Rock Farms and Nuclear Reactors

Chapters

Chapter 1 – Which concerns rock farming
Chapter 2 – Which describes the refuelling of a nuclear reactor
Chapter 3 – In which we hear from Zecora, but Luna has the last word

Chapter 1 – Which concerns rock farming

It should have been an excellent day for studying. A cold wind, blowing from the north, had caused the temperature in Ponyville to drop sharply. Ponies throughout the town had retreated into their houses and closed the doors and windows. Summer was over and it was time to start thinking about indoor activities and preparations for winter. A good day to stay indoors with a book – or a stack of books – which was just what I planned to do. Today I would disprove an old mares’ tale that said that there was somehow enough energy locked up in a teaspoon of water to provide all the power Equestria needed for a year. Utter nonsense. I had already drafted a letter to the Ponyville Express and just needed to check a few facts. I had a pile of relevant books stacked neatly on my desk. After a few minutes of staring out of the window, watching the wind shake the outer branches of my tree sending the leaves dancing in the air, I quit day dreaming, opened the first volume in my pile, and started reading:

Energy in Equestria

Life in Equestria is sustained by the energy from Celestia's Sun. Plants absorb this energy and store it. Ponies and other animals get their energy from plants through the food we eat. Without magic, energy can never be created or destroyed...

The sound of somepony hammering a hoof on the door downstairs momentarily disturbed my concentration, but I paid no further attention. Spike could take care of whoever it was. I continued reading.

...While nearly all energy in Equestria originates from the sun, there is an important exception: the energy present in the rocks beneath our feet, which produces heat deep in the core of our planet...

I heard the sound of a kangaroo hopping up the staircase. Actually it was a pony, and I had a pretty good idea which one.

“Hiya Twilight! Whatcha doing? I haven't seen you since yesterday...”

Pinkie Pie.

“...and I was gonna ask you about... Well actually I was gonna ask you loads of things. What's your favourite flavour of... Oh! You're stuck into studying. No worries. I won't bother you. I really just stopped by to ask if you could spare a bit of uranium. Have you got any?”

“Sure,” I answered without paying much attention to what she was saying, “have a look in the kitchen.”

“Okeydokeylokey.”

I looked up at the window and watched the reflection of her pink mane bouncing away, and breathed a sigh of relief. Maybe my afternoon of studying could go ahead as planned. Much as I enjoy Pinkie's company, I do prefer it when she gives some advanced notice before visiting, which lets me properly schedule the time, ensure I have an adequate stock of sugary snacks, and invite Rainbow Dash to come at the same time so when things get too much, I can just leave them planning pranks, and retreat to my bedroom study. I turned back to the page in front of me trying to ignore the noise from downstairs as Pinkie ransacked the kitchen for whatever she was looking for.

...Nuclear processes such as the fission of uranium atoms convert mass into energy, giving off heat...

Wait a moment. Did Pinkie just say 'uranium'?

I spun around to see Pinkie bouncing back into the room with a roll of paper in her mouth. She stopped in the doorway and dropped the scroll, letting it unroll all the way across the floor to my hooves revealing a long list.

“I've been through your kitchen cupboards, refrigerator and freezer and taken a full inventory,” she announced. “They contain: six sacks of oats; two bales of hay; eight pounds of carrots; four bags of apples; fourteen different varieties of tea; a large jar of cookies; thirty-five tubs of ice-cream; eighty-six bars of chocolate; five half-full bottles of maple syrup; some yellow mushy stuff that smelt a bit like peanuts; and twelve bottles of some really weird looking fluorescent liquid labelled 'experimental sample #01' to 'experimental sample #12'. I also found a badly stained copy of 'Magical Mysteries and Practical Potions'; a textbook on extragalactic astronomy; and a dictionary of griffin dialects.”

She looked up, having reached the end of the list. “But no uranium. Are you sure you keep it in your kitchen? That's not really a sensible place to store toxic material.”

“Sorry Pinkie,” I mumbled as my brain tried to process all the information it had been thrown. Must remember to ask Spike to tidy up the kitchen. “You want some... uranium?”

“Yeah, I need some five percent enriched uranium fuel pellets, or mixed oxides will do just as well.”

“What?” I said.

“Mixed uranium and plutonium oxide fuel.”

“No... I mean... What do you want it for?”

She rolled her eyes at me. This was evidently a stupid question.

“To make a sustained nuclear chain reaction. What else do you do with it?”

I stared back at her, unsure what to say. “Err... I'm sorry Pinkie, I don't have any uranium or plutonium.” Should I be apologising for that? Was it remiss of me to not have it in stock?

“Ah, too bad. I'll just nip out to the rock farm and get some more. I just thought given all the cool science stuff you have in your basement, you might have some. But, no problem, see you around. La-la-la-la-la.”

Pinkie skipped off down the stairs leaving me staring at the wall trying to get my thoughts in some sort of order: Pinkie Pie, uranium, nuclear chain reaction. This was not the first time I had been abruptly left in a state of complete bewilderment by my fuchsia-maned friend. In fact, on this occasion, Pinkie's explanation actually followed a logic I could recognise, even if it didn't add up to any sense whatsoever.

I suddenly became aware that a little dragon was standing in the doorway staring at me with an expression of concern.

“Are you okay Twilight?” said Spike, “you've gone kinda pale.”

I turned to face him. “Pinkie Pie said she needed some uranium,” I said.

“She must be baking a new flavour of cupcake,” he replied, licking his lips.

“Uranium is a radioactive heavy metal,” I shouted, “it's highly toxic!” It occurred to me as I said this that it might not be true for dragons. “And she said she wanted to make a nuclear chain reaction!”

“She's just being Pinkie Pie,” he said calmly.

He was right. We had been here before. And at this point the usual solution was to say 'It's just Pinkie Pie', pretend that this explained everything, and get back to whatever I was thinking about before, without further ado. Indeed experience had taught me that any other action might lead to random heavy objects dropping on top of my head. However this time, some level of intuition inside my brain was flashing a warning signal that if I ignored this, it might somehow end in Ponyville disappearing under an enormous pink radioactive mushroom cloud.

“Do you know what a nuclear reaction is?” I asked Spike.

“Erm... no.”

“You know the story of the Incantatem Fissio Individuuma?”

“Erm... no.”

“Have you still not read that book about obscure unicorn history that I gave you two years ago?”

“Erm...”

“It was one of the most important events shaping the foundation of the pre-classical era. During the ancient Equestrian wars, Starswirl the Bearded discovered a powerful magic to split atoms of uranium in a nuclear reaction, and thus convert matter into enormous amounts of free energy. He used it to defeat the Dark Shogun Sorcerers who were terrorising the Eastern Empire, but at a terrible cost. Whole towns and cities in Neighpon were laid waste, and the land remained poisoned for years. He swore the spell should never be used again, and never wrote it down.”

I did not mention that although it had never been written down, legend had it that the spell had been passed by word of mouth to his most trusted students. There were many stories about it. Some talked of a later, even more powerful enchantment which used this power to fuse hydrogen atoms together, releasing further energy. There were rumours that Princess Celestia knew it, but I found that difficult to believe. I could not associate my trusted mentor with such dark magic.

My number one assistant just looked at me blankly. I thought back to what I had read about Starswirl's terrible spell. The principle – to split apart atoms and reform them as lighter elements, so that the mass difference would be liberated as energy – was simple, but the magic to manipulate matter at this scale must be formidable. Was Pinkie really dabbling in such dark arts? She couldn't do magic as I knew it, but she had improbable powers of her own. Did she understand the danger? I made a decision: this needed further research.

“Spike!” I yelled, “I'm going out. Keep an eye on the library. And in the meantime, can you clean out the kitchen?”

I wrapped a scarf around my neck and ran out the door. Outside I scanned my field of view and caught sight of Pinkie hopping up a near vertical hillside in the distance with her characteristic gait. Boy, that pony could move fast. I focussed on the moving pink pony, calculating her expected trajectory, then closed my eyes and teleported to the summit of the hill.

It turned out I had pinned down her location more accurately than anticipated. On materialising out in the open countryside, I had a momentary vision of a huge grinning pink face bearing towards me, before we collided and were both sent rolling head over hooves down the hill.

I picked myself up groaning, while Pinkie bounced around me.

“Twilight! Did you find that you did have a stash of uranium hidden under your mattress?”

“Err... no... I... well... erm...”

“You want to see what I'm up to 'cause you're afraid if you don't, it might somehow end in Ponyville disappearing under an enormous pink radioactive mushroom cloud?”

“I... err... You don't mind?”

“'Course not. You can come with me out to the rock farm and meet Mom and Dad and the sisters and Rockie, my pet rock. It'll be totally cool!”

She trotted off and was soon halfway up the next hill. I cantered after her, struggling to keep up. It occurred to me that this was an opportunity to ask a question which I had been meaning to raise for some time. “Err, Pinkie?” I said as soon as I managed to draw level. “What exactly is a rock farm?”

“Duh!” she replied. “A place where you farm rocks of course. I told you about the rock farm where I grew up. You remember? When I told you about the day I got my cutie mark.”

Farming, as an exclusively earth pony activity, had been absent from the curriculum at Princess Celestia's School for Gifted Unicorns. I would readily admit that I was no expert on the subject. Nonetheless, I was a well-read student, and I was acquainted with a fair about of information on the subject from books, and from conversations with our friend Applejack. I was aware that it involved the cultivation of plant crops, such as apples and oats, and the rearing of animals for wool, eggs, milk, and potentially other purposes which ponies did not usually talk about. I couldn't see how rocks could be applied to this model.

“So,” I said, with what I hoped was the right level of sarcasm, “how does that work? You bury little pebbles in the ground and wait for them to grow into big boulders?”

“Nah. That would take too long.”

I decided not to interrogate further; I would find out the answer soon enough. We continued trotting up and down the hills which lay to the north-west of Ponyville. As we reached higher altitudes, the vegetation became sparser, and on the crests the wind was blowing strong, flattening out our manes and making me shiver. Eventually we reached the summit of a rocky outcrop from where we had an excellent view of the next valley.

“There you are,” said Pinkie proudly, “the family rock farm.”

I looked across the panorama. There were hardly any trees or plants. The flat bottom of the valley was strewn with rocks, from gravel to large boulders. Various farm buildings punctuated the landscape, linked by roads. It would be pretty dull, except that every barn, water tank, and many other buildings had been painted in bright vivid colours. Fluorescent murals depicted images of smiling happy ponies prancing under a sky filled with rainbows, streamers and balloons. It was impossible not to smile at this joyous art show.

“You like it!” A very satisfied Pinkie Pie threw her hooves around my neck and hugged me.

“Your artwork?” I asked.

“Yeah,” replied Pinkie. “Come on. You've got to taste Dad's rock cakes.”

We cantered down the hillside and into the farm complex together, past a large yellow and black sign marked: 'Caution Rocks Turning'. The site was larger than I had imagined, and clearly employed a lot of ponies. We passed a number of earth ponies, busy shifting rocks, or engaged in other activities. Of course Pinkie knew everypony and met them all with a smile and greeting. We reached a timber framed farm house with a sagging thatched roof, somewhat older than the other buildings. Pinkie caught sight of a light grey mare with her mane tied up in a bun. She then rushed towards her.

“Pinkie?” cried her mother.

“Hi Mom, what's new? I'm back, and Twilight's come with me, look...”

“P-Princess Twilight?”

“Hello, Cloudy Quartz isn't it?” I said politely, extending a hoof to greet her.

“J-just a moment.”

She darted to one side and into the house, through a wooden door, which she closed behind her. I waited outside with Pinkie, trying not to hear what was being said behind the door, and failing.

“It's Princess Twilight Sparkle. Quick! Clear up this mess. Get out the emergency cakes!”

“She's with Pinkie, it's just a casual visit.”

“There's nothing casual about a visit from royalty!”

I felt conscious of the mess the wind had blown my mane into, and of my faded old scarf (bought from the Canterlot flea market for half a bit). Judging by the sounds coming through the door, Pinkie's family were turning their kitchen upside-down. After a minute or two, Cloudy Quartz opened the door, smiling nervously. “Please come in,” she said. “Take a seat and I'll get you some tea. Help yourself to cakes.”

We walked through the door and into a large kitchen. It was not unlike the kitchen at Sweet Apple Acres, and pretty much how I imagine farmhouse interiors are throughout Equestria. The floor was laid with well-worn flagstones. Along the far wall were granite worktops, and a sink large enough to wash a foal; the other wall supported a wooden dresser stacked with plates, and a glass cabinet full of musical instruments (with a small label: 'Break glass in case of parasprites'). Behind a large table stood Pinkie's family: her mother, Cloudy Quartz; her father, Igneous Rock; and her sisters, Marble Pie and Limestone Pie. I had met them briefly when they visited Ponyville, but never really got to know them. The table was covered with a pretty floral table cloth, and stacked high with cakes, tarts, pastries, sandwiches, buns, cookies, pies and many other sweet treats. There was a porcelain tea service, pots of cream and jam, and teacups and pretty little plates sitting on doilies. It was a tea party fit for a princess. I wondered if I was fit to join it.

Pinkie had no inhibitions. At the sight of the feast, her eyes widened and her grin extended even further than normal around her head. “Awesome!” she cried, and stuck her face straight into an enormous chocolate gateau at the end of the table. I sat down and took a cup of tea and a rock cake.

“Pinkamena,” hissed her mother. “Behave yourself. We have a guest.”

“And you are such a totally super awesome host,” replied Pinkie, sticking her chocolate covered head out of the far side of the cake and grinning gleefully at her mother. She picked up a jam tart with her tongue, dipping it in a pot of cream, before retracting it into her mouth. I took a bite of my rock cake. It was delicious. I tried not to stare at Pinkie and instead smiled nervously at her parents. I wanted to ask what a rock farm was, but I didn't want to be told it was a place where you farm rocks.

“What sort of rocks do you farm here?” I said.

“This is a mixed rock farm,” said Igneous Rock. “We have diversified in recent years.”

“It's the best way,” said Limestone. “Putting all your rocks in one basket is too risky in the present climate.”

“And it's not sustainable in the long term,” added Marble.

“Rocks don't grow on trees,” said Igneous nodding.

“The building stone and pet rock trade is doing well,” said Limestone, “but it's still difficult for us to compete with the glittery imports from the Crystal Empire. The bulk of our business is now nuclear fuels and radioactive waste management.”

I ran this statement through my head. This sounded serious. Pinkie had now finished the chocolate gateau and was now standing with four hooves on the table, and her head in a bowl of trifle, making loud slurping noises. Cloudy smiled at me nervously.

“What does that involve?” I asked.

“Well,” said Limestone, “we take the fertile rocks from the south field, and stack them in a breeder reactor in the east barn, where they are irradiated to convert the fertile elements into fissile uranium and plutonium isotopes. We then break up the rocks, and extract the useful elements, and form them into fuel pellets, which we sell.”

“Then,” continued Marble, “we receive the spent fuel rods from nuclear power plants around Equestria. Once they've cooled down, we break them open, and extract any remaining fuel. Then we take the remaining highly radioactive waste, turn it into glass rocks, encase it in steel, and bury it deep underground.”

“Well that's the plan,” said Limestone.

“We're still waiting for the official authorization for the underground repository,” explained Marble.

“Those Diamond Dogs have lodged another objection. They’re a real nuisance,” said Igneous.

I ran all this new information on earth pony ingenuity through my mind. This was clearly a major industrial enterprise. “What's a nuclear power plant?” I asked.

Pinkie pulled her cream covered head out of the trifle bowl and gave me an enthusiastic smile. “Ooo, ooo, can I do my Pinkie Pie Introductory Nuclear Physics Demo?”

“Yes please,” I said. I noticed Cloudy looked worried.

“Yay!” cried Pinkie, sitting down in the middle of the table in front of a huge plate of rock cakes. Her mother put a hoof in front of her eyes. “You know about sub-atomic particles?”

“Yes,” I replied. “Protons, neutrons and electrons. Protons and neutrons stick together to form a small dense nucleus, surrounded by a cloud of electrons.”

“Which is your favourite? Mine's the neutron.”

I hadn't contemplated this question before. After a brief pause I replied cautiously, “I like electrons.”

Pinkie picked up a rock cake and held it in front of my face. “Now this is a uranium-235 atom. It's a really big fat atom with two hundred and thirty-five protons and neutrons all packed into a tiny nucleus. Sometimes uranium-235 atoms get fed up with being so big and fat, so what do they do?” - she paused briefly, for dramatic effect - “Nuclear fission! They fission in two!” She tore the rock cake into two pieces sending a shower of crumbs into my face.

“Pinkie!” said Igneous Rock.

“And when they fission in two,” said Pinkie, ignoring her father, “they send lots of neutrons flying out.” She picked out some raisins from the crumbled cake mixture in her hooves and flicked them in all directions. One hit me in the eye. “Then some of the neutrons will hit other uranium atoms, making them fission apart, and make more neutrons, which hit more atoms...”

To illustrate this, Pinkie juggled a dozen rock cakes in the air. By some improbable hoof work, she caused one to break in two, sending raisins flying out; these then hit other cakes, which broke apart in a further raisin explosion, thus depicting a chain reaction. In a few seconds the pile of cakes had been reduced to crumbs. I felt a little annoyed. Those cakes had been very good. I had been hoping to have a second one.

“In a nuclear power plant,” said Marble, “we sustain such a chain reaction in a nuclear reactor, and use the heat it produces to make hot water and generate electricity.”

“Question time,” said Pinkie. “What happens if we pack lots and lots of enriched uranium into a really small space?”

“Err...” I said, and then paused, unsure how to reply. I was trying to translate Pinkie's description into terminology I could follow and fit it around what I already knew. Heavy radioactive atoms such as uranium could decay as she described, and if there was enough present then you would get a chain reaction...

“You're slow Twilight,” said Pinkie, “Pumpkin and Pound Cake got it straight away. There would be a great big gianormous explosion!” She threw her forelegs in the air, sending a plate of éclairs flying into the wall.

The consequences of what Pinkie had said became clear in my mind. Earth ponies had a way of producing a nuclear reaction without any magic. All they need was a certain amount of enriched uranium – with a higher fraction of the unstable uranium-235, relative to the more abundant uranium-238.

“Isn't that all rather dangerous?” I asked nervously.

“Pinkie is getting a bit carried away,” said Limestone. “That would only happen if you had a critical mass of highly enriched uranium or plutonium. That's quite hard to make. We only enrich it by a few percent – enough to run a nuclear reactor. We're making nuclear fuel, not bombs.” The rest of her family nodded seriously.

This did not entirely reassure me. “But what if some villain broke in here and stole some material?” I said. “Wasn't Trixie working here at one point? If she'd had some plutonium when she was wearing the alicorn amulet, she could have done something terrible!”

At this comment, to my surprise, Pinkie's sisters both burst out laughing and had to support each other with their hooves. Igneous looked a bit embarrassed.

“Sorry,” said Limestone after she had recovered from her laughing fit, “that's just such a hilarious idea. Trixie making a nuclear bomb.”

“It's not that funny,” I said in what I hoped was a regal authoritative voice.

“Trixie bluffed her way into a job here,” said Marble. “She talked Dad into hiring her with lots of wild claims about what she could do. It quickly became clear that she didn't know anything about rocks. She thought yellowcake was a custard tart.”

“In the end we just paid her off with a bag of gold and told her to beat it,” said Limestone.

So a Great and Nuclear Armed Trixie wasn't a credible security threat. That was good to know, but I wasn't entirely reassured. There were more intelligent villains in Equestria. This probably wasn't Discord's style, but still, if rock farmers were making such potentially dangerous material, they really should be more careful.

Pinkie slid off the table, shook the cake crumbs out of her mane, and hugged her parents and sisters. “It's been totally super fun to see you again. Thanks for the awesome party, but I need to get back to Sugarcube corner. Can you get me four cans of uranium fuel for the Ponyville PWR?”

Limestone left the room and came back carrying a tray of tin cans, each labelled with a bright yellow and black radioactive trefoil symbol. Pinkie took these and placed them in her saddlebag. “And can I take some cakes for the twins? And some cookies? And you know how much Gummy loves your toffee...”

As Pinkie filled up her saddle bags with as many cakes and sweets as she could lay her hooves on, Limestone left the kitchen again and returned with a mouthful of paper forms. She dropped these on the table in front of her sister.

“Paperwork Pinkie, fill these out before you leave.”

“Aw, do I have to? It’s boring.”

“You know the regulators are very strict about this stuff. We need to keep detailed records.”

Pinkie picked up a pink crayon in her mouth and started scribbling on the form. Out of curiosity, I looked over her shoulder at the forms headed with the logo of the Equestrian Environmental Agency. At the top Pinkie had written: 'Dr P. D. Pie BSc MSc PE PhD (Nuclear Engineering, Maresachusetts Institute of Technology)'.

“You're a professional engineer?” I said.

“Yeah, you think they'd let me run a nuclear reactor without proper qualifications?” replied Dr Pinkie.

“You run a nuclear reactor?”

“Why else would I need uranium fuel?”

“But where?”

“Sugarcube corner of course. In the basement.”

“In the basement?”

“It wouldn't fit in my bedroom.”

“You run a nuclear reactor in the basement of Sugarcube corner?” I asked slowly, trying to piece together these new facts and redraw my picture of my sugar loving friend and her Ponyville home.

“Yeah. A small one. And you should totally come and see it. It's really cute.”

Chapter 2 – Which describes the refuelling of a nuclear reactor

As we walked back over the grassy hills to Ponyville, Pinkie Pie decided to tell me a chapter of her life story. I listened with interest as the story of how Pinkie arrived in Ponyville was a legend. Like all legends there were an infinite number of variations, and while the version recalled by Pinkie Pie was not necessarily reliable, it was still a valuable testimony from a primary source.

“So after I got my cutie mark and knew that my destiny was to throw lots of parties and make everypony smile, I hit a problem. I was stony broke, and parties can be expensive, especially if you want to do it properly with lots of cool food and drink and games and streamers and fireworks and... yes I know you can still have a lot of fun with just a few bits, but I wanted to throw lots and lots of really big parties for all my friends, and everypony was my friend. So I had to find a super high paid job to support a wild party lifestyle. I briefly considered becoming a banker, but I didn't want to have to wear a moustache to work every day. I mean, once a week would be fun, but every day? Nah. Anyway they didn't invite me for interview. Then Marble told me that engineering was a well-paid profession, and I remember Granny Pie was always saying how hard it was to find a reactor engineer to service her fast breeder. So I looked into it, and it sounded fun. I signed up for a correspondence course in civil engineering and got my degree. Then I got a masters and doctorate, and a job commissioning new reactors. My first assignment was to install a new reactor at Sugarcube Corner. After that the Cakes offered me a job as on site engineer. Once I'd shown them that I was a responsible pony, they also let me bake cupcakes, and once I'd shown them that I was really really responsible, they let me babysit the twins.”

Recollecting these details of her career excited Pinkie to an even more energetic state than her normal character. She jumped higher and higher with each bound, sending her heavy saddlebags bouncing in the air. “Why did the Cakes need a nuclear reactor?” I asked.

“It's what powers all the ovens, and the lights and the cookie machines at Sugarcube Corner,” explained Pinkie. “And it's not just Sugarcube Corner, we provide hot water and electricity to all of Ponyville. Including your library.”

“I thought the electricity in Ponyville came from the hydroelectric dam.”

“Oh, that provides some. It used to provide all the power, but when the town grew bigger, and seven hour bubble baths became fashionable, we needed another generator. The critical point came a few years ago when the Cakes installed a new cookie factory on their lower ground floor, so they offered to house the new power plant in the basement. Actually that wasn't the first plan. They first built some big wind turbines. That was a complete fiasco. Pegasi kept flying into them. Then they would go and sulk in the clouds and didn't maintain the weather properly, so there was no wind.”

“How come I never heard about this before?”

“Oh, well I guess nopony thought it worth mentioning. That's sorta how it is with nuclear power plants. You only hear about them if something goes wrong.”

We soon reached Sugarcube Corner. Mr and Mrs Cake were rushing around as usual, balancing trays of baked goods on their heads with uncanny skill. Their baby foals were sitting on the floor throwing toy bricks around. Pinkie thrust her head down to their level grinning manically. “Hey Pound! Pumpkin! Ready to help me refuel the nuclear reactor?”

Carrot Cake gave her a stern look. “They need to take their nap very soon Pinkie. You can play with them later.”

Pinkie looked disappointed, but she just said, “Okay, I was just asking. Come on Twilight.”

Pinkie, with saddlebags, jumped through a doorway which I assumed led to the stairs to the basement. I smiled at Carrot Cake, then trotted after her, but as soon as I was through the doorway, I tripped over my hooves and found myself sliding down a smooth tube which spiralled downwards. A few seconds later this dumped me on the floor next to Pinkie Pie.

“Ugh,” I groaned as I picked myself up, “where did the stairs go?”

“Stairs are slow, boring, and potentially dangerous,” said Pinkie. “Every year, hundreds of foals are hurt falling down steps, many of them seriously. So I, Pinkie Safety-Conscious Pie, replaced them with slides, which are quicker, safer, and much more fun.”

I looked around the underground room. It was a large hall, with a high ceiling, brightly lit, and full of noisy machines. A complex gear system drove a series of conveyor belts across the room at several different levels, linking a selection of large shiny metal enclosures, decorated in flashing lights. Rope and pulley mechanisms moved heavy bags across the ceiling, while robotic claws grabbed these and tipped the contents in various chutes. Heavy duty pistons were driving some sort of industrial stamping, and a network of transparent hoses directed the flow of brightly coloured liquids. I stared at this complex monster trying to make sense of all the moving parts.

“Is this a nuclear reactor?” I asked.

“Nope,” replied Pinkie, “this is the Cookie factory floor.” She reached a hoof into a metal container and withdrew a piece of chocolate chip filled gingerbread, which she thrust into my mouth. “The reactor is one floor down.” She dived through another doorway. I followed, more cautiously than before, and slid down another spiral slide. This deposited us in a very small room with walls lined with pegs supporting white coats.

“Put on a lab coat,” said Pinkie, tossing me a white garment.

“Why do we need to wear these?” I asked.

“For fun,” she explained. “And it will keep the dust off your coat.”

“What's this room?” I asked after pulling the coat over my hooves. “Where is the reactor?”

“This is an air lock.” Pinkie pulled a lever on the wall, which caused a door to swing shut across the slide outlet. There was a short hissing sound, then another door on the opposite side of the room swung open. We walked through this into a dark room. I could see a large number of electronic indicator lights lit up in the darkness.

“Hang on,” said Pinkie, “Lemme find the light switch.”

She walked into the darkness and a moment later the lights flickered on, illuminating a small room packed full of equipment. Control panels were mounted against the walls, covered with arrays of buttons, knobs, switches, and indicator lights. Above these were panels of pressure gauges, dials and other meters. I could only guess the function of most of these, but after staring at the wall panels, I found my brain automatically trying to make sense of it, with partial success. Lines drawn on one panel appeared to represent water pipes, and the various gauges showed the pressure and temperature at different points, and whether a network of valves were open or closed.

I was taken aback by the scale of it. Many ponies, on seeing my basement for the first time, have expressed surprise at the amount of random technology it contains. Actually it just houses a small collection of scientific instruments and miscellaneous electronics which I grabbed when the Canterlot University Physics Department was having a clear out. More than most Ponyville residences, it's true, but nothing remarkable. In contrast, Pinkie's basement had this vast array of the latest sensor and control technology.

“Wow,” I said. “Can you talk me through how this all works?”

“Sure,” said Pinkie. “Come and look outside.”

She bounded through another door on the side of the control room. This led out onto a balcony, overlooking a large cavern with smooth metal walls. I could make out a large number of pipes, leading down to a large open tank of water, containing a cylinder with a domed cover, glowing with an eerie blue light. Not unlike the coloured aura of unicorn magic.

“That's the reactor core,” said Pinkie proudly. “It's in the water tank to keep it cool and to shield us from the radiation. It's a pity it's so radioactive – otherwise it would make a great plunge pool. It glows with that cool blue light.”

“Cherenhoof radiation,” I said. “It's producing energetic particles, which move through the water faster than the light, making it glow. A bit like a sonic boom.”

“Oh so that's what it is,” said Pinkie.

“Don't you understand it?” I asked. “I thought you were a nuclear expert.”

“I'm an engineer Twilight, not a scientist. I don't have to understand it – at least not one hundred percent – I just have to make it work.”

“So how do you make it work?”

“We pack the uranium fuel in rods in the middle. The U-235 atoms spit out fast neutrons. They would just whiz away, but they’re surrounded by water, which is a neutron moderator – it slows them down. Chocolate milk would work as well as water, and it tastes better, but that would be a waste of chocolate milk. The slow neutrons then hit other uranium atoms in other rods, and start a chain reaction, which makes it really really hot. Once it gets going, we control it by pushing the control rods into the core. They're made of a neutron sponge which sucks up the neutrons so it stops the reaction. We stop it completely by pushing the rods all the way in. It's like that now as we shut it down for the summer.”

“What stops it getting too hot?” I asked.

Pinkie pointed to a network of pipes connected to the reactor. “Cold water goes in, round and round the core, and comes out super-hot – it would be boiling except it's at a super high pressure. The hot water then heats more water making steam, which whooshes through a turbine making electricity, and then we cool it with cold water from the river, which then goes all around Ponyville to heat everypony's home, and then back in the river.

“So you have a series of cooling water circuits to transfer the heat out of the core,” I said.

“Yeah,” said Pinkie, “lots of pipes of hot water and steam all over the place. I made a few modifications to make extra use of it.”

“Modifications?”

“Yes, I added extra hot water and steam delivery pipes to the spa, since they need so much of it. And a milk steaming nozzle in the control room, so we can make some frothy coffee and hot chocolate.”

Pinkie procured a tin opener from a draw under the control panel, which was labelled 'snacks'. She then took the yellow and black tin cans out of her saddle bag, and proceeded to remove the lids by lying down on the floor, gripping each can with her rear legs, holding the can opener with between her fore hooves and twisting the handle with her teeth.

“Grrr,” she said through her teeth, “why'd they make these things so difficult to open.”

Eventually she had removed the lids from the tins. Each one was lined with a thick layer of lead on the inside, surrounding ceramic pellets. She then got to her hooves and tipped the contents of the tins into a plastic scoop on the top of a machine at the end of the control panel. She then pulled a lever. The machine proceeded to make a rattling sound and a few indicator lights flashed.

“That's the fuel rod packing machine,” said Pinkie. “It stacks the pellets into fuel rods.” A moment later the machine ejected a set of long thin black metal rods into a basket on the floor.

“And what's all this other equipment?” I asked, surveying a selection of high-tech boxes lined up along the counter.

“That’s a radiation dosimeter, so we can check if anything gets contaminated with radioactive material. And that's the readout for the neutron monitors and temperature sensors.”

“And this one?”

“That's the coffee machine.”

“Now,” said Pinkie, standing with her fore hooves on the control panel, grinning at the array of indicator lights and gauges, “we need to exchange the fuel. I think it's this button.” She pushed a rectangular panel with a hoof. There was a noise outside the cabin. I walked back onto the balcony and looked down to the reactor and saw an elaborate piece of mechanical engineering swing into action, like something made by the Flim Flam Brothers. A set of robotic limbs, fitted with mechanical claws, moved out of the walls. Each claw picked up a wrench from a toolbox, then plunged into the pool and set about removing a set of bolts in a ring around the reactor vessel. Once this was complete, the domed cover was removed, allowing us to look inside the underwater reactor core and see a glowing array of cylindrical rods.

Pinkie pressed another button and two robotic arms then reached into the core and pulled out the spent fuel rods, while another two brushed past me, through the door into the cabin and picked the newly assembled rods from the basket. These were carried down to the reactor and pushed into the vacant slots, while the glowing removed fuel was moved to one side, still under the water. This task completed, the robot set about closing up the vessel and tightening all the bolts. Pinkie walked out onto the balcony beside me.

“We'll leave a few old rods in there, so there's enough kick to get it started,” she said.

“What do you do with the spent fuel?” I asked. “It must be highly radioactive.”

“It is,” agreed Pinkie. “Very. Packed full of dangerously unstable transuranic elements. Enough to kill a pony if you get too close, and hot enough to burst into flames if it gets out of the water. We'll leave it here for a bit to cool off then take it back to the rock farm and keep it somewhere safe for two hundred thousand years or so.” She looked down a clipboard she held in a hoof. “Okay. Replace fuel rods – check.”

Pinkie bounced back into the control cabin. I paused for a moment staring down at the glowing spent fuel rods, trying to estimate the amount of heat that much radioactivity could produce. If the water was to disappear, and the rods were exposed to air, they would burst into flames and fill the air with radioactive smoke. I shuddered at the thought, then took a few deep breaths to calm myself. Nothing to fear. In a worst case scenario I could always teleport us out of here, and the air-tight room will contain the fire. Unless it was damaged by the heat. No, I said to myself. That won't happen. Pinkie knows what she's doing.

I walked into the control room where Pinkie was standing up against an array of buttons with a puzzled look. “Okay. Restart the reactor. How do we do this? I think it's this one.”

She pushed a button. Immediately a red light started flashing and an alarm sounded. Pinkie pushed it again to cancel the action. “Okay not that one... Let’s try this one.” She pushed a hoof against another control. This caused exactly the same effect. “Hmm, what's wrong?” she said.

“How many times have you refuelled a reactor?” I asked.

“This is the first time.”

“What?”

“Well, there's a lot of energy in uranium fuel, and we've not been running at full capacity, so it doesn't need refuelling very often... Oh I know, we need to first pressurise the primary coolant.” She twisted a knob and pulled a lever. There was a noise from outside as a pump started somewhere, and a moment later the pressure reading on numerous gauges on the panel in front of me started rising.

Once the pressure had stabilized, Pinkie pushed another button. “Now we can raise the control rods and get it going.” We both watched the panel in front of us, on which the position of the control rods in the reactor core was indicated by an array of tiny lights on top of a drawing of the assembly. Surrounding this was a set of meters giving the temperature and pressure of the water, and digital displays giving the radiation level, and various other instruments whose function I could only guess. As soon as the lights showed the control rods were partially out of the core, the digits on the radiation counters started changing faster and faster as the rate increased tenfold, and the thermometer readings shot up.

“Yay!” cried Pinkie. “We have fission!” She jumped up and bounced around the room as the panel lights flickered. Then with a satisfied smile she checked off another item on her clipboard.

“You want some coffee Twilight?”

“Err, okay.”

She took a bag of coffee beans from a cupboard below the control desk and poured this into the top of the coffee machine. She then stuck her head back in the cupboard. “Out of sugar. And I need to get some fresh milk. I'll just pop upstairs. Keep an eye on the reactor will you Twilight? Don't let it get too hot.” With this she trotted out of the cabin into the air-lock door.

“Pinkie!” I cried, but she had already closed the sound-proof door.

What was I supposed to do? Check the reactor didn't get too hot? How hot was too hot? According to the thermometers the water in the core was at about 250 degrees. That seemed pretty hot to me. And if it did get too hot, what was I supposed to do. I stared at the panel tracing the route of the various cooling water circuits. What was the right course of action in such an event?

My tried and tested way of dealing with any problematic issue is to read a book. I looked around control room and identified a small shelf above an array of levers. I went over and read the titles of the books. These included several guides to baking cupcakes, party planning, and keeping alligators as pets. I then spotted a more promising title and levitated it off the shelf: 'Pressurized Water Reactor: Users' Manual.'

The first page contained a note explaining that the reactor warranty only applied to defects in materials or workmareship. The ACME Corporation would not accept any liability due to damage from customer misuse. In particular the warranty did not apply to damage to the core resulting from an interruption of cooling water. I flipped through the booklet, skipping the first chapter on the assembly of the flat-pack components. The later chapters explained the operation of the plant. It assured me that everything should run in a safe stable way, provided the user followed the instructions.

Unfortunately I had a good imagination, and my mind was quickly thinking up ways in which things could go wrong. What if the control rods were jammed somehow? And what if there was some blockage stopping the flow of cooling water. I looked up from the manual and noticed that the temperature had risen to 290 degrees. My heart started pounding fast. Was it still rising? How high should I let it go before I should stop the reactor? If it got so hot that the fuel rods melted, then we would have no way of controlling it. A molten mass of highly radioactive material would melt through the vessel. Nuclear meltdown. Then if it reached the cold water, it would fill the room with steam, and there would be an explosion. No. We're in a sealed underground air-tight container, which can no doubt take a high pressure. And there must be safety valves to stop an explosion. So the worst that can happen is we would just be dumping tons of radioactive water into the river. Nothing to worry about. Stay calm Twilight. Anyway the fuel rods are made from zirconium, which doesn't melt until 1855 degrees, so it should be fine. I stared at the thermometer which had crept up to 292 degrees.

With a hissing sound, the airlock opened and Pinkie Pie bounded back into the room, balancing a tray on her head. “Cupcake?” she said.

I took one of the cakes without paying attention. “Pinkie,” I said, “is it too hot?”

Pinkie walked over to the panel. “Nope, just perfect for making good coffee. Hey Twilight you wanna see how to make the perfect cappuccino? I've been getting pretty good at it.”

My eyes kept flicking between the reactor temperature gauges and Pinkie Pie.

“The base of a good cappuccino is a good caffé espresso,” she said. “To make that we need some hot water, pressurized to about sixteen bar.” She flipped a switch on the control panel and watched as the pressure reading on one of the meters rose. Then she put two cups below a nozzle on the control panel and pressed a button. The machine gurgled and dribbled some liquid into the cups. “Look at that Twilight, proper dark coffee. Do you like coffee? I love it, but it does make me sorta super-extra-coco-loco. Now the next step is to steam the milk. Trick is to use a jug of nice cold milk and...” She positioned a jug underneath a small metal pipe sticking out of the panel and pressed another button. Immediately there was a loud hissing sound and a cloud of white foam erupted from the jug. Not unlike what happens with Spike if I don't watch how much bubble bath he uses.

“Okay,” continued Pinkie, wiping off her milk foam beard with a hoof. “Now pour the milk over the coffee, add sugar, sprinkle on some cocoa, and voilà!”

She placed the cup of frothy coffee in front of me, then sat down on the floor and slurped up her own. She gave a happy smile, running her tongue around her mouth, then jumped up and bounced around the room in a crazy fashion, rebounding from the walls and ceiling, while singing a song to a familiar tune:

“All you have to do to make nuclear power,
Is a U-2-3-5 mix,
Now take a reactor and a cooling tower,
Add some neutrons, just a pinch,
Running this plant, it's such a cinch,
Raise the rods, let's start the mission,
Lift a little more - don't overheat the core,
And you'll have nuclear fission!
Fission! Safe, clean and easy!
Fission! Don't feel uneasy!
Fission! fission, fission, FISSION!”

She had been right about the coffee.

My eyes switched between the control panel and Pinkie Pie. Here I was, two storeys underground, in a small, enclosed, hermetically sealed space, with enough radioactive material to kill every pony in Ponyville, a nuclear reactor about to overheat, and the responsible engineer was the bright pink Element of Laughter on a sugar and caffeine high. I couldn't take any more.

“PINKIE!” I screamed.

Pinkie fell silent. She walked over to sit in front of me and put a hoof to my face.

“What's up Twilight?” she asked calmly.

“Don't you see how dangerous this all is!” I shouted. “If something goes wrong it could destroy all Ponyville.”

Pinkie looked me in the eye. She paused before saying solemnly, “Twilight. It's safe. I promise.”

“You promise?”

“Cross my heart and hope to fly, stick a cupcake in my eye.”

She looked at me with a deadly serious stare.

“How can you be so sure?” I asked.

She smiled. “Because there's loads and loads of security features, and an auto-shutdown safety system, and a backup system to back up the auto-shutdown system, and a backup backup system to back up the backup system, and a backup backup backup system... And it's designed to be super stable so it won't overheat. And if anything goes wrong we drop the control rods right down. Or failing that we can squirt a neutron absorber into the water. Then there are four independent cooling systems... It's built to be totally idiot-proof!”

“But how can you be sure it will all work as designed?”

“Earth ponies have been running these plants for many years,” she said. “Without any accidents...” She paused a moment and stopped grinning. “Well, with very few accidents... There was that occasion when some streamers got stuck in the fan on the secondary cooling circuit, but nopony has hurt and there was hardly any release of radioactive gas... And there was that case in Fillydelphia when that colt blocked the safety valve with bubble gum... And that one unfortunate incident in Vanhoover – that was a stupid reactor design – rock candy does not make a good neutron moderator. But relatively speaking, it's totally-ultra-super-mega-safe.”

“But there's still a risk,” I said.

“There's always a small risk,” said Pinkie. “But it's no bigger than the everyday risks we all face due to things like cupcake poisoning, traffic accidents, and attack by timberwolves, changelings and giant crabs.”

This did not reassure me. “Thanks Pinkie. It's reassuring to know I am more likely to be eaten by a giant crab than killed in a nuclear incident.”

“You're welcome.”

With a cheerful smile Pinkie looked up at the control panel. “Temperature and pressure is stable. All cooling circuits running fine. Now delivering hot water and electricity to all Ponyville.” She picked up her clipboard. “Just one thing left on the list.”

“What's that?” I asked.

“PARTY!”

Chapter 3 – In which we hear from Zecora, but Luna has the last word

The Successful Nuclear Reactor Refuelling Party was a typical Pinkie Pie affair. Sugarcube Corner was quickly filled with streamers, balloons, and party foods; followed by nearly every pony in Ponyville. Fillies and colts rushed around laughing and dancing. Soon it was hard to move without bumping into a friend, or five.

I was not in the mood for a party. I wanted to get back to my quiet library, write a few draft reports, then reread a long list of books on ancient history, sub-atomic physics and the philosophy of sustainability. But if there was one thing I had learnt since I moved to Ponyville, it was that when I felt anxious about something, I should talk to my friends.

I bumped into Rainbow Dash first. “Hiya Twilight, whatya been up to today?”

“I've been watching Pinkie Pie refuel a nuclear reactor.”

“Hey, you've seen it? Pretty cool huh? The way it glows in the dark.”

“I'm rather concerned about its long term safety.”

“Don't you worry Twi. Nothing will happen that I can't deal with.”

Just how would Rainbow Dash deal with a nuclear meltdown? I decided not to ask.

Rarity walked over to join us. “I must say, I do wish Pinkie would engage in something a little more elegant. But at least it's not as visually intrusive as those awful wind turbines.”

“Now hang on there.” Applejack walked over to join us. “Have you met Pinkie's family?”

“I saw them this morning,” I said.

“Well then y'know they're as honest and hard workin' as any other farming family in Equestria. I'll tell you, it ain't easy being a farmer, if your farm hasn’t got any soil. But they've done a mighty fine job building up a sustainable business, and I'm not going to let any prissy unicorns cut off their trade just 'cause it ain't elegant enough.”

I backed away as Rarity and Applejack glared at each other, and bumped into Fluttershy. Now here was a pony who would understand my concerns.

“Fluttershy, how do you feel about there being a nuclear power plant so close to home?”

“I... well... I... erm...”

“If something went wrong, it would be terrible for all your animal friends.”

“Oh... I'm sure Pinkie would never let anything bad happen.”

“Well, I know she would never mean any harm. But... you remember the mirror pool incident?”

“Oh... I try not to think about that.”

This wasn't getting me anywhere, and the music was giving me a headache. I waved goodbye to my friends and shuffled out through the crowd of ponies and into the street outside. It was just after sunset, my favourite time of day. I shook my mane, breathing in the cool evening air, and trotted away from Sugarcube Corner. I then decided to take a short walk before returning to the library.

Once outside of Ponyville, and the hustle of crazy party ponies, my head cleared and I managed to get my thoughts into order. I stopped on the bridge, and looked down at the river flowing underneath. If there was a significant leak of radioactivity, I thought, it would kill all the fish and water creatures, and it would flow into Everfree and poison a unique and irreplaceable ecosystem.

Was I being entirely rational about this? Pinkie Pie was right – there were many other conceivable disasters which could strike Equestria. With all her safety systems, the risk of an incident must be very small. And if earth ponies had indeed run these reactors for many years with few problems...

But could she really be sure? It was such complicated technology. And accidents did tend to happen around her. If it got out of hoof, the consequences could be worse than anything we had seen. Well maybe not quite as bad as when Discord was running wild, but it would be a lot more difficult to clean up the mess.

Was there an alternative? There weren't enough unicorns in Ponyville to run the electricity grid on magic, as was done in Canterlot. Nor was there the space for the kind of cloud-top arrays which collected the solar energy which drove the Cloudsdale weather factory. If further hydro dams or wind turbines were impractical, was there another option? The Equestrian railways were powered by coal. But that was dirty and expensive – coal mining was the preserve of the bat ponies, who lived in dark tunnels. The only answer I could think of was to try to persuade the ponies of Ponyville to use less energy. But any effort to get them to cut their bath times, would probably be no more successful than my group to teach ponies about history.

If only there was somepony, I thought, who understood history and ancient magic, they might also understand the dangers of nuclear power. As soon as I had this thought, I cantered off into the Everfree forest. I needed to talk with Zecora.

Not long later I was sitting in Zecora's home. In between taking sips of herbal tea, I explained to her what I had learnt that day: my visit to the rock farm, and subsequent demonstration of nuclear fission. I then explained about the potential dangers of such processes. Zecora listened to me patiently. If the prospect of the Everfree forest being covered in a blanket of radioactive fallout concerned her, she made no sign to show it. Eventually I ran out of dialogue, and there followed a long silence before she replied.

“Here deep within the Everfree,
All Life exists in harmony,
A fragile balance of many forces,
Our power comes from natural sources,
Nature thrives in this wild zone,
Where clouds move, all on their own.

In Ponyville, outside the border,
Life follows a different order,
Ponies and wild critters live together,
Pegasi patrols control the weather,
And rock farmers follow tradition,
Engineering nuclear fission.”

“That's how it is,” I said. “But if something went wrong, it would be disastrous for both Ponyville and Everfree. You know the history of the Incantatem Fissio Individuuma?” I sipped my tea and waited for her to reply. It occurred to me that I had never asked Zecora how old she was. When we first met, I had assumed she was just a little older than my friends and I, but the more I got to know her, the more I began to suspect she was actually far older.

“Your fears I can well understand,
A nuclear blaze would kill this land,
As a tool of war, it is unsurpassed,
Deadlier than any a magical blast,
Yet the terror that hit distant Neighpon,
Was over and done, many years gone,
And now, millennia hence,
Time has redeemed the offence,
Wildlife has returned to the place,
Poison is but a tiny trace.”

I nodded. “That was a long time ago, and nopony with any sense would do such a thing now. But with all this nuclear material around – what if it fell into the wrong hooves? Pinkie's family assure me they don't farm weapon-grade rocks, and it’s not so easy to enrich it. But can they really be sure? And this reactor – if it were to overheat, the fuel rods could melt and it could get out of control and lead to a major leak of radioactivity. Or worse, there could be an explosion which would spread fallout all around the region.” I realized I could now talk in a much calmer manner than I had done earlier with Pinkie.

“Meltdown would be a catastrophe,
I see you cannot rest worry-free,
When Pinkie claims it is safe and secure,
She fails to leave you feeling so sure,
For all the safeguards she can invent,
There will remain fear of an accident.”

“I can't understand how relaxed Pinkie, and my friends, seem about it. I mean, I've explained the dangers, and they seem to comprehend it, but they just don't take it in.”

“Why should they feel any unease?
Who would harm my little ponies?
Timberwolves, changelings, or Discord return,
All are beaten or befriended in turn,
With Celestia, Luna and you in charge,
Nopony fears radioactive discharge.”

She was right. Equestria had been in serious peril many times in my lifetime, but nopony was ever really scared. They all felt safe and secure, knowing that Celestia, or more recently, my friends and I, had taken care of Nightmare Moon, Discord, the changelings, and many other risks. But could I keep them safe from a nuclear incident? Should I try to protect them from Pinkie Pie?

“What I need to decide now, is what I should do about it.” I knew Zecora well enough to know she would not give me a clear instruction, but I wanted to hear what she would say. It was reassuring talking to her, even if she did not tell me anything I did not already know.

“If you have the power to find a solution,
You should follow through with such a resolution,
But if it lies beyond your ability,
What you cannot change, you must let be,”

“I know. That’s good advice. I don't think I can solve this. Well I can't provide Ponyville with a cheap, clean, risk-free fuel source. But should I try to persuade them not to run a reactor?”

“If you believe it is a risk to a friend,
It would be wrong not to bring it to an end.
As a princess, you have the power of the crown,
To order them to halt, and force a shutdown,”

That was the reality I faced. I could order Pinkie to decommission her reactor. It would upset her. For about five minutes, until she thought of something even crazier to do. Cloudy Quartz, Igneous Rock, and her sisters, would always think they had offended me with poor hospitality. And the Ponyville residents would sulk for weeks about rationed hot water and electricity. But all that was far preferable to the fallout from a nuclear accident. What should I do? Think about it of course. But the easy thing would be to keep putting off deciding anything, and then what if there was an incident? I looked back at my friend. “What would you do Zecora?”

“As I know you have understood,
I heat my home by burning wood,
A simple and sustainable way,
To get me by from day to day,
I take this approach of my free will,
But it would never work for all of Ponyville,
If ever it should come to pass,
That Ponyville switched to biomass,
I fear they would cut down every tree,
Then what would become of Everfree?
And so although it's not for the likes of me,
I’d rather they use atomic energy.”

Would that happen? Surely we could manage with a bit less energy, without needing to cut down the forest. But could I be sure of that? I envied Zecora. Living out here in Everfree, in harmony with her surroundings. Whatever happened, nopony would blame her. No wonder she was always so calm and relaxed about everything.

“I'll tell you a tale, to help you understand,
Of darkest Zebrica, which was my homeland,
A once prosperous land, and fertile too,
Where the number of zebras and ponies grew,
Yet tragedy would strike our society,
When we outgrew our supply of energy,
In search of fuel, we felled tree after tree,
This caused a problem which we could foresee,
But by greed or need, we missed the hint,
And failed to cut our carbon hoofprint,
When the trees were gone, the wind blew away the dirt,
What was once fertile, turned to a dry desert,
The land gave us neither fruit nor grass,
And we were forced to disperse en mass,
Since then I have travelled far, by land and sea,
And finally settled here in Everfree.”

I bowed my head slightly before the zebra mage. Zecora had experienced tragedy and loss far beyond anything I knew. But she always remained cheerful. We sat and finished our tea in silence, then, knowing I had learnt all I could from her for one day, I thanked Zecora, left her tree and walked back to Ponyville through the dark forest.

I walked into the library and stared at the pile of unread books on my desk by the window. It had been a long day, and I hadn't made any progress on my planned research. But I had learnt a lot. I felt I should send a report to Princess Celestia, and was about to call Spike to take down a letter, but I then realized I wasn't at all sure what I would say. I ran through a few possible lines in my head:

Dear Princess Celestia
Today I learnt a lot of details about nuclear physics and reactor engineering...

No that wasn't the way to start.

Today I learnt that you sometimes have to trust your friends, even if you find some of the things they do worrying...

No that wasn't right either.

Today I learnt that managing energy resources in Equestria is a difficult challenge and there is no ideal way...

No.

The truth was I wasn't sure exactly what I had learnt and this was just all too confusing to put into a letter. I would have to talk to the princess about it. Well, why not do that? I could just fly over to Canterlot for a princess-to-princess chat.

I walked out onto the balcony, spread my wings, and leapt off into the night, making for Canterlot Castle. It was a cold wind blowing against my face, but I pulled my scarf tight around my neck, and after pumping my wings for a few minutes I was pleasantly warm and enjoying the thrill of night flying. I really should do this more often, I thought to myself. Flying in the daylight is completely different. Although thanks to Rainbow Dash's coaching, I have got much better than I was, I still feel so self-conscious. Every time I fly past a farm, ponies come out and stare up, pointing their hooves at me, and saying to their foals 'That's Princess Twilight Sparkle. If you're a good little filly, and do what mother says, and work hard at school, and be true to your friends, then you can grow up to be like her'. But in the dark, there was none of that. I was invisible.

Flying higher, I stared at the stars, smiling at the constellations like old friends; then looked down at the ground, and the twinkling lights from villages and isolated farmsteads, no doubt powered by their own subterranean nuclear reactors. Soon, the magically illuminated towers of Canterlot, perched so majestically on the cliff edge, came into view. I wondered where I should land. Should I glide down to the gate and let the guards have the satisfaction of saluting me? Or just fly straight into the castle? I decided on the latter option, but as I came closer to the parapets, I remembered that Celestia would be asleep at this late hour. A better plan would be to visit the doughnut shop, and have a chat with Joe, and see Celestia in the morning. I decided to do one lap around the castle. Then, as I passed the tallest tower, I spotted another pony awake. Princess Luna was standing on her balcony, surveying the night sky. I flicked a wing to divert my course towards her.

“Twilight Sparkle,” cried the Princess of the Night as I landed beside her. “An unexpected meeting. But you are very welcome. What brings you to Canterlot on this fair night?”

“Greetings Luna,” I replied, “I came to talk with Celestia about something that I have learnt. Sort of. And something which I'm not sure of. And as she is still asleep, maybe we could...”

“Speak! There are still several hours until dawn, and some conversation would be most agreeable. I will gladly hear of that which is troubling you.”

I smiled at Luna's somewhat formal speech, which, at this late hour, on the castle tower roof, under the stars, seemed oddly appropriate. I sat down, and began to tell of my day's adventures. How I had learnt of earth pony atomic energy; my visit to the rock farm, and the Sugarcube Corner reactor; and then my conversation with Zecora; and my but-I-still-don't-know-quite-what-to-make-of-it-all feelings. Luna listened patiently, occasionally nodding or smiling, but not interrupting. At the end of my story, there was a long pause, while she looked up at her night sky, in thought, before replying.

“So you trust your earth pony friend, and she has assured you that her activities are not as dangerous as you fear. You understand why she runs her reactor, and you are not in a position to give her a realistic alternative. Yet still you feel uneasy about the whole thing, and you just wish she would find another way.”

After the conversations I had had earlier in the day, I was somewhat taken aback that Luna could understand and articulate my feelings so quickly and accurately. “Do you feel the same way?” I asked.

Luna nodded. She looked back up at the stars for a moment before continuing. “It has been the subject of a long standing... difference of opinion... between my sister and I. One which goes back over a thousand years. I tried hard to make her see, but without success.”

“I don't understand,” I said. “Does Celestia support nuclear power?”

“How do you think she makes her sun so infernally bright?”