Zircaloy neutron activation

The total yearly production of neutron-activation tritium in the PWR coolant is 400 Ci, as shown in Table 8.10. Another source of tritium in the coolant is fission-product tritium that diffuses through the fuel cladding and escapes through pin-hold penetrations through the cladding. Estimates of the amount of fission-product tritium reaching the coolant in LWRs with zircaloy fuel range from 0.2 to 1 percent of the total fission-production tritium produced within the fuel. 

The same conclusions are valid for zircaloy. A batch of this material (diameter 13 mm) has been recently analysed within BCR, with the results listed in Table VII-30. 14 MeV neutron activation analysis was not applied, due to the limited diameter of the material. 

Due to its favorable properties, the nuclear reaction Fe (n,p) Mn is one of the standard reactions for the determination of fast neutron fluences. Since iron is the main constituent of most of the materials to be investigated, this determination can be carried out without the use of a specific fluence monitor. The halflife of Mn of 312 days permits the use of this nuclear reaction for irradiation periods of up to about two years, provided that corrections for details of the irradiation history are made. Tlie favorable energy of the Mn y ray of 0.835 MeV (transition probability 100%) frequently allows a direct activity measurement by use of a high-resolution Ge detector only in the investigation of materials with low iron contents such as Zircaloy, a chemical isolation of the monitor nuclide prior to the activity measurement is leconunended. This can be carried out, for example, by precipita-... 

The thermal neutron flux to which a Zircaloy-2 specimen was exposed while in-pile was determined by measm ing and comparing the amount of the induced activities, Zr -Nb -, in the specimen and in a control sample of Zircalo,y-2. The latter was irradiated together with a cobalt monitor in a separate experiment in which the specimen and cobalt did not contact solution. Tor some experiments which contained steel specimens, similar measurements were made utilizing the activity. The fission power density in the uranium solution adjacent to a specimen was calculated from the resulting value for the thermal flux together with the value for the fission cross. section of uranium, assuming 200 Mev per fission. 

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