EDF should be advised to use hybrid bonds at the **high end of the allowable S&P equity-credit envelope**, subject to annual market capacity and execution limits.

Key reasons:

1. **Very severe 2022 credit deterioration**
   - EBITDA/EBE collapsed from **€18.0bn in 2021 to -€5.0bn in 2022**.
   - Operating profit fell to **-€19.4bn**, and net loss was **-€18.2bn**.
   - Operating cash flow turned sharply negative: **-€7.4bn** versus **+€12.6bn** in 2021.
   - Free cash flow was deeply negative after capex: operating cash flow of **-€7.4bn** plus investing outflow of **-€25.1bn**, including **€18.3bn** of capex.

2. **Leverage and funding pressure are very high**
   - Financial liabilities increased materially:
     - Noncurrent financial liabilities rose to **€71.1bn** from **€56.5bn**.
     - Current financial liabilities rose to **€71.8bn** from **€45.0bn**.
   - Total financial liabilities therefore rose by about **€41bn** year on year.
   - Equity declined from **€62.0bn to €46.6bn**, despite a **€4.2bn** equity issue.
   - This is a classic situation where hybrid capital can help preserve rating metrics by receiving partial equity credit while avoiding full common-equity dilution.

3. **Large structural investment needs**
   - EDF is a capital-intensive integrated utility with nuclear, network, generation, and concession assets.
   - Capex remains very high at **€18.3bn** in 2022.
   - Nuclear decommissioning and back-end-cycle provisions remain enormous at **€56.0bn**, even after declining from 2021.
   - The company is therefore not facing merely temporary refinancing pressure, but a large ongoing capital requirement.

4. **Existing hybrid capital structure supports continued use**
   - EDF already has perpetual subordinated bonds in its capital structure.
   - 2022 cash flow shows **€994m** of proceeds from subordinated liabilities and convertible instruments, and **€606m** of payments to holders of perpetual subordinated bonds.
   - Because hybrids are already established in EDF’s capital structure, incremental issuance is more credible and less of a structural novelty.

5. **Hybrid issuance would meaningfully improve adjusted leverage**
   - S&P caps equity credit on hybrids at **15% of total adjusted capital**.
   - Given EDF’s high debt burden and weakened equity base, maximizing eligible hybrid equity credit would provide material support to debt-to-capital and FFO/debt-style metrics.
   - This is particularly relevant because 2022 profitability and cash flow metrics are temporarily extremely weak, making balance-sheet support important for preserving investment-grade credit quality.

6. **Cost consideration is negative but not decisive**
   - Market rates rose sharply in 2022:
     - 10-year swap average rose to **1.927%** from **0.053%** in 2021.
     - Subordinated nonfinancial IG spread proxy rose to **2.295%** from **1.298%**.
   - Therefore, new hybrids would be more expensive than EDF’s historic funding cost.
   - However, the scale of EDF’s funding needs and rating pressure outweighs the higher coupon cost. The alternative would likely be more senior debt leverage or common equity support.

7. **Practical issuance constraint**
   - The prompt caps annual hybrid issuance at about **€3bn per year**.
   - Over the next 18 months, practical issuance might therefore be around **€4.5bn**, subject to market access.
   - Even if this does not immediately fill the entire 15% S&P equity-credit capacity, the strategic target should be to use the maximum permitted envelope because the credit need is exceptionally strong.

Overall, EDF exhibits the characteristics associated with the **15%** guidance bucket: very high financing needs, extreme leverage pressure, large ongoing capex, major negative cash flow, and a strong need to stabilize adjusted credit metrics. The presence of existing hybrids further supports continued issuance.

<answer>15%</answer>