What's Wrong With the Modular Pebble Bed Reactor?
1. It has no containment building.
2. It uses flammable graphite as a moderator.
3. It produces more high level nuclear wastes than current nuclear reactor designs.
4. It relies heavily on nearly perfect fuel pebbles.
5. It relies heavily upon fuel handling as the pebbles are cycled through the reactor.
6. There's already been an accident at a pebble bed reactor in Germany due to fuel handling problems.
More on what's wrong.

Cover-up of Radiation Accident at German Pebble Bed Reactor; Unit Permanently Shutdown

As Dr. Edward Teller, father of the H-bomb said, "Sooner or later a fool will prove greater than the proof even in a foolproof system." Accidents can and do happen in the inherently dangerous business of splitting the atom. Human error occurs at every level of development, construction and operation of the process. Material and component failures along with aging can break down or defeat operational and safety systems.

In 1985, the experimental THTR-300 PBMR on the Ruhr in Hamm-Uentrop, Germany was offered as accident proof--with the promise of an indestructible carbon fuel cladding capable of retaining all generated radioactivity. Following the April 26, 1986 Chernobyl nuclear reactor accident and graphite fire in Ukraine, the West German government revealed that on May 4, the 300-megawatt PBMR at Hamm released radiation after one of its spherical fuel pebbles became lodged in the pipe feeding the fuel to the reactor. Operator actions during the event caused damage to the fuel cladding.

Radioactivity was released with the escaping helium, and radioactive fallout was deposited as far as two kilometers from the reactor. The fallout in the region was high enough to initially be blamed on Chernobyl. Government officials were then alerted by scientists in Freiburg who reported that as much as 70 % of the region's contamination was not of the type of radiation leaking hundreds of miles away in Ukraine. Dismayed by an attempt to conceal the reactor malfunction and confronted with mounting public pressure in light of the Chernobyl accident only days prior, the state ordered the reactor to close pending a design review.

Continuing technical problems, damage to unused fuel pebbles and radiation-induced bolt head failures in the reactor's gas channels resulted in the unit's closure in late 1988. Citing doubts about reliability, the government refused to further subsidize utility funding and instead approved plans for decommissioning the reactor.

- From Three Mile Island Alert

Thus, nowhere on earth is there an operational "new and improved design of nuclear energy".