M. Ohta

M. Shibuya

T. Kabutomori

T. Kawano

Y. Sakuma

National Institute for Fusion Science (NIFS-Repository)

§9. Methane Decomposition Reaction on ZrNi Alloy Kawano, T., Sakuma, Y, Ohta, M. (Niigata University), Kabutomori, T. (The Japan Steel Works Ltd.), Shibuya, M. (JOC Corporation) A method of decomposing hydrogen mmpounds was developed by employing a zirmnium nickel (ZrNi) alloy. This method enables all tritium mmpounds (HID, CH3T, C2Hs T, etc.) in an exhaust gas to be demmposed into their respective elements, and the tritium itself to be removed in the form of hydrogen gas (HI). The method was developed through a series of experiments using methane. To ascertain the mechanism of methane decomposition on a ZrNi alloy, alloy samples were examined based on X-ray diffraction spectra before, during, and after the experiments (Fig.1.). (A) (E) 20 30 New ZrNi alloy After 13 hours Spent ZrNi alloy o 1-1 A: 40 50 60 28/Degrees A: Z rN I 70 e: Z rC 0: N I 80 Fig.1.1YPical X-ray diffraction spectra. As a result, the chemical reaction equation (1) explaining methane decomposition on a ZrNi alloy was proposed and discussed. ZrNi+ (l+a)Ca. ~ ZrC + Ni + aC + 2(1+ a)H2. (1) The equation (1) shows that one molecule of ZrNi can demmpose (1+ a) molecules of methane and generate 2(1+ a) molecules of hydrogen. The value of a can be determined by using the weight of the ZrNi used and the decomposed methane volume derived from the experiment. The a -value thus obtained was bigger when a larger decomposed methane volume was obtained. Therefore, if the decomposition mndition is mnsidered to be better when the total methane volume decomposed is larger, the a -value can be used as an index to identify a good mndition or not. Under a practical good mndition for us, though, the decomposition rate of more than a certain value should mntinue for a sufficient time length, and a larger volume of methane should be decomposed within the limited time span. It is important that a larger methane volume decomposes in a limited time span to maintain a good decomposition rate. However, the a -value is derived based on the entire time range and is not directly mnnected with the limited time span. So we have to derive and examine the a -value directly related to the limited time span. However, it is impossible to determine the a -value of the limited time span because the weight of ZrNi mnsumed within that time cannot be determined from a practical decomposition experiment. Thus, we investigated whether the a -value based on the entire time range can be used to evaluate the practical good decomposition mndition in which a large volume of methane is decomposed within the limited time span. In the actual investigation, different decomposition rates of 10,20,30,50, and 70% were studied and the methane volume demmposed in a partial range limited by the rates was examined. The relationship between the methane volume thus obtained and the value of a derived from the entire range was investigated. ~ ...!<: -....... ......:l ~ 500 ~-Q) 400 ~ ...c: ~ 300 El "'d Q) 200 fIl 0 P-El 100 0 <.) Q) 0 0 0.0 0.4 0.8 1.2 1.6 Value of at Correlation Coefficient 2.0 0.999 0.997 0.992 0.986 0.971 0.954 2.4 Fig. 2. Correlation between value of a t and decomposed methane volume of V jo A result is shown in Fig.2. In Fig.2, the value of a was found to be strongly mrrelated to the methane volume decomposed within the limited time span. We thus mnclude that the a -value based on the entire time range can be used as an index to estimate whether a decomposition mndition is better or not from the view point of actual processing work 403 

Methane Decomposition Reaction on ZrNi Alloy

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