V.5. DISCUSSION ON THE RESULTS AND ADDITIONAL CONSIDERATIONS

The results presented above were calculated on historical data for all nuclear units in Belgium from 2012 to 2021.

First, it is important to mention that Doel 4 and Tihange 3 units are the most recent nuclear units in Belgium and hence could experience less outages than older units. However, these units will be extended beyond a 40-year lifetime and will therefore have to undergo LTO works as it was already the case for Tihange 1, Doel 1 and Doel 2. These LTO works could lead to either extended planned outages or ‘long-lasting’ forced outages due to the analysis performed or to the critical operations to be performed. In addition, as it can be observed on the graphs in BOX 3-7 of Chapter 3, ‘long-lasting’ forced outages also happened on the two most recent units.

PO rate =

Total days 2012 → 2021

Note that ‘technical’ forced outages, ‘long-lasting’ forced outages and planned outages should be considered as independent and cumulative.

V.3. EVENTS CONSIDERED AS ‘LONG-LASTING’ FORCED OUTAGES

A defined number of events were considered as ‘long-lasting’ forced outages, based on information available on the AFCN/ FANC website:

1. Indications of microflakes in the nuclear vessel of Doel 3 and Tihange 2 [AFC-1];

2. Doel 4 sabotage [AFC-2];

3. Concrete degradation on bunkers of Doel and Tihange (D3/D4/T2/T3) [AFC-3];

4. Concrete issue during LTO on Tihange 1 [AFC-4]. The unit-by-unit details are presented in ‘Details on unit per unit type of historical availability events per unit’.

V.4. HISTORICAL AVAILABILITY OF NUCLEAR UNITS

By considering both ‘technical’ forced outages and ‘long-lasting’ forced outages on all Belgian nuclear power plants, a forced outage rate of 20.5% is determined:

FO rate = ’Technical’ FO rate + ’long – lasting’ FO rate = 4.0% + 16.5% = 20.5%

Note that the ‘technical’ forced outage rate is in line with the ‘unplanned capacity loss factor’ calculated by the IAEA at world level [IAE-1].

While forced outages are assumed to be independent from climatic conditions and therefore calculated on the whole year (which is confirmed by historical data), planned outages are mainly foreseen outside of winter periods. Elia assumes that no planned outages occur during winter for thermal units in Belgium (nuclear included) unless those planned outages are already foreseen under REMIT for the upcoming three years. However, as visible on the graphs in BOX 3-7, historical observations show that planned outages also occurred during winter for nuclear units in Belgium.

It is therefore of interest to also analyse the unavailability rate due to planned outages in winter as well, as these can have an impact on adequacy. Therefore, a planned outage rate is calculated on winter periods only:

PO days in winter 2012 → 2021

PO rate = = 8.1 [%]

Total days in winter 2012 → 2021

It is also important to note that average values do not include the discretionary impact that ‘forced long-lasting events’ can have. The occurrence of such an event on Doel 4 or Tihange 3 would result in an entire unit of over 1 GW being unavailable for a long period. This is different when looking at other types of units where there are more units but also generally of smaller size meaning that the impact of an outage is less severe.

Although planned maintenance outages for nuclear units are typically scheduled outside of the winter period to min-

V.6. CONCLUSION

The forced outage rate for Belgian nuclear units considered in the CENTRAL scenario includes both ‘technical’ and ‘long-lasting’ forced outages, resulting in 20,5% imise the impact on security of supply, it is important to acknowledge that certain circumstances might necessitate maintenance works during winter for nuclear units. Nuclear units may have unique constraints and considerations compared to other thermal units (e.g. fuel cycles), which can influence the scheduling of maintenance activities. In addition, there is no official view on the maintenance works and LTO planning for the two units that are assumed to be extended in the CENTRAL scenario. Such risks are not incorporated in the values used in the CENTRAL scenario (composed of both the ‘technical forced’ and the ‘long lasting forced’ outages) as it is assumed that nuclear extension works and maintenance will be performed outside of critical periods for adequacy. So-called ‘common mode’ failures of units are not explicitly taken into account in this analysis as the values provided only look at averages. Some ‘long-lasting’ forced outage events can have an impact on more than one nuclear unit. Indeed, given the similar design/construction of the two most recent units, any anomaly found in one unit could also be found in the other one. Common mode failures have already occurred several times in Belgium (microflakes, concrete degradation on bunker buildings) but also in France. Combined with the discretionary nature of these events, the impact on the contribution of nuclear units to adequacy is exacerbated.

In addition to the forced outage rate there is an additional risk from the planned outage rate during winter of 8.1%. Sensitivities on the nuclear availability assumptions are integrated in this study.