Gas-analysis apparatus

Description

NNL are currently contracted to carry out a series of trials to measure radiolytic gas generation from materials associated with spent nuclear fuel. One of the specific technical objectives is to determine the change in gas composition with time. NNL are currently contracted to carry out a series of trials to measure radiolytic gas generation from materials associated with spent nuclear fuel. One of the specific technical objectives is to determine the change in gas composition with time. Because these measurements are to be made using irradiated material there are two significant constraints: • the quantity of material (predominantly a powder) used in each test must be minimised; • the samples and vessels must remain within a hot cell facility (see Appendix for details), therefore: — sample lines between the text vessels and the measurement system located outside the hot cell will be long (~ 6–10 m); — items in the hot cell will receive significant radiation doses and must be suitably radiation hardened; — all operations on equipment located in the hot cell (setup, operation, maintenance and dismantle) must be carried out remotely using master slave manipulators (see Appendix for examples); — ambient temperature may vary in the range 5 oC-40 oC during the year. NNL has developed a preliminary concept for undertaking the required measurements, shown in Figure 1: Figure 1 — Initial Sampling Concept. Some relevant characteristics of the proposed system are: • Individual tests will be conducted on a few grams of irradiated material in high integrity vessels with a total volume of ~ 3 cm3 and a free volume of ~ 2 cm3. • Connecting pipework to be narrow-bore, high pressure piping (nominally 1.6 mm, 1/16” bore). • The gas generated, in the test and whose composition needs to be measured, will depend on the test material and may be composed of either: — hydrogen and sub-stochiometric quantity of oxygen (the degree of sub-stoichiometry is currently unknown); — roughly equal amounts of hydrogen, carbon dioxide, carbon monoxide and methane, with trace amounts of higher hydrocarbons. • Small quantities of Kr and He may be released from the test materials as a result of radioactive decay, and their presence would need to be accounted for. • The reference sampling process would involve: — evacuating the manifold and isolating it; — opening the valve for designated test vessel valve to equalize pressure with manifold following which the valve would be closed to leave a gas sample of around 50 μL in the manifold; — sweep the sample using a carrier gas to it to the measurement instrument. • An equilibrium is expected to form which will limit the overall pressure generated. It can be assumed that the experiment will be terminated if the pressure exceeds a value which is expected to be less than 50 BarG. • Tests will be conducted for a number of source materials and test conditions, leading to between 20 and 30 simultaneous tests. Scoping calculations suggest that: • gas will be generated at a rate of ~ 10-9 moles per day; • the pressure rise will be ~ 1.5 x 10-5 Bar.d-1; and • the concentration of each species will increase by: — ~ 90 ppm per week of hydrogen, or — ~ 20 ppm per week each of hydrogen, methane etc. • The tests may last between 3 and 12 months. NNL considers that the measurement of gas composition at intervals during the test is challenging and that the gas sampling and measurement techniques required are outside of its area of expertise. NNL is therefore requesting assistance from suppliers to help identify credible means of making the proposed measurements in order to enable NNL to define a specification for a subsequent open procurement process to provide a suitable measurement system.