Crawl Out Through the Fallout (Radiation in Twilight: 2000)

Like a disease, radiation is an "unseen" threat in the Twilight World. Unlike a disease, which is amenable to medical intervention, radiation sickness is not particularly treatable apart from providing supportive care and a character's chance of surviving is only dependent on their CON score and their accumulated exposure. 

View of Chernobyl from a ruined window(sepia-tone modified image from this VICE article)

Radiation is a mid-late threat as it takes time for the risk of radiation sickness to build up through repeat exposure but unlike other threats that can be resolved or reset, the threat of radiation worsens over time the more exposure a character has during the game and there's no way to decrease this risk through medical treatment.

I'm Radioactive! - Radiation Exposure 

I'm waking up to ash and dust
I wipe my brow and I sweat my rust
I'm breathing in the chemicals
I'm breaking in, shaping up, then checking out on the prison bus
This is it, the apocalypse

Whoa... 

- "Radioactive", Imagine Dragons 

The rules for radiation and the potential for radiation sickness are given on pages 242-243 of the v2.2 corebook (although as each page has a half-page image, the rules really only cover one page of dense text). Although potentially radiation sickness could be considered a "disease", the rules use separate mechanics, adding another "mini-game" to the overall system.

Starting rads are calculated according to pages 23-24. For military characters, this is No. Terms x2 x D6 (effective maximum 84 rads for 7 terms) and civilian characters 1D6 x 1D10 (max 60 rads). A high score puts starting characters at risk of radiation sickness with any further exposure but otherwise, most characters will not have any issues until more than an hour of exposure to a crater or their second and subsequent exposures.

Radiation Illness CON modifiers
(T2k v2.2 corebook page 244)

Rads less than 50 have no effect, anything greater requires a CON check on D10 multiplied by a modifier on the table on page 244 depending on the character's *total* rads accumulated:

• Slight illness is a risk at 50+ rads and becomes automatic at 400+ rads
• Serious illness is a risk at 100+ rads and becomes automatic at 600+ rads 
• Death is a risk at 300+ rads and becomes automatic at 800+ rads 

Fortunately, radiation is relatively easily avoided compared to disease - the main source is impact craters usually found in the ruins of larger cities or occasionally during a travel Encounter (a 1 in 10 chance if an Item encounter is triggered except in cantonment or disputed regions). As only a few years have passed since the nuclear exchange, most craters will be readily identifiable even if partly eroded although this may be more difficult in urban ruins also damaged by conventional explosives.

The radioactive areas associated with craters are larger than the visible crater however and range from 3/4 km across to about 1.5km across. Other sources of radiation eg leaking reactor cores or radioactive waste are not explained except for a nuclear detonation. A Geiger counter confirms the presence of radiation, allowing exposure to be avoided. The game suggests that a lack of animals or vegetation as a ready clue - this is not strictly correct as plants can actually tolerate a level of radiation. 

At a rad accumulation rate of 1D6 per minute in a crater area, on average an hour of exposure without protection exposes a starting character to ~210 rads (60 minutes x 3.5 rads on average), running the risk of slight illness *and* serious illness, but not the risk of death unless they've had additional exposures already. This assumes you don't roll 60D6 (one dice for every minute) or multiply a single D6 roll by 60 which seems potentially disastrous (max 360 rads from one-hour exposure).

Higher and/or longer periods of exposure have the following averaged effects:

• 2 hours (~420 rads) automatically causes slight illness and runs the risk of death. 
• 3 hours (~630 rads) automatically causes serious illness.
• 4 hours spent in a crater without protection (~840 rads) is certain death. 

A nuclear detonation (~6000 rads) is noted to be immediately fatal.

A character travelling in an "enclosed" vehicle accumulates 1/10th the rads, a radiologically "shielded" vehicle only 1/100th the rads. A MOPP suit probably provides protection as a "shielded" vehicle but it's not explicitly stated in the corebook. It is possible to survive the radiation effect of a nuclear blast in an enclosed vehicle if not directly exposed to the shockwave and blast, although the crew will suffer serious illness at least as the dose is 600 rads (only 60 rads in a "shielded" vehicle).

Radiation Sickness

Once a character has 50+ rads, if exposed to significant to radiation the character must make up to 3 CON based checks (one each for death, serious and slight illness in order)), *every* time they are exposed to radiation. Unlike diseases, there are no modifiers that affect this check, the only way to reduce the risk is to avoid or reduce exposure in the first place. An exposed character only has to check once per day - this seems to just be a mechanical simplification for the game as it's possible to be exposed more than once several hours apart from different sources.

Radiation Exposure Infographic
(Mayo Clinic website via raytodd.blog)

There is no Medical: Diagnosis check involved in diagnosis although some of the symptoms (nausea, vomiting, headache) could be mistaken for infectious disease and supportive care, supervised by a character with that skill, is needed to reduce the period of incapacitation (see below).

Death is always checked for first at accumulated 300+ rads - failure of the CON check results in slight illness within 1D6 hours (see below), then serious illness 2D6 days afterwards (1D6 days if 300+ rad exposure) with incapacitation lasting 1D6 days or more during which the character *dies*. No treatment ameliorates this, making radiation one of the few "auto-kill" threats in the game.

Slight illness occurs within 1D6 hours of significant exposure and results in *halving* of STR, AGL and INT for a day (2 days if rads exposure is 600+). This is debilitating but not incapacitating and oddly does not affect CON or increase Fatigue like a disease would, nor does it make the character more prone to a superadded infection.

Serious illness has a delayed onset of 2D6 days (1D6 if rad exposure 300+) and incapacitates the character for at least 1D6 days, followed by a "general" illness period with the same effects as slight illness above that last 1D6 weeks. The only "medical" treatment of serious illnesss is essentially supportive and considered equivalent to the same amount of time as for two serious wounds (as per page 211):

"First, the caregiver must spend half an hour per wound level, per body area damaged, per day, tending to the wounds... Second, once per day the caregiver must pass an Average check of his or her Medical asset. If no medical equipment is available (a doctor's kit is minimum), then the task check becomes Difficult. Failure means that one of the two days' worth of time to be saved was lost. In other words, if the task is failed one day during the treatment period, only one day is saved from the normal healing time. If the task is failed twice, no days are saved. Note that failing the task a third time (or more) does not add time to the basic healing rate unless a Catastrophic Failure Is rolled on this third check (or beyond)."

This calculates out to two serious wounds (2 x 3 x 30 minutes, 3 hours) or almost a whole 4 hour period of medical care per day, provided medical equipment is available. Lack of this supportive care results in a longer duration of serious illness by up to 3 days (1 extra day per 2 days of incapacitation). Specifics of this supportive care are not given other than supervision by a character with a Medical asset, presumably Diagnosis as this is similarly used for disease.

Note:  it seems an oversight that serious illness at least does not inflict Fatigue levels or increase infection risk by reducing CON to half as lethargy, blood system dysfunction and impaired immune function are characteristic of radiation sickness, but it's possible this is to avoid the potentially lethal "double-hit" combination of radiation and disease affecting the same character at once. A Fatigue level of two in the post recovery "general illness" phase similar to other major diseases would seem a reasonable optional rule.

"General" illness refers to the recovery period following serious illness and is similar to the debility phase but confusingly named - an example of how the two sub-systems vary and create separate "mini-games" within the overall rules and add to the complexity.

Option: Chelation Therapies

Note: this optional detail is added after the initial post's publication thanks to "swaghauler" - I think it adds to the overall canon rules without affecting the role of radiation in the game.

"The one thing that GDW did not discuss in the initial publication is the methods of treating Radiation or even Heavy Metal exposure in order to reduce the RADS absorbed by the exposure. In their defense, this was not available to the public at large in the '80s when they were writing the game.

Potassium Iodide Tablets: These can be taken shortly after exposure (up to 1 hour) in order to "bind" some of the radioactive particles and pass them from the body through the kidneys. This will remove 1D6 rads from the exposure total.  

Prussian Blue Treatment: I have only seen this in injectable form but it may be available in an oral form. Like PI tablets, this will bind to various radioactive elements and allow you to pass those rads by urination. It will reduce exposure by 2D6 rads.

DTPA (Diethylene Triamine Pentaacentic Acid): I don't know if this is oral or injectable but it will bind to radioactive metals in the system and can reduce the RADS absorbed by 1D6. It can also be used to treat heavy metal poisoning. It provides a bonus of 1 to the CON checks (see my Food Contamination Table in the Storing Food thread).

Lithium Dioxide: An injection that can help one fight off heavy metal poisoning just like DTPA above.

I have no idea what the Availability or Costs of these meds should be. Input is obviously welcome."

- Post by "swaghauler", Juhulin Forums April 2019

Conclusions

Overall, from my reading, the rules for radiation sickness seem to model real-life "acute radiation syndrome" reasonably well from a mechanics perspective and the difference in mechanics to disease seems justifiable - radiation is an insidious but avoidable threat that builds in lethality over time but has little chance of medical intervention. 

As a scenario driver, radiation is useful more as a negative influence to prompt the player group to avoid a particular area, at least until they have obtained the appropriate equipment and/or vehicles to negotiate or significantly reduce the risk. The lack of treatment and the inevitable increase in debility through accumulated exposure provides a different tempo and from a campaign perspective, it's more relevant mid-late game and likely irrelevant in the early phases of a campaign. 

So if fuel and then food dominate the early phase of a default Polish campaign pre-Winter and armed conflict and disease are otherwise constant threats, in my mind radiation looms as a potential consequence of a long-term stay in a landscape littered with nuclear craters.