FUEL ELEMENT DEVELOPMENT PROGRAM FOR THE PEBBLE BED REACTOR. Quarterly Progress Report for February 1 to April 30, 1960
Emphasis was shifted in the Pebble Bed Reactor (PBR) Fuel Element Development Program from coatings on the sphere surface to coatings on individual fuel particles as the major deterrent to fission-product leakage. In a highlevel irradiation test, cracks developed in the coatings of specimens coated with pyrolytic carbon and siliconized silicon carbide. In another high-level irradiation test, a graphiie sphere fueled with Al/sub 2/O/sub 3/-coated UO/sub 2/ particles is showing excellent fission-product retention. The leakage factors for long-lived volatile flssion products such as Kr/sup 85m/, Kr/sup 87/, Kr/sup 88/, Xe/sup 135/ are ranging from 10/sup -9/ to 10/sup -6/. If this degree of fission-product retention is maintained in a large power reactor, it would result in essentially a "clean" primary loop. A simple crack in a fuelelement surface coating will permit the release of all of the volatile fission products in that specimen except those retained by the fuel particles. In view of the failures in surface-coated specimens tested to date, it appears to be a difficult task to ensure coating integrity in a large number of specimens because of their low thickness-to-diameter ratio and exposure to external loads on the fuel element. The test of a single specimen fueled with coated particles takes on added statistical significance, since about 500,000 "fuel elements" are actually being tested. The acceptability of graphite as a fuel-element matrix material was demonstrated when four types of graphite fueled with UO/sub 2/ suffered no significant deterioration in structural properties after irradiation to about 6000 kwh which is above the present design objective of the 125 Mw(e) PBR. Thus the incorporation of coated fuel particles, having excellent fission-product retention, into a graphite sphere, having excellent structural properties, offers a simple, rugged fuel element capable of producing high coolant temperatures while retaining most of the fission products. It is this type of fuel element which will receive major emphasis during the remainder of the PBR Fuel Element Development Program. The study of the preparation of graphite blanket elements loaded with ThO/sub 2/ by the thorium nitrate infiltration process was completed. It was found that graphite densities below 1.45 g/cc and more than five infiltration steps were required to achieve the desired ThO/sub 2/ loading. A study of the use of natural graphite to produce high-density graphite bodies was started. Densities greater than 2.0 g/cc were produced in a single pressing. The design and construction of an in-pile loop to study fissionproduct behavior in a recycled helium stream were continued. (For preceding period see NYG-9057.) (auth)
- Research Organization:
- Sanderson and Porter, New York
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AT(30-1)-2378
- NSA Number:
- NSA-15-001757
- OSTI ID:
- 4157817
- Report Number(s):
- NYO-9058
- Resource Relation:
- Other Information: Decl. May 23, 1960. Orig. Receipt Date: 31-DEC-61
- Country of Publication:
- United States
- Language:
- English
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