Coolant Activities

When corrosion products are deposited on the fuel surfaces, they are activated by neutron capture. Some of the most prominent of these activities are 55Fe, 63Ni, 60Co, 54Mn, 58Co, and 59Fe. These radionuclides will then be found in the reactor coolant. 

Fission products can be released from defects in the fuel rods or from tramp uranium on the fuel cladding. Of special importance are the volatile fission products 131—i35j M7 i38Xe in BWR steam). Cations include the Sr and Cs isotopes, 

Impurities in the water and water activation products also contribute to the radioactivity of the coolant water. Tritium is produced as a low yield ( 0.01%) fission product that can diffuse out of the fuel, by activation of boron or fiLi impurities in PWRs. 24Na and 38C1 are produced by neutron activation of water impurities. In BWRs, the primary source of radiation fields in the coolant and steam systems during normal operations is 7.1s 16N. This nuclide is produced by 160(n, p)16N reactions from fast neutrons interacting with the coolant water. This 16N activity can exist as N07, NO in the coolant and NHj in the steam. 

Define or describe the following terms or concepts (a) crud, (b) axial offset anomaly, (c) accelerator transmutation of waste, (d) UREX process, (e) LLW, (f) TRU, (g) HLW, (h) SNF, (i) Purex process, (j) back end of the fuel cycle, and (k) pyroprocessing. 

Define or describe the following terms or concepts (a) yellowcake, (b) orange oxide, and (c) green salt. 

---

Authors of the report [7.5] have noted, that such lead-bismuth coolant activity gives rise to the problems even under normal operating conditions. They consider that in case of the cover gas leak rate of 0.01% of its volume per day, release of o to the central hall may cause (if gas circuit is not cleaned from polonium) 200 fold exceeding of its maximum permissible concentration (mpc) [7.1]. To ensure that mpc value is not exceeded for personnel in the central hall, it is necessary to comply with very strong requirements for the reactor cover gas circuit leak-tightness. 

Lane, J. A., Calculation of Pile Coolant Activities, ORnL-CF-49-7-240, July 26, 1949. 

In the most of fuel cycles the primary circuit coolant activity was about (1-5) 10 Ci/L... 

REACTOR COOLANT ACTIVITY LIMIT FOR OPERATING REACTORS... 

According to Hiittig et al. (1990), the amount of uranium released from defective fuel rods and deposited on in-core surfaces can be assessed from the coolant activity levels of various short-lived fission products such as I, I, Cs, calculating their source strengths under the assumption of a direct and instantaneous release to the coolant. Though the releases of these isotopes from failed fuel rods are quite small (due to their short halflives), such data can provide only an upper limit for the uranium contamination if there are simultaneously fuel rod failures in... 

In evaluating fuel rod failures from the presence of these fission products in the primary coolant, it has to be considered that some of them are also formed by neutron activation of metallic core materials, e. g. Zr/ Nb, Mo/ Tc, Sb. Determining which of these two production mechanisms is responsible for the coolant activity of the isotopes just mentioned is often difficult. In some cases, the shutdown spiking can be used to identify their origin from failed fuel rods however, in most cases this effect is not unequivocal since the radioactive corrosion products also show such a spiking (see Section 4.4.). 

Besmann, Th.M., Lindemer, T. B. Chemical thermodynamics of the system Cs-U-Zr-H-l-O in the light-water reactor fuel-cladding gap. Nucl. Technology 40, 297-305 (1978) Burman, D. L. Methods for estimating numbers of failed rods from coolant activity analysis. Proc. Workshop Fuel Integrity Monitoring by Coolant Activity Analysis, Charlotte, N. C USA, 1986... 

Schuster, E., von Jan, R., Fischer, G. Evaluation of fuel performance from coolant activity data. Proc. ANS/ENS Internal. Top. Meeting on LWR Fuel Performance (Fuel for the 1990s), Avignon 1991, Vol. 1, p. 285-294... 

Figure 4.36. Comparison of Co coolant activity concentrations and radiation dose rates at the main coolant pipework (Marchl and Riess, 1993 a)...

Dobrevsky, I., Winkler, R. A new point of view on the drastic change in coolant activity by power transients in PWRs. Report IAEA TECDOC-667 Coolant Technology of Water Cooled Reactors, Vol. 1, Chemistry of Primary Coolant in Water Cooled Reactors, Vienna 1992, p. 56-58... 

Limits for the permissible specific activity of the reactor coolant should be stated in order to ensure the protection of persormel and the environment as well as to provide a measure of fuel integrity, as discussed in the safety analysis report. If online measurement of coolant activity is used to monitor the fuel cladding integrity in operation, the minimum provisions for the detection and, where appropriate, identification of failed or suspect fuel should be stated. 

Defects in the fuel cladding may result in the release of fission products to the coolant, which can add significantly to the activity of the coolant and contamination of the coolant circuit. Defective fuel elements should be removed as soon as possible after a failure occurs to reduce the exposure of site personnel from this source. Where refuelling is not on-load, means should be provided for detecting failed cladding, appropriate limits should be set for the coolant activity and the plant should be shut down within a prescribed time interval if these are exceeded. 

IV-3. In the case of LWRs, parameters relating to the solubility in water of oxides at the temperature and pH of the coolant are very important parameters that determine the behaviour of corrosion products in the primary coolant. More specific details of the relevant parameters for coolant activity in PWRs are given below ... 

IV-16. During power transients, fission products are released to the coolant in a short time period through the cladding defects. This release is the cause of a spike in the activity of the coolant. The magnitude and period of the release are difficult to predict, but reasonably bounding values can be derived from operating experience. In Ref. [IV-1], a correlation of the release and the duration with the pre-transient coolant activity is reported. 

Coolant activity monitoring for compliance with plant technical specifications. 

In 1986, in-core sipping equipment designed and manufactured by Siemens KWU was purchased [22,23]. Since then, fiiU core sipping tests have been performed in all cases where the occurrence of a leak has been demonstrated by operational data. The decision to perform sipping tests was taken based on primary coolant activity measurements obtained during reactor operation and iodine spike analysis. 

Thus In ref. 25 It Is demonstrated that the inclusion of multlstep (x,n) reactions leads to the generation of long-lived A1 Isotope, which after dozens of years will be responsible for fast reactor coolant activity and will not allow to do without remotely-controlled equipment during dismantling, as was believed earlier when only single-step reactions were considered. 

---