ML24346A319
| ML24346A319 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 12/11/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24346A130 | List:
|
| References | |
| LO-175762 | |
| Download: ML24346A319 (1) | |
Text
Response to SDAA Audit Question Question Number: A-19.1-61 Receipt Date: 04/22/2024 Question:
Per the request documented in ML24269A008, dated October 24, 2024, only the relevant portions of the question and response are included SDAA FSAR Section 19.1.4.2.1.4, "Release Categories," describes the approach for demonstrating conformance with the Commission's large release frequency safety goal. This section states that the iodine core inventory release fraction that results in an acute 200 rem whole body (red marrow) mean dose at the site boundary is calculated.
SDAA FSAR Section 19.1.4.2.1.4 also describes three types of potential radionuclide releases to the environment that were evaluated: (1) a core damage sequence with containment and reactor pool bypassed, (2) a core damage sequence with leakage of radionuclides through the containment vessel and reactor pool bypassed, and (3) a release occurring at the bottom of the reactor pool. It is unclear to the staff if the third type of potential radionuclide release assumes containment leakage, containment bypass, or both.
NuScale is requested to:
1.Provide the iodine core inventory release fraction that results in an acute 200 rem whole body (red marrow) mean dose at the site boundary.
2.Discuss if the third type of potential radionuclide release assumes containment leakage, containment bypass, or both.
Response
- 1. NuScale added the release fraction value to the Standard Design Approval Application.
NuScale Nonproprietary NuScale Nonproprietary
- 2. The third type of release involves a dropped module on the bottom of the ultimate heat sink, and consists of the full core completely bypassing containment. NuScale added this information to the Standard Design Approval Application.
Markups of the affected changes, as described in the response, are provided below:
NuScale Nonproprietary NuScale Nonproprietary
NuScale Final Safety Analysis Report Probabilistic Risk Assessment NuScale US460 SDAA 19.1-38 Draft Revision 2 Audit Question A-19.1-61 Based on simulation results using the MACCS code (NUREG/CR-6613, 1998), athe iodine core inventory release fraction of 1.4 percent of the iodine core inventorythat results in an acute 200 rem whole body (red marrow) mean dose at the site boundary is calculated. Three types of potential radionuclide release to the environment are evaluated: a core damage sequence with containment and reactor pool bypassed, a core damage sequence with leakage of radionuclides through the CNV and reactor pool bypassed, and a release of the full core inventory tooccurring at the bottom of the reactor pool (bypassing containment). Key points of the calculation are:
The site boundary is modeled as the minimum distance from the edge of the RXB to the site owner controlled fence, which is assumed to be 690 ft (0.131 miles).
Dose receptors are stationary and unsheltered.
The release is at ground level.
The dose exposure duration is 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> following the radionuclide plume reaching a dose receptor.
A two-hour release duration is assumed for containment bypass scenarios.
For sequences involving an intact CNV, the release is 0.2 weight percent per day for the entire release with deposition in the CNV considered.
For modeling a dropped module, radionuclide scrubbing by the pool is considered.
The mean acute whole body dose over all weather trials in one year is used.
Radionuclide deposition in the Reactor Building is not considered.
The iodine group release fraction from a single module that results in a 200 rem whole body mean dose at the site boundary is used to distinguish between Release Categories 1 and 2.
RC1: Core Damage with Successful Containment Integrity A bounding analysis is performed to evaluate the potential source term for RC1, the release category associated with an intact containment as depicted by CET end state NR. The calculation of the whole body dose to an individual standing at the site boundary assuming leakage from a single module at the Technical Specification limit demonstrates that the maximum dose is a fraction of the dose associated with a large release.