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Vol.1, No.4, NT15 EJAM (1-4-NT15) - PWR Secondary Water Chemistry Control Using High pH with Ethanolamine

PWR Secondary Water Chemistry Control Using High pH with Ethanolamine

The Kansai Electric Power Co., Inc.

KEYWORDS：
PWR, Secondary water chemistry, Feedwater, Steam generator, Sludge, Heat exchange, Demineralizer, Ethanolamine, pH

1. Technical summary

Classification
(I: Inspection, II: Repair, III: Replacement, IV: Preventive Maintenance, V: Others(Operation Management))

Secondary water chemistry control during plant operation has an important effect on steam generator (SG) maintenance in pressurized water reactors (PWRs). It can mitigate the degradation of the heat exchange coefficient or heat rate due to the formation of scale deposits and sludge accumulation in SGs (Fig.1). Operation using high pH secondary water chemistry control with Ethanolamine (ETA) is one of the main methods used to reduce corrosion product transportation to the secondary side of the SGs and thereby maintain the long-term integrity of the SGs. The Kansai Electric Power Co. (KEPCO) is introducing high pH operation using ETA after it eliminated the copper based materials in the secondary systems of its plants.

Fig. 1 Schematic diagram of the secondary system (Takahama unit 1)

Based on the data collected during the field tests, the use of ETA contributed to reduced transport of iron from the secondary system steam drain lines and a resulting lower concentration of iron in the feedwater system without a significant increase in the concentrations of other impurities (Fig 2). This was facilitated by the lower volatility of ETA at high temperatures and the consequential increased concentrations in the steam drains as compared with other pH control chemical reagents (Table 1).

EJAM1-4-NT15-Fig.2_Field_data_of_high_pH_chemistry_and_locations_of_the_components_contributing_to_the_decrease

Fig. 2 Field data of high pH chemistry and locations of the components
contributing to the decrease in the transport of iron

Table 1 Representative chemical reagents for the pH control
in the secondary side of PWR

Chemical reagent

Ammonia

Morphorine

Ethanolamine

Dimethylamine (DMA)

Formation

NH₃

	NH

	O

		H		H
		\|		\|
H₂N	—	C	—	C	—	OH
		\|		\|
		H		H

		H
		\|
H₃C	—	N	—	CH₃

Volatility at 150℃

9.6

0.78

0.26

13.2

2. Scope

(1) Components: Secondary coolant circulating system in a PWR

(2) Material: Material used for the components (e.g., heat exchangers, piping) in the secondary system; this includes alloys 690 and 600 (nickel based alloys), austenitic stainless steels, carbon steels, etc.

(3) Condition: Chemical additive conditions for the plant which implemented high pH chemistry are given in Table 2. The resulting feedwater chemical conditions with the high pH chemistry are shown in Table 3.

Table 2 Conditions for water chemistry control of high pH with ETA

Chemistry Control Item	Conditions
Percentage of flow through the condensate demineralizer^*1	Approx. 10%
Concentration^*2 of chemical additives in the feedwater
Hydrazine	> 100 ppb
Ethanolamine	9 ppm

*1:	After the period required for the stabilization of the plant conditions, condensate flow is partially bypassed around the demineralizer system.
*2:	The target value is achieved by pump injection of the chemical solution.

Table 3 Chemical conditions in the feedwater

Sampling Location	Items	Value^*
Feedwater	pH Dissolved oxygen Iron Copper	9.7～9.8 < 5 ppb 1～2 ppb < 0.2 ppb

*:	The value is the achievable target condition based on analysis data obtained during field tests at Takahama Unit 1 for high pH water chemistry control using ETA.

3. Features

(1) Low concentration of iron in the feedwater
As described in the technical summary, the high pH secondary water control using ETA resulted in a very low feedwater iron concentration. The concentrations of iron and copper in the secondary water are shown in Fig. 3 as a function of the change in water chemistry control and feedwater pH.

(2) Amount of sludge removed from SGs
As a result of the reduced iron transport to the SGs, less sludge was removed from the SGs during the refueling outages.

*:	High pH chemistry was implemented after copper containing materials (e.g., brass tubes) were replaced.

Fig. 3 Concentrations of iron and copper in the secondary water
with a change of feedwater pH

4. Examples of Application

The KEPCO plants that have finished replacement of the copper material in their secondary systems are preparing for the application of this water chemistry control using ETA.

5. Reference

[1] H. Ikoma, et al., "The Application of High pH Operation to the Secondary Water Chemistry at Takahama-1", Proceedings of international conference on water chemistry of nuclear reactor systems, Jeju, Korea, (2006).
[2] T. Shiomi, et al., "The application of ethanol amine in Kansai’s plants", Proceedings of 2002 EPRI workshop on condensate polishing, New Orleans, USA, (2002).
[3] N. Higuchi, et al., “Overview of the use of Ethanolamine in Mihama unit 2”, Proceedings of 1998 JAIF International Conference on Water Chemistry in Nuclear Power Plants, Kashiwazaki, Japan, p.599, (1998).

6. Contact

Japan Society of Maintenology (ejam@jsm.or.jp)


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