Definition of Waste Gas Storage Tank Radioactivity Limits
HPPOS-004 PDR-9111210080
Title: Definition of Waste Gas Storage Tank Radioactivity
Limits
See the memorandum from J. S. Bland to J. P. Stohr dated
August 28, 1980, and the incoming request from J. P. Stohr
dated July 2, 1980. The wording "equivalent Xe-133" and
"considered as Xe-133" in Standard Technical Specifications
allow the licensee to use area radiation monitoring
readings coupled with a calculational method to approximate
inventories in waste gas delay tanks (WGDT).
NUREG-0472, "Radiological Effluent Technical Specifications
for PWR's," Section 3.11.2.6 limits the amount of
radioactivity in each waste gas storage tank to (x) curies
of noble gas. Section 3.11.2.6 further states that the
activity shall "be considered as Xe-133." However, the
document fails to provide a definition of "considered as
Xe-133" or provide a definition of how this determination
is to be made. There is also inconsistent wording between
NUREG-0472 which presents a "considered as Xe-133" limit
and the STS Guidance Document (NUREG-0133) which describes
the limit as "Xe-133 equivalent."
The wordings "Xe-133 equivalent" and "considered as Xe-133"
were included for the purpose of identifying to licensees
the applicable use of area radiation monitor readings in
determining an approximate tank radioactivity inventory.
The intent of the STS requirement was not to require daily
isotopic analysis of the WGDT inventories. Instead, the
licensee is allowed to use area radiation monitor readings
coupled with a calculational method to approximate tank
inventories. Realizing that isotopic distributions change
with increased storage times, licensees must demonstrate
the applicability of any calculational method employed for
this purpose.
In determining the curie limits during licensing, NRR
evaluates the expected radionuclide distribution and
conservatively establishes a limit such that under accident
conditions (decay tank rupture) offsite dose will be less
than 0.5 rem. The limit, as presented, is a cumulative sum
of the total radionuclide distribution evaluated during
licensing. Therefore, considering the inventory limit as a
gross activity limit is consistent with the formulation of
the "considered as Xe-133" limit and the STS basis which
describes the limit as "Xe-133 equivalent."
Regulatory references: Technical Specifications
Subject codes: 7.3, 9.1
Applicability: Reactors