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IAEA-CN-155-006 NUCLEAR POWER PLANT LIFE MANAGEMENT: STRATEGY FOR LONG TERM OPERATION OF THE BEZNAU NPP UNIT 1 AND 2 H. Rust Nordostschweizerische Kraftwerke AG (NOK), Switzerland E-mail address of main author: herbert.rust@nok.ch ABSTRACT The strategy for attaining long-term operation (LTO) of the Beznau nuclear power plants (NPPs) (2 Units) is given. The requirements, technical evaluations for LTO, in addition to considerations for fuel, radwaste disposal, staff and materials management and economic factors, are described. It is shown that, thanks to optimum management strategies, including backfitting and operational improvements, there are no technical reasons to prevent LTO. INTRODUCTION Both Beznau NPPs (KKB) are of the Westinghouse two loop PWR type with a rated electrical output of 380 MWel and have been operated on base load demand since 1969 and 1972 respectively. The design base uses rather conservative assumptions. By performing selective measures, such as large investments in backfitting, the safety of the plants has been continuously enhanced. Through focussed modernisations and careful maintenance, the overall condition of both Units is excellent. A comprehensive ageing management programme (AMP) for all safety related structures, systems and components (SSC) was set up and started 15 years ago, according to the requirements of the Swiss Federal Nuclear Safety Inspectorate (HSK). The AMP contains all essential actions of evaluation and control of the ageing concerning the material and also conceptual ageing. The permanently increasing demand for electrical energy in Switzerland, as well as economic factors, led NOK to evaluate LTO of KKB. Beside hydro power, nuclear power covers 40 % of the demand in Switzerland. A new nuclear law in Switzerland allows unlimited operation of a NPP as long as safety goals are met. The performed analysis and conclusions for a potential LTO is presented in the paper, including aspects such as technical issues, fuel, radwaste, elusive risks, personel mangement and economics to assure LTO with the best achieveable safety level. TECHNICAL EVALUATION The necessary actions to address and control the ageing mechanisms of the civil strucures have been established in line with the AMP. The procedures for implementing these actions are in place and are continously executed. The technical feasibility for the essential actions required for a LTO up to 60 years is given. A systematic registration of the actions to control ageing of all electrical systems and components occurrs in line with the AMP. The main challenge is not the material related ageing but the availability of products and manufacturers and the conceptual ageing due to obsolescence. Backfitting and modernisation of complex systems are permanent tasks. In the years 2000/2001 the original reactor protection and control system, manufactured by FOXBORO, was replaced by fully digital system TELEPERM XS. In the years 2003/2004 the entire turbine I&C was replaced by the digital system ADVANT Also in the electrical area, the technical feasibility for the essential actions for LTO up to 60 years is given.

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IAEA-CN-155-006 Beznau Unit 1 was orderd in 1965 and connected to the grid in July 1969. At the time of the plant design, the design transients were part of the individual equipment specification. The design base uses rather conservative assuptions. Table 1: Comparison design / actual after 37 years of operation

Heat up 200 55°C/h 81 25°C/hCool down 200 55°C/h 80 25°C/hR-Trip > 10% Pn 220 32Load ramp up 14000 5%NL/Min 1000 1.5%NL/MinLoad ramp down 14000 5%NL/Min 1000 1.5%NL/MinUF Pressurizer Nozzle 1 0.47UF Charging Nozzle 1 0.21UF RHR Nozzle 1 0.25

Design Actual

Potential of KKB after 37 years of operation

0

20

40

60

80

100

Heat up Cool down R-Trip > 10% Pn Load ramp up

Load rampdown

UF PressurizerNozzle

UF ChargingNozzle

UF RHR Nozzle

Nature and position of Transients

Plant

Life R

eserv

e [%]

The AMP attests generally good conditions for the major components of the nuclear steam supply system (NSSS). Exceptions are some materials, such as Alloy 600, used in the reactor pressure vessel. Special attention is required in the area of embrittlement and fatigue of selected components. Selective replacement of several components is necessary. Maintenance activities requires more resources especially for the qualified test methods requested by the authorities. The investigations and analysis show also for the NSSS the technical feasibility for the essential actions for a LTO up to 60 years is possible. Most of the systems and components of the balance of plant have been replaced in the past years. Starting in 1993 with the HP-turbines, the condensers and the pre-heaters followed by

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IAEA-CN-155-006 the entire turbine controls. The last big component, the moisture separator/re-heater, will be replaced in the 2007 outage in Unit 2. The balance of plant is ready for LTO up to 60 years. Potential of KKB after 37 years of operation

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HP-Turb ine LP-Turbine LP-Bla ding S top va lve ca sing Bypa ss va lve ca sing S te am -Line (HP -Turb ine )

Plan

t Life

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[%]

> total replacement 1995

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HP-Turb ine LP-Turbine LP-Bla ding S top va lve ca sing Bypa ss va lve ca sing S te am -Line (HP -Turb ine )

Plan

t Life

rese

rve

[%]

> total replacement 1995 BACKFITTING AND MODIFICATION Backfitting of the Beznau Units has been an almost continuous undertaking in line with the developing state of technology, but it is also based on feasibility and tailored to address spe-cific requirements. In 1979, the licensing authority performed a comprehensive safety reassessment. As a consequence, a major backfitting program was started. Its design basis was an assumed break of the two main steam lines outside of the reactor building. In order to provide adequate core cooling under these conditions, but also to satisfy the desire for a separate safety injection train, a high-head borated water injection system as well as a redundant power supply were included. The practical implementation of the requirements, which was named NANO, has been the provision of two bunkered emergency heat removal systems, one for each Unit, which can supply ten hours of core cooling in the event of a loss of the main heat sink with the primary loop remaining intact. In the eighties the first probabilistic safety analyses (PSA) was carried out. Today the Beznau living PSA (BERA) has the potential of being a very effective decision making tool by assessing the cost/benefit ratio of any particular backfitting measure. Since 1980, NOK invested more than 1000 million Swiss Francs for major backfitting and modification activities in both Units. Three categories of backfitting measures may be identified as follows: - Continuous plant modifications involves some 80 to 120 measures taken every year to

improve plant safety, reliability, maintenance and operation. - Optional plant renewal stands for improvement to plant safety undertaken outside

licensing authority requirements. - Compulsory plant renewals are based on requirements of the licensing authority. Examples of continuous plant modifications: - Replacement of radioactive liquid waste treatment systems - Digital radiation monitoring system - Plant information system

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IAEA-CN-155-006 - New pressurizer safety valves - Steam generator replacement in both Units - Replacing of high pressure turbines and preheaters Examples of plant renewals, based on requirements of the licensing authority: - New reactor pressure vessel relief system (Post TMI) - Thermal H2-recombiners inside containment (Post TMI) - Bunkered emergency heat removal system (NANO Project) - Seismic requalification of mechanical/electrical equipment - Additional emergency feed water system (ERGES Project) - Filtered containment venting system (SIDRENT Project)

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IAEA-CN-155-006 What was backfitted and modified in KKB?

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B un k er s ys t em

S G R ep l ac e m

e n t U ni t 2

S G R ep l ac e m

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P r oj e ct AN I S

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I B EZ

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a l Co n d. / P re h ea t er

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P r oj e ct S ID RE NT

Projects

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. CHF

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Beznau PSA History

Results of Full-Scope Level 1 PSA incl. External Events (Seismic, Fire, etc.)

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006

Year

Core

Dama

ge Fr

eque

ncy [

per y

ear]

1986 - 1988: Seismic upgrades

1988 - 1990: 3rd DC-Bus

1990: EPO improvements

1991 - 1993: Emergency bunker system

1994 - 1996: 2nd Hydro-Supply1998 - 2000: 3rd Aux. Feed system

Target CDF value: IAEA, USNRC

Target CDF value: IAEA for future plants

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IAEA-CN-155-006 REACTOR PRESSURE VESSEL The RPV surveillance programme was conceived at the time of manufacture, reflecting the pressure vessel Codes and Surveillance programmes needs according to the ASME Codes and other requirements at the time. Materials are available for reconstitution for extended fracture toughness tests, if required.The capsules have been removed periodically, covering a end-of-life fluence in excess of 60 years. The results of Charpy and fracture toughness measurements show sufficient toughness for brittle fracture avoidance. RPV Embrittlement

Plant HeatupRCS Pressure in Function of Effective Full Power Years

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Allowable Pressure 33 °C/hr, barg) 45 EFPYAllowable Pressure 33 °C/hr, barg) 54 EFPY

The internals and the head penetrations of the RPV demand special attension. The split pins in the upper internals and the baffle bolts in the lower have to be inspected and, if necessary, replaced. The head penetrations are made of Inconel 600 and therefor susceptible to PWSCC. All 36 penetraions in both Units have been tested several times with no indications so far. CONTAINMENT PRESSURE VESSEL The steel containment pressure vessel of Unit 1 needs special attension due to corrosion attacks in the area of the restraint to the concret strucure. Three causes fostered corrosion in a narrow area: leaking membrane in the fuel transfer tube, inadverted actuation of containment spray system and cavity liner leakage. Several measures are completed or on the way. Detailed stress analysis, using two dimentional axisymetric ANSYS model and parametric study using different values of corrosion penetrations have been carried out. The results of the analysis show, that despite very conservative assumptions, the calculated stresses are well below the allowable ASME limits.

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IAEA-CN-155-006 Steel containment pressure vessel

Stress Intensity (SINT) vs. Operating Time

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SINT effective SINT allowed Wall Thickness NUCLEAR FUEL: ACQUISITION / DISPOSAL In the area of fuel acquisition, storage and disposal, long term contracts until 2020 are in effect. Fuel management is an important financial aspect of operation. The Beznau Units feature mixed-oxide (MOX) fuel and the average burn-up values are 58’000 MWd/tU. Spent fuel elements are first stored in the fuel-pools and later stocked in storage containers in a facility on the site. There is sufficient storage place available, even for LTO. A national company owned by the utilities is assigned to search for a underground final repositary facility. ELUSIVE RISKS Elusive risks, such as a nearby hydro plant, that is part of the emergency power supply of KKB, new earthquake analysis for all NPP’s in Switzerland and aspects of the environment in the sector of nuclear energy are covered by the study for a LTO of KKB. PLANT STAFF AND MATERIALS MANAGEMENT The workforce of KKB, currently 490 people, will show a slightly increasing tendency due to longer overlapping times concerning retirements of staff and increasing maintenance activities as well as requires testing qualifications for ISI. The need of spare parts depends on the maintenance strategy and will be additionally complicated as a result of exclusion of manufacturers from the market and obsolescence. The inventory of spare parts will be systematically reduced before the shutdown of KKB.

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IAEA-CN-155-006 ELECTRICITY MARKET / EXTERNAL INFLUENCING FACTORS The electricity market in Europe and particularly in Switzerland as well as external influencing factors such as CO2 issues are covered by the study. For the economic aspects, the entire study was carried out in terms of three scenarios; optimistic, realistic and pessimistic cases, for 50 years as well as for 60 years of full-power operation. A comparison between the production costs versus the market prices shows good perspectives. The nuclear power laws in Switzerland allow NPPs to operate as long as the safety is maintained. Additional requirements in connection with periodic safety reviews (every 10 years) are to be expexted ECONOMICS The LTO economic model for investments covers two operation periods, 50 as well as 60 years. For both cases, three scenarios - optimistic, realistic and pessimistic - have been evaluated. Beside the investments, the following cost-typs are included in the LTO economic model: - Fuel - M&O - Material and external labour - Personnel - Accruals and deferrals for decommissioning and fuel disposal - Expenses - Interest - Amortisation - Exceptionally outage length due to modifications, backfittings or replacements Some activities have to be implemented regardless of the operating time of 50 or 60 years. That is the reason wherefore the lapse of the production costs for 60 years is lower then for 50 years because of the longer amortisation period.

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IAEA-CN-155-006 The Investments, 50 years of operating

02005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

kCHF

pessimisticrealisticoptimistic

02005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

kCHF

pessimisticrealisticoptimistic

Investments, 60 years of operating

02005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029

kCHF

pessimisticrealisticoptimistic

02005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029

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pessimisticrealisticoptimistic

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IAEA-CN-155-006 Influence of outage durations

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normal RA normal RV + RA addition for 50/60 years

Full production costs, 50 years of operation

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IAEA-CN-155-006 Full production costs, 60 years of operation

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Comparison of production costs / market prices

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030

Operating Time [Y]

CHF [

Rp/kW

h]

60 Y 50 Y

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IAEA-CN-155-006 Comparison of production costs / market prices (assumptions)

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030

Operating Time [Y]

[Rp/k

Wh]

Best Case Worst Case Comparison of production costs / market prices

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Operating Time [Y]

[Rp/k

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60 Y 50 Y Best Case Worst Case

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IAEA-CN-155-006 CONCLUSIONS The SSCs in both Units of Beznau NPPs are in good condition and well able to fulfill their design and operational functions for up to 60 years of full-power operation (LTO). The investments made in improvements and replacements, plus optimized monitoring and inspections have all contributed to the very safe operation to date with also the best pre-conditions and prospects for LTO. The evolution of the state of science and technology are followed and where necessary, in order to further improve safety and reliability, implemented. The continuation of recruitment and training of personnel and the adoption of best practices and safety culture is a permanent activity for the Units. The radwaste issues and spent fuel storage aspects are technologically solved, and there is presently enough capacity to store radwaste for several years to come, before it is finally disposed with. Based on the NPP’s operational histories to date and the results of inspections and replacements of SSCs, there are no technological reasons why the Beznau NPPs Units 1 and 2 cannot continue to produce reliable supplies of electrical power at a commercially attractive price and in the safest possible manner.