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Tavoiteohjatun kunnossapidon keskeinen suunnitteluvaihe on kunnossapitoluokittelu. Tässä pyrkimyksenä on määrittää kullekin laitepaikalle sen kunnossapitoluokka vikakriittisyyden perusteella. Vikakriittisyys tarkoittaa laitepaikalla mahdollisesti esiintyviä toiminnallisia vikoja, joilla on merkittäviä laitostason seurauksia esimerkiksi turvallisuuden ja tuotannon suhteen, sekä myös välittömiä vahinkokustannuksia, jotka laitteesta riippuen voivat olla hyvinkin suuria. Vikakriittinen laitepaikka laitteineen on ehdokas ylempiin kunnossapitoluokkiin. Onnistunut kunnossapitoluokittelu ohjaa kunnossapitotehtävien valintaa ja suunnittelua laitteille, koska jokaiseen luokkaan liittyy johdon riskisuhtautumista heijastava konkreettinen vaatimusmäärittely laitteen toimintavarmuudelle tai kunnossapidon kustannustehokkuudelle.

Kunnossapidolla on keskeinen rooli laitoksen tuotannollisten, taloudellisten ja turvallisuuden kannalta tärkeiden tavoitteiden saavuttamisessa. Kunnossapidon suunnittelu on taitolaji jossa yhdistyy strateginen suunnittelu ja vahva tekninen osaaminen. Oikeaoppinen kunnossapidon suunnittelu hyödyntää kertynyttä käyttökokemusta niin, että kunnossapidolle asetetut tavoitteet ovat linjassa laitoksen strategisiin tavoitteisiin. Tämä ei ole helppo tehtävä. Tavoiteohjatun kunnossapidon suunnittelumenetelmän päämääränä on tuottaa kunnossapito-ohjelma, joka vastaa laitoksen johdon riskisuhtautumista asetettuihin tavoitteisiin nähden. Menetelmä 'pakottaa' johdon tekemään riskipäätöksiä - mutta hallitusti.

Tämän tavoiteohjatun kunnossapidon suunnittelumenetelmää kuvaavan artikkelisarjan aiemmissa osissa on käsitelty yrityksen perustavoitteista lähtevää kunnossapidon tavoitteiden määrittämistä ja seurantaa sekä vikakriittisyyteen perustuvaa kunnossapitoluokittelua. Tässä artikkelisarjan viimeisessä osassa käsittelemme kunnossapitotehtävien valintaa. Kunnossapitotehtävien valinnan lähtökohtana laitteelle on sen kunnossapitoluokka ja laitepaikalle asetettu toiminnallinen vaatimus. Kunnossapitotehtävien tarkoitus on paljastaa ja estää vikoja. Kunnossapitotehtävien valintaa auttamaan on laadittu logiikkapuu. Kunnossapito-ohjelma koostuu yksittäisistä kunnossapitotehtävistä ja niiden jaksotuksista sekä varautumisesta ennakkohuoltoihin ja vikakorjauksiin.

Tavoiteohjatun kunnossapidon suunnittelumenetelmää kuvaavan artikkelisarjan osassa kaksi käsittelemme kunnossapidon tavoitteiden määrittämistä lähtien yrityksen perustavoitteista. Siinä missä yrityksen ja laitoksen tavoitteiden määrittäminen on periaatteessa ylhäältä alas ohjautuvaa, niin kunnossapidon tavoitteiden määrittäminen perustuu varsin pitkälle kunnossapidossa ja tuotannossa vallitsevaan tilanteeseen sekä siellä karttuvaan käyttökokemukseen ja osaamiseen. Näitä näkökulmia viisaasti yhdistämällä tulisi laitostason tavoitteet entistä paremmin saavuttaa tehokkaammaksi suunnitellulla kunnossapidolla. Tämä edellyttää talouden, organisaation ja tekniikan osaamisen yhdistämistä tavoiteasetannassa.

Tässä raportissa kuvattu riskitietoisen ja kustannustehokkaan kunnossapidon suunnittelumenetelmä on tarkoitettu ydinvoimalaitosten laitteiden ja teknisten järjestelmien jatkuvan kunnossapito-ohjelman kehittämiseksi ja ylläpitämiseksi vastaamaan yrityksen tavoitteita. Suunnittelumenetelmän ydin on EBRCM:ksi (Experience Based Reliability Centred Maintenance) kutsuttu menettelytapa, jossa hyödynnetään käyttökokemusanalyysiä ja päättelylogiikkaan yhdessä laitepaikkojen kunnossapitotehtävien valitsemiseksi ja kunnossapitostrategian suunnittelemiseksi.

The challenge for maintenance planning is to identify appropriate objects and tasks for preventive maintenance and ensure that there are sufficient provisions for any necessary repair actions. In this paper we will present a maintenance planning approach, called value-driven maintenance planning, to emphasize the fact that the objectives of the company are the reference points for judging; a) the functional requirements for the equipment and systems, and b) the acceptable cost-benefit ratio for controlling functional failures. The three basic phases of the value-driven maintenance planning approach are:• the definition of the fundamental and means objectives of the production plant, • the classification of equipment into maintenance classes, each associated with a functional requirement specification, and • the selection of maintenance tasks (including timing) for equipment assigned to the equipment locations. This paper focuses on the two first points, detailing the analysis logic within the context of a case study on a gasification plant in Finland.

Tämä väliraportti sisältää menetelmäkuvauksen inhimillisperäisten vikaantumisten järjestelmällisestä tutkinnasta voimalaitoksen kunnossapitohistoriasta. Esimerkkikohteena virheiden tunnistamiselle, tutkinnalle sekä analyysitietojen käsittelylle ja tulosten esittämiselle on Loviisan voimalaitoksen kunnossapitohistoria. Menetelmäkuvaus perustuu inhimillisten virheiden ja yhteisvikojen tutkintaa varten tarvittujen menetelmien kehitykseen ja käyttöön Olkiluodon ja Loviisan voimalaitosten 1990 luvun puolivälistä alkaen tehdyissä VTT:n analyysisovelluksissa. Käytettyjä tutkimusmenetelmiä ja tietorakennetta on sen jälkeen yksinkertaistettu käytännön analyysikäyttöön Loviisan voimalaitoksen ylläpidon vuonna 2004 tekemän in-kind tutkimuksen yhteydessä. Menetelmäkuvausta tullaan päivittämään etenkin inhimillisperäisten yhteisvikojen tutkinnan osalta vuonna 2005, kun voimalaitoksen in-kind tutkimusta tehdään edustavasta määrästä yhteisvikoja sekä tietorakenteen osalta, kun kunnossapitohistoriaa uudesta LOMAX laitostietojärjestelmästä on tutkittu. Tämä väliraportti on myös tarkoitettu tiedottamista, tarkastusta, kommentointia ja palautteenantoa varten.

A survey is presented outlining the use of condition monitoring information in three Nordic nuclear power plants. The questions of the survey relate to the role of condition monitoring in strategic, as well as operative, maintenance planning and decision-making. The survey indicates that condition monitoring is increasingly implemented at nuclear power plants, but very selectively and in a rather slow pace for predictive maintenance. A combined strategy of condition based maintenance and predetermined preventive maintenance is applied for importantequipment such as main circulation pumps and steam turbines. A realistic aim is to reduce the number of costly or error prone maintenance and disassembling inspection activities by condition monitoring given that the approach enables a good diagnosis and prediction. Systematic follow-up and analysis of such condition monitoring information followed by a case-specific planning and decision making of timely and rightly directed maintenance actions can justify an extension of the intervals of a number of predetermined inspection, maintenance or periodic testing tasks.

The article describes an approach to evaluate and improve the effectiveness of the maintenance strategies of technical systems in operating nuclear power plants. In the Experience Based Reliability Centred Maintenance (EBRCM) approach, the analyses of the history of occurred faults and the preventive maintenance programme are combines. In order to direct the analysis of the maintenance significant items, the components of the plant are classified based on their significance for reaching the maintenance objectives such as plant safety, plant availability and work safety in failure situations. Maintenance analysis is direct to those significant components, which exhibit a high number of failures. The other of less maintenance significance, but which exhibit high maintenance costs are also analysed to improve the cost-effectiveness of maintenance.

In the area of reliability centred maintenance (RCM), VTT Industrial Automation has focused in the development and application of an experience based reliability centred maintenance approach. As a part of the R&D programme at Barsebäck Kraft AB, reliability and maintenance optimisation studies were conducted by evaluating existing maintenance programmes at the plant using this approach. VTT Industrial Automation contributed to the development of the methodology for systematic maintenance analysis and steering and review of its application by plant personnel in the evaluation of the maintenance action programme of the hydraulic scram system. In order to limit analysis resources in this study, a decision analysis approach was used to rank some 1400 items in this standby safety system, and the most significant component places of them were selected as analysis significant items. The experince based RCM study resulted in proposals for shortening some preventive maintenance intervals, the introduction of additional preventive maintenance actions and the suggestion of additional condition monitoring, to reduce the number of recurrent faults. The modern condition monitoring and signal processing can be useful in prevention of failures, and in timing and improving the cost-effectiveness of maintenance. Condition monitoring can enter the Maintenance Management in existing plants in two-ways: 1) long-term maintenance strategy planning, where the important equipment places for condition monitoring are identified, and 2) short-term maintenance planning and decision-making based on condition monitoring information. The paper will, as a background for the co-operation between VTT Automation and HRP in the field of maintenance decision support, outline: 1) A description of application of the decision analysis approach to rank the 1400 items of the above mentioned hydraulic scram system for selection of the most significant component places for further detailed analysis. A similar decision analytic approach is planned to be defined for assessment of the importance of different equipment places for implementation of condition monitoring as a part of the maintenance strategy evaluation of existing plants. 2) A plan of a survey of the collection and management of condition monitoring information for short-term maintenance planning at several Nordic nuclear power plants.

The paper describes an approach to evaluate and improve the effectiveness of the maintenance strategies of technical systems in operating power plants. In the Experience Based Reliability Centred Maintenance (EBRCM) approach, the analyses of the history of occurred faults and the preventive maintenance program are combined. Changes in the maintenance programs are proposed for reduction of faults or increasing the cost-efficiency of maintenance. The justification of changes is based on simple maintenance indicators and study of the underlying failure and maintenance data. To make the analysis resource-efficient and generate easily the maintenance indicators, suitable data analysis and warehouse tools are used. They facilitate the online access and treatment of the work orders and other planning information in plant information systems. In order to direct the analysis to the important items from maintenance point of view, the equipment of the plant are classified based on their importance for reaching the maintenance objectives such as plant safety, plant availability and worker protection. Maintenance optimisation is directed to those important equipment which exhibit a high number of failures. The other equipment of less maintenance importance, but which exhibit high preventive maintenance costs and low numbers of failures are also analysed to improve the cost-effectiveness of maintenance. After experiences from performing two case studies, both on a standby safety system and a continuously operating process system, Barsebäck Kraft AB adopted the experience based RCM approach as standard method for evaluation of the maintenance action programs and planning of modifications in them. The strength is the applicability and continuity of this method, i.e. each year again.

Several objectives which may be conflicting must be considered when making strategic maintenance decisions. Studies of decision cases have shown that the methods of decision analysis provide a systematic and clear basis for making complex decisions under multicriteria conditions. Such decision criteria might be system safety, availability, maintenance cost and work culture. A decision analysis approach provides a structure for identifying and ranking the significant decision options, decision criteria and information needs for making of the decisions. For instance, the results of probabilistic safety assessment and maintenance analysis, together with other engineering knowledge, can be used in a decision analysis to solve a decision problem.Experiences from practical cases of decision analysis have indicated that a better decision support procedure could be achieved by the introduction of tentative decision models and a tailored planning tool. Decision models were constructed based on knowledge obtained from earlier decision and reliability analyses and the collection of expert knowledge. A spreadsheet tool for qualitative and quantitative decision analysis was defined and developed. The tool helps to prepare, perform and document the decision analysis sessions with the decision models being stored in the tool. At present, decision criteria for strategic decision cases such as plant shutdown or continued operation in a fault situation, need of component replacements by repeating faults, ranking of optional modifications and the need for condition monitoring have been modeled.

This report provides an analysis and evaluation of incident analysis methods and practices applied by the Finnish regulator Radiation and Nuclear Safety Authority (STUK) and the two Finnish nuclear power plant operators Teollisuuden Voima Oy (TVO) and Fortum Power and Heat Oy (Fortum). The study was conducted in 1998-99. The research material was based on tape-recorded interviews as well as internal directions and event investigation reports provided by the three participating organisations. A framework for analysis and evaluation was developed as part of the study on the basis of referenced root cause analysis and operating experience review methods, selected (foreign) inspection reports, scientific papers and research literature. Well-known inspection methods and principles, such as ASSET and MTO/HPES, provided important guidance to this work. This study shows that although all the evaluated organisations had rather comprehensive incident analysis arrangements, more focus and priorisation is needed. Deficiencies were identified mostly in the areas of recording, assessment and classification of new events and observations, use of existing operating experience data, utilisation of information technology based tools, and allocation of work and resources. In general, the direct causes of identified events can be detected and removed, but more emphasis should be given to the prevention of recurrence. This requires a more efficient feedback loop that can be created and maintained by focusing on the root causes of significant events, tasks and activities in which the originating errors occurred, and weaknesses of defensive barriers, and by implementing periodic operational experience reviews. A strategy document for the operating experience feedback process, and firm procedures for the initial assessment of new events and the carrying-out of data analyses would help.

An industrial process plant should be operated effectively from the economic point of view, and undisturbed production should be ensured with long-term minimum cost. At the same time, the risks for the owners, plant workers, public and environment should be kept as low as reasonably possible. Usually, enterprises develop strategies to cope with economical production, environmental requirements and occupational safety. These strategies lean on the general goals and objectives set for the economy and society's confidence in the plant. From a wide perspective, the goal of maintenance and operability activities of a successful industrial plant is the assurance of long-term asset management by keeping the plant continuously in a condition as good as new. Maintenance has a key role in controlling the risks caused by equipment damages, system failures or plant disturbances. However, there are many ways to organise and perform maintenance, and each maintenance option has its own characteristics with respect to benefits, costs and risks. The decision maker should be able to estimate the effects of maintenance and to evaluate benefits, costs and risks in order to create the most appropriate maintenance strategy, which should bc based on the goals set for the use of the plant and be in accordance with advanced enterprise strategies.

The most nuclear power utilities have established goals and objectives for their nuclear power plants, including e.g. 1) operating the plant effectively from primarily the safety and secondly the economic point of view, 2) ensuring safety of the public and the plant workers, and 3) providing uninterrupted electric power to the shareholders with long-term minimum cost. The maintenance goals should reflect these goals at a more functional level. In a larger perspective, the goal of the plant maintenance and op-erability activities may be assurance of long-term asset management by keeping the plant continuously in a good condition like new (Mokka 1996). Avoiding faults causing plant disturbances during the operating period may be the most important performance goal which should not be put in danger by minimis-ing the number of maintenance work during the annual maintenance and refuelling outage. More detailed goals and objectives may be to carry out the necessary work at the optimal time during the outages or operation, and to minimise the unavailability time of safety related equipment. One internal objective may be to carry out the maintenance work at budgeted cost. It is expected that every maintenance organisation will, together with its parent organisation, identify its own goals and objectives (EURO-MAINE 1997).

This report contains an international overview of applications of living probabilistic assessment and development of operational safety indicators. Features of an ideal living PSA tool are summarized as well as a limited survey of code systems for managing a living probabilistic safety assessment (living PSA) is included. The international survey is used as an input for planning and performance of related tasks within the Nordic NKS/SIK-1 project conducted in 1990-93. The research notes are distributed to the Nordic organizations involved or interested in the subject. The report includes an overview and conclusions from technical reports and articles available and presentations and discussions related to development and use of the above methods for the evaluation and management of the operational safety of nuclear power plants. A large part of this material is based on material collected and discussed in connection to international specialist meetings relating to the subjects. In the area of living PSA tools there are many computer codes being developed. The present versions approach rapidly the level of usability needed for performing and maintaining living PSA and continuous risk monitoring. The living PSA applications are still in most cases research efforts in which the applicability of the PSA technique is tested in a small scale. For the moment, there are very few actual living PSA applications actively in use at the plants. The performance and safety indicators have been in a strong development phase during the last few years. Many utilities, regulatory bodies and international organizations have started to use performance indicators for quantitative evaluation of nuclear power plant operations. It is generally emphasized that performance and safety indicators are intended to be one of the several tools for use by plant and regulatory staff when tracking contributing factors of deteriorating as well as improving developments. Subsequently, the use of numerical indicators is expected to facilitate a more efficient utilization of operating experiences for making decisions on corrective actions to be taken at the plant. The use of the probabilistic methods for operational safety monitoring is encouraged, although a probabilistic approach also has met with some opposition. In any case, it is recommended that international cooperative research continues with the development of applying safety indicator concepts and operating experience feedback practices to dynamic and living PSA modelling.

Raportissa kuvataan ulkomaisia ydinvoimalaitosten vanhenemistutkimuksia ja käyttöiänpidennysohjelmia. Vanhenemistutkimuksilla pyritään selvittämään, voidaanko laitteiden ja rakenteiden käyttövarmuus ja turvallisuus säilyttää läpi laitoksen käyttöiän. Yleensä tavoitteena on myös tutkia teknisiä ja taloudellisia mahdollisuuksia jatkaa laitoksen käyttöikää suunniteltua pidemmälle heikentämättä laitoksen turvallisuutta. Ydinvoimalaitosten käyttöiänhallintaa käsittelevät tutkimusohjelmat koostuvat yleensä seuraavista vaiheista: vanhenemisen kannalta merkittävien kohteiden valinta, kohteiden vanhenemismekanismien tunnistaminen ja toimenpiteiden suunnittelu vanhenemisen vaikutusten ehkäisemiseksi. Kohteiden valinnassa käytetään asiantuntija-arvioita, käyttökokemustietoja ja jonkin verran myös riskianalyysien tuloksia, jotta tutkimukset osataan suunnata vanhenemisen ja turvallisuuden kannalta merkittävimpien laitteiden ja rakenteiden analysointiin. Vanhenemismekanismien tunnistamiseksi voidaan analysoida käyttökokemuksia sekä koestaa laitteita ja materiaaleja laboratorio-olosuhteissa. Vanhenemisen vaikutusten ehkäisemisessä on keskeisessä asemassa kunnossapidon ja tarkastusten suunnittelu ja kehittäminen vastaamaan paremmin vanhenevan laitoksen tarpeita. Raportin pääpaino on Yhdysvalloissa käynnissä olevien tutkimusohjelmien kuvaamisessa. Yhdysvaltojen tutkimusten lisäksi kuvataan Ranskassa ja Japanissa tehtyjä laajoja selvityksiä laitosten käyttöiänpidennysmahdollisuuksista, Myös muissa ydinenergiaa tuottavissa maissa tehdään jatkuvasti tutkimuksia, joista raporttiin on poimittu joitakin lähinnä kunnossapidon kehittämiseen liittyviä esimerkkejä. Ulkomailla tehtyjen ydinvoimalaitosten vanhenemistutkimusten tuloksia voi parhaiten seurata osallistumalla alan kansainväliseen yhteistyöhön. Tällainen tiedonvaihto taas edellyttää hyvätasoista omaa tutkimusta. Vanhenemistutkimuksessa ja käyttöiänhallinnassa hyvien tulosten saavuttamiseksi on tärkeää pitää yllä kansallisia tutkimusohjelmia, joissa on mahdollista yhdistää asiantuntemusta sekä materiaali-, rakenne-, kunnossapito- että luotettavuustekniikan alueilta.