atw 2018-04v6

inforum

atw Vol. 63 (2018) | Issue 4 ı April

Radionuclide Metals Concrete Other

materials

Reused Recycle Both reuse and recycle Demolition

Surface

(Bq/cm 2 )

decree were also the requirements

imposed by the Italian Nuclear Regulatory

Body ISPRA. According to these

requirements, the components and

materials of RB3 were classified by

ENEA, taking into account the various

areas of the plant and the history of

its functioning, into four main

categories:

A) materials and components which

were both in contact with possibly

contaminated or activated process

fluids and subject to neutron flux;

B) materials and components which

were in contact with possibly

contaminated or activated process

fluids but not directly irradiated by

neutrons;

C) materials and components which

were irradiated by the neutron flux

but which never went into contact

with possibly contaminated or

activated process fluids;

D) s.c. “exempt” materials, which

were never irradiated and never

went into contact with possibly

contaminated or activated process

fluids.

The only component classified in the

A category was the aluminium vessel;

the only components in the B category

were the heavy water distribution

pipings. Exempt materials, given their

unirradiated and uncontaminated

status, were subject only to a general

screening through CANBERRA In Situ

Object Counting Systems (ISOCS) to

estimate any possible level of presence

of 60Co and 137Cs; if the measured

levels were below the decision threshold

of the measuring system in terms

of mass concentration levels, then

Surface

(Bq/cm 2 )

| | Tab. 1.

Surface or mass activity concentration levels for clearance.

Mass

(Bq/g)

these materials were automatically

discarded from the plant without any

further radiological analysis. This

demonstrates the “instrumental” zero

of this category of materials hence the

“exempt” classification. All materials

which had been classified as “exempt”

were released unconditionately, for a

total mass of about 30 tons, between

March 2013 and May 2015. For all the

other three categories, the clearance

levels imposed by the Regulatory

Authority are summarized in Table 1.

These were derived either from the

Italian L.D. n. 230/95 or from RP 89

[3] and RP 113 [4] publications. In

presence of more than one radionuclide,

the sum of the ratios of

the measured concentrations to the

respective levels must be lower than 1.

The components and materials

were further grouped by ENEA into 12

s.c. “homogeneous groups” using

material and historic criteria; homogeneous

groups are therefore constituted

by components (or parts of

them) made by the same material and

possibly with a homogeneous and

uniform activity content.

3 Radiological Characterization

of Homogeneous

Groups

Before the radiological characterization

of the batches of materials from

the various homogeneous groups

started, a preliminary, special campaign

was conducted to exclude the

presence of various isotopes among

those given in Table 1, expecially in

the most potentially activated or

contaminated materials (category A).

Surface

(Bq/cm 2 )

Mass

(Bq/g)

3 H 10,000 100,000 1 10,000 1 1

14 C 1,000 1,000 1 10,000 1 1

Mass

(Bq/g)

54 Mn 10 10 1 10 0.1 0.1

55 Fe 1,000 10,000 1 10,000 1 1

59 Ni 10,000 10,000 1 100,000 1 1

60 Co 1 10 1 1 0.1 0.1

63 Ni 1,000 10,000 1 100,000 1 1

90 Sr 10 10 1 100 1 1

125 Sb 10 100 1 10 1 1

134 Cs 1 10 0.1 10 0.1 0.1

137 Cs 10 100 1 10 1 1

152 Eu 1 10 1 10 0.1 0.1

154 Eu 1 10 1 10 0.1 0.1

Generic Alfa 0.1 0.1 0.1 0.1 0.1 0.01

241 Pu 10 10 1 100 1 1

In particular 54Mn, 59Ni, 90Sr,

125Sb, 134Cs, 137Cs, 239Pu, 240Pu

and 241Pu were excluded from

further analyses finalized to the unconditional

release of materials. Then,

for each homogeneous group, a precharacterization

measurement campaign

was con ducted with a three-fold

aim: 1) to verify if the hypothesis on

the homogeneity of activity for that

given group held; 2) to evaluate the

minimum number of samples to be

analized

for the subsequent characterization

phase; 3) to evaluate the value of

isotopic ratios of 55Fe to 60Co and

of 63Ni to 60Co, so to limit the next

analyses only to the research of 60Co

contents. After that, and using typically

13 multiple measurements for

each batch of each homogeneous

group, summations of the ratios

between measured activity concentrations

and limits (Table 1) over all

the relevant isotopes were carried out.

If these summations resulted

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