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

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

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

Plutonium Solutions and Metals

239

Metallic 239Pu

239

PuO2(a)

239

PuO2(b)

Parameter

Pu(NO3)4

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 are 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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