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SCRAM is an educational simulator of a nuclear power plant, developed by Chris Crawford from June to November 1980 and published by Atari in June 1981. It models a pressurized water reactor (PWR) called 'Silicon Valley Nuclear Power Station Unit 2', resembling the name and operation of Three Mile Island Nuclear Power Plant Unit 2, which suffered a partial nuclear meltdown in March 1979. 16k and 24k versions were included on one cassette, with the program released for the Atari 800 and capable of running on upgraded versions of the Atari 400.


Before joining Atari, Crawford gave talks to school students about energy policies, eventually writing two simplistic simulations to help demonstrate complex topics. With the release of the first Atari 8-bit computers, Atari wanted educational software to balance the large number of games previously released for the Atari 2600; Crawford worked on improving and 'gamifying' his simulations, eventually releasing both as commercial software (Energy Czar, which simulated potential effects of changing government energy policies, preceded SCRAM by six months).

The Meaning of 'SCRAM'

A SCRAM refers to an emergency shutdown of a nuclear reactor - in the type of reactor modelled in-game, this is undertaken by inserting unreactive masses into the reactor core and halting any nuclear reaction, and is also referred to as a 'reactor trip'. SCRAMs do not immediately cool the reactor or halt power generation.

The origin of the term SCRAM is unknown, but is often believed to be an acronym such as 'Safety Control Rod Axe Man' or 'Safety Cut Rope Axe Man', in relation to the shutdown procedures of the earliest experimental reactors. The manual for the game claims it stands for 'Start Cutting Right Away, Man!'. Although an actual SCRAM is only undertaken in emergency situations, the same steps are usually required in a routine shutdown procedure.


The player is tasked with keeping a nuclear power plant operating and producing power. Earthquakes can occur at random intervals (with frequency related to 'risk', effectively the game's difficulty setting), with each earthquake damaging one component of the plant. When this occurs the player must identify the damaged part and send in workers to repair it; a limited supply of workers means that eventually the player will be unable to effect repairs. When the plant is run improperly (whether by design, operator error, or damaged components) more serious problems can occur, such as 'Steam Voiding' and coolant loss. Gameplay ends when the player performs a cold shutdown and safely reduces the reactor temperature to below 200 Fahrenheit, or when a reactor meltdown occurs.

With the exception of the game endings, the only other explicit statement to the player is the 'Steam Voiding!' warning, which occurs when the reactor temperature is too high, and requires rapid intervention to avoid a meltdown. The player must otherwise identify dangerous situations by examining various measures of temperature and pressure; problems are usually indicated by rapid changes in values, which the game indicates with a horizontal bar either above or below numbers.

The majority of the game mode is described only in the manual, which also includes a short primer on thermodynamics, nuclear power plant components and operation, and a description of the Three Mile Island accident in terms of the game simulation.

Developer Comments

Public awareness of the safety and dangers of nuclear power generation was raised significantly by the Three Mile Island accident. In January 1982 - six months after SCRAM's release - a minor accident occurred at Ginna Nuclear Generating Station in Wayne County, New York, leading Nightline to devote an episode on nuclear safety, with Crawford interviewed about his game by Ken Kashiwara.

"A nuclear power plant is a very dynamic thing. I wanted something that shows the functioning of it, how all of the pieces fit together, because it is a complex machine that is highly interactive... That's what I wanted to get across, and a computer was the best way to do that.

"The best way to learn about something is to play with it. Now, it's no good to play with the real thing, though. You don't teach three-year-olds how to drive by throwing them into a car and letting them go, and you don't teach nuclear operators how to run a nuclear power plant by letting them run a real power plant."

During Crawford's demonstration of the game, Crawford simulates a problem by fiddling the system:

"I can come over here to these main feed water pumps and turn them off if I want and see what happens when I do that. [high-pitched voice] Oh boy, I mean, let's see what happens when we turn off the main feed water pump. OH NO! Steam voiding? Oh no! [regular voice] The reactor gets a little warm all of a sudden. So, I blew it.

"Once you think you know then you go back and play it as a game, because you raise the risk level and earth quakes start to come. They break components down, they break pumps, they break valves... There's an earthquake! So I've got an earthquake coming here shaking up that power plant, and it broke something, you can hear it go "clang" because something broke. Uh-ho, steam voiding. I'm in trouble already. What broke? Well, I analyze the situation, I look at the temperatures on the right side of the screen. I see 96 and 63, the 63 is a falling temperature; that tells me that one of these circulating water pumps broke, so I send 5 workers in to repair it. They repair the pump, and everything's going... start cooling off again."

Transcribed by Jeff from a recording of the original televised interview

(Crawford was unaware the camera was recording at the time - Kashiwara had suggested going over the basics beforehand to reduce Crawford's nervousness, and this was used for the interview - but later stated he appreciated the misdirection.)

Crawford's opinion of SCRAM eventually became negative. Discussing it in Chris Crawford on Game Design, released in 2003, he wrote "Scram was a stupid game devoid of entertainment value... If I had it all to do over again, I would start my design process by asking myself , "What is fun and interesting about nuclear power plants?" The answer, of course, would be "Not much," and I would walk away from the idea of building such a game."

Gameplay Details

According to the manual, the aim of the SCRAM game is to generate as much electricity as possible and then safely shutdown the reactor. A game's score is the number of megawatt hours of net energy (MWH) produced; this resets on a reactor meltdown or when the risk is changed. Objectives are only shown in the manual, with no specific rewards or penalties in-game.

The Risk level, which the player can change at any time from 0 to 9, determines the game's difficulty. At risk 0, there are no interruptions and the game continues until the player shuts down or purposefully melts down the reactor. At other levels earthquakes will strike the plant at random intervals, with higher risk levels increasing the frequency of earthquakes.

Each earthquake will damage one random component (with some exceptions, such as never damaging inactive pumps). The player is not told which part is damaged, and must identify it from changes in plant measurements, such as reactor and coolant temperature. Workers can be sent in to repair components; the player begins with 80 workers, who can be dispatched in groups of five and do not return (the in-game explanation for this is to limit their radiation exposure). The maximum is thus sixteen repairs, but if the player misidentifies damage and sends workers to a functioning component they also do not return. The player is informed after sending in workers whether the part was broken; workers will always succeed at repairing a broken part.

Changing the risk level resets the total MWH, but not the state of the reactor.


Risk LevelPassing Score (MWH)Rewarded Title
9300Reactor Operator
9500Senior Reactor Operator

Simulation Details

Reactor Model

SCRAM simulates a pressurized water reactor (PWR), which is a type of light water reactor. PWRs remain the most common reactor design in Western countries, but are now superseded - Generation II reactors, including the PWR design, have generally not been constructed since the 1990s.

The simulation includes a number of interconnected components:

  • Primary Loop/Reactor Coolant System
    • Reactor
      • Core: The nuclear fuel, which generates energy and heat
      • Control Rods: Affect the energy/heat production of the core
      • Reactor Vessel: Transfers heat from the core to water under very high pressure
    • Pressurizer: Assists in keeping reactor pressure within safe limits
    • Steam Generator: A connection allowing heat to be transferred from the high-pressure heated water to lower pressure water in the secondary loop, causing it to boil and form steam, without actual mixing of water
  • Secondary Loop/Main Feedwater System
    • Turbine & Generator: Uses steam to produce electricity
    • Condenser: Causes the steam to cool from contact with the tertiary loop and condense into water, so it can be heated again
  • Tertiary Loop/Circulating Water System
    • Hyperbolic Cooling Tower
  • High Pressure Injection (HPI) System: A safety system to add water to the primary loop, usually to increase pressure (and avoid steam voiding) or replace water lost through damage
  • Auxiliary Feedwater System: Equivalent of the HPI for the secondary loop

Simulated Parameters

  • Reactor internal temperature
  • Reactor pressure and boiling point
  • Reactor inlet/outlet temperatures
  • Secondary loop inlet/outlet temperatures
  • Tertiary loop inlet/outlet temperatures
  • Pressurizer steam/water ratio
  • Steam generator steam/water ratio
  • HPI water tank level
  • Auxiliary water tank level
  • Instantaneous generator power output

Temperatures are displayed in Fahrenheit, and pressure in psi (pounds per square inch). Most limits are impossible to encounter (the reactor would become inoperable long before), with the exception of the turbine/generator - it can output a maximum of 999 MW.

User Interaction

The player has total control over pumps and valves across the plant, as well as the ability to raise and lower the control rods. The HPI and auxiliary systems and a quench tank connected to the pressurizer have valves that allow them to be connected or isolated from the coolant loops. Each coolant loop and the HPI and auxiliary systems have one or more pumps working together, allowing more pumps to be activated to increase coolant transfer or to replace a damaged pump.

The player is also able to alter the risk level at any time, or reset the entire reactor to its initial state.


Earthquakes that occur on risk levels above 0 will always damage exactly one component, though the component is chosen randomly each time, with limitations:

  • Only pumps and valves can be damaged by earthquakes
  • Pumps can only break when enabled
  • Valves can break whether open or closed

(This allows some metagaming by enabling pumps on unnecessary systems behind closed valves - this has no effect on the main reactor, but reduces the chance of a more important component being damaged.)

Damaged parts are only visible through the effect on temperatures, otherwise appearing to operate normally. Parts can be repaired by sending in workers - who will always succeed if the part is actually broken. Most other components of the plant, including the turbine, cannot be damaged.

The reactor is 'designed' to run at pressures of 2200-2300 psi. If the pressure is increased to more than 3000 psi, a 'loss of cooling accident' (LOCA) can occur. This is irreparable and necessitates an immediate shutdown. Steam Voiding can also occur if the core temperature is too high - this does not directly cause damage, but is an indicator of an impending meltdown.

Meltdowns occur if the core reaches a temperature of 5000 F, and end the game.


At risk level 0, with no earthquakes to damage components and thus no need to expend workers or HPI/auxiliary water, the game can be played indefinitely. At higher risk levels the supply of workers will eventually be depleted, preventing an infinitely-high 'score'.

The simulation continues until the reactor melts down or the player performs a 'cold shutdown' (lowering the temperature of the reactor to below 200 F).


The game manual mentions several inaccuracies or omissions and their reasons. Particularly, a vast number of backups, redundant systems and other safety features are ignored (such as alternate methods to cool the core) for the purpose of gameplay, as well as the containment building since it has no effect on the simulation. Additionally, no safety systems are automated.

The general simulation speed is vastly increased, with meltdowns occuring in two minutes versus a more accurate real-life estimate of six hours. Earthquakes occur more often than expected, even on lower difficulties and considering the time dilation, but would not typically damage a single valve or active pump - in fact, reactors are specifically designed to withstand probable earthquakes.

Losses from the tertiary loop (water removed from the cooling tower via evaporation or air currents) are also not considered.

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