 22

5. RECOMMENDATIONS FOR INCORPORATING THE AUTOMATED CONTROL 23SYSTEM IN A PROTOTYPE REACTOR INSTALLATION

6. APPROXIMATE COSTS OF AN AUTOMATED CHEMISTRY CONTROL 24SYSTEM FOR A CANDU 600 MW STEAM GENERATOR

7. CONCLUDING REMARKS 25

ACKNOWLEDGEMENT 25

1. INTRODUCTION

1.1 GENERAL

Failures of steam-generator tubes have been known to occur in

power stations throughout the world. In a fossil-fired generating station

the result is a shutdown for tube-repair or replacement. In a CANDU nuclear

reactor, such a failure could be more costly, because in addition to the

outage, there may also be isotopic degradation of valuable heavy water. The

prime cause of failures is localized corrosion, a term which includes pitting

corrosion, crevice corrosion and stress-corrosion cracking. Boiler-tube

failures in CANDU1s have been very rare, their performance in this regard

being much superior to the world average for nuclear power plants.

The CANDU PHW* has two separate heat transport systems, with

heavy water circulating in the primary heat transport side and natural water

in the secondary side. Both systems require precise chemical controls, the

ultimate aim of which is to minimize metal corrosion. Corrosion on the primary

side can lead to activity transport. Corrosion on the secondary side can lead

to boiler-tube failure antff breakdown of the barrier between the two systems.

The chance of such corrosion is greater in those CANDU 600 MW reactors which

will make use of saline wkter for condenser cooling.

Atomic Energ^ of Canada Limited - Power Projects, designers ofi

the CANDU 600, recognized that automatic control of the feed and boiler water

chemistry would give greater assurance of station reliability. Their desire

for close control was influenced by the choice of a relatively new material,

Incoloy 800, as the material of boiler-tube construction. There was also

evidence in the indust/ry that the probability of failures increases with

increasing unit size and rating. CANDU 600 boilers will be larger, operate

at higher températures and higher heat fluxes and use different construction

materials than the boilers on which most of AECL's experience is based.

* CANada Deuterium Uranium - pressurized Heavy Water

- 2 -

With this in mind, the Analytical Science Branch of the Whiteshell

Nuclear Research Establishment (WNRE), already experienced with in-line

analytical instrumentation, was asked by AECL Power Projects Division to

devise and demonstrate a scheme to sample, analyze and control the chemistry

of the steam generator automatically. The development of a system for this

purpose is summarized in this report.

1.2 BOILER-TUBE CORROSION

The two fundamental requirements for accelerated corrosion of

boiier-tubes are (1) impurities in the boiler water which become corrosive

when concentrated, and (2) an impurity-concentrating mechanism. Water chem-

istry conditions in certain regions of a steam generator can deviate substan-

tially from the bulk-water chemistry specifications. For example, when boil-

ing occurs within a porous deposit on the tubes, a concentrating mechanism

is provided by evaporation and retardation of diffusion. In such situations,

the presence of strong solutions of sodium hydroxide has been found to cause

"caustic embrittlement". Acidic conditions are equally undesirable.

Minimization of boiler-tube corrosion is achieved, according to

one school of thought, by maintaining high purity of feedwater and boiler

water. Maintenance of high purity reduces formation of deposits on the tubes

or support plates and eliminates species that become corrosive when concen-

trated. According to a second view, it is impractical to prevent potentially

corrosive species from entering the boiler water, and it is thus feasible

only to counteract the effects of such species by adding a non-corrosive

buffering chemical such as sodium phosphate. Sodium phosphate is beneficial

in that it causes calcium or magnesium ions to precipitate as phosphates

rather than to deposit on the tubes as sulphate and silicate scales. The

phosphates are less adherent and can be more easily removed from the boiler

by blowdown.

- 3 -

1.3 AECL APPROACH TO STEAM-GENERATOR CHEMISTRY CONTROL

Both approaches have merit and Atomic Energy of Canada Limited

(AECL) has decided to incorporate both into the chemistry control of the

CANDU 600 secondary water. In the absence of a condenser leak, the chemical

control will be by the "zero solids", or "all volatile treatment (ÂVT)" mode.

During this treatment, the pH of the feedwater is adjusted by addition of a

volatile amine such as cyclohexylamine. A low level of dissolved oxygen in

the feedwater is ensured by the addition of hydrazine which is also volatile.

During AVT, the boiler is unprotected if ingress of potentially corrosive

chemicals should occur. For example, if a seawater-cooled condenser should

leak during AVT, the system would be incapable of altering the tendency of

the boiler water toward acidic conditions. In this situation the alternative

to immediate shutdown of the station is the addition of phosphates, which

will offer some protection until the leak can be located and repaired. This

should be done quickly and is best accomplished by an automatic system using

continuous on-line sensors.

1.4 CONGRUENT PHOSPHATE TREATMENT (CPT)

When mono-, di- and tri-sodium phosphate are added to water, they

hydrolyze. If the correct proportions are maintained, a buffered condition

will result. The extent of buffering is described by the designation ZpZphos

Where Zphos - [ N a ] / CP0 4 and CP04

= t W + tH2PO4] + t H P 0 4 = ]

In simplest terms, this is defined as the ratio of moles of sodium associated

with the orthophosphate species and OH ions, to moles of orthophosphate.

Laboratory experiments carried out in the Soviet Union and the Unitea States

indicate that a Z value between 2.2 and 2.85 is desirable. AECL speci-

fications require the maintenance of 2 to 10 mg/kg orthophosphate and Zphos

of 2.2 to 2.6. Variations outside this range can lead to corrosive conditions.

The maintenance of orthophosphate at a low level is believed to minimize a

phenomenon known as "phosphate hideout".

Congruent phosphate treatment is maintained by phosphate additions

based upon analytical measurements of the orthophosphate content, and deter-

mination of the Z , from the pH of the boiler-water at 25°C and the ortho-

phos

phosphate concentration. A mathematical relationship exists among the three

variables. Figure 1.

1.5 CHEMICAL SPECIFICATIONS FOR FEEDWATER AND BOILER WATER DURING

LEAKING AND NON-LEAKING CONDENSEPx CONDITIONS

The present AECL chemical specifications for the feedwater in

systems using high nickel alloys for boiler tubes and copper alloys in the

feedtrain or condenser are:

Parameter

pH at 25°CDissolved 0 , yg/kgHydrazine, yg/kgIron, yg/kgCopper, yg/kg

Permissible Range

8.<10<<

.8 - 9.25- 201010

Desired Value

9.1< 510

< 10< 10

The chemical specifications for the boiler water during normal operation

are:

Parameter Permissible Range Desired Va]ue

pH at 25°C depends on amine solution usedFree caustic, mg/kg < 0.1 < 0.1Dissolved 0 , yg/kg < 5 < 5Silica, mg/kg < 5 < 5Total dissolved solids, mg/kg < 10 < 10

During a condenser leak, the boiler-water chemical specifications become:

Parameter

pH at 25°CPhosphate, mg/kgtNa]/Cp0 raolar ratio

Free caustic, mg/kgDissolved 0^, yg/kg

Fluoride & chloride, mg/kg

Permissible Range

8.5 - 10.62 - 102.2 - 2.6zero< 5

< 75

Total dissolved solids, mg/kg < 40

Desired Value

9.462.3zero< 5

as low as possible< 40

- 5 -

IÔ5 lô4mol/kg

IÔ3 l ô 2 lô1

10 100 1000 10000Totai Phosphate Concentration,

100000

FIGURE 1: Relationship of pH, orthophosphate concentrationand Zphos ' at 25"C.

- 6 -

2. PROGRAM FOR THE DEVELOPMENT OF AN AUTOMATED SYSTEM

Automatic analysis and control to meet the above specifications

are potentially more rapid, precise and reliable than manual control using

data provided by a laboratory. The main requirements of such a system,

which is intended to become part of the CANDU design for domestic use and

export, were determined to be:

- An ability to control the chemistry in the All VolatileTreatment mode,

- The reliable detection of a condenser leak and, if the leakis large enough, initiation of automatic control of theboiler using Congruent Phosphate Treatment (in the case ofseawater-cooled condensers, A.5 L/h of seawater was takenas the maximum tolerable leak rate).

It was also desirable to provide an ability to log data and diagnose system

behaviour, with the added advantage of giving the chemist a summary of past

steam-generator conditions at regular intervals or upon demand.

Early in the program, a design for the chemistry control system

for the CANDU 600 steam generator was proposed. Figure 2 shows a much sim-

plified version of this design. A central, dedicated mini-computer is the

basic component of the system. Chemical analysis information is fed to it

by commercial on-line analyzers located at strategic points on the boiler

circuit. Depending on the information from these analyzers, the computer

actuates valves which control the addition of appropriate chemicals at the

correct places. For example, operation of the phosphate system is such that

the automatic addition of phosphate to the boiler will begin when a cooling-

water leak is confirmed by a signal from the sodium analyzers. The computer

controls the phosphate concentration and the Z , set-points by feedback,

on the basis of information supplied by on-line, continuous analyzers meas-

uring the phosphate concentration and pH of the composite boiler blowdown.

In addition to initiating CPT control, the computer can log and display data

from all analyzers, interpret alarms, and execute preventive action to correct

Turbine

Ferromognetic detectorTurbidity, pH

OxygenHydrazine

Condenserextractionpumps

Boilerfeed pumps

FIGURE 2: Schematic of automatic chemistry control system proposed for a CANDU 600 steam generator,

abnormal system conditions. It was initially perceived that the hydrazine

and pH control would be?-/analog-based and would be independent of the computer.

In the actual event both were placed under direct digital control by the

computer.

Prior to installation of a prototype in a CANDU station, it was

desirable to test several aspects of the design. Saskatchewan Power Corpora-

tion expressed interest in such development work. At their Boundary Dam*

station two older boilers, Units 1 and 2, are operated continuously in CPT

chemistry and three others, Units 3, A, and 5, are operated continuously in

AVT chemistry. A cooperative program was undertaken to establish the con-

fidence necessary to proceed with a prototype nuclear station chemistry con-

trol installation.

3. THE EXPERIMENTAL PROGRAM

For reasons of efficiency and economy, it was believed unneces-

sary to demonstrate at Boundary Dam a complete chemistry control system.

Key elements were therefore selected for testing. These included the com-

puter , the control algorithm, sodium analyzers for leak detection, and the

on-line phosphate and pH instruments. In addition, commercial dissolved

oxygen analyzers were compared, hydrazine mixing and reaction rates were

studied and a hydrazine analyzer was tested on-line with feedback control.

The on-line calibration of analyzers, and data display and print-out were

also selected for demonstration. Concurrently a rapid on-line procedure for

phosphate analysis was developed.

A block diagram of the Boundary Dam Station test arrangement is

shown in Figure 3. Boundary Dam is a lignite coal-fired station with dust

and fly ash prevalent. The location and protection of the analyzers and

computer were carefully considered. The computer was housed in a clean,

air-conditioned room serving other station instrumentation. It was connected

Located at Estevan, Saskatchewan, Canada.

Analyser room unit#5• sample unit#5

Analyser room unit#4sample unit#4

to boiler #1

sample fromboiler #1

dosing pumps

alibratiounit

alibrationunit

Temporary analyser roomUiiit#lRelay room unit#5

calibrationunit I

FIGURE 3: Schematic of the Boundary Dam Station demonstration lay-out.

- 10 -

by communication cables to the analyzer rooms of Units 4 and 5, and to a

temporary plywood and plastic shelter housing the phosphate and pH analyzer

at Unit 1. The hydrazine and dissolved oxygen analyzers were located in

another clean instrument room. Data transmission lines of up to several

hundred feet in length were used successfully.

The computer had three tasks: data-logging, congruent phosphate

treatment selection, initiation and control, and automatic analyzer calibra-

tion. The data-logging mode* included sampling data from all analyzers once

per minute and checking for alarm conditions. The data collected at one

minute intervals were examined and discarded, except that at five-minute

intervals they were displayed on the screen, typed out on reports and stored

in the computer files. Figure 4 is an example of a five-minute report. The

computer values of sodium ion (ug/L) dissolved oxygen (yg/L), hydrazine (ug/mL),

phosphate (ug/mL) and pH are shown for three time periods of 11 May, 1977.

Also included in the listing is the Z . value for the Unit 1 boiler and thephos

temperature of the sample delivered to the sodium ion monitor at these times.

The number of significant figures is not an indication of precision and would

be 'rounded-off' to three in the prototype installation. Similarly, the ex-

ponential notation should be ignored. The stored data were typed three times

daily, to provide a summary report. Figure 5 illustrates the format and a

portion of such data.

In the CANDU prototype, sodium analyzers would monitor the con-

denser of the unit being controlled and the computer would initiate congruent

phosphate treatment upon confirmation of a leak. For the Boundary Dam tests,

it was necessary to simulate a leak by means of an electrical signal. This

meant that the sodium analyzer tests need not necessarily be done on the

boiler under phosphate control, and it was convenient to install these anal-

yzers on Unit 4 which operates in the all volatile treatment mode. When the

leak simulation signals were given to the computer, it demonstrated its ability

- 11 -

MONTR 1 8 : 2 9 0 5 / 1 1 / 7 7

NA+ IOXYGNHYDRZZPHOSP04PHTEMP

MONTR

1269E007.8274E00

1.1724E012.3166E0H

9.83 72E009.4985E00

6.B873E01

18:33 05/11/77

NA+OXYGNHYDRXZPHOSPO4PHTEMP

MONTR

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I.1551E012.3103E00

9.8772E009.4918E01

6.0&73E01

18:38 05/11/77

NA+ 1.1124E00OXYGN 7.7104E00HYDRZ 1 . 1 5 5 1 E 0 1ZPHOS 2.3245E00PO4 9.9173E00PH 9.S119E00TEMP 6.0873E01

FIGURE 4: TjT>ical five-minute report showing the concentrations (yg/L)of sodium ion, dissolved oxygen, hydrazine in Unit 5 feedwaterand levels of ZPHOS, orthophosphate (yg/mL) and pH in Unit 1boiler. The temperature (°F) refers to that of the sampleflowing to the sodium ion analyzer.

'ZPHOS1 refers to [Na]/Cp0 , the ratio of orthophosphate-derivedsodium ion concentration to the sum of phosphate ion concentrations.

- 12 -

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FIGURE 5 : Portion of typical eight-hour summary report.

- 13 -

to confirm the indication using its leak detection logic, then bring the

boiler into congruent phosphate chemical control by initiating the operation

of monosodium phosphate and disodium phosphate dosing pumps. Data from three

of the analyzers (sodium ion, dissolved oxygen and hydrazine) could be dis-

played on a cathode ray tube, as illustrated in Figure 6. The deviations

observable at 0030 and 0830 hours are artifacts of the automatic calibration

process. In a reactor installation it is foreseen that all analyzer data

could be displayed in this way upon demand. Figure 7 shows the format of the

automatic CPT control summary report. The last two columns indicate the Z ,pnos

set-point (SET Z) and the phosphate setpoint (SET P) during the time interval

reported.

Figures 8-12 show the results of several tests that were conducted.

In each figure, the upper plot is of the boiler water orthophosphate concentra-

tion with its scale on the left, and the lower plot is of the boiler water

Z , with its scale on the right. The time-of-day scale is across the bottom.

The setpoint values are marked with horizontal dashed lines and the start of

each test is indicated by a vertical arrow. It should be recalled that since

boilers #1 and #2 at Boundary Dam station operate continuously under CPT con-

ditions, our tests did not start at a zero PO, concentration but at some finite

small value.

In the first test, shown in Figure 8, an initial rapid injection

into the boiler was performed. The conditions in the boiler before the test

began were a phosphate concentration of 10.2 pg/mL and a Z , of 2.19. Thepnos

setpoints to be reached were 12.0 ug/mL and 2.30 respectively. Within about

15 min, the setpoint levels were reached after an overshoot of not more than

0.5 ug/mL in phosphate level and 0.01 in the Z , . A s stated in an earlierpnos

section, for the CANDU prototype, the permissible error between the actual

boiler conditions and the setpoint levels is ± 2ug/mL for phosphate and ±0.1for Z , .

phos

The next test, shown in Figure. 9, was also an initial injection.

In this test a decrease in the Z . level from its initial value of 2.33 tophos

a set-point at 2.25 was required. The phosphate level was to be increased

to 17 lig/mL from 14 ug/mL. Again the injection was very rapid and the change

was established to within 0.5 ug/mL and 0.02 Z , after about 20 minutes.phos

- 14-

FIGURE 6• A typical CRT display showing the behaviour of hydrazine,dissolved oxygen and sodium ion over a ten-hour period.

- 15 -

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FIGURE 7 : Portion of typical eight-hour report showing Congruent Phosphatecontrol behaviour (Set Z refers to the Zpj,os setpoint and Set Prefers to the orthophosphate setpoint).

'ZPHOS'= [Na]/C.PO,

- 16 -

130

12-0

11-0

% 10-0

PO4 setpoint

ZPHOS Setpoint

Test Injection

2-35

230

2-25

a.N

2-20

2-15

1430 1500 1530 1600

TIME, hours

FIGURE 8 : Illustration of the behaviour of the Congruent Phosphate Treatmentcontrol system during an injection test. (Increasing Z , noblowdown).

Z = [Na]/Cp0, > the ratio of orthophosphate-derived sodium ionconcentration to the sum of phosphate ion concentrations.

•15

'14

PO4 Setpoint

TestInjection

-PHOS Setpoint

1800 1900

TIME, hours (March 16,1977)

235

N

230

225

FIGURE 9: Illustration of the behaviour of the Congruent PhosphateTreatment control system during an injection test.(Decreasing Z , , no blowdown).

phos

- 18 "

Figure 10 illustrates a situation in which the initial injection

tailed to change the 2 , value to the setpoint level and the controllerphos

took over. The starting conditions were 12.2 yg/mL phosphate and Z 2.27.phos

During the course of this test, it was known that several disturbances were

acting upon the boiler. As intended by its design, the controller detected

these and managed within 2.5 hours to bring the phosphate level to its

setpoint and come within 0.03 of the Z . setpoint.phos r

Figure 11 shows the results of a test in which there was no blow-

down. Identifiable disturbances were imposed by causing the controller to

believe the phosphate pump rates were larger than they were in fact. The

initial conditions were 17 ug/mL phosphate and 2.2 Z , . The setpoints were

20 ug/mL phosphate and 2.30 Z , . The initial injection failed to cause thepnos

setpoints to be reached. However, the controller eventually adjusti.d to the"disturbances" and brought the Z , to within 0.01 of its setpoint. The

phos

controller allowed the phosphate level to overshoot by 1 yg/mL because of the

lack of blowdown and as a consequence of adjusting the Z ,

Figure 12 illustrates the long-term ability of the CPT control

system to maintain the PO, and Z . setpoints. Under controlled climb condi-4 phos

tions the boiler chemistry was to go from initial conditions of 7 yg/mL phos-phate and Z , 2.3 to setpoints of 10 yg/mL phosphate and 2.4 Z , . While

phos phos

the boiler blowdown was in continuous operation, the setpoints; were reached

after two hours. After 16 hours, the blowdown was inadvertently cut off. Up

to that time, it was counteracting the tendency of the boiler to increase in

phosphate level while trying to adjust the Z , precisely. After the shut-off

of the blowdown, the tendency of the controller to adjust the 7. , preciselyi prios

resulted in a 2 yg/mL overshoot on the phosphate level setpoint. However,throughout the test, the Z . value was maintained for 24 hours within 0.03

pnos

of the setpoint and the phosphate level was maintained within the ± 2 yg/mL

specification called for.

All analyzers in the system for a CANDU prototype installation

would have temperature and flow monitor and alarms, and automatic calibration.

In the Boundary Dam tests, the alarms were demonstrated for the sodium analyzer

- 19 -

2-45

— - 2-40

2-35

Q.N

-230

225

1530 1630 1730

TIME, hours (March 16,1977)

FIGURE 10: Illustration of the behaviour of the Congruent PhosphateTreatment control system during an injection and controlledclimb test.

- 20 -

22

"M 20

17

P04 Stlpoint

. à injection

Titt • kMdnn ond conlroHsd_ _ cSnbjjndir (blurted

conation.

zPH06 Stlpoint

• M S

- B40

- 238

- 225

220

1600 1700 1800 1900 2000 2100TIME, hour* (March 17,1977)

FIGURE 11: Illustration of the behaviour of the Congruent Phosphate Treatment control syst€during injection and controlled climb testing. (Controlled disturbances wereintroduced and boiler blorjdown was inoperative during this test.)

19 KO II M I» M t» M ÏT M !• » Si

Elapsed Time, Hours

FIGURE 12: Illustration of the long-term ability of the CPT control system tomaintain PO, and Z , setpoints.

- 22 -

only, while three analyzers (hydrazine, sodium and phosphate) were automatic-

ally calibrated. In response to computer signals, the calibration unit sequen-

tially fed the appropriate analyzer a sample to each of two standard solutions.

The analyzer response no these standards was used by the computer to calculate

a calibration scale for conversion of subsequent sample signals to the correct

corresponding chemical concentrations and units.

Detailed descriptions of the many tests done at Boundary Dam and

their results are provided in a series of eight project reports. Experi-

ence with commercial on-line analyzers is also noted and one report describes

the phosphate analyzer developed for this application. The computer and

analyzer system was operated for several months, culminating in automatic

feedback control of hydrazine and phosphate chemistries in operating boilers.

4. SUMMARY OF RESULTS OF THE DEVELOPMENT WORK

Upon completion of the experimental program at Boundary Dam, the

chemistry control was successfully demonstrated in operation to the representat-

ives of several provincial utilities. It was clear that such a system is of ji

interest to operators of both nuclear- and fossil-fuelled power stations and

that a technical foundation has been established which permits progression

to a prototype installation.

In summary, it was shown that:

- hydrazine concentrations could be maintained automatically anddissolved oxygen levels thereby controlled,

the computer algorithm was appropriate for control in either AVTor CPT modes and for the selection of CPT upon detection of acondenser leak,

the system could control the boiler's chemistry within set limitsfor an extended period of time,

- automatic calibration of the on-line analyzers could be donesuccessfully,

the data-logging, printout and display functions of the computerwere successful and an aid to good chemistry management.

- 23 -

5. RECOMMENDATIONS FOR INCORPORATING THE AUTOMATED CONTROL 3YSTEM IN APROTOTYPE REACTOR INSTALLATION

For a prototype installation on a CANDU 600, it is recommended

that the prototype system have certain specific characteristics:

1. It should be based upon digital control using a dedicated mini-

computer whose role will include data treatment and system

diagnosis. A cathode ray tube display capability is desirable.

2. The on-line analytical instruments should be automatically

calibrated by the computer.

3. Instruments providing control measurements should be dedicated

to one sample point. Instrument-switching between multiple

sample points is undesirable, because time lags are incompatible

with good chemistry control.

4. Samples should be reduced in pressure prior to entering the

instruments by the use of drag valves, and cooled by a two-

stage system which uses a roughing cooler followed by a more

precise finishing cooler.

5. The computer, analytical instruments and coolers should be

housed in an air-conditioned, humidity-controlled room.

6. The pH and hydrazine control should be by digital rather then

by analog means. Initial injection of hydrazine should be as

close to the condenser as possible. Specifically, the hydra-

zine control loop should be located between the deaerator outlet

and the high pressure heater outlets.

7. After installation of a CFT control system, assurance of its

readiness until the day it is needed must be considered.

- 24 -

There are several possibilities, the best being either routine

start-up of the pumps and check of the chemicals, valves, etc.

to maintain all components in a state of readiness, or control

of the boiler continuously in the CPT mode.

Responsibility for the data produced should be vested in the

station chemist.

6. APPROXIMATE COSTS OF AN AUTOMATED CHEMISTRY CONTROL

SYSTEM FOR A CANDU 600 MW STEAM GENERATOR

The installed costs of the proposed system in 1977 dollars

are estimated to be:

Sample conditioning system (including sample lines, cooling,pressure reduction and valves)

Analyzers and cabinets (sixteen analyzers)

Automatic calibration facilities (for six analyzers)and flow and temperature monitors (for sixteen analyzers)

Computer (including a keyboard, CRT for annunciation anddata display, and hard copier)

Computer programming and installation

Manual backup stations for pH and hydrazine control

Chemical feed system (including 4 tanks, 4 pumps, piping,motor starters, low-level alarms and valves

Analyzer room (to house computer and analyzers)

THOUSANDS OF

DOLLARS

$ 40

$ 60

$ 6

$ 60

$ 20

$ 4

$ 30

$ 20

TOTAL COST $240

- 25 -

7. CONCLUDING REMARKS

The development work carried out at Boundary Dam has demonstrated

that the automatic chemistry control system proposed for CANDU 600 steam gen-

erators is technically and financially practical. Such a system will give

steam-generator operators added confidence in the integrity of their boiler

components and make practical chemistry mode-switching. In addition, it

will provide station chemists with a better capacity for rapid management

of steam-generator chemistry. It is, nevertheless, important to note that in

the event of condenser leakage, the change of chemistry regime from all vola-

tile treatment to congruent phosphate provides temporary protection only, and

is not a substitute for repair.

ACKNOWLEDGEMENT

This project was the work of many people of Saskatchewan Power

Corporation and Atomic Energy of Canada Limited. We wish particularly to

acknowledge the contributions of Messrs. B. Baker, A. Whyte, R. Portman,

M. Myers, J. Westdal and G. Young.

The International Standard Serial Number

ISSN 0067-0367

has been assigned to this series of reports.

To Identify individual documents in the serieswe have «aligned an AECL-nnmber.

Please refer to the AECL-nnmber whenrequesting additional copies of this document

from

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