Table 7.1. Subcritical, Single Parameter Limits for Plutonium Solutions and Metals (AMSI, 1983b)

DOE-STD-1128-98

Table 7.1. Subcritical, Single Parameter Limits for Plutonium Solutions and Metals

(AMSI, 1983b)

Plutonium Solutions and Metals

Parameter

Po(NO3) 4

Metallic 239Pu

PuO2(a)

PuO2 (b)

239

Mass of fissionable nuclide, kg

0.48

5.0

10.2

Diameter of cylinder of

15.4

Solution, cm

Volume of solution, L

7.3

Concentration of fissionable

7.3

Nuclide, g/L

Cylinder, diameter, cm

4.4

7.2

12.6

Slab thickness, cm

5.5

0.65

1.4

2.8

Maximum density for which

19.82

9.92

Mass and dimension limits

are valid, g/cm3

(a) Oxides containing no more than 1.5% water by weight at full density.

(b) Oxides containing no more than 1.5% water by weight at no more than half density.

Double contingency requires that process designs incorporate sufficient factors of

safety to require at least two unlikely, independent, and concurrent changes in

process conditions before a nuclear criticality accident is possible.

Protection, or defense in depth, should be provided by either (a) the control of two

independent process parameters (which is the preferred approach, if practical) or (b) a

system of multiple controls on a single parameter. In all cases, no single credible

event or failure shall (DOE Order 420.1A, Section 4.3.3) result in the potential for a

criticality accident. The basis for selecting either approach is to be fully documented.

The two parameters that are controlled in the double contingency analysis process

must not be related by common mode failures. Judgment is required in determining

whether two events are related and, consequently, whether they represent two

contingencies or a single contingency. For example, exceeding a storage limit and

then flooding an area with water would constitute two independent events. However,

a fire followed by the flooding of a storage area with fire suppression water would

constitute a single event.

The double contingency principle is to be applied to all nuclear criticality safety

analyses for processes, systems and equipment, storage, and transportation of fissile

materials. Should contingencies be determined to be related, efforts are to be made to

separate the contingencies. If this is not practical, an exemption process is identified

in DOE Order 420.1A.

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