Is tritium an issue for High Temperature Reactors?

In a High Temperature Reactor, tritium is produced by a number of mechanisms such as ternary fission and neutron capture on boron (in control rods), lithium (in graphite) and 3He (in the He coolant). Due to its high mobility, some of this tritium ends up in the primary helium cooling circuit from where it can be extracted by the coolant purification system to keep the partial pressure of tritiated compounds low. Nevertheless, the partial pressure of tritium in the coolant is the driving force for permeation across the heat exchanger from the primary cooling system into the secondary cooling system. From there the contamination may further propagate and ultimately end up in the environment. In the frame of the European HTR technology project ARCHER, the aim of this work was to revisit earlier work on this subject in the light of new requirements and to perform a parameter study indicating which combination of the different tritium control options are capable of meeting possible future safety limits, complemented by suggestions for a viable tritium control strategy. We have done this on the basis of the Chinese HTR-PM reactor. For this purpose, a conceptual steam generator lay-out based on the Fort Saint Vrain design (helical coil tube bundle type with Incoloy 800 as the tube material) was assumed, both for the rather conservative HTR-PM temperatures and for higher temperatures. Using the obtained steam generator characteristics in combination with a tritium balance sheet and reasonable assumptions on operating conditions and safety requirements, we described the individual and combined effect of several operating parameters on tritium control. Our results indicate that compliance with plausible tritium control requirements can indeed be achieved with reasonable effort both for electricity generation using a closed steam cycle and for process steam generation with an open steam cycle. However, for new-build HTR, definite country-specific licensing requirements (e.g. chronic and accidental tritium release) are yet to be determined and will shape the required tritium control strategy.

FUETTERER Michael;  D'AGATA Elio;  RAEPSAET Xavier; 

2014-11-25

Tsinghua University

JRC84291

http://www.htr2014.cn/?type=common&action=conferenceprogram&PHPSESSID=e12f89ee864a84bfe1e5c96f5df4f628,    https://publications.jrc.ec.europa.eu/repository/handle/JRC84291,