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Identification and quantification of organ species in power station feedwater
Author(s)
Stwayi, Mandisi Buntu
Date Issued
2013
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
It is possible for organic material to enter the steam/water cycle of a power station in number
of ways. Make-up water, chemical additives and ion exchange resin leachates are usual
sources of organics entering the system during normal power operation. Other sources
include cleaning agents, lubricants, bacteria and condenser inleakage that can enter the
steam/water by contamination during outages or damaged plant during operation.
Although the steam/water cycle is a closed loop, water and steam is lost by imperfection in
design and construction, material degradation and defective components. Normal operation
includes interventions that occasionally require or result in a loss of steam and / or water
from the secondary system. From several strategic positions on the secondary cycle on both
the water and steam lines, continuous sample flows via the sampling system to the online
analysers and grab sampling points. All of operational losses of steam and water require the
secondary system to be made-up. Make-up water is the source of natural organic matter
(NOM) that enters the system during normal operation. Water treatment that includes
chlorination for disinfection causes the formation of disinfection by-products (DBP) and of
specific interest are organochlorides such as chloroform as a product f ram reaction of
chlorine with NOM and microorganisms.
Organochloride breaks down under the plant thermohydraulic conditions resulting in the
.increase of the chloride ion concentration. Chloride in contact with metal surfaces has a
detrimental effect on the structural integrity for power plants. lnconel, a metal alloy consisting
of nickel, chromium and iron is used for the manufacture of steam generator (SG) tubes of
PWRs worldwide because of its physical properties. SG tubing is by far the most vital
component of this type of nuclear power plant and lnconel is susceptible to chloride induces
pitting corrosion. Chloride also causes stress corrosion cracking (SCC) in austenitic stainless
steels that constitute the balance of the plant systems. For these reasons it is imperative that
plant chemists must continue to strive to keep the chloride concentration as low as
achievable.
Over the years it has been observed that high secondary make-up at Koeberg Nuclear
Power Station (KNPS) results in corresponding increased chloride levels in the steam
generators even though the make-up water tanks chloride analysis is low. The elevated
chloride concentration following high system make-up has been attributed to trihalomethanes
(THM) being present in the make-up water. Chemicals are added to the secondary circuit with the intent to establish the most favourable
chemical condition that will mitigate plant degradation by limiting corrosion mechanisms. It is
usual to have additives that control pH and dissolved oxygen in the secondary system of a
pressurised water reactor (PWR). Historically inorganic additives such as trisodium
phosphate and later ammonia have been used to control pH. Recent developments have
established that organic amines have superior properties and are often the preferred
additive. Plants that use amines add to the organic loading and this has consequences that
are important to consider.
In power plant chemistry ion exchange (IX) resins are used to remove impurities from the
process water. Ion exchange is extremely effective for retaining inorganic ionic species but
organic compounds are not readily retained. These IX resins are organic polymers and under
certain physical conditions break down resulting in the leaching of organic material into the
process water increasing the organic load.
For this work, water samples of the secondary cycle from PWR, KNPS, have been analysed
to gain a better understanding of the overall effect of organic material on the system
chemistry. During normal plant operation sources include NOM, chemical additives and ion
exchange resin leachates. This work focuses on the analysis and profiling of organic material
entering the system during normal operation with more specific focus on organochlorides
because of its potential detrimental effect on the plant construction materials.
In the attempt to identify and quantify organic species at KNPS methods for identification and
quantification of organic species at KNPS were developed and implemented. This was
achieved by purchasing Total Organic Carbon (TOC) analyser and also specific analytical
column were purchased and installed in the Ion Chromatography (IC) System to enable it to
have capabilities to quantify organic anions such as formate, acetate, oxalate and glycolate
in single run along with the inorganic anions. The TOC and IC work was performed at KNPS
while some of the samples were sent to various laboratories for further organic
characterisation and also for trihalomethanes (THM) analysis. Koeberg Nuclear Power
Station surveillance procedures were updated to reflect a surveillance requirement for TOC
in the water production plant systems.
This research project has also initiated various other projects at KNPS. One of the projects
was the anion resin routine clean-up process where the organic material, that fouls the anion
resins are removed by soaking the resin in a solution containing 5 % sodium chloride and 2
% sodium hydroxide and this process is also known as a "brine washed". Procedures were compiled and they are currently being utilised by KNPS chemistry staff. Another project that
was initiated was to replace the anion resins in the water production plant.
This project has also initiated a strategy and recommendation on how KNPS should deal with
poor water quality and these recommendations were communicated to Engineering Group so
that appropriate modification may be initiated. TOG analysis was performed at various
strategic points around the water production plant and secondary systems to develop an
organic profile which had not previously been performed at KNPS.
of ways. Make-up water, chemical additives and ion exchange resin leachates are usual
sources of organics entering the system during normal power operation. Other sources
include cleaning agents, lubricants, bacteria and condenser inleakage that can enter the
steam/water by contamination during outages or damaged plant during operation.
Although the steam/water cycle is a closed loop, water and steam is lost by imperfection in
design and construction, material degradation and defective components. Normal operation
includes interventions that occasionally require or result in a loss of steam and / or water
from the secondary system. From several strategic positions on the secondary cycle on both
the water and steam lines, continuous sample flows via the sampling system to the online
analysers and grab sampling points. All of operational losses of steam and water require the
secondary system to be made-up. Make-up water is the source of natural organic matter
(NOM) that enters the system during normal operation. Water treatment that includes
chlorination for disinfection causes the formation of disinfection by-products (DBP) and of
specific interest are organochlorides such as chloroform as a product f ram reaction of
chlorine with NOM and microorganisms.
Organochloride breaks down under the plant thermohydraulic conditions resulting in the
.increase of the chloride ion concentration. Chloride in contact with metal surfaces has a
detrimental effect on the structural integrity for power plants. lnconel, a metal alloy consisting
of nickel, chromium and iron is used for the manufacture of steam generator (SG) tubes of
PWRs worldwide because of its physical properties. SG tubing is by far the most vital
component of this type of nuclear power plant and lnconel is susceptible to chloride induces
pitting corrosion. Chloride also causes stress corrosion cracking (SCC) in austenitic stainless
steels that constitute the balance of the plant systems. For these reasons it is imperative that
plant chemists must continue to strive to keep the chloride concentration as low as
achievable.
Over the years it has been observed that high secondary make-up at Koeberg Nuclear
Power Station (KNPS) results in corresponding increased chloride levels in the steam
generators even though the make-up water tanks chloride analysis is low. The elevated
chloride concentration following high system make-up has been attributed to trihalomethanes
(THM) being present in the make-up water. Chemicals are added to the secondary circuit with the intent to establish the most favourable
chemical condition that will mitigate plant degradation by limiting corrosion mechanisms. It is
usual to have additives that control pH and dissolved oxygen in the secondary system of a
pressurised water reactor (PWR). Historically inorganic additives such as trisodium
phosphate and later ammonia have been used to control pH. Recent developments have
established that organic amines have superior properties and are often the preferred
additive. Plants that use amines add to the organic loading and this has consequences that
are important to consider.
In power plant chemistry ion exchange (IX) resins are used to remove impurities from the
process water. Ion exchange is extremely effective for retaining inorganic ionic species but
organic compounds are not readily retained. These IX resins are organic polymers and under
certain physical conditions break down resulting in the leaching of organic material into the
process water increasing the organic load.
For this work, water samples of the secondary cycle from PWR, KNPS, have been analysed
to gain a better understanding of the overall effect of organic material on the system
chemistry. During normal plant operation sources include NOM, chemical additives and ion
exchange resin leachates. This work focuses on the analysis and profiling of organic material
entering the system during normal operation with more specific focus on organochlorides
because of its potential detrimental effect on the plant construction materials.
In the attempt to identify and quantify organic species at KNPS methods for identification and
quantification of organic species at KNPS were developed and implemented. This was
achieved by purchasing Total Organic Carbon (TOC) analyser and also specific analytical
column were purchased and installed in the Ion Chromatography (IC) System to enable it to
have capabilities to quantify organic anions such as formate, acetate, oxalate and glycolate
in single run along with the inorganic anions. The TOC and IC work was performed at KNPS
while some of the samples were sent to various laboratories for further organic
characterisation and also for trihalomethanes (THM) analysis. Koeberg Nuclear Power
Station surveillance procedures were updated to reflect a surveillance requirement for TOC
in the water production plant systems.
This research project has also initiated various other projects at KNPS. One of the projects
was the anion resin routine clean-up process where the organic material, that fouls the anion
resins are removed by soaking the resin in a solution containing 5 % sodium chloride and 2
% sodium hydroxide and this process is also known as a "brine washed". Procedures were compiled and they are currently being utilised by KNPS chemistry staff. Another project that
was initiated was to replace the anion resins in the water production plant.
This project has also initiated a strategy and recommendation on how KNPS should deal with
poor water quality and these recommendations were communicated to Engineering Group so
that appropriate modification may be initiated. TOG analysis was performed at various
strategic points around the water production plant and secondary systems to develop an
organic profile which had not previously been performed at KNPS.
Additional information
Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2013
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