ML19270E335
| ML19270E335 | |
| Person / Time | |
|---|---|
| Issue date: | 11/27/2019 |
| From: | Michael Case NRC/RES/DSA |
| To: | Mike Franovich Office of Nuclear Reactor Regulation |
| Salay M | |
| Shared Package | |
| ML19114A117 | List: |
| References | |
| Download: ML19270E335 (4) | |
Text
November 23, 2019 MEMORANDUM TO: Michael X. Franovich, Director Division of Risk Assessment Office of Nuclear Reactor Regulation FROM: Michael J. Case, Director /RA/
Division of Systems Analysis Office of Nuclear Regulatory Research
SUBJECT:
CLOSEOUT TO RESEARCH ASSISTANCE REQUEST FOR INDEPENDENT REVIEW OF REGULATORY AND TECHNICAL BASIS FOR REVISING THE DESIGN-BASIS ACCIDENT FUEL HANDLING ACCIDENT This memorandum closes out the Office of Nuclear Reactor Regulation (NRR) Research Assistance Request (RAR), dated June 5, 2019, to finalize a fuel handling accident (FHA) transport model which is available in the Agencywide Documents Access and Management System (ADAMS) under Accession Number ML19113A152. Note that Sandia National Laboratory and other experts in the field were contacted to support in finalizing the FHA transport model.
Prior to the June 5, 2019 RAR, the NRR Division of Risk Assessment, Radiation Protection and Consequence Branch (ARCB), requested the Office of Nuclear Regulatory Research (RES),
Division of Systems Analysis, Fuels and Source Term Code Development Branch (FSCB), to perform an independent review of the staff re-evaluation of the fission product release and transport model for the Design-Basis Accident (DBA) FHA described in Regulatory Guide 1.183, Appendix B. This request was through an Informal Assistance Request (IAR). The main objective of the IAR was to revisit the original studies forming the technical basis for the FHA dose analysis methodology and seek input in updating the model with current information and practices consistent with other DBAs.
RESs IAR response, dated December 28, 2018, confirmed the NRR staffs re-evaluation and recommended improvements to the fission product transport model. These improvements would be established from the current understanding of reactor fuel pin physics and iodine chemistry under the environmental conditions in which fuel handling operations are taking place.
The NRR staff then developed the updated FHA fission product transport model under these conditions. Several NRR and RES staff-level meetings and presentations were held to discuss the re-evaluation findings and potential impact that the updated FHA transport model would have on staff and licensees.
CONTACT: Michael Salay, RES/DSA 301-415-2408
M. Franovich In follow-on June 5, 2019 RAR noted above, NRR requested RES to finalize the alternative FHA fission product transport model, have it peer-reviewed, and formally submit it to NRR through an inter-office memo as an acceptable method for staff use. The RAR concluded that considerable margin exists regarding the scrubbing effects of iodine in the spent fuel or reactor pool and that the current staff DBA FHA fission product transport model can be refined while still maintaining conservatism.
The current model assumes the initial conditions of the damaged fuel bundle is at operating reactor temperature and pressure. A small fraction (5 percent) of the available iodine inventory in the fuel pin gap is available for release to the pool water instantaneously. To model the scrubbing effects of iodine in the pool water, a single lumped parameter known as the iodine decontamination factor with a numerical value of about 200, has been assumed to represent not only the iodine immediately released following the postulated fuel rupture but also represented re-evolution of iodine. The re-evolution release has been assigned to the immediate release for the purposes of determining the decontamination factor for simplicity.
The alternative model assumes the entire fuel pin gap inventory of iodine (100 percent) is available for release between two separate release phases; the first from the initial gaseous release, the second from re-evolution. The first phase conservatively assumes 5 percent of the available iodine is subsequently decontaminated by passage through the overlying pool of water by a limiting numerical value of 667 which is dependent on pool water temperature and fuel pin pressure. The second phase conservatively assumes the remaining 95 percent as cesium iodine to completely dissociate into the pool water within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> then slowly re-evolve into the building atmosphere as elemental iodine due to the low pool water pH for up to 30 days.
A case study was performed to analyze the radiological consequences of the alternative FHA fission product transport model. The purpose was to determine the impact of the alternative model by comparing the computed radiological consequences to various licensing-basis FHA analyses which apply the current model and whether the revised results would exceed the radiological accident dose limits of 10 CFR 50.67 and the FHA-specific dose acceptance criteria listed in Regulatory Guide 1.183 and Standard Review Plant Chapter 15.0.1. In general, the alternative model computes estimated radiological consequences at the applicable dose-receptors that are 91-98% lower than those computed with the current model. The alternative model impact on licensing-basis FHA analyses would have similar reductions in computed doses.
The technical justifications provided included:
- A summary report detailing how RAR elements were addressed (ADAMS Accession Number ML19248C704). (Enclosure 1)
- A report providing the alternative DBA FHA analysis methodology (ADAMS Accession Number ML19248C668). This alternative captures the proposed revised FHA transport model and limitations for its applicability. (Enclosure 2)
- A report providing a calculational tool to compute various input parameters for the alternative DBA FHA model (ADAMS Accession Number ML19248C683). (Enclosure 3)
- A report providing the technical basis for the alternative DBA FHA model (ADAMS Accession Number ML19248C647). The report describes the re-analysis of the original
M. Franovich studies using modern data analysis tools to confirm results and conclusions. A new re-evolution model was developed based on experimental data. (Enclosure 4)
A copy of each of these documents is attached.
These deliverables document the independent review to support and finalize the updated FHA fission product transport model. These documents close out the RAR.
RES has established an online quality survey to collect feedback from user offices on the usefulness of RES products and services. This survey can be found online at the hyperlink: https://drupal.nrc.gov/res/quality-survey. I would appreciate the responsible manager or supervisor completing this shortabout 5 minutessurvey within the next 10 working days to present your offices views of the delivered RES product.
Enclosures:
As stated
M. Franovich
SUBJECT:
CLOSEOUT TO RESEARCH ASSISTANCE REQUEST FOR INDEPENDENT REVIEW OF REGULATORY AND TECHNICAL BASIS FOR REVISING THE DESIGN-BASIS ACCIDENT FUEL HANDLING ACCIDENT DATED NOVEMBER 23, 2019.
DISTRIBUTION:
M. Case, RES R. Lee, RES M. Salay, RES E. Dickson, NRR A. Veil, RES R. Furstenau, RES G. Bowman, NRR ADAMS Accession Number: ML19114A117 OFFICE RES/DSA/FSCB BC:RES/DSA/FSCB D: RS/DSA NAME MSalay RLee MCase DATE 11/25/19 11/16/19 11/27/19 OFFICIAL RECORD COPY