Principal Research Results

Water Chemistry Guidelines of Light Water Reactors

BackgroundIn recent years,various technical options of water chemistry appear, and water chemistry technology is further diversified
and complicated by the increase in nuclear power plants of different generations. For this reason, it is required to clarify systematicallythe knowledge, experience, and technical bases about the water chemical management cultivated so far. Moreover, it is also required
to pass on water chemical management technology correctly to the next generation. Based on such a background and the request ofFederation of Electric Power Companies, Central Research Institute of Electric Power Industry drew up light water chemical guidelines.

Objectives
For the purpose of realizing the water chemistry operation guide of light water reactor power plants, to systematically compile knowledge about the water chemistry of Japanese light water reactors, which are at a globally high level, and to draw up BWR
and PWR water chemistry guidelines.

Principal Results
1. Constitution of light water chemistry guidelines.
BWR water chemistry guidelines consist of three volumes, i.e., (1) “BWR water chemistry guideline”, (2) “BWR waterchemistry at startup and shutdown, a cold-and-warmth shutdown, and hydrogen injection”, (3) “Zinc injection and Noble-metals injection” aiming at the reduction of radiation exposure and SCC inhibition, as shown in Table -1. On the other hand, PWR water chemistry guidelines consist of four volumes. From a viewpoint of the integrity of nuclear reactor structural material and fuel cladding, (4)“PWR primary water chemistry guideline”, (5) “ PWR primary water chemistry guideline at startup and shutdown “ were drawn up.
From the viewpoint of steam generator integrity and dose-rate reduction, (6) “PWR secondary water chemistry guideline” and (7) “PWR secondary water chemistry guideline at startup and shutdown” were drawn up.
2. BWR water chemistry guidelines
As an example, the limited value of water qualities during the normal operation time is shown in Table -2.
A setup of limited values of water qualities was defined from the three points of view, i.e., the integrity of structural material
integrity, and the soundness of fuel cladding, and the exposure reduction, and the technical bases were specified. The permissible maximum value of water qualities was defined in order that “a level 1” might maintain the integrity of a plant, and “a level 2” are the limited values for maintaining the integrity of a plant.
“The recommendation value 1” is a desired limited value defined in order to usually maintain an operating standard. On theother hand, “the recommendation value 2” is a policy objective value on the water chemistry control which can be attained over a long
period of time in good operational condition. Concerning the new technology of Zinc injection and Noble-metals injection, it focusedon arranging the present knowledge.
3. PWR water chemistry guidelines
As an example, the recommended pH control method of PWR primary coolant is shown in Fig. -1. The pH control method
was determined from the three points of view, i.e., the integrity of nuclear reactor structural material, the soundness of fuel cladding,and the dose-rate reduction. On the other hand, the limited value of secondary system was defined from a viewpoint of the integrity ofa steam generator and secondary system instrument.

Future Developments
Seven guidelines drawn up so far will be revised and combined together into three volumes: BWR, PWR primary system,and PWR secondary system. Moreover, water chemistry standardization will be attained about “water quality analysis”, “water chemical management”, and “corrosion potential distribution in LPR and in-core”.
Main Researchers:
Hideo Hirano, Ph.D., Senior Research Scientist and Masafumi Domae, Ph.D., Research Scientist, Materials Functions and Mechanism
Creation Sector, Materials Science Research Laboratory
Reference
1. BWR Water Chemistry Guideline - Zinc injection and Nobel Metal Chemical Addition - CRIEPI Report W03802 (March, 2004)(InJapanese)
2. PWR Water Chemistry Guideline - Start-up and Shutdown- CRIEPI Report W03803 (March, 2004)(In Japanese)82

5. Nuclear - Improvement of economics and reliability of LWR power generation

Table 1 Constitution of Light Water Chemistry Guidelines

Operation Condition

Type ofReactor

Normal Operation
BWR

Startup and Shutdown, Cold- and Warmth- Shutdown,
Hydrogen Injection
Zinc Injection, Nobel Metal Injection

PWR

Primary
SystemNormal Operation
Startup and Shutdown

SecondarySystem

Normal Operation
Startup and Shutdown

Table 2 Water Chemistry of BWR coolant
Control ItemLevel 1

Level 2

Recommended
Value 1

Recommended
Value 2

Measurement
Frequency

Item

Unit

Conductivity

μS/cm

≦ 10

≦1

≦ 0.4

≦ 0.15

Continuation

pH−−Ｄ(25℃)

4 〜 10

5.6 〜 8.6―ppb≦ 500≦ 100―

≦ 15

Ｗ

SO42―

ppb

―

―

≦ 100

≦ 10Ｍ

Silicappb――≦ 1,000―

Ｗ

Dissolved
Oxygen

ppb

―

―

≦ 400

―

Ｄ

Impurities ofMetalppb――≦ 200―

Ｗ

I 131

Bq/g

―

―

―

―

Ｗ

Boron

ppb

―

―

≦ 200―

Ｍ

Notes；D：１time/day-measurement, W：１time/week-measurement, M：１time/month-measurement

StructuralMaterial Integrity

Dose-Rate
Reduction

Fuel Cladding
Integrity

Combination of B
and Li concentration

Optimal pH(Combination of B andLi concentration)

Upper Limit ofLithium content

4Lithium Concentration (ppm)

Cl

Li = 3.5 ppm
pH = about 6.8 (285℃)
Li Concentration + 0.4 ppm

3

Li = 2.2 ppm
2
Li = 1.8 ppm
101800

1500

1200

900

6003000

Boron Concentration (ppm)

Fig.1 Recommended pH control method of PWR primary Water

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