Zone 1 Ventilation Exhaust System

Chapter 2 contains detailed descriptions of the Zone 1 and 2A portions of the ventilation system. Ventilation system ducting provides the necessary confinement pathway during normal ventilation system operation to ensure filtration of exhaust gases prior to atmospheric release. The Zone 1 ventilation exhaust system contains redundant series-parallel charcoal filter banks located in the MER. The Zone 2A ventilation exhaust system contains charcoal filter banks located in the MER. In addition, ventilation system hot exhaust from Zone 1 and Zone 2A is routed through a HEPA filter before entering the HCF stack. These ventilation systems are described in more detail in Chapter 2. 

Since the Zone 1 and Zone 2A ventilation exhaust systems are not required to operate under abnormal and accident conditions, the exhaust fans have no safety function. However, these exhaust systems interface with the SCB and the Zone 2A canyon/Room 109 environments, respectively. Therefore, the exhaust ducting and filter plenums constitute extensions of the respective radioactive material confinement boundaries, and thus provide both defense in depth and worker safety functions. 

Furthermore, when the ventilation system is operating (and thus removing radioactive material from the HCF confinement structures) radioactive halogens and radioactive particulate matter are removed from the exhaust gases by charcoal filters in the Zone 1 and Zone 2A ventilation exhaust systems and HEPA filters in the hot exhaust system. Thus,... 

Zone 1 and Zone 2A ventilation exhaust systems (hot exhaust ducting, charcoal filters and plenums, and HEPA filters and plenums) Defense in depth Worker safety 1. Remove iodine and radioactive particulate matter from Zone 1 and Zone 2A ventilation exhaust when the ventilation system is operating 2. Provide a confinement boundary to the HCF stack for ventilation system hot exhaust 1. HEPA and charcoal filters are in service 2. Confinement design (Design Feature)... 

When the ventilation system is operating, the pressure in the Zone 2A canyon and Room 109 must be maintained negative with respect to worker occupied areas of the HCF. The Zone 2A ventilation exhaust system maintains the Zone 2A canyon and Room 109 pressure < -0.76 mm (0.03 in) WG with respect to worker occupied areas (Zone 2) of the HCF. 

Zone 1 and Zone 2A Ventilation Exhaust Systems Safety Function... 

The safety function of the HCF Zone 1 and Zone 2A ventilation exhaust systems is to provide a controlled, filtered path for radioactive releases during normal and abnormal operating conditions. Radioactive particulate matter and iodine are rerhoved from Zone 1 and Zone 2A exhaust air by means of HEPA and charcoal filters, respectively. 

Table 4.4-4 provides performance criteria needed to demonstrate that the functional requirements for the Zone 1 and Zone 2A ventilation exhaust systems are met No operational events can affect the ability of the HEPA and charcoal filters to perform their safety functions, since these functions ahe only required when the HCF ventilation system is operating. Furthermore, failure of filter bank inlet or outlet dampers to remain open during ventilation system operation will essentially stop the flow of Zone 1/Zone 2A exhaust air to the HCF stack. The only events that could affect the ability of the charcoal filters to perform their safety function are a fire in the MER or an external event such as an earthquake or aircraft crash that would destroy the MER. The only events that could affect the ability of the HEPA filters to perform their safety function are similar events. 

As indicated in Section 5.3, there are no SLs or LCSs associated with the Zone 1 and Zone 2A ventilation exhaust systems. However, since these systems provide defense in depth against off-site radioactive material releases during normal and abnormal operating conditions, the following LCO is established for the processing operation mode (see Table 5.4-1) ... 

A ventilation system fan sequencing interlock ensures that Zone 1 confinement boundary integrity is not compromised by either exhaust fan faiiures or operational errors. This interlock automatically starts the backup exhaust fan if the operating exhaust fan fails, thereby maintaining the desired directional airflow control across ventilation exhaust system boundaries. Thus, no operator action is required to maintain Zone 1-to-Zone 2A differential pressure in the event of exhaust fan failures. 

Additionally, to limit the buildup of contamination in the above designated areas, airflow is established to continually remove airborne contaminants. Airflows in the system are established at prescribed flowrates such that they are adequately filtered prior to being discharged to the environment. All air drawn from Zone 1 is exhausted through charcoal and HEPA filters to remove halogens and particulate contaminants from the exhaust air prior to release to the atmosphere. These ventilation filter systems are equipped with test ports and are periodically checked for operating efficiency. In addition to the ventilation system filters, in-box filtere are used to reduce the levels of airborne contaminants that are drawn into the Zone 1 ducting. 

In the MER, a separate fan exhausts 400 cfm from the Zone 1 Filter Room and discharges it into the ventilation exhaust. The purpose of this system is to exhaust any airborne contamination that could result from Zone 1 ventilation system filter replacements or fan maintenance to the HCF stack. 

The Zone 2A canyon boundary serves as a secondary confinement area that surrounds the SCBs (Zone 1). This secondary confinement volume is exhausted by a separate ventilation system. The Zone 2A ventilation system also draws on Room 109 so that any potential contamination from waste is appropriately controlled. When both moveable shield walls are in the up position, a negative pressure differential will exist between Room 109 and the Zone 2A canyon. When either of these shield doors are lowered, this pressure differential will approach zero. However, the airflow through Room 109 into the Zone 2A canyon, which acts to mitigate the undesired migration of contamination, will be maintained. All exhaust from Zone 2A is filtered through a HEPA filter located in the Zone 2A canyon and a charcoal filter located in the MER prior to being combined with the Zone 1 exhaust flow in the MER. 

Analysis of the ventilation system indicates that combustion gases will not damage downstream components of the system (Mitchell and Naegeli 1999). Cooling of combustion gases in the approximately 20 feet of ducting from an SCB to the Zone 1 exhaust plenum will not appreciably decrease the gas temperature. However, the exhaust from each SCB is diluted by a factor of 10 1 in the Zone 1 exhaust plenum. Thus, the combustion gas exhaust from Zone 1 would have a temperature of no more than approximately 250 F and damage to the ventilation system due to the fire is an improbable event. 

The Zone 1 and Zone 2A ventilation exhaust ducting and HEPA and charcoal filters are passive components. Their safety-related function is performed continuously while the HCF ventilation system is in operation. When the ventilation system is not operating, no isotope processing operations are being conducted, and any residual radioactive materials are in nonvolatile states and are confined within the SCBs and Zone 2A canyon. Thus, the functional requirements applicable to the filters are ... 

When the ventilation stem is operating, Zone 1 exhaust airflow must be routed to charcoal fiRers before being exhausted from the HCF stack. Piping and ductwork from the SCBs route airflow generated by ventilation system tens to redundant, 2-stage charcoal filter plenums in the MER. 

A TSR requirement to verify that Zone 1 and Zone 2A ventilation exhaust HEPA and charcoal filters are in-service vwll be implemented to assure that exhaust gases are being filtered when the HCF ventilation system is in operation. A TSR requirement to verify the ventilation system fan sequencing interlock is operable vvnil be implemented to ensure that proper building airflow patterns are maintained in the event of exhaust fan failures. The ventilation system exhaust ducting provides only an inherent passive safety function (i.e., confinement) and no specific TSR controls are required to ensure continued performance of this function. 

A ventilation system fan sequencing interlock ensures that the backup exhaust fan is automatically started upon loss of the primary operating fan. An alarm alerts the operations staff upon loss of the operating Zone 1 exhaust fan. 

HCF operators must verify that Zone 1 exhaust charcoal filters are in sen/ice during ventilation system operation. 

Local Exhaust Ventilation Local exhaust ventilation requires the management of much smaller volumes of air compared to general ventilation. Local exhaust systems capture contaminants at or near their source before hazardous substances reach the breathing zone of people. A system moves the air to locations where people will not be present. To meet air pollution standards, exhausted air may need treatment to remove and collect contaminants. 

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