ASTM E910-2018 pdf free download

ASTM E910-2018 pdf free download.Standard Test Method for Application and Analysis of Helium Accumulation Fluence Monitors for Reactor Vessel Surveillance
1. Scope
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 ofneutron dosimetry. The various applications of this test method for reactor vessel surveillance are as follows: 1.1.1 Helium accumulation fluence monitor (HAFM) capsules, 1.1.2 Unencapsulated, or cadmium or gadolinium covered, radiometric monitors (RM) and HAFM wires for helium analysis, 1.1.3 Charpy test block samples for helium accumulation, and 1.1.4 Reactor vessel (RV) wall samples for helium accumu- lation. 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 appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.3 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
4. Summary of the HAFM Test Method
4.1 Helium accumulation fluence monitors (HAFMs) are passive neutron dosimeters that have a measured reaction product that is helium. The monitors are placed in the reactor locations of interest, and the helium generated through (n,α) reactions accumulates and is retained in the HAFM (or HAFM capsule) until the time of removal, perhaps many years later.The helium is then measured very precisely by high-sensitivity gas mass spectrometry (1, 2). 4 The neutron fluence is then directly obtained by dividing the measured helium concentra- tion by the spectrum-averaged cross section. Competing he- lium producing reactions, such as (γ,α) do not, except for 9 Be(γ,α), affect the HAFM results. The range of helium concentrations that can be accurately measured in irradiated HAFMs extends from 10 −14 to 10 −1 atom fraction. This range permits the HAFMs to be tested in low fluence environments yet to work equally well for high fluence situations. 4.2 Typically, HAFMs are either individual small solid samples, such as wire segments (3) or miniature encapsulated samples of small crystals of powder (4), as shown in Fig. 1. As with radiometric dosimetry, different materials are used to provide different energy sensitivity ranges. Encapsulation is necessary for those HAFM materials and reactor environment combinations where sample melting, sample contamination, or loss of generated helium could possibly occur. Additionally, encapsulation generally facilitates the handling and identifica- tion of the HAFM both prior to and following irradiation. The contents of HAFM capsules typically range from 0.1 to 10 mg. 4.3 Following irradiation, encapsulated HAFMs are cleaned and identified in preparation for helium analysis. Helium analysis is then accomplished by vaporizing both the capsule and its contents and analyzing the helium in the resulting gases in a high sensitivity mass spectrometer system (5). The amount of 4 He is determined by measuring the 4 He-to- 3 He isotopic ratio in the sample gases subsequent to the addition of an accurately calibrated amount of 3 He “spike.” Unencapsulated HAFMs, for example, pure element wires, are usually etched to remove a predetermined layer of outer material before helium analysis (3). This eliminates corrections for both cross con- tamination between samples and α-recoil into or out of the sample during the irradiation.