ASTM E910-07(2013)

5.4 An application for the HAFM method lies in the direct analysis of pressure vessel wall scrapings or Charpy block surveillance samples. Measurements of the helium production in these materials can provide in situ integral information on the neutron fluence spectrum. This application can provide dosimetry information at critical positions where conventional dosimeter placement is difficult if not impossible. Analyses must first be conducted to determine the boron, lithium, and other component concentrations, and their homogeneities, so that their possible contributions to the total helium production can be determined. Boron (and lithium) can be determined by converting a fraction of the boron to helium with a known thermal neutron exposure. Measurements of the helium in the material before and after the exposure will enable a determination of the boron content (5.5 By careful selection of the appropriate HAFM sensor material and its mass, helium concentrations ranging from ∼10⁻¹⁴ to 10⁻¹ atom fraction can be generated and measured. In terms of fluence, this represents a range of roughly 10¹² to 10²⁷ n/cm². Fluence (>1 MeV) values that may be encountered during routine surveillance testing are expected to range from ∼3 × 10¹⁴ to 2 × 10 ²⁰ n/cm², which is well within the range of the HAFM technique.

5.6 The analysis of HAFMs requires an absolute determination of the helium content. The analysis system specified in this test method incorporates a specialized mass spectrometer in conjunction with an accurately calibrated helium spiking system. Helium determination is by isotope dilution with subsequent isotope ratio measurement. The fact that the helium is stable makes the monitors permanent with the helium analysis able to be conducted at a later time, often without the inconvenience in handling caused by induced radioactivity. Such systems for analysis exist, and additional analysis facilities could be reproduced, should that be required. In this respect, therefore, the analytical requirements are similar to other ASTM test methods (compare with Test Method E244).

1.1 This test method describes the concept and use of helium accumulation for neutron fluence dosimetry for reactor vessel surveillance. Although this test method is directed toward applications in vessel surveillance, the concepts and techniques are equally applicable to the general field of neutron dosimetry. The various applications of this test method for reactor vessel surveillance are as follows:

1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.