Method and apparatus for controlling accidental releases of tritium

An improvement in a tritium control system based on a catalytic oxidation reactor wherein accidental releases of tritium into room air are controlled by flooding the catalytic oxidation reactor with hydrogen when the tritium concentration in the room air exceeds a specified limit. The sudden flooding with hydrogen heats the catalyst to a high temperature within seconds, thereby greatly increasing the catalytic oxidation rate of tritium to tritiated water vapor. Thus, the catalyst is heated only when needed. In addition to the heating effect, the hydrogen flow also swamps the tritium and further reduces the tritium release.

This invention relates to an improved tritium control system, particularly 
a tritium control system based on a catalytic oxidation reactor. More 
specifically, this invention relates to a system for controlling 
accidental releases of tritium into room air. 
Current guidelines for tritium handling facilities require that tritium 
concentration in room air be maintained as low as practicable, which is 
generally interpreted to mean a tritium concentration of less than 10 
microcurie (.mu.Ci) per cubic meter of air. The room air in such 
facilities is first circulated through a heated catalyst which oxidizes 
gaseous tritium (T.sub.2) to tritiated water vapor (THO+T.sub.2 O). The 
air stream is then passed through an absorbent bed which traps the 
tritiated water for subsequent disposal. Purified air is recirculated to 
the room interior. 
The tritium removal system described above is normally in continuous 
operation to scavenge trace amounts of tritium from room air. Provision 
must also be made, however, for emergency hold-up of an accidental spike 
release of tritium with concentrations in the range of several curie per 
cubic meter of air (a million times greater than normal). Such an 
emergency tritium removal system is usually held in stand-by status to be 
activated by a tritium monitor when the tritium concentration exceeds a 
specified limit. 
A conventional tritium effluent control system is described in "Tritium 
Effluent Control Project at Mound Laboratory" by Carl J. Kershner, in 
Proceedings of the Symposium on Tritium Technology Related to Fusion 
Reactor Systems, Oct. 1 and 2, 1974, U.S. Energy Research and Development 
Administration, June 1975. The tritium control system described by 
Kershner includes an emergency containment system (ECS) which is an 
automatically actuated room air detritiation system based on a catalytic 
oxidation reactor and water-presaturated adsorption/exchange column 
concept. The ECS is held in stand-by status. In the event of an accidental 
release of tritium to the laboratory or equipment rooms, the ECS is 
automatically activated and the quick action pneumatic dampers divert the 
room air supply and exhaust through the ECS and the air is recirculated 
until the room air concentrations are returned to safe operating levels. 
One of the operating costs associated with emergency tritium hold-up 
systems is that of heating the catalyst. Electrical resistive heating of 
large catalyst beds can easily consume megawatts of power. This is a 
continuous operating cost since the emergency system must be maintained in 
constant readiness for an accidental tritium release. The cost for 
electricity is so prohibitive that the catalytic oxidizers in most systems 
are operated at room temperature, relying on increased catalyst mass to 
compensate for the decrease in catalytic efficiency at lower temperature. 
Since the catalyst is usually based on a noble metal such as palladium, 
platinum, or the like, the use of increased catalyst mass is itself a very 
expensive solution to the high cost of electrical heating. 
SUMMARY OF THE INVENTION 
The present invention provides an improved method and means for emergency 
containment of an accidental release of tritium into room air for use in 
tritium control systems based on a catalytic oxidation reactor. In 
accordance with the present invention, the catalyst is heated only when 
needed. This is accomplished by automatically flooding the catalytic 
oxidation reactor with hydrogen, preferably at a flow in at least 
stoichiometric amounts relative to the oxygen in the room air, when the 
tritium concentration of the air exceeds a prespecified level. The sudden 
dumping of hydrogen heats the catalyst to a high temperature within 
seconds, thereby activating the catalyst and greatly increasing the 
catalytic oxidation rate of tritium to tritiated water vapor. In a 
particular embodiment of the invention, means is provided for igniting the 
hydrogen in the catalytic oxidizer to insure initiation of combustion in 
the event that the catalyst has become inhibited as a result of exposure 
to moist room air. 
In addition to its heating effect, the hydrogen flow also swamps the 
tritium spike, that is, it decreases the tritium partial pressure by 
perhaps a factor of 1000. The concentration of tritiated water admitted to 
the adsorber beds is thereby diluted by this same factor. Thus, the 
present system for tritium removal performs the dual functions of catalyst 
activation and hydrogen swamping by a simple inexpensive mechanism which 
is activated only in an emergency situation. 
It is, therefore, an object of this invention to provide an improved 
tritium control system. 
More particularly, it is an object of this invention to provide an 
improvement in a tritium control system based on a catalytic oxidation 
reactor. 
Specifically, it is an object of this invention to provide a method and 
apparatus for controlling accidental releases of tritium into an 
atmosphere. 
Other objects and advantages will become apparent from the following 
detailed description made with reference to the accompanying drawing.

DETAILED DESCRIPTION OF THE INVENTION 
The invention will now be described in detail with reference to the FIGURE 
which is a schematic representation of a tritium handling facility 
containing an improved tritium control system in accordance with the 
present invention. 
Referring to the FIGURE, numeral 11 represents a tritium handling facility. 
The tritium control system consists of a catalytic oxidation reactor 13 
for catalytic oxidation of tritium to tritiated water vapor, and an 
adsorber bed system consisting of three adsorbent beds 15 for containment 
of the tritiated water vapor formed in reactor 13. Catalysts and 
adsorbents suitable for the aforementioned purposes are well established 
in the art. 
A pressurized hydrogen source 17 is connected to reactor 13 by means of a 
normally closed fast-acting valve 19 which is actuatable by tritium 
monitor 21. Tritium monitors having 1.mu. Ci/m.sup.3 sensitivity and a 
detection range from 1 to 20,000.mu. Ci/m.sup.3 with digital and 
logarithmic recorder display are commercially available. 
Under normal conditions, the catalytic oxidation reactor is operated at 
room temperature and valve 19 is closed. The normal room air also passes 
through the adsorber system, maintaining the adsorbent saturated with 
H.sub.2 O. Tritium monitor 21 is preset to actuate valve 19 when the 
monitor senses a concentration of tritium in the room air in excess of a 
specified safe operating level. Room air is introduced via line 23 into 
reactor 13, where oxidation of tritium to tritiated water vapor takes 
place, and is then circulated through the adsorbent beds 15 for 
containment of the tritiated water. The adsorbent in the beds can be 
removed and disposed of or regenerated in place when required. The 
purified air is vented to the atmosphere by means of stack 25. Means 27, 
such as a spark, may be provided to insure initiation of combustion of the 
hydrogen in the event that the catalyst has become inhibited as a result 
of exposure to moist room air. 
In the event of an accidental release of tritium into the room air, the 
tritium monitor 21 automatically actuates valve 19 when the tritium 
concentration in the air exceeds the specified safe operating level, 
flooding the catalytic oxidation reactor with hydrogen. The catalyst is 
immediately heated by means of the heat generated by combustion of the 
hydrogen, thereby activating the catalyst and increasing the catalytic 
oxidation rate of tritium to tritiated water vapor. When the room air 
concentration is returned to a safe operating level, valve 19 is closed 
for normal operation. Thus, the catalyst is heated to high temperatures 
only when needed. 
It is believed that catalyst activation is accomplished by the 
catalytically promoted reduction, by hydrogenation of oxides formed on the 
catalyst, whereby heat is generated. It is, therefore, desirable to 
provide a flow of hydrogen in at least stoichiometric amounts relative to 
the oxygen in the room air. Under normal operation, the catalyst may 
become sufficiently inhibited, as a result of continuous exposure to 
ordinary moist room air, that it may fail to respond to the hydrogen. In 
order to allow for such a contingency, it is desirable to provide a means 
for igniting the hydrogen in the catalytic oxidizer, with oxygen in the 
room air, to insure initiation of combustion and consequent activation of 
the catalyst. 
As an example of the present invention, consider a 100,000 std ft.sup.3 
/min capacity tritium effluent control system using a platinum/palladium 
catalyst, such as is commercially available, for example, from Air 
Products Corporation or Engelhard Industries, and a molecular sieve 
adsorbent system. Under normal conditions the system is operated around 
room temperature (40.degree.-80.degree. C.); room air passes through the 
catalytic oxidizer and the adsorbent beds, then out of the stack. 
Continuous exposure of the molecular sieve to ordinary moist room air 
maintains the sieve in a saturated condition at all times. A source of 
hydrogen under a pressure of about 1500 psig is connected to the catalyst 
oxidation reactor by means of a normally closed quick acting valve. A 
tritium monitoring device is preset to open the valve when the device 
senses a tritium concentration in the room air at some preset value in 
excess of 10.mu. Ci/m.sup.3 such as 40.mu. Ci/m.sup.3. In an emergency 
situation, the quick-acting valve is automatically opened to permit 
hydrogen flooding of the reactor at a flow in stoichiometric amounts to 
the oxygen in the air. A spark may be used to insure initiation of 
combustion. The catalyst is immediately heated, thereby activating the 
catalyst and increasing the catalytic oxidation rate of tritium to 
tritiated water vapor which is then trapped on the adsorption bed. The 
purified air is vented to the atmosphere. When the room air concentration 
is returned to a safe operating level, the quick acting valve is closed 
and normal operation is resumed. 
For safety reasons, it is preferred to operate the present tritium effluent 
control systems as a "once through" system. That is, the purified air is 
vented to the atmosphere rather than recirculated. The present invention 
minimizes pollution of the atmosphere in the event of an accidental 
release of tritium. The present invention is useful in fusion research 
facilities, tritium confinement systems, or in facilities for the recovery 
of tritium from various forms of tritiated wastes. 
Although the invention has been described with reference to a particular 
embodiment, it is to be understood that various changes and modifications 
may be made without departing from the true spirit of the invention.