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Ageing Management Improvement of Open-cycle Cooling Water System for Operating License Extension in Qinshan Nuclear Power Plant

The Fourth International Conference on NPP Life Management

Lyon, France September 15, 2017

Zhang Feng

Research Institute of Nuclear Power Operation China National Nuclear Corporation

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Table of contents

1. Plant OCCW system introduction

2. Scoping and screening of OCCW

3. Ageing management review of OCCW

4. Ageing management improvement of OCCW

5. Conclusions

Nuclear Power Plant

Units under operation

Units under construction Until 17th of Sep, 2017

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1. Plant OCCW System Introduction

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Reactor type: CNP300 The installed capacity : 300 MWe The designed capacity factor: 65% FCD: Mar 20,1985 Operation: Dec 15, 1991 Design life: 30 years Current license expired: 2021 Formally start OLE: Jun, 2014 Submit OLE application: Dec, 2016

year 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

Qin shan 98.68 95.16 90.24 90.99 96.11 94.52 86.67 92.14 100 98.49

advance 87.12 88.04 89.13 90.71 91.19 91.94 90.90 91.96 93.05 92.86

medium 75.80 77.36 78.98 79.02 80.08 79.41 79.53 80.57 83.19 83.10

WANO performance index in the past 10 years before OLE program

1. Plant OCCW System Introduction

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Plant OCCW System:

The OCCW system was designed to provide to cooling water for component cooling water heat exchangers and emergence diesel generator cooling water heat exchangers, and remove heat to the ultimate heat sink (Hangzhou Bay) during normal and accident operating condition, ensure the reactor under safe operation during normal and accident operating condition.

1. Plant OCCW System Introduction

Intake

Outfall

siphon well

escape canal

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2. Scoping and screening of OCCW

Scoping Criterion 2: Non-safety related SSCs whose failure prevents safety-related SSCs from fulfilling their safety-related function.

Scoping Criterion 3: Fire protection design, fire detection and fire extinguishing systems described in FSAR.

Scoping Criterion 4: The mitigative option and preventive option for the beyond design basis events described in FSAR.

Scoping Criterion 5: Significant modifications permitted or proposed by regulatory authority.

OLE Technical Policy

The system functions of OCCW satisfy the OLE safety evaluation scoping criterion 1, 4, 5 described in OLE Technical Policy issued by nuclear safety regulatory authority.

Scoping Criterion 1: SSCs described in FSAR to perform the fundamental safety function of controlling nuclear reactivity, removing the reactor core heat, containing the radioactive product and control operating discharge, limiting the accident discharge.

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Auxiliary Building: Tube side of component cooling water heat exchangers

EDG Building: Tube side of emergence diesel generator cooling water heat exchangers

2. Scoping and screening of OCCW

Sea Water Pumps

Intake

siphonic well Auxiliary building

EDG building

2 series water supply pipe

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2. Scoping and screening of OCCW

Screening Result of OCCW system:

Component cooling water heat exchanger: head, nozzle, bulkhead, tubes, tube-sheet

EDG mid-cooling water heat exchanger: head, nozzle, bulkhead, tubes, tube-sheet

Sea water pump: pump casting, cover, inlets and outlets, welding joint

Sea water filter: filter shell, cover, flange

Valves: valve body, cover

Piping: piping component

expansion joint: sylphon bellows, flange, nozzle, inner sleeve

Passive and Long-lived mechanical components in OCCW system satisfy the ageing management review screening criterion described in OLE Technical Policy. Criterion 1: Components that their structure and features do not change when performing intended functions;

Criterion 2: Components that do not subject to replace at regular intervals or based on their qualified life.

OLE Technical Policy

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3. Ageing management review of OCCW

Component Material Environment Ageing Effect Plant AMPs

Heat exchanger rubber lining rubber Sea water

Hardening and loss of strength due to elastomer degradation Loss of material due to erosion

Preventive maintenance; Corrosive inspection

Heat exchanger components

Low alloy steel (with rubber liner)

Sea water

Loss of material due to general, pitting, crevice, and microbiologically-influenced corrosion; fouling that leads to corrosion;

Preventive maintenance; Corrosive inspection

Heat exchanger tubes

Titanium alloy, Copper alloy Sea water Reduction of heat transfer due to

fouling

Biocide treatment; Flow monitoring; Flushing

Filter, pump, valves component

Stainless steel Sea water

Loss of material due to pitting and crevice corrosion; fouling that leads to corrosion

Preventive maintenance

Piping component

concrete lining Sea water

Changes in material properties due to aggressive chemical attack; Loss of material due to abrasion, cavitation, aggressive chemical attack, and leaching

Preventive maintenance (reachable position)

Piping component (underground)

Low alloy steel (with fiberglass)

Air in trench Loss of material due to general, pitting and crevice corrosion Catholic protection

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3. Ageing management review of OCCW

Preventive maintenance

Component cooling water system heat exchangers: disassembly inspection, 32M Flush the tubes and clean the sediment on the head; inspect the rubber lining of head and bulkhead; inspect the weld joint between tube and sheet. Sea water pumps: disassembly inspection, 2C Inspect the corrosion and wear of impeller, gasket ring and axle sleeve; measure and adjust the gap between these components. Electric sluice valves of sea water pump inlets and outlets: disassembly inspection and qualification, 3C Check whether blocking exists in the inlet and outlet; check the corrosion status of the inside surface; clean the sealing face; replace the seal components. Rotary sieve: disassembly inspection, 6C Inspect the corrosion status of flange surface; perform PT inspection for suspected area; once corrosive pitting, scouring, scratch, sunken and cracking exist, measure the deepness and repair it.

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3. Ageing management review of OCCW

Corrosive inspection

Preventive anticorrosive inspection of OCCW was only suitable for corrosion sensitive components, including: the interior of following components: sea water pumps and their inlet and outlet, sea water side of heat exchangers and EDG cooling water tanks; the exterior of the sea water piping, components and supports in the pump building, auxiliary building, EDG building and outside building area. Plant developed corrosion inspection and repair procedure for rubber, concrete, coating and glass.

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3. Ageing management review of OCCW

Catholic protection

Potentiostat and reference voltage indication, at least 4 times per week

Fractional anode current indication, at least 1 time per week

statistical analysis the voltage percent of pass and catholic protection system total current.

The following positions are recognized as key targets for excavation inspection in future:

1.5 inches positive pole: protection current ≥1.5A for continuous 2 times;

3 inches positive pole: protection current ≥6.5A for continuous 2 times.

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3. Ageing management review of OCCW

Previous ageing management review results

Preventive maintenance and preventive anticorrosive program included inspections for most of the OLE components, however, several drainage and exhaust valves within the OLE scope were lack of management measure;

For several ageing effects, there was not enough management measure, for example, reduce of heat transfer capability, no monitoring measure had been performed;

Several plant management measures were proved not sufficient enough, some ageing degradation still observed, such as blocking and corrosion perforation.

Blocking of sea water heat exchanger tubes Corrosion perforation inside the sea water piping

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4. Ageing management improvement of OCCW

Modification for open-cycle cooling water system

During the original design stage of the plant, because of the imperfection of the domestic nuclear safety surveillance codes, the OCCW was designed as non-safety related system. This issue was identified during the first Periodic Safety Review (PSR). After that, the issue was eliminated through modifications. The system was designed as nuclear safety class III.

U-Steel

Concrete

Concrete cover

The modifications were performed in three stages: taking trench to install sea water piping instead of directly buried under ground in site area; choosing advanced designed and good performance equipment in the sea water pump building; Modifying the overhead sea water system components and piping in auxiliary building.

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4. Ageing management improvement of OCCW

Enhanced measure for preventing blocking and bio-fouling

Biocide treatment is a fundamental method to mitigate blocking and microbiological corrosion. QNPP regularly injected 1ppm sodium hypochlorite into the sea water prior the sea water pump, however it was proved not effective enough. Blocking in the tubes of heat exchanger was observed at that time. In order to ensure the safety operating of OCCW system, the biocide treatment scheme is adjusted corresponding to the inspection result of accumulations of bio-fouling agents, corrosion products, and silt.

Operating specification is also improved. Plant periodically changes over sea water pumps according to operating specification to avoid system blocking due to silt and sediment sedimentation.

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4. Ageing management improvement of OCCW

Expanded and standardized inspection for ageing degradation

During the OLE ageing management review, it was found several components within the OLE scope were lack of management measure. For some safety important components that excluded from the preventive maintenance programs, supplementary inspections were newly stipulated. For example, the nuclear safety related small-bare drainage and exhausting piping valves are usually not in the scope of preventive maintenance program. In order to confirm whether these valves could sustain their intended function during extended operation period, regularly sampling test is required to identify the ageing status.

In order to further standardize the inspection activities, components are divided into different groups according to component type/material, and each group components are managed by the same or analogous inspection measure. For QNPP, four groups exist: Concrete lining; Rubber lining; Components metal base; Heat exchanger tubes.

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4. Ageing management improvement of OCCW

Protection coating

Some components employ protection coating on the internal surface. For this coating, visual inspection is taken to check whether the surface is integrated, smooth or shining, whether defect exists, such as crocking, cracking, bubbling, spall, split or pulverization. Concrete lining inspection For concrete lining inside the sea water piping, the plant mainly takes the visual inspection, assisted with knock diagnosis. Once obvious thickness reduction is observed, thickness measuring is necessary. Check focus on whether the concrete surface is integrated or smooth, whether defect exists, such as cracking, delaminating, hollowing and loose holes, inspect the evidence of rust distribution scope.

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4. Ageing management improvement of OCCW

Rubber lining inspection

For rubber lining, the plant mainly takes visual inspection, assisted with knock diagnosis. For the suspected flaw, the plant performs electric spark inspection. Trending analysis contains thickness and hardness of rubber. Check focus on whether the rubber surface is integrated or smooth, whether defect exists, such as bubble, scar, split, pinhole, cracking, disengage in lapped joint, delaminating between metal base and rubber. Measure the thickness and hardness of rubber. Metal base inspection

If the coating and lining failure, metal base inspection is performed. Mainly taking visual inspection, when necessary, magnifier and endoscope are applied to observe the corrosion feature and grade. Inspection focus on scope and deepness of corrosion area. Rusty spot area should not exceed 1/2 of equipment internal surface. Rusty scale should be uniform and compact. Deepness of corrosion area should not exceed 20% wall thickness.

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4. Ageing management improvement of OCCW

Additional monitoring for heat transfer capability

As sea water heat exchangers are vulnerable to blocking and bio-fouling, it is necessary to test and verify the capability of heat transfer. Different measures of heat transfer capability monitoring were taken according to the setting situation of current monitoring points.

CCW heat exchangers: heat transfer science methodology, calculate the fouling resistance, heat transfer coefficient, temperature difference between inlet and outlet work medium, confirm these parameters are within the designed scope.

EDG heat exchangers: temperature methodology, test the work medium inlet temperature under the limited flow and heat load.

Components Working medium side Sea water side

T(inlet) T(outlet) Flow T(inlet) T(outlet) Fow

CCW heat exchangers X X X X X X

EDG heat exchangers X X X X

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4. Ageing management improvement of OCCW

SATLO SUGGESTIONS:

Fundamental Overall Problem:

Ageing management programmes for mechanical components do not have in all cases

adequate provisions to ensure effective ageing management during the LTO period.

Fact 1) The procedure which is used to implement the Buried Piping AMP does not

identify the need for specially qualified or trained staff doing specialized work in the area

of cathodic protection.

Fact 2) The acceptance criteria in the Buried Piping AMP and implementing

procedure for the cathodic protection programme would allow for extended periods

without effective cathodic protection (i.e., maintenance periods) without modification of the

inspection schedule.

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Improvements are raised to sustain the intended function of components during extended

operation period. These improvements include:

Adjusting biocide treatment scheme, periodically changing over sea water pumps to

prevent blocking and bio-fouling;

Expanding inspection scope and standardizing inspection measure to detect potential

ageing degradation on base metal and lining;

Additional monitoring of heat transfer capability to track the decline of heat transfer

capability for safety related sea water heat exchangers.

Based on the AMR result and improvements, QNPP developed an ageing management

program for OCCW which has been applied and proved effective in managing the ageing

degradation of OCCW.

5. Conclusions

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THANK YOU!