ABWR — Tk = 330 °C, Tc = 35 °C

η Xh = 72.4 %, η energy = 37.8 %. Direct-cycle BWR: steam generated directly in the core, no steam generator. The condensation temperature of 35 °C reflects the air-cooled condenser design basis per NRC SDAA.

The direct-cycle architecture eliminates steam generator irreversibilities. The source (31.2 %) is comparable to the EPR despite a simpler secondary circuit. With Tc = 35 °C, the condenser share (18.6 %) is lower than would appear at 15 °C.

📐 Exergy Balance

• ABWR

RBMK-1000 — Tk = 324 °C

η Xh = 65.2 %, η energy = 33.7 %. Direct-cycle boiling water channel reactor, 284 °C / 285 bar.

Six feedwater heaters (7.1 %) operate over a wide temperature range. HP1 turbine is the most loaded individual stage (10.3 %), fed by direct-cycle steam at moderate quality.

📐 Exergy Balance

• RBMK-1000

VVER-1000 — Tk = 313 °C

η Xh = 65.9 %, η energy = 33.5 %. Modern horizontal steam generator (PGV-1000M), primary at 278 °C / 160 bar.

The source (19.7 %) is the lowest among all WCR detailed models, reflecting the well-matched primary temperature and horizontal SG design. The turbines (46.8 %) are consequently the dominant component — a paradoxical sign of a well-optimised source side.

📐 Exergy Balance

• VVER-1000

VVER-70 — Tk = 283 °C

η Xh = 57.5 %, η energy = 27.7 %. K-70-29 turbine, saturated steam at 29 bar, moisture separator only (no reheater). Novovoronezh units 1–2, 210 MWe (3 × 70 MWe), 1964 design.

Modelling note: The K-70-29 turbine operates on saturated steam with a moisture separator only — no reheater. The feedwater temperature Talim is not documented in available sources for the Novovoronezh plant; it has been estimated from the known thermal power (760 MWth) and electrical output (210 MWe). A ±20 °C uncertainty on Talim propagates to approximately ±3 pts on the source % and FWH % individually, but affects η Xh by less than ±0.5 pt.

📐 Exergy Balance

• VVER-70

CANDU Pickering — Tk = 292 °C

η Xh = 68.4 %, η energy = 33.5 %. Natural-uranium reactor, primary at 260 °C / 45 bar.

The condenser (25.7 %) is the highest among all detailed WCR models — a consequence of the low primary temperature (260 °C) and a relatively simple feedwater heating circuit.

📐 Exergy Balance

• CANDU Pickering

Superphénix — Tk = 600 °C

η Xh = 64.7 %, η energy = 43.3 %. Sodium-cooled fast reactor with intermediate Na–Na heat exchanger (IHX). Steam at 487 °C.

The SG superheater (11.5 %) is the dominant SG component — steam rising from saturation (~310 °C) to 487 °C against secondary sodium. The turbines (16.0 %) are the most balanced of all reactors. The IHX costs only 4.1 % for its fundamental safety function.

📐 Exergy Balance

• Superphénix

HTR-PM — Tk = 624 °C

η Xh = 58.6 %, η energy = 41.7 %. Helium coolant at 750 °C outlet, six-stage turbine, steam at 566 °C / 138 bar.

Note on source accounting: The steam generator (20.6 %) is modelled as an internal exchanger without a Tk annotation and is not counted in the Source % column above.

The full source chain (core + SG) represents 64.1 % of total irreversibilities — comparable to the AGR structure, where the CO₂ circuit also contributes significantly to the source term.

HTR-PM Shindao Bay: a second exergy balance has been computed from operational data published by Dong et al. (Nat. Commun. 16, 2778, 2025), based on the HMI readings of the actual plant. The Shindao Bay plant was operating at ~80 % of rated power, with turbine polytropic efficiencies of ~70 % (vs 83–93 % at nominal). The exergy balance reveals a drop from η Xh = 60.9 % to 50.4 % — entirely attributable to the turbines, which rise from 18.9 % to 30.5 % of total irreversibilities. The source and condenser contributions are barely affected.

A full comparison between the nominal design and the Shindao Bay operating data is presented on the dedicated HTR-PM page.

📐 Exergy Balances

• HTR-PM nominal
• HTR-PM Shindao Bay — model based on HMI data from Dong et al. (2025), not validated by original authors

→ See also: HTR-PM — Design vs Shindao Bay operating data

Canadian SCWR — Tk = 670 °C

η Xh = 68.5 %, η energy = 47.6 %. Supercritical water-cooled reactor, direct cycle, coolant outlet at 625 °C / 25 MPa. The highest η energy of all reactors in the corpus — a direct consequence of the supercritical steam conditions.

The source dominates at 51.9 % — seemingly paradoxical for a high-efficiency reactor, but thermodynamically consistent: at Tk = 670 °C the Carnot factor (1 − T₀/Tk) is 0.570, so even a well-matched heat exchange still attributes a large fraction of the exergy budget to the source. The condenser (11.1 %) is among the lowest in the corpus — only the AGR and HTR-PM go lower — a direct benefit of the high steam temperature.

The FWH contribution (10.5 %) is notable: nine feedwater heating stages (4 LP heaters, a deaerator and 4 HP heaters) operating over a wide temperature range from the condenser (~30 °C) to the supercritical feedwater inlet (~314 °C) generate significant mixing irreversibilities. This is the thermodynamic price of regenerative heating in a supercritical direct cycle.

Note on the SCWR model: the Canadian SCWR design studied here is based on the pre-conceptual design described in Chatoorgoon (2008) and Leung et al. (2010). Primary data for a validated prototype are not yet available. The exergy balance reflects the thermodynamic model used in Chapter 8 of the book.

📐 Exergy Balance

• Canadian SCWR

EPR Flamanville 3 — Tk = 334 °C

η Xh = 73.4 %, η energy = 38.5 %. Eight feedwater heaters, double reheat, steam at 294 °C / 78 bar. The most thermodynamically efficient reactor in the corpus.

The FWH contribution (1.5 %) is the lowest in the corpus — eight stages each operating at a small temperature difference. No single component dominates: this well-distributed balance is the signature of a highly optimised cycle.

📐 Exergy Balance

• EPR Flamanville 3