Online Fuel Failure Detection and Damage Severity Analysis for Thorium-Based AHWR Fuel Matrix—An Empirical Analysis

  • R. RajalakshmiEmail author
  • Roshini Robin
  • K. Umashankari
  • A. Rama Rao
  • P. K. Vijayan
Conference paper


A clad failure results in the escape of fission products from the fuel to coolant. Continued operation of the reactor with the presence of failed fuel would cause excessive radioactive contamination of the main heat transport (MHT) system and its associated components. Therefore, online detection and precise location of failed fuel in the core are necessary for the safe and healthy operation of the reactor and to reduce the man-rem exposure. For the development of online system for iodine and gaseous fission product monitoring for AHWR, an empirical analysis was carried out to compute these fission product release rate data for thorium-based AHWR mix-oxide fuel consisting of (Th–U233)O2 and (Th–Pu)O2. The release rate and activity concentration rates in the coolant were calculated for various types of fuel failures, and a feasibility study was carried out for online gaseous fission product and iodine monitoring using HPGe detector and high-resolution gamma-ray spectrometer system. Further, this paper also discusses the different methodologies for identifying severity of fuel damage.


Fuel failures Tramp fissile content Counts Escape time constant Surface-exchange coefficient 


\( R_{i}^{0} \)

Release rate in atoms/s of fission products from fuel pellets into fuel-clad gap.

\( B_{i} \)

Fission product birth rate in the fuel in atoms/s.


Typical AHWR fuel length in meters i.e. 3.5 m.

\( y_{\text{c}} \)

Cumulative yield of the nuclide i in atoms/fission.


Linear power rating of the defective fuel pin in kW/m.

\( D^{\prime } \)

Empirical diffusion coefficient in s−1.


Number of defective fuel pins.

\( N_{i} \)

Inventory in fuel gap in atoms.

\( v_{i} \)

Escape time constant, s−1.

\( \alpha \)

Surface-exchange coefficient in (m s−1) between the gap and coolant.


Defect size in mm2.

\( \lambda_{i} \)

Decay constant of species i, s−1.


Reactor water mass, kg.

\( \beta_{\text{c}} \)

Reactor water cleanup (RWCU) system removal time constant, s−1 defined as / assuming 100% efficient.


RWCU flow rate, kg/s.

\( \beta_{\text{s}} \)

Steam removal time constant, ss−1 which is defined as FW.

\( \varepsilon \)

Iodine carryover \( = \frac{{{\text{the concentration of species }}i\;{\text{in the condensate}}}}{{{\text{the concentration of the species }}i{\text{ in the reactor water}}}}. \)


Steam flow rate, kg/s.

\( v_{\text{s}} \)

Sample volume of the detector in cc.

\( \eta \)

Detector efficiency for a particular gamma energy.

\( I_{\gamma } \)

Yield of a particular energy gamma radiation from a radioisotope.

\( w_{\text{s}} \)

Weight of the sample in mg.


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Copyright information

© Springer Nature Singapore Pte Ltd. 2019

Authors and Affiliations

  • R. Rajalakshmi
    • 1
    Email author
  • Roshini Robin
    • 1
  • K. Umashankari
    • 2
  • A. Rama Rao
    • 1
  • P. K. Vijayan
    • 1
  1. 1.Bhabha Atomic Research Centre, Reactor Engineering DivisionTrombay, MumbaiIndia
  2. 2.Bhabha Atomic Research Center, Reactor Physics Design DivisionTrombay, MumbaiIndia

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