---
category: Nuclear Concept
summary: MUF ('material unaccounted for') is the nuclear industry term for the discrepancy
  between expected and measured quantities of nuclear material in a facility, whose
  large-scale irregular occurrence at the NUMEC plant is central evidence in allegations
  that Israel diverted enriched uranium for its nuclear weapons program.
tags:
- Concept
- Nuclear
- Accounting
---

MUF, or "material unaccounted for," is a term commonly used in the nuclear processing industry. It refers to the difference between the amount of nuclear material that is supposed to be present in a facility and the amount that is actually measured. This discrepancy can arise from various factors, including inherent process losses, measurement uncertainties, and, in some cases, diversion of material.[^1]

At the [NUMEC](/organizations/nuclear-materials-and-equipment-corporation/) plant, MUF became a significant issue, with over two hundred pounds of enriched uranium unaccounted for. The [AEC](/organizations/atomic-energy-commission/) eventually worked out complicated rules for accounting for MUF, enabling private firms to estimate how much missing but accountable uranium was believed to be in a plant's air filtration system or buried in its waste pits. The AEC accepted these estimates as realistic and deferred assessments of penalties, assuming that no reprocessing firm would divert or steal uranium if it resulted in a stiff fine.[^1]

[^1]: Hersh, Seymour M. *The Samson Option: Israel's Nuclear Arsenal and American Foreign Policy*. Random House, 1991. Chapter 18.