V. HISTORICAL AVAILABILITY OF THE BELGIAN NUCLEAR UNITS

This appendix provides more detailed information on how the historical availability of Belgian nuclear units is determined. The historical availability is then used as basis to define the assumed values in the CENTRAL scenario. This appendix aims to complement the information already presented in BOX 3-7.

• 2021 State of Reliability by NERC [NER-1];

• Electricity Capacity report by National Grid [NAT-1];

• Common data used in the ERAA & TYNDP studies by ENTSO-E.

Other sources were consulted as well but provided no clear distinction between unavailability types.

Due to the stringent safety protocols and regulatory framework surrounding nuclear facilities, outage calculations for nuclear units require a more meticulous approach. Indeed, it is important to be able to distinguish the different type of outages and their associated probability.

V.1. OVERVIEW OF OUTAGE TYPES FOR NUCLEAR UNITS IN BELGIUM

Regarding historical availability of nuclear power plants, four independent and cumulative statuses are defined, considering that forced outages could be split between ‘technical’ and ‘long-lasting’ forced outages: of the results with the results found in a literature review, the final list of outage indicators was proposed for consultation. The overview of resulting indicators taking into account the feedback from the public consultation can be found in Section 3.4.4.

BOX 3.7). These events are assumed to be independent from climatic conditions and can therefore occur at any time during the year and therefore have an impact on the available capacity during winter.

The full report submitted to public consultation can be found in [ELI-18].

• The unit was available (presented as ‘Available’ in BOX 3.7).

• The unit was in a planned outage A planned outage is considered as usual maintenance but also includes longer planned maintenance periods needed to solve issues encountered after a ‘long-lasting’ forced outage (presented as ‘Planned Unavailability’ in the analysis in BOX 3.7). Regular maintenance is assumed to be performed outside of the critical periods for adequacy even though some planned outage events have been observed during winter when looking at historical data. Some planned outages also need to respect the fuel cycle of the unit and cannot easily be moved. For this reason, an independent indicator on planned outage during winter is integrated in the conclusions. Note that planned outage also includes the long-term operations (LTO) outage periods which are significantly longer than regular planned outage periods as they include additional works to be performed to extend the unit lifetime.

• The unit was in ‘technical’ forced outage. A ‘technical’ forced outage is usually an unexpected event or malfunction leading to the shutdown of the unit to fix a well-defined and limited issue (presented as ‘Technical Force Outage’ in

• The unit was in a long-lasting’ forced outage A long-lasting forced outage is an unpredictable event, leading to a long-lasting shutdown of the unit (presented as ‘Long-lasting Force Outage’ in BOX 3.7). Similarly to ‘technical’ forced outages, these events are assumed to be independent from climatic conditions, meaning that they can occur anytime during the year and therefore impact adequacy in winter. This assumption is confirmed by looking at historical data. Note however that longer planned outages required to fix these long-lasting events are not considered in this category. The split between ‘long-lasting’ forced outage and longer planned outages required to fix those is based on information of the AFNC/FANC website and on a case-bycase analysis on planned outages of the different nuclear units. More details can be found in the section ‘Details on unit per unit type of historical availability events per unit’. In this study, outages for nuclear units are modelled using a four-state Markov chain with the four states being, available, planned outage, technical forced outage, and long-lasting forced outages. A more in-depth explanation can be found in methodology Appendix C.

V.2. DETERMINING OUTAGE RATES

The outage rates for Belgian nuclear units are calculated on historical daily nomination data from 2012 to 2021 for all nuclear units in Belgium.

First, the technical forced outage (TFO) rate is calculated as:

‘Technical’ FO rate = TFO days 2012 → 2021 (TFO days+Available days ) 2012 → 2021

Regarding ‘long-lasting’ forced outages (LLFO), the following formula is used to calculate the corresponding rate:

'Long lasting' FO rate = - ’ Technical’ FO rate (TFO days + LLFO days)2012 → 2021

TFO days + LLFO days + Available days 2012 → 2021

Finally, the planned outage rate is calculated as the planned unavailability on the total period:

PO days 2012 → 2021