22-Mec-B3 Energy Conversion and Power Generation · December 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. National Examinations, December 2014 — 07-Mec-B3 Energy Conversion and Power Generation. Three hours, closed book. Section A is calculative (Questions 1–4) and Section B is descriptive (Questions 5–6); a candidate answers three from Section A and one from Section B, four questions of 15 marks each constituting a complete 60-mark paper. Reference data for particular questions are bound in as attachment pages 9–13, reference formulae and constants as pages 14–17, and the Granet & Bluestein steam tables as pages 18–35. All six questions are solved here, because the set is a study resource rather than a three-hour sitting.
Reference texts. I. Granet and M. Bluestein, Thermodynamics and Heat Power, 6th ed. (the steam tables bound into this paper) · M. M. El-Wakil, Powerplant Technology (station heat balances, condensers, feedwater heating, nuclear and renewable plant) · Y. A. Çengel and M. A. Boles, Thermodynamics: An Engineering Approach, 9th ed. (Brayton and Rankine cycle analysis) · Y. A. Çengel, Heat and Mass Transfer, 6th ed. (surface-condenser and recuperator performance).
Property data. Every enthalpy, entropy and saturation temperature quoted below is read from the tables bound into this examination paper — General Constants on page 15 (\(c_p\) and \(c_v\) for helium, air and water), the Question 2 enthalpy table on page 10, the Koeberg condenser data sheet on page 11, the Belledune heat balance diagram on page 13, and Granet & Bluestein Tables A.1–A.4 on pages 19–35. Where a table entry has to be interpolated the interpolation is shown.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
The question that governs everything else here is what the utility means by “2000 MW.” If it means firm capacity that can be counted on at the winter evening peak, nuclear and wind are not comparable products, and the comparison becomes a discussion of what each can and cannot be asked to do. That distinction runs through every aspect below.
Number of generating units. Two 1000 MW-class units, or three units of about 700 MW in the CANDU range, cover the requirement on the nuclear side. On the wind side, a modern utility-scale machine of 3.6 MW gives 556 turbines, and even the largest machines available for onshore Canadian deployment would leave more than 400. The contrast is not merely arithmetical: it drives the number of contracts, permits, grid connections, access roads, maintenance crews and landowner agreements by roughly two orders of magnitude. Against that, 556 turbines can be built in tranches that each earn revenue as they are commissioned, while a nuclear unit earns nothing until the whole of it is complete.
Land and space requirements. A two-unit nuclear station occupies a few square kilometres of dedicated, secured, exclusively-used site — Darlington and Bruce are useful Canadian benchmarks. A 2000 MW wind array at conventional spacing of five rotor diameters across the prevailing wind and ten along it needs about 0.7 km2 per 3.6 MW machine, so roughly 400 km2 of array area. The crucial qualification is that only one to two per cent of that is physically occupied by foundations, pads and roads; the rest remains in agricultural or grazing use. So the honest statement is that wind uses a hundred times the territory and a comparable amount of exclusive ground, which makes siting a question of land-use compatibility and public acceptance rather than of land availability.
Environmental impact. Neither option emits carbon dioxide, sulphur dioxide, nitrogen oxides or particulate matter in operation, which is the premise of the question. Their residual impacts are entirely different in kind. Nuclear power produces a small volume of intensely radioactive spent fuel requiring institutional control on a geological timescale, needs a substantial cooling-water withdrawal with its associated thermal plume and entrainment of aquatic organisms, and carries a very low-probability, very high-consequence accident risk that dominates public perception. Wind produces no waste stream of consequence, needs no cooling water at all, but imposes diffuse landscape, noise, shadow-flicker and avian and bat mortality effects over a very large area, and its blades remain difficult to recycle. A Canadian environmental assessment would treat these as different questions, not as more or less of the same question.
Reliability, capacity factor and the ability to follow load. This is where the two diverge decisively. A modern nuclear unit achieves a capacity factor of 85–92 % and its unavailability is scheduled — planned outages of known duration, at times of the utility's choosing. Onshore wind in most Canadian regions achieves 30–40 %, and its unavailability is dictated by the weather, uncorrelated with demand and only partly forecastable. Numerically, 2000 MW of nuclear at 90 % yields about 15.8 TWh a year; 2000 MW of wind at 35 % yields about 6.1 TWh. To deliver the same energy would take roughly 5100 MW of wind, and even then it would not deliver the same capacity, because the wind can be still across an entire region on the coldest evening of the year. Utilities recognise this by assigning wind a capacity credit of only ten to twenty per cent of nameplate. On load-following, a CANDU or PWR can manoeuvre over a useful range but is operated as baseload for both economic and fuel-management reasons; a wind farm can only be curtailed downward, never dispatched upward. Neither is a load-following resource in the sense a hydro or gas plant is.
Effluents and emissions. Nuclear operation releases small, regulated quantities of tritium and noble gases and a large low-grade heat rejection to water or air; the fuel cycle carries mining, milling, conversion and long-term storage burdens. Wind releases nothing in operation, and its life-cycle emissions arise almost entirely from steel, concrete and transport during construction. Both are an order of magnitude below any combustion alternative.
Construction and grid connection. Nuclear construction is a decade-long, capital-intensive project concentrated on one site, with heavy demand on specialised skills, and a well-documented history of schedule risk; a decision taken today for a 2024 need is already tight, and a new-build programme would very likely miss it. Wind construction is modular, fast and repeatable — two to three years for a large array — and its schedule risk lies in permitting and transmission rather than in the machines. On grid connection, the nuclear station makes one high-voltage connection at a point the utility chooses, but its loss is the single largest contingency on the system and sets the spinning-reserve requirement. The wind array needs an extensive collector network and often new transmission to reach the resource, but no single failure is significant; its system cost appears instead as reserve, ramping and voltage-support obligations to absorb the variability.
Maintenance. Nuclear maintenance is concentrated, highly regulated and skilled, on planned outage cycles, with an eventual mid-life refurbishment. Wind maintenance is dispersed and logistical — hundreds of gearboxes, blades and converters at hub height across hundreds of square kilometres, with weather-dependent access.
Recommendation. If the utility genuinely needs 2000 MW of firm, dispatchable capacity by 2024, nuclear is the only one of the two that supplies it, and the recommendation is a two-unit nuclear station — with the immediate caveat that a new-build project decided now will not be in service by 2024, so the realistic nuclear route is life extension or refurbishment of existing units to preserve the capacity that already exists. Wind alone cannot meet a firm capacity requirement of this size without a comparable quantity of firm backup, which would defeat the purpose. The defensible answer for most Canadian utilities is therefore a portfolio: nuclear or refurbished nuclear to carry the firm baseload requirement, with wind added as a low-impact energy resource that displaces fuel and emissions from the marginal plant whenever it blows, backed by the hydro or gas capacity the system already holds. Recommending wind as the sole answer to a capacity need, or dismissing it because its capacity factor is low, would both misread what the two technologies are for.
