Radiochemical Neutron Activation Analysis for Trace Chlorine in Steels and Alloys

Abstract

Chlorine is usually present at low concentrations in reactor materials and thermal neutron activation of (35)Cl produces (36)Cl, which has a long half-life and is a radionuclide of significance in nuclear waste disposal. This paper describes a radiochemical method that has been developed to measure low concentrations of Cl in reactor stainless steels, so that the amount of (36)Cl in radioactive wastes can be estimated. The method is based on the irradiation of a 1 g sample in a thermal neutron flux of 10(16) n m(-)(2) s(-)(1), followed by dissolution in HNO(3) with the addition of stable KCl carrier/tracer. The Cl is precipitated as AgCl, and the recovery is measured gravimetrically. The (38)Cl, which has a half-life of 37 min, is measured with γ-ray spectrometry. The entire process, from irradiation to the end of counting, takes ∼1.5 h. The recovery is near-quantitative, and the detection limit for Cl in most stainless steels is below 1 mg/kg.

Using the nuclear activation AMS method for determining chlorine in solids at ppb-levels and below

“…The upper limit achieved with the latter method was 260 ppb. Similar studies using 38 Cl detection and NAA published in the past found detection limits ranging from 300 to 50 ppb, depending on the sample composition [3,4].…”

Determination of36Cl in Nuclear Waste from Reactor Decommissioning

“…A 50-mg aliquot of stable chlorine was added to the sample as a carrier. The concentration of Cl in concrete was measured as 48.4 ( 4.1 ppm; the reported concentrations of Cl in graphite, aluminum, and lead samples are below 10 mg/kg, and Parry et al 26 reported less than 2 mg/kg Cl in several types of steel. Since less than 5 g of sample was used in this work, the contribution of Cl from the sample (<0.1%) can therefore be ignored.…”

“…No Cl concentration was determined in this steel sample. Parry et al 26 tried to determine Cl in steel samples using radiochemical neutron activation analysis, but found that the concentration of Cl in all six kinds of steel tested was below the detection limit (0.1-1.8 mg/kg). The concentrations of Ni and Fe in the steel samples were estimated to be 12 and 45%, respectively.…”

“…It has been reported that to dissolve 0.7 g of stainless steel required 17.3 g of Cl as HCl; dissolution with KCl and HNO 3 significantly reduced the amount of Cl needed, but the figure was still 1.0 g of Cl as KCl. 26 The addition of such large amounts of Cl will make the further separation of Cl by anionexchange chromatography more difficult, requiring a large column and a large volume of eluent. The large amount of Cl and NH 4 -NO 3 in the eluate would also need a large volume of cocktail to produce a clear solution for counting, and this would raise the detection limit for 36 Cl.…”

“…25 Steel and other metals such as aluminum and lead are also used extensively in nuclear reactors, and 36 Cl will also be produced from the chlorine present as an impurity in these materials. 26 Reactor water also contains 36 Cl, some from the chlorine present as an impurity in the water and the rest leached from the reactor materials. 27 High 36 Cl activity has also been found in ion-exchange resins, which concentrate 36 Cl from the reactor water.…”