Zone 2A Ventilation System

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. 

The SCBs serve primarily to confine radioactive material. The boxes are joined by sealable pass-throughs, which allow the passage of material into and out of the SCBs from the Zone 2A canyon. The SCB manipulators, which penetrate both the SCBs and the Zone 2A canyon, are sealed with a manipulator boot. The Zone 2A canyon is separated from the Zone 2 lab area by an airlock that maintains the negative operating pressure established for the Zone 1 and Zone 2A ventilation systems with respect to Zone 2. 

The makeup-air unit supplying Zone 2 receives its air from the building distribution system, the Zone 3 ventilation system (fan 3), boosted by fan 13 and recirculated by fan 11. The volume of makeup air is determined by the amount of air exhausted from the east and west Zone 2 sections, the amount of makeup air supplied to Zone 2A (which includes the Zone 1 supply air), less the amount of infiltration air into Zone 2. In addition to maintaining the correct pressure differential, the Zone 2 system provides at least four air changes per hour in Zone 2 and provides necessary environmental conditioning. The volume of recirculated air is regulated by a manual intake damper located in the intake duct of the Zone 2 filter and cooling coil. 

Radiological (contamination) Nitrogen release in SCB causes overpressure and contamination of Zone 2A canyon or Zone 2. Ventilation system failure. Process fission products and actinides as loose contamination in SCB. 

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. 

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. 

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 ... 

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. 

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. 

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) ... 

Inservice verification and testing of safety-related SSCs is conducted by HCF personnel in compliance with TSR surveillance requirements. These operational activities consist of Zonel-to-Zone 2A and Zone 2A-to-Zone 2 ventilation system differential pressure verification, differential pressure instrumentation channel functional testing, ventilation fan sequencing interlock operability testing, and ventilation system hot exhaust filter operability verification. Details of these TSR surveillance tasks and the frequency with which they are to be performed are formalized in an operational surveillance procedure. 

When used without a clarifying adjective or phrase and when not specifically associated with the HCF ventilation system, the term Zone 2A" identifies the hot cell canyon as described... 

The EMCS (FIDs A and B) receives pressure and fan current information from transducers throughout the ventilation system and displays the data on the operations center computer it also uses the information in calculations of flow rate which are displayed on the computer and at the LCPs. Differential pressures (e.g. Zone 1 to Zone 2A, Zone 2A to 2) are calculated and displayed. The alarms which annunciate at the computer and the LCPs are generated in the FIDs from comparisons with predetermined alarm setpoints. 

Fire (radiological and toxic material) Forklift fire incident causes transfer cask breach with possible target exposure and airborne release Failure of electrical equipment or system in SCBs, SGB, ventilation hood, Zone 2 or Zone 2A canyon Lightning strike External fire (vehicle accident, aircraft crash, other building fire) irradiated isotope production target, up to 20,000 curies. Volatiles in process cold traps, up to 70,000 curies. Same material as toxic spill. Residual radiological contamination. 

Ventilation system failure causes contamination of Zone 1, Zone 2A canyon, or Zone 2 (CP-13) II D 3... 

Normally, all of the above possible radiological inventories at process stations would be contained by the process SCB, they wouid be drawn into the ventilation system, and trapped on ventilation system filters. If the SCB failed, or a pre-existing failure were undetected, the radiological inventory could be released directly into the Zone 2A canyon. 

It is expected that under normal operational conditions, the airborne concentration level In the Zone 2A canyon would be well below the derived air concentration (DAC) limits (2E-8 ci/m3 for 1-131 from 10 CFR 835). This assessment is based on normal handling and containerization of process materials and the fact that the Zone 2A canyon volume is continually circulated by the ventilation system. However, contamination above these levels may exist in the canyon on a transient basis. An accident condition, such as simultaneous process spill and SCB failure, could hypothetically release a target s volatile contents, or 100% of the iodine inventory directly to the canyon. These theoretical contamination levels can also serve as a basis for evaluation of the potential consequences of ventilation failure. 

The Design Basis Earthquake (DBE) is a natural phenomena event, and is based on DOE-STD-1021. During normal HCF operations, the ventilation system maintains a zone-to-zone pressure hierarchy, which controls the migration of radiological contaminants. The normal flow of air sweeps contaminants that are present in contaminated confinement zones (Zone 1 and 2A) through filters, which are designed to capture and retain the contaminants. In the event of a DBE, many of these systems are expected to fail, and the normal pressure hierarchy would not be maintained. 

---