Lecture 14: Is Nuclear Power Safe? Calculating the Number of Deaths Caused by Nuclear Accidents...

Overview

R. Scott Kemp calculates the number of deaths caused by nuclear accidents, focusing on cesium-137 and iodine-131 releases from Chernobyl and Fukushima. By applying the linear no-threshold (LNT) model and UNSCEAR data, he estimates a "typical" INES 7 accident could cause approximately 230,000 deaths worldwide from cancer, primarily due to the difficulty in empirically detecting these radiation-induced cancers against background rates.

Key takeaways

A 'typical' major nuclear accident (INES 7) could cause approximately 230,000 worldwide cancer deaths, primarily from Cesium-137 and Iodine-131.
The linear no-threshold (LNT) model is used to estimate radiation risk, converting person-sieverts to potential cancer fatalities.
Historical accident rates (10^-4 per reactor year for INES 7) are significantly higher than Probabilistic Risk Assessment (PRA) predictions, suggesting PRA underestimates risks.
Nuclear power's estimated death rate is 1.4-2.3 deaths per terawatt-hour, placing it as relatively safe but not as safe as some initial claims suggested.
Discrepancies in death toll estimates stem from differing methodologies, geographic scope, and contamination-to-dose conversion factors.
Beyond Design Basis Accidents, often caused by human error or unforeseen events, are the primary drivers of significant nuclear accident risk.

Chapters

0:00 Introduction to Nuclear Accident Externalities

R. Scott Kemp aims to quantify the number of deaths caused by nuclear power accidents as part of externality calculations.
This calculation is necessary to compare nuclear power's safety profile against other energy sources like wind, solar, and natural gas.
The focus is on safety externalities, specifically the impact of nuclear accidents.

3:53 Key Isotopes in Reactor Accidents

Cesium-137 and Cesium-134 are significant long-term isotopes released in reactor accidents.
Iodine-131 is also important due to its high initial dose, despite its short half-life.
Cesium's chemical similarity to potassium allows it to distribute widely in the body, while Strontium-90 (similar to calcium) concentrates in bones.

9:07 Chernobyl Accident Overview

Chernobyl was an RBMK-type reactor accident (INES 7) with no containment, leading to steam explosions and fires.
The accident released 85 petabecquerels of Cesium-137 and significant non-noble gas activity.
European spatial average contamination was 7 kilobecquerels of Cesium-137 per square meter.

15:10 Accounting for Population Density and Food Uptake

The calculation must consider population density, as people are not evenly distributed across contaminated land.
Ukraine's agricultural output means grain grown there uptakes cesium, leading to ingestion doses.
The European spatial average contamination is adjusted upwards to account for these factors.

17:30 Fukushima Accident Overview

Fukushima was a BWR-type reactor accident (INES 7) initiated by a tsunami, leading to cooling system failures.
It released 21 petabecquerels of Cesium-137, significantly less than Chernobyl.
Venting of containment and explosions released radioactive material, with much of it dispersed into the Pacific Ocean.

22:25 Global vs. Local Contamination from Fukushima

Fukushima's contamination spread globally, with North America receiving significant fallout.
The average contamination in North America was roughly 1% of that in Japan, but over a land area ~100 times larger.
UNSCEAR estimated a factor of 1.6 difference between European and global contamination, suggesting global contamination is roughly twice local contamination.

25:33 Estimating a 'Typical' Nuclear Accident

A 'typical' accident is weighted between Chernobyl (RBMK, no containment) and Fukushima (BWR, containment).
The calculation uses a weighted average: 1/3 of Chernobyl's release and 2/3 of Fukushima's release, adjusted for multiple reactors at Fukushima.
This results in an estimated release of 9 petabecquerels of Cesium-137 for a typical accident.

30:13 Irradiation Pathways: Ground Shine, Inhalation, and Ingestion

Radiation exposure occurs through three main pathways: ground shine (external irradiation), inhalation of airborne particles, and ingestion of contaminated food/water.
The availability of isotopes in the environment depends on their chemistry and environmental reactions.
UN (1982) data provides conversion factors from contamination (Bq/m²) to dose (Gy).

33:28 Calculating Ground Shine Dose

Using Chernobyl contamination levels (10 kBq/m²) and a conversion factor (9 µSv/kBq/m²), the ground shine dose is calculated.
The dose is integrated over time, considering the 30.2-year half-life of Cesium-137.
The calculated dose commitment from ground shine is approximately 9.9 x 10^8 man-sieverts for Chernobyl.

38:52 Incorporating Internal Dose Pathways

UN data indicates total dose (external + internal) is higher than external dose alone.
For Chernobyl, external irradiation was 150 units, and total dose was 220 units, implying internal pathways contribute significantly.
A scaling factor of 220/150 is used to convert external dose to total dose, accounting for ingestion and inhalation.

45:00 Calculating Total Person-Sieverts

The population of Europe is estimated at a stable 750 million people for the calculation.
The total dose is integrated over time, considering radioactive decay.
The calculation yields approximately 860,000 person-sieverts of exposure for a typical accident in Europe, considering only Cesium-137.

51:54 Converting Person-Sieverts to Cancers

Using the linear no-threshold (LNT) model, a baseline cancer risk of 20% and an excess relative risk of 0.64 per sievert are applied.
This results in an estimated 110,000 excess cancers from Cesium-137 in Europe.
Assuming half of cancers are fatal, this translates to approximately 55,000 deaths.

57:26 Comparison with BEIR VII Report

The BEIR VII report estimates solid cancer mortality at 610 deaths per 10,000 person-gray.
Converting person-sieverts to person-grays (assuming 1 Sv = 1 Gy for beta/gamma), 860,000 person-sieverts becomes 860,000 person-grays.
Applying the BEIR VII factor yields approximately 52,000 deaths, closely matching the previous calculation.

1:03:20 Including Iodine-131 and Other Isotopes

Iodine-131 contributes significantly to the total dose, estimated at 3.4 million person-sieverts from Chernobyl.
Rescaling Chernobyl's total dose (including iodine and other isotopes) to a typical accident suggests a total dose of 2.3 million person-sieverts.
This increases the estimated deaths to 2.7 times the Cesium-137-only calculation, approximately 150,000 deaths in Europe.

1:07:20 Globalizing the Death Toll

UNSCEAR's factor of 1.6 is used to scale European dose to global dose, accounting for wind patterns and ocean dispersal.
Multiplying the European estimate by 2.7 (for all isotopes) and 1.6 (for global spread) yields approximately 230,000 deaths per typical major accident worldwide.
This figure represents only cancer deaths and does not include other health effects like teratogenic effects or deterministic diseases.

Summary, takeaways, and chapters were generated by AI from the video's transcript and may contain errors. The video belongs to its creator, MIT OpenCourseWare.