Re: Containment High Range Area Monitors

[LIPTONW@dteenergy.com]

At a BWR (This may also be true for a PWR, but I don't know.)  the
Containment 
High Range Radiation Monitors ("CHARMS") are NOT for an operating reactor.  
Their sole use is for estimating the potential release during an accident in 
which the reactor is shut down.  They primarily measure the noble gas and 
iodine concentration in the primary containment, although they can't 
differentiate.  Using an expected source term, which predicts the noble gas
to 
iodine ratio, decaying for time after shutdown, and then assuming the design 
basis leakage rate from primary containment, the potential off site doses
can 
be calculated IF there were to be a release.  At Fermi 2, we've modeled 3 
source terms:  (1) coolant - no fuel damage, (2) gap - minor fuel damage 
allowing the release of the "gap" activity, and (3) core - major fuel
damage.  
The choice of model is based on dose rates and knowledge of the state of the 
core, eg., has the reactor water level dropped below the top of active fuel?
 
This gives the emergency response personnel the ability to evaluate the 
potential impact of the accident in its early stages and recommend timely 
protective actions to local authorities. 
 
Thus, the CHARMS have no set points.  By the time you use them, you are past 
worrying about tech specs.   
 
The opinions expressed are strictly mine. 
It's not about dose, it's about trust. 
 
Bill Lipton 
liptonw@dteenergy.com 
 
 
You wrote: 
 
Is there any one out there in RADSAFE area who have experiences in 
calculating alarm set point 
for radiation monitoring systems in nuclear power plants. 
  
I am intersted in calculation of alram setpoint for "containment high range 
area monitors" 
which I think were forced to be installed for monitoring any accident 
conditions in containment  
after TMI accident as one of the action items   
In general they are able to measure gamma dose rate upto 10E6 R/h. 
If dose rate reaches the alarm setpoint value, it gives containment purge 
and exhaust isolation signal. 
So it is pretty important to determine the setpoint value in terms of the 
safety operation and public safety.  
 
I am thinking of several criteria which can be applied to setting the alram 
value. 
  
  1) 10CFR 20 limit 
     I am afraid that this could gives too low value.  
     Do you think this would be appropriate in terms of its high detection 
range? 
  2) 10CFR100 limit 
 
Setpoint values for purge isolation signal are described in technical 
specifications 
(Engineered Safety Feature Actuation System) in a final safety analysis
report. 
I wonder if there are NRC's position papers or guidelines published for 
utilities. 
 
 
I would appreciate sharing your experiences and knowledge.       
 
Please repond to me directly.     
 
 
Thank you 
 
 
Sung-Jun Maeng 
Korea Electric Power Research Institute 
South Korea 
 
Email : sjmaeng@kepri.re.kr 
Fax : 0082-42-865-5704 
Sung-Jun Maeng 
Radaition Safety Group
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