Copyright 2008, Toshiba Corporation. CDCC PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., Reduction of Radiation Exposure at Aged BWR Plants by Water Chemistry Nov Hidehiro Urata and Kenji Yamazaki Toshiba Corporation 1/23

2/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 Content 1.Background and Introduction 2.Water Chemistry Approach and Results 3.Conclusion

3/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 Roles of Water Chemistry at Operating BWRs  Increase of radiation level due to ageing and up-rating of plant and higher burn-up fuel implementation is a concern regarding roles of water chemistry at operating nuclear power plants.  Main purposes of water chemistry –Radiation level reduction Improvement of work environment Reduction of radwaste – Improvement of safe and reliable operation Structural material integrity Fuel integrity Background and Introduction

4/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 At aged BWR plants, radiation dose reduction for maintenance repair works, and mitigation of SCC are most important roles of water chemistry Optimum water chemistry Radiation reduction Secure and Reliable Operation Fuel material integrity Structural material integrity Radwaste reduction Radiation dose reduction Background and Introduction

5/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 From Y. Hayashida 2007 ISOE Asian Symposium, Seoul Korea Sep Radiation Exposure (Person Sv) Outage (days) Oversea BWR （ Good case) Japanese BWR A: Reduction of works and Improvement of works B: Improvement of radiation environment B A Rationale Exposure Reduction by A+B C: Possible effects of up- rating and higher burn-up Importance of radiation level reduction Background and Introduction

6/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 Water chemistry for control of recontamination under low ECP Reduction of dose rate Hydrogen Water Chemistry Dose rate Dose rate increase Water chemistry modification Operation Objective Chemistry Remedy Mitigation of SCC Modification of oxide Increase of Co-60 Conc. Chemical Decontamination Influence on Dose Rate Factors Recontamination Decon. Operation Dose rate Factors affecting radiation level buildup at aged BWR plants Background and Introduction

7/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 Low DFMedium DF High DF DF ( Decontamination Factor) Dose before decon/after decon) Re-contamination Rate (arbitrary unit) Re-contamination after chemical decontamination depends on “ Decontamination Factor”. Background and Introduction Medium Decontamination factor is preferable but not always obtained. Mechanism of the dependence should be evaluated.

8/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 Water Chemistry Approach and Result 1.Issues to be evaluated (1) Dependence of Recontamination on Decon. Factor (2) Water Chemistry for suppression of radiation level build up after water chemistry modification and chemical decontamination 2. Approach (1)Experimental approach by using BWR simulation loop (2)Parameters –Low ECP (ex. HWC) –TiO2, Zn (countermeasures)

9/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 Water Chemistry Approach and Results Experimental (1) Procedure Specimen preparation Pre-filming Chemical decontamination Co-60 deposition test Measurement/Analysis (TiO 2 treatment) Reduction (Oxalic acid) Oxidation (ozone) Reduction (Oxalic acid) HCl Repetition Oxalic acid ： 2000ppm ， 95C Ozone ： 3ppm,80C Hydrochloric acid ： 2mol/l,80C

10/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., mm 10mm 0.3mmt SUS316L Water Chemistry Approach and Results Experimental (2) Co-60 deposition test loop

11/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 HWC m-HWC The V-shape dependency was reproduced. Dependency is much strong under HWC. The V-shape dependency was reproduced. Dependency is much strong under HWC. Co-60 W/O Zn W/O TiO2 Water Chemistry Approach and Results Results (1) Dependence on decon. factor Low DFMedium DFHigh DF On Stainless steel specimen HWC FW DH>1.0ppm m-HWC FW DH<0.5ppm

12/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 Low DFMedium DFHigh DF After decon Oxide removed unevenly No residual oxide But rough After Co-60 test Large oxide evolved infrequently Smallest Oxide and uniform Large oxide evolved No decon Oxide deposited uniformly Not changed Water Chemistry Approach and Results Results (1) Dependence on decon. factor

13/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 Low DF Medium DFHigh DF After decon After Co-60 test Residual oxide causes the irregular oxide growth and enhances Co-60 deposition and migration Oxide film uniformly formed suppress further corrosion and Co-60 deposition Rough surfaces causes the increase of surface area and oxide growth and enhance the Co-60 deposition ： Cr 2 O 3 ： 60Co ： Fe 2 O 3 ： NiFe 2 O 4 Chemical decontamination with adequate control is important to suppress re-contamination. Water Chemistry Approach and Results Results (1) Dependence on decon. factor

14/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 Zinc is effective for suppression of recontamination under both HWC and m-HWC, even after inadequate decon. Water Chemistry Approach and Results Co Low DF Medium DF High DF On stainless steel specimen) HWC- W/O Zn HWC- With Zn m-HWC-W/O Zn m-HWC- With Zn Results (2) Control by water chemistry - Zn -

15/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 Low DFMedium DFHigh DF After decon After Co-60 test W/O Zn With Zn Oxides are formed uniformly and closely packed by zinc injection. Water Chemistry Approach and Results Results (2) Control by water chemistry - Zn -

16/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 TiO2 can suppress Co-60 deposition to very low level and has synergy effect with Zn. Water Chemistry Approach and Results Co-60 ＊ Low DFMedium DFHigh DF On Stainless steel specimen Ref No treatment TiO2 deposition TiO2 deposition and Zn Results (3) Control by water chemistry - TiO2 -

17/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 Low DFMedium DFHigh DFRemarks Ref. No water chemistry counter measure TiO 2 TiO2 covers surfaces and smaller corrosion oxides are produced. TiO2 + Zn Water Chemistry Approach and Results Results (3) Control by water chemistry - TiO2 -

18/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 HWC + ZnM-HWC and TiO2 Surface morphology Suppression effect on Co-60 deposition Zn prevents oxide film growth. ZnCr 2 O 4 is formed in the inner oxide layer and prevent Co-60 migration. (1)TiO 2 layer may block the migration of Co-60 and prevent CoFe 2 O 4 formation (2)Radicals produced by TiO 2 may oxidize Fe 2+ to Fe 3+ and prevent ferrite formation. ： 60Co ： Fe 2 O 3 ： NiFe 2 O 4 ： Cr 2 O 3 ： TiO2 ：Ｚ nCr 2 O 4 Water Chemistry Approach and Results Results (3) Control by water chemistry - TiO2 -

19/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 Before ferrite (CoFe2O4) formation, Fe2+ can be oxidized to Fe3+ and Fe2O3 is formed. Further discussion is needed to establish the mechanism for Co-60 deposition prevention. (Cathodic reaction) 2O 2 + 8H + +8e - -> 4H 2 O TiO 2 Heat Excitation h+h+ e-e- SS H 2 O + h + -> OH ・ + H + OH - + h+ -> OH ・ O 2 + e - -> O 2 - (Anodic reaction) Fe ->Fe e - 3Fe H 2 O ->Fe 3 O 4 + 8H + + 8e - SS Possible explanation on role of TiO2 Water Chemistry Approach and Results

20/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 Corrosion Potential (ECP) Current Oxidation ofSteel Reduction ofOxygen Reduction of ECP Phto-electricCurrent TiO2 for SCC Mitigation K. Takamori, International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, Aug Snowbird Utah TiO2 technology for BWR SCC mitigation is developed by Toshiba and TEPCO. ECP of stainless steel is decreased by TiO2 with photon, or without photon under low-HWC chemistry.

21/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 Conclusion - 1 Effects of Decontamination factor on re- contamination 1.The V-shape relationship between Co-60 deposition and DF could be clearly seen, especially in case of HWC condition. 2.In case of low DF, poorly protective residual oxides accelerate the re-contamination. 3.Under HWC condition, recontamination with inadequate DF is accelerated and thus control of decontamination is particularly important.

22/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008 Water chemistry control 1. Zn injection can effectively suppress Co- 60 deposition regardless of DF. 2. TiO2 can effectively suppress Co-60 deposition regardless of DF. 3.TiO2 technology is a promising candidate for simultaneous accomplishment of SCC mitigation and radiation exposure reduction. 4.Synergy effect of TiO2 and Zn can be seen. Conclusion - 2

23/23 Copyright 2008, Toshiba Corporation. CDCC , PSN ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008