ML24284A326
| ML24284A326 | |
| Person / Time | |
|---|---|
| Site: | Hermes File:Kairos Power icon.png |
| Issue date: | 10/10/2024 |
| From: | Gardner D, Lighty R, Polonsky A Kairos Power, Morgan, Morgan, Lewis & Bockius, LLP |
| To: | NRC/OCM |
| SECY RAS | |
| References | |
| RAS 57148, 2-M 50-611-CP, 2-M 50-612-CP, 50-611-CP, 50-612-CP | |
| Download: ML24284A326 (0) | |
Text
UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION BEFORE THE COMMISSION In the matter of:
KAIROS POWER LLC (Hermes 2 Test Reactor Facility)
Docket Nos. 50-611-CP 50-612-CP October 10, 2024 KAIROS POWER LLC RESPONSES TO COMMISSION HEARING QUESTIONS Kairos Power LLC (Kairos Power) provides the following responses to the questions in the Commissions September 25, 2024, Order (Transmitting Hearing Questions) regarding the mandatory hearing for the Construction Permit Application for the Hermes 2 Test Reactor.
Kairos Powers responses are limited to those questions directed to it.
Responses to Commission Questions Question 1 PSAR Section 2.2.2.4, Summary of Risks from Air Traffic, states that DOE-STD-3014-2006 provides a screening value for which the risk of an aircraft accident is considered acceptable.
The PSAR further notes that the total crash frequency for all airway, helicopter operations, airport takeoff operations, and airport landing operations at the Hermes 2 facility exceeds this criterion. Given this, PSAR Section 2.2.2.4 states that the safety-related portion of the Reactor Building structure will be designed to withstand the impact of a small non-military general aviation aircraft as described in Section 3.5. PSAR Section 3.5.3.4 states that the design of the safety-related portion of the Reactor Building is evaluated for the effects of aircraft impact from light general aviation aircraft, rather than a specific aircraft.
Section 2.2.3.1 of the Staffs SE states that [t]he staff will review the basis for selecting the critical aircraft type for designing the safety-related portion of the reactor buildings during a future review of the operating license (OL) application of the Hermes 2 facility. No further aircraft type information is provided in the SE.
In response to pre-hearing question number 7 during the Hermes 1 construction permit mandatory hearing, Kairos suggested that over 90% of projected flight operations would be general aviation aircraft such as a Cessna 172R (single engine) or Beechcraft Baron 58P (multi-engine). By contrast, in its response to the same pre-hearing question, the Staff stated that it expects that aircraft characteristics similar to those of the Beechcraft King Air 350i may be used in establishing the aircraft impact design basis for the reactor building.
2 Given the significant differences in the speed and weight of the aircraft referenced by Kairos and the Staff for the Hermes 1 review combined with the high likelihood that substantial portions of the safety-related portions of the reactor buildings will be designed and built by the time of the operating license review, please address the following:
a) What basis do you plan to use during the operating license phase of Hermes 2 to determine the acceptable aircraft type for the purpose of designing the safety-related portions of the reactor buildings?
Kairos Power Response to Question 1 a) Kairos Power will evaluate the frequency of flights and crash rates for specific aircraft types to determine those that meet the screening criteria. For those aircraft types that meet the screening criteria, an assessment will be made to determine the consequences of an accidental aircraft impact on safety-related structures of the Hermes 2 facility. Based on this evaluation, the aircraft or aircrafts selected that the safety-related portions of the Hermes 2 facility will be designed to be protected against will be presented in the Hermes 2 OLA. This approach is consistent with the guidance outlined in DOE Standard DOE-STD-3014-2006, Accident Analysis for Aircraft Crash into Hazardous Facilities, in particular Section 3 through Section 6. Providing the evaluation in the OLA provides reasonable assurance that the final design will conform to the design basis because the aircraft will be selected during detailed design which will be prior to Kairos finalizing the OLA.
Question 2 PSAR Section 2.4, Hydrology, for the Hermes 2 facility incorporated only minor changes compared to the Hermes 1 PSAR (all related to references to the two-unit Hermes 2 facility). As noted in Section 2.4 of the Staffs SE, a difference between Hermes 1 and Hermes 2 is that the intended licensing period is increased from 4 years to 11 years. Section 2.4.3.1 of the SE further notes:
The Hermes 1 SE describes staffs evaluation and findings with regard to dam safety during the facilitys 4-year operating lifetime. The staffs findings are applicable to Hermes 2s longer operating lifetime of 11 years because the ongoing oversight and inspections carried out by the Tennessee Valley Authority (TVA) as part of its dam safety program will continue throughout the 11-year proposed licensing term of Hermes 2, providing the staff with reasonable assurance that a dam failure resulting in site flooding would be very unlikely.
However, in response to pre-hearing question number 8 during the Hermes 1 construction permit mandatory hearing, the Staff stated:
For flooding hazards from potential dam failures, consideration of a limited operating life was necessary to approve the siting because the Staff did rely on the 4-year operating period, in part, to assess the suitability of the site.
3 The Staff also noted in response to pre-hearing question number 9 that:
This determination was also based on the limited (4-year) period of Hermes operation combined with the lower risks associated with management and operations programs of the responsible federal agency for relevant dams in the vicinity of the proposed Hermes site. Tennessee Valley Authority owns, operates, and regularly inspects the dams following the requirements of its dam safety program. This oversight further supports Staffs determination that sunny-day failure of the dams would be unlikely.
a) Has the Tennessee Valley Authority made any changes in its oversight of dams in the vicinity of the proposed Hermes 2 site to permit the longer operating term of 11 years rather than 4 years? If so, please describe the changes.
Kairos Power Response to Question 2 a) Kairos has not asked Tennessee Valley Authority (TVA) if it has made any changes in its oversight of its dams in the vicinity of the proposed Hermes 2 site to permit the longer operating term of 11 years rather than 4 years (for Hermes 1), because such changes are not necessary to demonstrate reasonable assurance of protection of public safety and the environment for Hermes 2 CPA approval.
In its review of the Hermes 1 CPA, the Staff included the 4-yr planned operating period of Hermes 1 as part of its approval. However, Kairos Power did not agree with that conclusion, because the annual probability of the design basis flood occurrence of 4x10-5 is very low (the 25,000-yr return period is very high) relative to the proposed operating period. When considering Hermes 2, the difference between a 4-yr operating period for Hermes 1 and an 11-yr operating period for Hermes 2 is not statistically significant when both are compared to the low probability (high return period) of occurrence of the design basis flood. The design basis flood evaluation with a 4x10-5 probability of annual occurrence (25,000-yr return period) results in a dry site and is conservative with respect to DOE design-basis flooding criteria required for Hermes 1 and Hermes 2.
The probabilities of other hypothetical extreme events that result in higher flooding elevations than the Hermes design basis flood include the PMF scenario and the sunny day failure of Norris Dam, but these events have a lower probability (higher return period) than the design-basis flood. The probability associated with a PMF is 1x10-6 (1,000,000-yr return period). While a hypothetical simulation of a sunny day failure of Norris Dam does not have an associated probability, Fell et. al., 2001 (Reference 1),
identified that the probability of dam failures is on the order of 1x10-5 (100,000-yr return period) (Reference 2). Therefore, these events are less likely than the design-basis flood.
Kairos understands that TVA has a program of inspection and maintenance for its dams that it carries out on a regular schedule to keep its dams safe. TVAs structural assessment and ongoing monitoring of its dams is protective, regardless of the operating life of Hermes 1 and 2.
4
References:
- 1. Fell et al. 2001. The Status of Methods for Estimation of the Probability of Failure of Dams for Use in Quantitative Risk Assessment. Fell, R.; Bowles, D.S.;
Anderson, L.R.; Bell, G.
- 2. Fell et al. identified probabilities of dam failures on the order of 1x10-5. Historical annual frequency of failures (Table 4) for dams commissioned between 1928-1992, concrete gravity, for all failure modes, after 5 years of operation, the frequency of failure was 1.4x10-5 or about 70,000-yr return period.
Question 3 Section 5.2.1.2 of the Hermes 2 PSAR states that the Intermediate Heat Transport System (IHTS) is equipped with safety-related rupture disks located in the intermediate inert gas subsystem, in the gas space above the Intermediate Salt Vessels.
As described in Section 3.6.3.2 of the Staffs SE, The rupture disks are used to prevent overpressure in the IHTS during a postulated superheater tube leak or rupture event. The rupture disk standpipes and vent lines would also provide a relief path for the steam from a superheater tube rupture to prevent the steam from reaching the [Intermediate Heat Exchanger (IHX)]. While the IHX, including the IHX tubes, are classified as non-safety related, the staff noted that failure of one or more IHX tubes following a superheater tube rupture could lead to unanalyzed conditions due to potential Flibe-water interactions or higher than assumed levels of BeNaF ingress into the PHTS [Primary Heat Transfer System].
In its letter of July 17, 2024, the ACRS noted that the safety-related rupture disks are proposed by Kairos to prevent the pressure rise associated with a superheater tube rupture from reaching the point where the tubes in the IHX fail. Further, the ACRS stated:
The design of the passive rupture disks in the intermediate coolant loop and the time needed for disks to actuate (relative to the event-generated pressure wave and the speed of sound in the salt) will be critical in mitigating the progression of this event and limiting overall damage. In light of the uncertainties associated with the progression of this postulated event, we believe strong preventive measures are preferred over mitigative ones. Were Kairos to be unsuccessful in designing the rupture disks to protect the IHX tubes, the safety classification of the IHX, the intermediate loop, or both may have to be reconsidered.
In Section 13.1.10.3.2 of the SE, the Staff acknowledged the uncertainties: In the absence of any explicit modeling or experimental data, the staff finds that there is large uncertainty in the progression of events following a postulated superheater tube break or rupture.
10 C.F.R. § 50.34(a)(8) requires that the PSAR include, in part, identification of those structures, systems or components (SSCs) which require research and development to confirm the adequacy of their design; and identification and description of the research
5 and development program which will be conducted to resolve any safety questions associated with such SSCs; and a schedule of the research and development program showing that such safety questions will be resolved at or before the latest date stated in the application for completion of construction of the facility. PSAR Section 1.3.9, Research and Development, identifies SSCs that require additional research and development; however, this section does not discuss design of the IHTS safety-related rupture disks.
a) Is additional research and development needed to produce a final design of the IHTS rupture disks to ensure that design bases are met?
b) If the answer to part (a) is yes, what research and development activities are required and what is the schedule for their completion?
Kairos Power Response to Question 3 a) No. Additional research and development, as defined in 10 CFR § 50.2, is not required to produce a final design for the IHTS rupture disks to ensure that design bases are met.
10 CFR § 50.2 defines "Research and Development" as:
- 1) theoretical analysis, exploration, or experimentation; or (2) the extension of investigative findings and theories of a scientific or technical nature into practical application for experimental and demonstration purposes, including the experimental production and testing of models, devices, equipment, materials, and processes.
Kairos Power recognizes that more design work is needed to provide the level of detail required in the final safety analysis report (FSAR), as part of the operating license application (OLA). However, the design work that will ensure the IHTS will meet its design bases is not exploratory or theoretical as described in the 10 CFR § 50.2 definition of Research & Development. The use, design, and function of rupture disks are well understood and their use in providing relief from overpressure events is not new.
The uncertainty described in the ACRS letter is due to the preliminary state of the IHTS design, not from uncertainty on whether a rupture disk can perform a pressure relief function. The type of additional design work needed to make the determinations described in the Staffs SE Section 3.6.3.2 are described in PSAR Section 5.2 and two Requests for Confirmation of Information, RCI-01 (ML24103A243) and RCI-03 (ML24135A382).
Kairos Power did not request Commission approval of the safety of any Hermes design feature described in the PSAR, consistent with 10 CFR § 50.35(b). Therefore, providing this additional normal design information at the time of the OLA is consistent with the regulations in 10CFR §50.34.
b) Not Applicable. See response to question a).
6 Respectfully submitted, Executed in Accord with 10 C.F.R. § 2.304(d)
DARRELL GARDNER Sr. Director, Licensing KAIROS POWER 2115 Rexford Road, Suite 300E Charlotte, NC 28211 Phone: 704.769.1226 Email: gardner@kairospower.com Signed (electronically) by Ryan K. Lighty RYAN K. LIGHTY, ESQ.
MORGAN, LEWIS & BOCKIUS LLP 1111 Pennsylvania Avenue, N.W.
Washington, D.C. 20004 Phone: 202.739.5274 Email: Ryan.Lighty@morganlewis.com Executed in Accord with 10 C.F.R. § 2.304(d)
ALEX S. POLONSKY, ESQ.
MORGAN, LEWIS & BOCKIUS LLP 1111 Pennsylvania Avenue, N.W.
Washington, D.C. 20004 Phone: 202.739.5830 Email: Alex.Polonsky@morganlewis.com Counsel for Kairos Power LLC
UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION BEFORE THE COMMISSION In the matter of:
KAIROS POWER LLC (Hermes 2 Test Reactor Facility)
Docket Nos. 50-611-CP 50-612-CP October 10, 2024 CERTIFICATE OF SERVICE I hereby certify that, on this date, a copy of the foregoing KAIROS POWER LLC RESPONSES TO COMMISSION HEARING QUESTIONS was served upon the Electronic Information Exchange (the NRCs E-Filing System) in the above-captioned docket.
Signed (electronically) by Ryan K. Lighty RYAN K. LIGHTY, ESQ.
MORGAN, LEWIS & BOCKIUS LLP 1111 Pennsylvania Avenue, N.W.
Washington, D.C. 20004 Phone: 202.739.5274 Email: Ryan.Lighty@morganlewis.com Counsel for Kairos Power LLC