Distribution and release of tritium in high-temperature gas-cooled reactors as a function of design, operational, and material parameters

Abstract

This report summarizes work performed up to June 1973 relative to the description of the behavior of tritium in a high-temperature gas-cooled reactor; the main objective was the development of a computer code with which accurate assessment of tritium distribution in HTGRs could be made. The resulting code, TRITGO, is operational and, subject to the limitations discussed below, may be used for determining parameter sensitivity and for defining future research objectives. However, many extensions and amplifications that were evidently desirable were not included. Some of these are indicated in the text. (For example, the special role of the fuel element purge system in removing tritium released by the fuel in a reactor such as the Peach Bottom HTGR is not fully described.) In addition, it is now recognized that a slow, temperature-dependent release of tritium must occur from fuel particles, as well as from graphite and other solids. In the present version of TRITGO, this is handled by a partition factor corresponding to immediate release of a small fraction and permanent retention of the remainder. Similarly, fuel replacement in the core is not presently incorporated in the illustrative calculation. Representative values of the input parameters have been taken from PSAR descriptions of the Fort St. Vrain Reactor. The relationship between code output and the performance of an HTGR remains to be established critically.

Scoping Analyses on Tritium Permeation to VHTR Integarted Industrial Application Systems

“…The INL TPAC is a numerical tool based on the mass balance equations of tritium-containing species and hydrogen (i.e., HT, H 2 , and HTO) coupled with a variety of tritium sources, sink, and permeation models. In the TPAC, ternary fission and thermal neutron caption reactions with 6 Li, 7 Li 10 B, 3 He were taken into consideration as tritium sources. Purification and leakage models were implemented as main tritium sinks.…”

“…The primary tritium birth mechanism is ternary fission of fuel (e.g., 233 U, 235 U, 239 Pu, and 241 Pu) by thermal neutrons. Tritium is also generated in VHTR from 6 Li, 7 Li, 3 He, and 10 6 Li and 7 Li are impurities in the core graphite material such as the sleeve, spine, reflector, and fuel matrix. 3 He is an impurity in the reactor coolant helium.…”

“…Tritium is also generated in VHTR from 6 Li, 7 Li, 3 He, and 10 6 Li and 7 Li are impurities in the core graphite material such as the sleeve, spine, reflector, and fuel matrix. 3 He is an impurity in the reactor coolant helium. Because helium coolant leaks from the primary loop to the containment vessel, helium is supplied to the primary coolant as a make-up with an impurity of 3 He.…”

“…In VHTRs, tritium is generated from ternary fission of the fuel and neutron reactions with lithium impurities in the graphite, boron control materials in the reflector block, and naturally occurring 3 He in the helium coolant. Tritium diffused from the reactor core and formed in the helium primary coolant by 3 He reaction with neutron ( 3 He(n, p) 3 H) will be circulated or permeated to the secondary coolant and the intermediate heat transfer loop. Finally, the permeated tritium enters the product hydrogen in the HTSE through heat exchange surfaces.…”

“…The main mechanisms of tritium transport are diffusion, bulk transport, and permeation (See Figure 1-1). Tritium is a radioactive isotope of hydrogen with the half-life of 12.32 years, which is mainly generated in the reactor core (Compare et al 1974). (Wichner and Dyer 1979).…”