20.10.2023

Mobile NPPs and what they are «eaten» with

Boris Plavnik

Let's talk about mobile nuclear power plants in detail.

Why would we need such a thing at all? For it provides power supply for remote objects: military and industrial. In case of a sudden shutdown of a conventional power plant (whether as result of natural or man-made disaster), a mobile one can be quickly moved to the site and resolve the problem until the normal power grid is restored.

Those days the nuclear industry was very innovative, and actually everything was designed from scratch. Nevertheless, in 1957 the nuclear icebreaker «Lenin» was launched, the experience of which could be relied upon up to now. So in 1960, Obninsk Institute of Physics and Energy initiated the TPP-3 (Thermoelectric Power Plant) programme.

TPP-3 Self-propelled Power Plant

It’s one thing to build it into a huge ship, and it’s another – to put it at a land chassis. The choice was made for a caterpillar chassis. However, the largest platform, the T-10 heavy tank, was still not enough - it had to be lengthened from 7 to 10 rollers. Even having got such a design, the power plant had to be deployed on four self-propelled vehicles. The first one carried a reactor (two-circuit water-water reactor), the second one - a steam generator, the third one - an electricity generator, and the fourth one carried a control centre.

The dimensions were limited by railway transport standards, hence the appearance of the machines. And that is why they were grimly nicknamed «coffins». The plant was designed and built in less than a year, which is not bad for such a new project.

Upon arrival at the site, the machines would be put in the required order, connected to each other - thus the reactor would be prepared to operate. The output power of 1.5 MW was pretty much in view that electricity generation required a lot less fuel than diesel generators and one working cycle would last up to  250 days.

This one got neon inside :).

The plant tests were conducted until 1965 and resulted in successful proof of the viability of mobile NPPs. Nevertheless, TPP-3 was admitted to be unsuitable for economics. In parallel, a navigable NPP project was probed, but the military abandoned it.

But that was not the end of the story. In 1963 a kind of tender for projects of mobile NPP was conducted, which was initiated by military again. The project was supposed to generate a smaller rate of power (500-800 kW), but the rest of requirements became stricter: temperature regime should have been from -50 to +35 °C, the plant should have been able to operate in high humidity, and the facility should have had the ability to fit into the dimensions both of an aircraft cabin and railway carrier. So, the projects were introduced by the Institute of Nuclear Energy of the BSSR Academy of Sciences (Minsk), PhEI, (Physics and Energy Institute, Obninsk), АEI (Atomic Energy Instite named after Kruchatov, Moscow) and EDBME (Experimental Design Bureau of Mechanical Engineering, Nizhny Novgorod). Preference was given to the first project, but the initiation of the work started 10 years later, when a special design bureau was established. And even some more than 10 years passed before the prototype was produced, which was named «Pamir-630D».

Pamir 630D in its entirety

... and part of its reactor

The main feature of the single-circuit reactor was the use of nitrogen tetraoxide (N₂O₄) as a coolant and working body.

In the first place, it allowed to reduce the size and mass of the plant, and in the second, – it reduced greatly water consumption, which had been specified in the technical requirements. It sounds great, but the substance is extremely aggressive, especially at the points of phase transitions. The problem was partially solved by adding nitrogen monoxide, but that was true only for the reactor zone. The «cocktail» was called nitrin. But it still had one nuance: when reacting with water, N204 turns into nitric acid, with all the consequences... whatever it means. Under normal conditions, this tetraoxide stays in the form of an orange vapour. One day, while testing the facility, a small leak occured, and one of the design bureau's employees unintentionally inhaled this gas... which reacted with the moisture in his lungs. The result was fatal.

Nevertheless, the use of nitrin allowed the reactor unit to be crammed into a semi-trailer with a total weight of 65 tonnes. The second trailer of the same type housed the generator unit, the tractor for them was MAZ-537. Three more KRAZs carried the reactor control system and the standby power unit. Compared to TPP-3, some few less unique vehicles were used in the project. The capacity of this NPP constituted 630 kW, which is reflected in its name.

Operating was possible only in stationary mode. Upon arrival at the site, the semi-trailers would be put on jacks, their wheels would be removed (who knows why) and the semi-trailers would be connected to each other. The other vehicles would be parked no closer than 150 metres from the reactor. The plant was controlled by two computers having a third one in hot standby.

The prototype was ready by the end of 1985 and began to undergo various tests. But at the end of April of the following year an accident occured at ChNPP (Chernobyl Nuclear Power Plant). The degree of radiophobia sharply increased, and uncomfortable questions arose such as «Why is this experimental atomic reactor is placed in such close proximity to the capital of the Soviet Republic?». So in the wake of this, in 1988 the project was closed down and the only prototype was scrapped.

That was the end of the history of mobile nuclear power plants on "land". It was pretty evident that the downsides of placing such plant into road transport with rigid mass-dimension frames included difficulties of fitting anything into it with no safety guarantees acceptable for nuclear projects.

However, mobile nuclear power plants got their living on the water - two and a half years ago Rostechnadzor issued a licence to Akademik Lomonosov navigable power unit; on 22 May 2020 it was put into commercial operation and since June, 30 it has been supplying heat to the Pevek HTS (Hydro Technical Structures).

Source: habr.com