At Chernobyl, the burning graphite released radiation for ten days. The pebbles are less radioactive than conventional fuel assemblies and more pebbles are required to produce the needed heat inside the reactor. There will be many more truck and railroad transports needed to remove the wastes. This will increase the numbers of vehicle accidents and the odds of another radiological accident involving these vehicles traveling across the country. Creating even more nuclear waste without a final depository plan is unconscianable.
Recent history shows that some companies have falsified fuel quality.
In fact, there have been instances of fuel sabotage and tampering over the last few decades. Germany and Japan have shut down plants or refused fuel shipments once the problems were discovered. The industry acknowledges that there is approximately 1 defect per pebble associated with these layers. There was a pebble bed reactor accident at Hamm-Uentrop West Germany nine days after the Chernobyl accident. Operators subsequently caused damage to the fuel during attempts to free the pebble.