Setting the UCert Insurance Cap

Figure 1. Minimum Buffer Zone Radius. Individual units must abide by mini-buffer radius or be treated as a single unit.

Underwriter Certification(UCert) of nuclear power requires Congress to set a liability cap for each plant based on the plant's weather conditions, and surrounding population distribution. Some choir members have doubted Congress's ability to accomplish such a technical task. Up to now, the UCert Manual has been silent on just how this might be done. With Version vC, this is no longer the case.

Here's a brief summary of the proposed procedure. If Congress were to use this methodology, all they would have to do is decide on the numbers in brackets.

The UCert insurance cap for each plant shall be based on the total compensation which would be required under a credible worst case release, which will depend on local weather conditions and the surrounding population distribution. That worst case can and should be extremely unlikely; but we need say nothing about its probability, nor the dependence of that probability on a particular technology. That is the job of the underwriters, when they set the premium. A technology that is deemed ``safer" by the insurers will be rewarded with a lower premium.

Buffer Zone Exemption

The plant shall have a buffer zone per UCert rules, Figure 1, which is 2 kilometers for a 3 GW thermal plant. There shall be no UCert compensation for exposure within the buffer zone. Plant employees and anybody else who are required to stay in the buffer zone will be covered by Worker Compensation and employee/union contracts.

No ingestion compensation

The cap assumes no ingestion of foodstuff contaminated above legal maximums. This is easily enforced as we saw at Fukushima and Windscale. For practical purposes, all the heavy, non-volatile stuff will fall within the buffer zone, even in a Chernobyl-like release. This means we only have to worry about inhaled material during plume passage and groundshine thereafter.

Release Amounts

Under the above assumptions, essentially all the public exposure will be from I-131, Te-132, Cs-134, and Cs-137, as has been the case in all previous releases. The Chernobyl explosion was an extreme case for a non-war caused release.¹ The upper bound estimates for the release of iodine and tellurium at Chernobyl were 60% of the inventory. For cesium it was 40%. The cap shall be based on the release of these percentages of the max (end of fuel life) inventory of these four isotopes.

Release Duration

Assume uniform release over [1 day]. A really big release such as Chernobyl and Fukushima will almost certainly be longer than this. For unfavorable weather, the more concentrated a given release is the greater the harm.

Weather

Assume current population distribution. Run HYSPLIT or equivalent for each [day|week] in the last [10] years.² Compute the UCert compensation for each resulting plume, assuming no mitigation, low-end weathering. Base cap on the [95] percentile worst weather. (95% of the time the weather will be more favorable than this.) The cap calculation shall be redone every [5] years, to adjust for changes in the population distribution.

Technologically Agnostic

This procedure, based on what's possible, avoids requiring politicians to make judgements about the safety of any particular design. At the same time, it will force utilities and coops to balance the costs of remoteness against the benefits of remoteness in plant siting. The current system is an abject failure in that regard.

1. If a release results from a military or terrorist attack, the compensation will be paid by the general public and the UCert cap no longer applies.

2. HYSPLIT is a NOAA plume model which takes as input a past weather pattern and a user specified release and computes the resulting plume concentration and deposition through time by isotope. These results can be translated to maximal dose rates through time by location, which in turn can be combined with the population distribution to calculate the UCert compensation for the postulated release.