The dumpload (or dump load) hypothesis is:- so-called nuclear power stations are "dumploads" or "dump loads" - in effect giant electric kettles which waste energy by heating and boiling water. As far as I know the initiator of this idea was the online Canadian commentator, 'cactusneedles'.
 What is a dumpload? Well, everyone knows from experience what happens when power supplies are too low: equipment dims or operates slowly, or malfunctions. Brown-outs and blackouts are the way such events are described when they happen on a large scale.
However, there are problems with oversupply of power too - equipment may overheat, run too brightly, explode or melt, or otherwise malfunction, usually in damaging ways. If you google or bing 'dumpload' you'll find advice aimed at people using domestic gasoline generators or domestic windpower - their dumploads are usually resistors, which in effect are electric heaters.
 Please give an example! OK - imagine a popular TV event - ball game, for example. In the interval, 2 or 3 or 5 or 10 million people may make coffee (US) or tea (Britain)! A typical British kettle uses 3 kilowatts; if 5 million people do this in a period of several minutes, this act alone increases demand by 3000 watts x 5,000,000 - a total of 15 Gigawatts. Note that 'the current record holder for the largest coal fired power plant [is] 5.78 gigawatts.' Just boiling water to drink can cause a huge absolute variation in load, though it is still only a part of the total load.
Added 27 August 2014: Let me give a few more examples of the need to match power supply to equipment. People often aren't aware that the voltage supply they are using is monitored and adjusted all day long.
• Lightning strikes. These are powerful enough to destroy and vaporise metals. Evidently, they are too powerful for normal electrical equipment.
• At the other end of the scale, some readers may have tried powering light bulbs/ globes for mains use with an ordinary small battery. There is of course little or no light. In the same way, run-down batteries give little light with bulbs. As LEDs, which use low power, become more popular, no doubt there will be incidents where they are connected to the mains and are ruined.
• The above examples are extreme; but the same logic applies to domestic and industrial electrical equipment. If the voltage and alternation is right, they are designed to operate correctly. They are often said to 'take the right amount', but of course this depends on the voltage being set correctly. There are meters which measure AC voltage, which can be watched and seen to fluctuate.
• Another example familiar to many people shows up in foreign travel: for example, UK electricity is 240V alternating at 50 cycles per second. In the USA, domestic electricity is 110V at 60 cycles. An American electric shaver plugged into a hotel socket will blow; a British electric shaver plugged into a US socket will work feebly. This is why they sell adaptors!
• Yet another example is earth / ground connections. To dump a gigawatt by earth / ground connection would generate a huge amount of heat in the earth itself, where the heat would be unable to escape. The design would be unsafe, since if the rods melted there would be a huge power surge.
• To see dumploads in action in small circuits, not connected to a grid, Google 'caravan and motorhome dumploads'. A typical specification reads: 'Our 500w dump load is utilised to ‘bleed-off’ excess power from your off-grid power system when your battery bank is fully charged. These 500w dump loads are designed to be connected to either our 45A diversion controller or 60A diversion controller working off a 12v or 24v off-grid power system. ...' The 'diversion controller' directs the right amount of power into the dumpload, depending what's turned on in the motorhome.
• Many coal or gas burning power stations incorporate their own dumploads: the site has for example coal delivery arrangements and storage areas, feed mechanism to the boilers, turbine room(s), feeds to the pylons, plus cooling towers to operate when the output is too large, and ash disposal.
Comments based on doubts in fakeologist.com, by 'psyopticon' on August 27, 2014 Canadian time]
 Note that power consumption consists of a base load, more or less analogous to 'fixed costs' in a business. Depending on the time of year, heating and industrial and street and shop lighting, factory and office consumption, and other stable elements, make up the fairly predictable base load. Then on top of these are the variable loads.
 Note that it is much more difficult to start up a power station and bring it online, than it is to waste surplus electricity. This is the crucial reason why it makes sense to plan for and build dumploads. If power stations could be fired up and brought online instantly, the problem wouldn't arise.
 Is there supporting evidence for the hypothesis that some or all 'nuclear power stations' are dumploads?
Yes. Here are some facts from several sources---
*There have been large-scale blackouts in which, despite being connected to grids, nuclear power supplied zero electricity.
*There appear to be no parts of the world exclusively supplied by nuclear power: the EIA state no such place exists.
*On a smaller scale, evidence of the motive force of supposed nuclear powered ships is inconclusive. The EIA's only examples are nuclear subs (invisible) and aircraft carriers (refueled each day with jet fuel, for the jet fighters of course - but that fuel could also be running the aircraft carrier).
*It is in practice hard to tell in which direction electric power is moving. (One of Enron's frauds was to claim electricity was generated out of state).
*The secrecy and security make investigation difficult. It's entirely possible that the nominal controller of a nuclear plant would be unaware of the actual practice - he may believe he's adjusting his equipment to increase power supply out, whereas in fact his actions simply reduce the the power coming in to be wasted.
*Only about 15% of electricity world-wide is 'nuclear'. This figure is a plausible range to allow for wastage of power when domestic demand fluctuates.
*China has built large numbers of coal-fired power stations, despite being supposedly a nuclear power. Why haven't they built nuclear power stations?
*Why have the extravagant claims made for nuclear power - virtually free, unlimited, unmetered, electricity - failed so incredibly to even begin to come true?
* All the contracts to maintain these installations (according to Alex Jones - not checked) are exclusively with Jewish companies. Why would they need to do this?
* Google for 'patents electric steam boiler'. Like patent 1543514, which is a 5 megawatt steam boiler. Doesn't really prove that nuclear electrical generation is fake. But, why do they have them?
*Note added 11 Sep 2012: A reader found this site by searching with the keyphrase 'If they can have nuclear aircraft carriers, why not nuclear factories?'—A factory is comparable is size with an aircraft carrier; its lighting, heating, conveyors, robots, machinery could be powered by nuclear power if nuclear power is genuine. So why doesn't this happen? This site suggests it doesn't happen because it doesn't work.