Nuclear Fusion Reactor System

By: J. Duncan Law-Green

Traveller Tech Brief

Abstract

This article will attempt to set out, in some detail, the anatomy of fusion reactor systems in Traveller (more specifically, those used as starship power plants), the fusion reactions they use, their most common failure modes, and the methods and expected results of sabotaging power plants.

Introduction

For the majority of Traveller players, fusion power plants are simply clever little boxes which hum away in the rear of the vehicle producing oodles of power, and occasionally having to be fed with glasses of water. Being the incredibly destructive creatures they are, however, players will sooner or later want to sabotage the power plant of an enemy vehicle or ship or repair their own after combat damage or accident. After facing some embarrassing questions (one player in my group is a physicist, another a nuclear engineer) I composed this article.

Regular or Super Unleaded?

The standard Traveller references on power plants (SOpM being the most instructive) state that the fusion reactor is fuelled by "hydrogen." What they fail to state is that there are three different isotopes of hydrogen, with quite different abundances and nuclear properties. These are:

1H (Protium): Stable (non-radioactive.) Consisting of one proton and one electron, protium is by far the most abundant isotope in the Universe.

2H (Deuterium): Stable. Consisting of one proton, one neutron, and one electron, Deuterium is present to an abundance of approximately one part in 5,000 in "natural" hydrogen extracted from seawater.

3H (Tritium): Radioactive. Decays to Helium-3 by proton emission with a half-life of 12.5 years. Consisting of one proton, two neutrons, and an electron, Tritium's natural abundance is negligible -- it has to be "manufactured" by a variety of possible routes.

Current research on fusion power production is concentrating on deuterium-deuterium, deuterium-tritium, or deuterium-Helium-3 fusion, as these require the lowest plasma energies. At first this suggested to me that Traveller power plants were standard deuterium-tritium reactors, but further examination of Traveller texts has ruled this out. My reasons for this are detailed below.

Wot? No Tritium?

My first reservation is based on the health and security hazards involved in handling large quantities of radioactive material such as tritium. Starport scenarios make no mention of the necessity of shielding fuel lines or storage tanks! Also, tritium is important in the manufacture of "clean" or laser-triggered fusion warheads -- I would think it is the Imperium's interest to regulate the sale and supply of tritium.

Second, there is a serious problem with wilderness refueling, whether it be from oceans, gas giants, or Oort clouds. The references state that purification plants are intended to remove "trace" impurities which may interfere with the operation of the reactor. For a deuterium-fueled reactor, however, 4,999 parts in 5,000 of the fuel intake is "impurity." Ships without a purification plant would be in serious trouble.

Third, the scenario "Wrong Way Valve" in Challenge #31 specifically states that a starship's fuel tanks are filled with ordinary water. (It makes no mention of the repeated electrolysis necessary for deuterium separation.)

Thus, it is clear that Traveller fusion reactors are remarkable devices which can be fueled by "natural" hydrogen (primarily protium.) I say remarkable, because the plasma energy and magnetic confinement requirements for protium fusion (via the "proton-proton" chain, as in the center of the Sun) are several orders of magnitude greater than those for other types of fusion. It seems the only way to duplicate this process is to construct a reactor the size of a small star! However, there is still hope ....

C, NO Other Way

As I stated previously, it is believed that the sun produces energy by fusing protium via the "proton-proton" chain. Some giant stars fuse hydrogen by a different route, known as the "CNO catalytic cycle", so-called because isotopes of carbon, nitrogen, and oxygen participate in the nuclear reaction, lowering the plasma energy sufficiently for it to become a practicable proposition. The CNO catalyst is not consumed in the reaction, and only relatively small amounts are necessary to produce sustainable fusion. For those of you who are interested, the details of the cycle are shown below.

12C + 1H -> 13N + y

13N + 1H -> 14O + y

14O -> 14N + e+ + y

14N + 1H -> 15O + y

15O -> 15N + e+ + y

15N + 1H -> 12C + 4He

Anatomy of a Traveller Fusion Reactor

All starship power plants possess a small "purification" plant known as an HHSU (Heavy Hydrogen Separation Unit.) This unit partially separates the deuterium from a small volume of the fuel. The deuterium-enriched fuel is used when the reactor is in "warm-start" or "park" mode. Because the reactor uses deuterium-deuterium fusion in "warm-start" and CNO fusion in normal operation, it is known as a split-cycle or twin-cycle reactor.

The components of a starship reactor system are discussed below.

1. Containment Vessel: A highly rigid vessel typically constructed of superdense metal, inlaid with superconducting field coils. Contains the plasma "bottle", either of toroidal ("tokamak") or spherical ("ball lightning") configuration.

2. Ignition Capacitors: Supply the initial energy pulse to establish the

3. Power Transfer Circuit: Fusing plasma is passed through a MHD system, directly producing electric power.

4. Thermal Transfer Circuit: Containment vessel cooled by liquid sodium or high-pressure argon. System links through at least two heat-exchanger loops to hull radiator strips. Turbine generators in coolant circuit produce supplementary power and low-pressure steam for ship systems.

5. Helium Purge Circuit: Removes waster helium from containment system. May be discarded or retained for ship's cryogenic systems.

6. HHSU: See above.

7. Deuterium Warm Start Reservoir: ("Ignition module".) Holds the supply of deuterium-enriched fuel prior to warm-start of reactor.

8. Catalyst "Scavenge" Circuit: Maintains level of CNO catalysts in containment vessel.

9. CNO Catalyst Reservoir: ("Sustainer Module".) Holds the supply of CNO catalyst when the reactor is at "warm start", or powered down.

Failure Modes and Sabotage Opportunities

Or: I thought you checked the sustainer module...

Containment Failure:

There are sufficient failsafes built into the field coil system that a catastrophic failure of the magnetic bottle is highly unlikely. The "ball lightning" bottle configuration tends to be self-sustaining for short periods ... meaning that the sphere of plasma can punch its way out of the containment vessel if the coil system fails.

To sabotage the field coil system:

Formidable, Engineering, Electronics, 10 min (Hazardous, Fateful)

Conversely, the magnetic bottle may be too small, or the catalyst level too high for the fuel volume being injected...in which case a thermonuclear explosion will result. To achieve this, the majority of the reactor control firmware must be rewritten, and the diagnostic circuitry disabled.

To rewrite the reactor control firmware to cause an explosion:

Impossible, Computer, Engineering, 18 min (hazardous)

Coolant Failure:

In the event of a partial or complete coolant failure, the reactor should flip to warm start or power down automatically. If the ship is in flight, the computer will offer an override option to the crew - but the consequences of reactor overheat are highly unpredictable. You have been warned.

Deuterium Failure:

If the deuterium separator or reservoir fail, the reactor will not cold start. Period. A potential saboteur may decide to remove the ignition module to cripple an enemy starship. On a small starship (under 500 tons), the ignition module is typically 40cm x 20cm x 15cm and weighs 16 kg.

To remove ignition module:

Formidable, Engineering, Dex, 30 sec (hazardous, uncertain)

Referee: Task is difficult if reactor design is familiar to engineer.

On Some Truth, diagnostic circuit is triggered.

Catalyst Failure:

If the catalyst scavenge circuit fails, or the sustainer module is removed, interesting things can happen.The reactor will appear to operate normally at full power, but sometime - between 15 seconds and 20 minutes after power up - it will flip back to warm start without warning and will not restart. This can be troublesome if the ship happens to be a couple of kilometers up in the air at the time.

On small starships, the sustainer module is typically 25cm by 12cm by 10cm and weighs 6kg.

To remove sustainer module:

Formidable, Engineering, Dex, 40 sec (Hazardous)

Referee: As ignition module above.

Joseph Heck (joe@mu.org) 21 August 2000
http://traveller.mu.org/house/fusion.html