ML070110419
| ML070110419 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 12/27/2006 |
| From: | Pressey L Southern California Edison Co |
| To: | Kalyanam N NRC/NRR/ADRO/DORL/LPLIV |
| Kalyanam N, NRR/DORL/LP4, 415-1480 | |
| References | |
| TAC MC5495, TAC MC5496 | |
| Download: ML070110419 (5) | |
Text
From: Lynn.Pressey@sce.com To: N. Kaly Kalyanam <nxk@nrc.gov.
Date: Wed, 27 Dec 2006 09:37:54 -0800
Subject:
Re: One question on the AST LAR Hi Kaly, We completed an evaluation of Raddose V assessment software to determine what changes would be necessary to implement the AST PCN. That evaluation (which was completed in April, 2006, identified 6 things that needed to be changed prior to implementing the AST PCN.; however none of the changes were to the software itself. This is documented in AR 041201316 assignment
- 5. The six items identified as needing to be done in the evaluation were as follows:
- 2. Update Technical Team Notebook
- 3. Update 40.200 "don't use Source term capability in a SGTR"
- 4. Update 40.100 - "new Iodine removal factors"
- 6. Place Note on RadDose V computers stating "don't use Source term capability in a SGTR These items are currently being worked, but can not be completed/implemented until we get approval to implement the PCN. We have requested 6 months to implement this PCN after approval so that these items can be completed. I am including the text in the AR that explains the evaluation that was performed.
Can you give me an update on the convolution issue when we talk at 1130?
"The base AR states "Problem description ---A LICENSE AMENDMENT REQUEST, PCN-555 (ALTERNATIVE SOURCE TERM) IS BEING SUBMITTED TO THE NRC. THIS AR IS TO ASSESS THE LICENSE AMENDMENT REQUEST FOR COMMITMENTS AND TRACK THOSE COMMITMENTS AND IMPLEMENTATION ACTIONS."
This sub assignment states: "DETERMINE WHAT CHANGES TO RADDOSE V ARE NECESSARY IN ORDER TO IMPLEMENT PCN-555, "ALTERNATIVE SOURCE TERM."
PCN-555 changes the way we calculate iodine source term. Currently we consider iodine to be mostly a gas and a small portion particulate.
Alternate Source Term changes iodine source term calculations to treat iodine as mostly particulate and a small portion of it to be gas.
John Scott's evaluation of how dose assessment will change with the implementation of PCN-555 "Alternate Source Term" is pasted below. He states that we have guidance that would allow us to make minor changes in the calculation of source term during a steam generator tube rupture design
base accident but the regulatory guidance is still not sufficient to make substantive changes to the process of determining an accident source term and calculating potential off-site dose consequences in accordance with the concepts defined by AST.
One option to compensate for PCN-555 is to modify Raddose V to account for the change in calculating source term for steam generator tube ruptures now and then change Raddose V again when we get further regulatory guidance for source term calculations and on the dispersion model. Another option would be to prohibit the Raddose V operator from calculating source term and depend on the technical team for the calculation of source term. Then change Raddose V when we have enough guidance to make all the changes at once.
Raddose V runs on Windows 3.1 and is compiled with a severely outdated Visual Basic 3.0 compiler. The vendor has indicated that any changes to Raddose V would require a major rewrite of the software at a considerable cost.
Current practice is to rely on the technical team for the determination of source term. The operator, even though he has the ability, does not use Raddose V to calculate source term. Brian Ashbrook the manager of Emergency Preparedness, John Scott, and I agreed that it would make more sense to rely on the technical team for the calculation of source term (which we do now) and enforce the prohibition of using Raddose V to calculate source term in the operator's procedure. Then when we get further guidance, if we ever do, address changing Raddose V then.
Brian Ashbrook, John Scott, and I agree that Raddose V would not be changed at this time and that the following actions should be accomplished to compensate for that decision.
- 2. Update Technical Team Notebook
- 3. Update 40.200 "don't use Source term capability in a SGTR"
- 4. Update 40.100 - "new Iodine removal factors"
- 6. Place Note on RadDose V computers stating "don't use Source term capability in a SGTR Brian Ashbrook will handle making the assignments for tasks 1, 3, 4, 5, and 6 in his 041201316-10 LPA assignment (see the notes section of that assignment.) The technical team notebook update is covered in LPA assignment 041201316-7.
The determination above fulfills the requirements of this LPA sub assignment and allows me to close this LPA.
John Scott's Evaluation--------------------------------------------------------------------
"The regulatory guidance is still not sufficient to make substantive changes to the process of determining an accident source term and calculating potential off-site dose consequences in accordance with the concepts defined by AST. SONGS should make only minor changes to the current practice used to determine accident source terms for the steam generator tube rupture event to comply with the guidance. We should not change our atmospheric dispersal models to treat iodines as a particulate until additional guidance is issued by the Commission.
SONGS applied to the NRC to adopt the AST described in RegGuide 1.183 for use in design basis calculations. In design basis calculations worst case assumptions are typically applied. Emergency Planning assumptions should be as accurate as possible for a given condition to preclude overly conservative Protective Action Recommendations (PARs).
Prior to RegGuide 1.183, design basis calculations were required to assume that the iodine was predominately elemental gas. The AST concept defined in RegGuide 1.183 acknowledges that most iodine released from the fuel pin gap to the RCS is in the form of Cesium Iodide (CsI). Physically, CsI would be a particulate salt in air and would dissolve into water yielding Cesium cations and Iodine anions. The RegGuide also revises the timing of the release, core release fractions, and the adopts the concepts of TEDE and CDE. SONGS applied to use the AST in our design basis calculations to provide additional margin to the requirements for post-accident Control Room habitability. At the time of the application, an intuitive evaluation and preliminary read of the RegGuide led me to believe that the source term determination process and the dispersal models would have to be revised.
RegGuide 1.183 redefined iodine behavior in the conditions that would exist in a post-LOCA containment environment. The chemical and physical behaviors defined in this document for the post-LOCA containment appear to be accurate. The RCS would initially flash to steam. The CsI would be an airborne particulate. Containment Sprays would wash in down and the CsI will dissolve into the water inside containment. The solubility of the Iodide anions is pH dependent. In an acidic environment (RCS and RWST are acidified with Boric Acid) the iodide would recombine to an elemental form.
Large portions would evaporate back into the containment atmosphere as a gas. In a basic environment the iodide will stay in solution, and would exist largely as a particulate in the air volume inside containment. SONGS system design cannot guarantee a basic pH inside containment following a LOCA until the containment spray system uses all the water from the RWSTs and switches to recirculation mode (RAS). At that point the TriSodium Phosphate in the baskets in 17' elevation of containment are guaranteed to be dissolved and sprayed through the containment. Until that point, iodine must be assumed to be elemental and gaseous in form. This time period for RAS can be as little as about 40 minutes for the design basis large break LOCA, but can be several hours for a small break LOCA.
Iodine behavior in the containment appears accurate. However, the guidance for other accidents (ESF leakage, Main Steam Line Break, and Steam
Generator Tube Rupture) continues to require that iodine released to the environment be treated predominately as elemental gas in design basis calculations. This is counterintuitive because iodine is such a strong halogen, it will quickly combine with any available cation to create a particulate salt in air or dissolve in water.
Until further guidance is issued in the form of a revision to the NRC Resource Technical Manual (RTM), or the NRC's source term and atmospheric dispersal model (RASCAL) is revised, the existing design basis guidance requires us to treat iodine dispersal with gaseous models.
This is the current SONGS practice in both source term determination and atmospheric dispersal, so no changes are required at this time." "
"N. Kaly Kalyanam"
<NXK@nrc.gov> To "Lynn Pressey" 12/27/2006 07:51 <lynn.pressey@sce.com>
AM cc Subject One question on the AST LAR
- 3. Raddose V dose assessment software will be evaluated by June 30, 2005, to determine what specific changes may be warranted in order to maintain consistency with the manual dose assessment calculation methodology.
Can you please tell me if this task was completed as stated? SONGS supplement dated March 10, 2006, has the same commitment as was in the original letter (application dated December 27, 2005).
Please send me a reply as soon as you can.
Thanks Kaly
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Re: One question on the AST LAR Creation Date 12/27/2006 12:37:54 PM From: <Lynn.Pressey@sce.com>
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