Entergy's nuclear plant trips and it blames MISO!
Though Entergy originally blamed MISO for the forced outages on May 26, public records now confirm that River Bend went offline on May 21 — five days earlier!
On Memorial Day, May 26, 2025, MISO declared a Conservative Operations period starting at 10:45 EST and terminating at 22:00 EST (I didn’t see a Conservative Ops termination notification). So, for 11 hours and 15 minutes, this Conservative Ops lasted. I assume this Conservative Ops period ended based on Entergy’s second press release, which pasted below.
Over 100,000 customers lost power in Louisiana region. See
https://x.com/davantelewis/status/1927433268250423571
During Conservative Ops, MISO states, “the conservative operations notification asks MISO members to defer, delay, or recall any non-essential maintenance. This notification provides MISO member operators an indication that system conditions may require special attention.”
This indicates that the Grid conditions are Yellow under Conservative Operations. Green indicates normal operating conditions. After Yellow, the next Grid conditions are Orange, Dark Orange and Red.
Orange is “The grid is stable and MISO has issued an Energy Emergency Alert 1 (EEA1).”
Source: MISO
Dark Orange is “The grid is stable and MISO has issued an Energy Emergency Alert 2 (EEA2).” And Red is “MISO has issued an Energy Emergency Alert 3 (EEA3).”
As you can imagine, each step ratchets up the actions that MISO takes and orders utilities in MISO to take.
For instance, under Orange – EEA1 – “EEA1 is the first level of emergency action, triggered when MISO can no longer meet the forecasted demand and operating reserve requirements without intervention. In other words, it indicates that power demand may exceed supply if no action is taken. By declaring EEA1, MISO operators can access additional generation to boost the electricity supply and maintain grid reliability.”
MISO Conservative Operations notification
This was the wording of the MISO’s May 26 Ops notification - “MISO has declared a Conservative Operations Initiate effective starting 05/26/2025 10:45 EST until 05/26/2025 22:00 EST.
Affected Region(s): South Region - EES, CLEC, LAFA, LAGN, LEPA, SME, EMBA, LAGT
Conservative Operations Initiate
Declared due to:
This declaration is occurring because: Unplanned Generation outages, Unplanned Transmission outages, Limited capability of transfers into area,”
MISO didn’t say what exactly happened on its website. I am sure we will learn more from MISO’s presentation soon at a Reliability Sub Committee meeting.
But Entergy was quick to blame MISO (“Action taken as directed by MISO”) for an outage it faced on its own side.
MISO Maximum Generation Emergency Declarations History for the South Region (2022-June 2024)
When looking into May 26 MISO’s Conservative Ops notification, it is worth noting the history of MISO Max Gen Declarations for the South Region. An entire summary if available here. I am only showing data for the South region from 2022 to June 2024 in the table below:
Source: Rao Konidena based on MISO data
We can compare what happened in the South region with the rest of the MISO region for the same time period in the next table.
MISO Balancing Authority1 had the same amount of declarations - nine- during that time period. Interestingly, MISO Central and North Regions had only four declarations compared to the nine in South region during that same time period (2022 - June 2024). Does this mean, there are more emergency declarations in the South region compared to the Central and North regions? Possibly.
Source: Rao Konidena based on MISO data.
Local news breaks that two nuclear plants were on outage
We now know that not one but two nuclear plant shutdowns caused these MISO Conservative Ops notifications. According to WWL Louisiana news story, “WWL Louisiana has learned the region's two nuclear power plants were down Sunday, causing widespread power outages in the New Orleans area.”
As we’ve since learned, the River Bend outage wasn’t a surprise trip. According to the Nuclear Regulatory Commission and reporting from NOLA.com, River Bend went offline on May 21 due to a known leak in the cooling system. Entergy identified the faulty valve on May 23 and completed repairs over the weekend. The plant returned to service at partial capacity on Monday, May 26. So the outage was not sudden or unplanned on the day of the blackout.
“The Waterford 3 nuclear plant was in the midst of a previously planned outage on Sunday afternoon, as part of regularly scheduled refueling and maintenance," a spokesperson for Entergy said. “Entergy typically conducts maintenance on its utility plants in the spring and fall, when loads are lower. The Waterford 3 maintenance and refueling outage was conducted in accordance with that policy and was planned months ahead.””
So, one nuclear plant – Waterford 3 was on planned outage and another nuclear plant – River Bend - had shut down due to a faulty valve on May 21 in the reactor’s cooling system, according to this NOLA.com news story.
Waterford 3 is 1152 MW, according to Entergy’s website. River Bend is 967 MW.
Waterford 3 was scheduled for a 30 day outage starting April 6th 2025, according to the Outage Calendar website. So, what happened to Waterford 3? Why didn’t it come back online on May 6th as planned if the Outage Calendar website is accurate?
But these combined nuclear plant outages in Louisiana caused MISO’s wholesale prices to surge to $1556 at the Louisiana pricing hub. See MISO Locational Marginal Pricing (LMP) map picture below.
Source: Zack Fradella on X showing $1556/MWh at the Louisiana node during outage period.
This means that a price surge is what could happen if nuclear plants trip in a small region like MISO South.
Recall, MISO North and South regions are constrained by transmission. It is called Regional Directional Transfer Limit (RDTL). This was put in place after SPP and others complained to FERC when Entergy decided to join MISO, not SPP.
Source: MISO
MISO Board has so far approved transmission build out – Tranche 1 and 2 for the North region, not South region. Tranche 3 is focused on the MISO South region and Tranche 4 is focused on the MISO North-South transmission interface limit.2
Most stakeholders in MISO know that South does not want to pay for transmission in the North region and vice versa. This is why MISO asked FERC and FERC approved a cost allocation methodology for each region.
Even though MISO plans for the entire MISO region that includes North and South, transmission costs are not shared across the entire MISO. I am sure these nuclear plant outages will lead to more discussions on transmission costs and the expansion of transmission lines across the North and South regions.
It’s also telling that Entergy’s persistent refusal to invest in transmission in South Louisiana continues to isolate the region. Despite high prices at the Louisiana node, nearby regions with lower-cost electricity couldn’t help. This “load pocket” vulnerability has been documented for years. The PSC Staff noted in a 2023 report that Entergy doesn’t evaluate transmission unless tied to a specific plant — unlike utilities in other states. That’s not a MISO problem. That’s an Entergy planning failure.
What Really Caused the Outages? A Timeline That Doesn’t Add Up
What’s now clear is that Entergy’s early explanation—pinning the blackout on an unexpected nuclear trip—was misleading. The River Bend nuclear plant was taken offline on May 21, five full days before the Memorial Day weekend outage. The cause was a valve leak, which Entergy reported to the NRC. Yet despite this lead time, MISO called for forced outages with almost no advance notice to utilities. According to the New Orleans City Council, Entergy was given just three minutes on Sunday before being told to cut power. This is where the real failure lies: a breakdown in planning and forecasting between Entergy and MISO, not a surprise plant trip.
As Logan Burke of the Alliance for Affordable Energy asked: “The question is, what else do we not know about?” MISO cited “unplanned generation and transmission outages” — but no details have been released. Why weren’t 280 MW of industrial demand response activated? Why wasn’t the public asked to conserve power days earlier? These are questions the City Council and Louisiana PSC are now demanding MISO and Entergy answer.
Entergy’s press releases
Entergy’s first press release on May 25th states, “Entergy Louisiana and Entergy New Orleans forced to initiate periodic power outages to customers
Action taken as directed by MISO”
https://www.entergynewsroom.com/news/entergy-louisiana-entergy-new-orleans-forced-initiate-periodic-power-outages-customers/
Entergy’s second press release on May 25th (no time stamp3) states, “Order for required power outages ends for Entergy Louisiana and Entergy New Orleans
Action taken as directed by MISO”
https://www.entergynewsroom.com/news/order-for-required-power-outages-ends-for-entergy-louisiana-entergy-new-orleans/
MISO’s Balancing Authority includes Manitoba Hydro, the Canadian utility with transmission ties to Minnesota Power. Manitoba Hydro is not technically in the MISO market. That’s the difference between MISO Balancing Authority and MISO Market Footprint.
https://www.misoenergy.org/planning/long-range-transmission-planning/
There are time stamps for Entergy Texas news releases.