The pebble bed modular reactor was first developed by Germany in
the 1950s. More recently, the design has been embraced by the
People's Republic of China and the Republic of South Africa. Unlike
light water reactors that generate heat from fuel assemblies
comprised of fuel rods, pebble-fueled HTGRs utilize thousands of
60-mm diameter fuel spheres (pebbles) comprised of TRISO particle
fuel microspheres. As this reactor type is deployed across the
world, adequate methods for accounting for the nuclear material
within each fuel pebble must be found. Current safeguards methods
for the reactor focus on redundant containment and surveillance
(C/S) systems to deter the proliferation of fuel pebbles. The
disadvantage to this approach is the loss of continuity of
knowledge (CoK) in normal and off-normal conditions should both C/S
systems fail. One solution to maintaining CoK is to develop a
system to identify each fuel pebble that is inserted and removed
from the reactor. Work was performed to develop and evaluate the
use of inert microspheres placed in each fuel pebble, whose random
placement when imaged, could be used as a fingerprint for that fuel
pebble. Multiple materials for the inert microspheres and imaging
methods were considered to develop the chosen system. To prove the
concept, work was performed to determine the optimum number of
inert microspheres for a high match confidence. Reactor models were
also developed to determine the reactivity impact of inert
microsphere inclusion in either the fueled or non-fueled regions of
the fuel pebble. Finally, a qualitative assessment of the chosen
imaging system was performed using surrogate materials.
- E.T. Gitau and W.S. Charlton,
"Use of a Microsphere Fingerprint for Identity Verification of Fuel Pebbles in a Pebble-fueled HTGR,"
JNMM 40(2), 19-25 (2012).
- E.T. Gitau, W.S. Charlton,
"Safeguards System Development for a Pebble-Fueled HTGR,"
Proceedings of the INMM 52nd Annual Meeting, Palm Desert, CA, July 17-21, 2011.
Dr. Xu Yuanhui, the vice general manager of Chinergy, holds a uranium-filled graphite pebble at the Tsinghua University pebble bed nuclear reactor research facility, in Nankou, China. (Source: Shiho Fukada, NYT News Service)