Launch and Reentry of Space Nuclear Systems AC 450.45-1 45 A.8 HIGH FIDELITY RADIOLOGICAL SAFETY ANALYSIS.
A.8.1 The high-fidelity radiological safety analysis (HFRSA) process involves applying probabilistic risk assessment methods and calculating the risk to the public for all reasonably foreseeable events and failures of safety-critical systems during normal and malfunction operations in all mission phases. The HFRSA should be complete enough for the FAA to validate the accuracy and findings of the HFRSA to make a licensing decision. For SNS, it is the consequence analysis side that introduces the greatest challenges and highest uncertainty in the HFRSA because of the complexities of radiation transport, exposure, biokinetics, and dosimetry. The end conclusions of the HFRSA are the PER for the most exposed individual for each event and failure.
A.8.2 The guidance provided in ACs 450.115-1 and -1A, High Fidelity Flight Safety Analysis provide applicants a good starting point for performing the HFRSA, but lacks the specific information needed to calculate the ionizing radiation exposure risks. To compute this additional information, applicants are encouraged to utilize computer codes developed by the NRC, the DOE national labs, or the computational methods underpinning the existing nuclear safety analyses. If none of these options are viable, applicants could make bounding assumptions without biases that may prove to be conservative using the worst-case radioactivity characteristics of the SNS, as identified in the RMR addendums. For all HFRSA, applicants should clearly demonstrate the accuracy of the fundamental scientific principles and statistical validity underpinning the analysis.
A.8.3 The purpose of HFRSA is to calculate the PER for all reasonably foreseeable events the SNS could experience, so the SNS risks can be accurately assessed. Doing this will necessitate determining the probability, location, accident type, radioactive material composition, dispersion, exposure pathways, and exposure magnitudes for ionizing radiation exposure to members of the public. This includes scenarios where the SNS remains intact, and those that result in uncontrolled radioactive release to the environment at some point. The HFRSA is a significant undertaking and will be more involved than the flight safety analysis for a non-SNS mission.
A.8.4 Specific accident environments that may need to be considered when performing the HFRSA include but are not limited to those shown in Table 6 of this AC.
Launch and Reentry of Space Nuclear Systems AC 450.45-1 46 Table 6 – Accident Environments for HFRSA Consideration Accident Environment Physical Mechanisms Dynamic Acceleration, Shock, Vibration Explosive Overpressure Kinetic ΔP, dP/dt Thermal T, ΔT, ∇T, dT/dt Nuclear Radiation Fluence Chemical Chemical Reactivity A.8.5 Where P is Linear Momentum, T is the Temperature, t is the Time, Δ is the Difference Operator, ∇ is the Gradient Operator, d/dt is the Differential Operator.
A.8.6 Accident environments include fireball temperatures, explosive debris fragment velocities, and speeds for ground impact. Other accident environments include pressure gradient, atmospheric lapse rate, wind, and precipitation, which can affect the transport of released radioisotopes on the ground and in the atmosphere. Break-up state vectors – position (location and altitude), velocity, and acceleration are important initial conditions for the transport equations of motion.
A.8.7 These accident scenarios may, in and of themselves, pose hazards to people and property. They are addressed in non-nuclear portions of launch and reentry licensing.
From a nuclear safety perspective, they also impose hazards to the physical barriers to radioactive release that can result in radiological release and dispersal resulting in a PER that must be determined by the HFRSA to satisfy acceptable levels of risk in Chapter 7 of this AC. When complete, the HFRSA provides the information shown in Table 7 of this AC. An iterative process may be beneficial to develop this information by considering the results of safety analyses required for non-nuclear and nuclear missions.
In some cases, the results of the HFRSA may inform decisions regarding the performance of safety mitigations employed by the launch or reentry vehicle. Like all nuclear safety analyses, the HFRSA should be based on sound underlying scientific principles and valid statistical methods.
Launch and Reentry of Space Nuclear Systems AC 450.45-1 47 Table 7 – Information Produced by a HFRSA Information Produced by a HFRSA Rationale Normal operational occurrences analysis for each stage of the mission, including launch, ascent, on orbit, departure from orbit, reentry, and end of mission (EOM).
This information quantifies the baseline risk of the SNS and is used to develop the environmental review.
The PER to the most exposed member of the public during normal operations.
This information quantifies the baseline risk of the SNS and is used to develop the environmental review.
Histograms showing the number of people expected to receive various TEDs above background radiation levels up to the highest dose for normal operations.
This information quantifies the baseline risk of the SNS and is used to develop the environmental review.
Normal operations analysis for return to orbit, on orbit, and EOM disposal, if applicable.
This information is used to assess whether a commercial SNS might impact national assets with radiation detection capabilities.
It is also used during the safety and payload reviews, and potentially to develop the environmental review.
A radiation emission heatmap showing the maximum expected radiation from the SNS out to 100 km from the vehicle when operating in space.
This information is used to assess whether a commercial SNS might impact national assets with radiation detection capabilities.
It is also used during the safety and payload reviews, and potentially to develop the environmental review.
Accident analysis for each stage of the mission, including launch, ascent, on orbit, departure from orbit, reentry, uncontrolled reentry, and EOM disposal.
This information is used to validate the calculated SNS Tier level, to develop the environmental review, and to calculate the maximum probable loss (MPL).
The PER to the most exposed member of the public for each failure chain with a probability greater than 1x10-7.
This information is used to validate the calculated SNS Tier level, to develop the environmental review, and to calculate the MPL.
Launch and Reentry of Space Nuclear Systems AC 450.45-1 48 Information Produced by a HFRSA Rationale Histograms showing the number of people expected to receive various TEDs above background up to the highest dose for each scenario with a probability greater than 1x10-7.
This information is used during the safety and payload reviews, and potentially to develop the environmental review.
Severe accident analysis for each stage of the mission, including launch, ascent, on orbit, departure from orbit, reentry, uncontrolled reentry, and EOM disposal.
This information is used to determine the risk to the public and to assist in the development of the environmental review.
The PER to members of the public for the failure chain that produces the highest PER to a member of the public, and the probability of that failure.
This information is used to determine the risk to the public and to assist in the development of the environmental review.
A histogram showing the number of people expected to receive various TEDs for the failure chain with the highest PER to a member of the public, for various TEDs from background up to the highest dose.
This information is used to determine the risk to the public and to assist in the development of the environmental review..
A.8.8 Additional information on performing probabilistic risk assessment and public exposure calculations for nuclear systems is also available from various nuclear agencies and organizations. Some of these documents are listed in chapter 3 of this AC, but more specific probabilistic risk assessment guidance and standards are available elsewhere.
This information may be very useful to applicants where the SNS merits an RHA or HFRSA. The following is a brief list of some, but not all, of the references available at the time of this AC which may aid applicants in performing their nuclear safety analyses:
A.8.8.1 American Nuclear Society (ANS).
• ANS RA-S-1.4-2021, Probabilistic Risk Assessment for Advanced Non-Light Water Reactor Nuclear Power Plants.
• ANS 6.1.1-2020, Photon and Neutron Fluence-to-Dose Conversion Coefficients.
• ANS 8.23-2019 Nuclear Criticality Accident Emergency Planning and Response.
• ASME/ANS RA-S-1.3-202x, “Standard for Radiological Accident Offsite Consequence Analysis (Level 3 PRA) to Support Nuclear Installation Application” (revision of trial-use standard ASME/ANS RA-S-1.3-2017)
Launch and Reentry of Space Nuclear Systems AC 450.45-1 49 A.8.8.2 American Society of Mechanical Engineers (ASME).
• ASME RA-S-2008, Standard for Level 1/Large Early Release Frequency Probabilistic Risk Assessment for Nuclear Power Plant Applications.
Note: ASME/ANS RA-S-1.3-202x, “Standard for Radiological Accident Offsite Consequence Analysis (Level 3 PRA) to Support Nuclear Installation Application” (revision of trial-use standard ASME/ANS RA-S-1.3-2017) ANS RA-S-1.3-2017 and ASME/ANS RA-S-1.3-2017 refer to a joint standard under trial use development by ASME and ANS. It has not been made a final standard.
A.8.8.3 Department of Energy
• DOE-STD-1628(series), Development of Probabilistic Risk Assessments for Nuclear Safety Applications.
A.8.8.4 Nuclear Regulatory Commission
• NUREG-1513, Integrated Safety Analysis Guidance Document.
• NUREG-2201, Probabilistic Risk Assessment and Regulatory Decision-making:
Some Frequently Asked Questions.
• NUREG-2199, An Integrated Human Event Analysis System (IDHEAS) for Nuclear Power Plant Internal Events At-Power Application.
• Regulatory Guide 1.200, Acceptability of Probabilistic Risk Assessment Results for Risk-Informed Activities.
• Regulatory Guide 1.233, Guidance for a Technology-Inclusive, Risk Informed, and Performance-Based Methodology to Inform the Licensing Basis and Content of Applications for Licenses, Certifications, and Approvals for Non-Light Water Reactors.
• Regulatory Guide 1.247, Acceptability of Probabilistic Risk Assessment Results for Non-Light Water Reactor Risk-Informed Activities.
Note: This regulatory guide was issued for trial use at the time of this AC publication.
A final version may now be available.
Launch and Reentry of Space Nuclear Systems AC 450.45-1 50 A.9 RADIOLOGICAL EMERGENCY RESPONSE PLAN.
A.9.1 Consistent with DOE and NRC practices, a radiological emergency response plan (RERP) is needed when an SNS contains sufficient material to have off-site safety implications (Title 10 CFR Chapter I 2021). This determination is made when the amount of radioactive material, as indicated in the RMR, exceeds the thresholds of Title 10 CFR 30.72 Schedule C (Title 10 CFR Chapter I 2021). For the accident environments the SNS may experience, the release fractions stated in Title 10 CFR
30.72 Schedule C may not be appropriate. To avoid making a non-conservative assumption, the FAA uses a default assumption that the SNS release fraction is 1.0, unless evidence is presented to show that the release fraction is lower. This has the net effect of reducing the threshold quantities listed in Title 10 CFR part 30.72 Schedule C unless evidence is provided.
A.9.2 In cases where there are multiple isotopes present, an RERP is required when the sum of all the ratios on any RMR or RMR addendum between SNS isotopes and Title 10 CFR 30.72 Schedule C thresholds exceeds 1.0 (Title 10 CFR Chapter I 2021). For example: consider an SNS with only two isotopes, A and B, where the release fractions of Title 10 CFR 30.72 Schedule C are shown to be correct:
(𝑆𝑆𝑆𝑆𝑆𝑆 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴)𝐴𝐴 (10 𝐶𝐶𝐶𝐶𝐶𝐶 30.72 𝑆𝑆 𝐴𝐴ℎ 𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 𝐶𝐶 𝑇𝑇ℎ𝑟𝑟 𝑒𝑒 𝑟𝑟ℎ𝑜𝑜𝑒𝑒𝑒𝑒)𝐴𝐴 = 0.55 And (𝑆𝑆𝑆𝑆𝑆𝑆 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴)𝐵𝐵 (10 𝐶𝐶𝐶𝐶𝐶𝐶 30.72 𝑆𝑆 𝐴𝐴ℎ 𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 𝐶𝐶 𝑇𝑇ℎ𝑟𝑟 𝑒𝑒 𝑟𝑟ℎ𝑜𝑜𝑒𝑒𝑒𝑒)𝐵𝐵 = 0.9 A.9.3 The combined value of all isotopes on this SNS would be:
0.55 + 0.9 = 1.45 A.9.4 Because the combined value 1.45 is greater than 1.0, an RERP would be required for this SNS.
A.9.5 RERP’s can be created by applying the principles and process of NUREG 0654/FEMA (Radiological Emergency Preparedness) REP-1 Rev. 2 Preparation and Evaluation of Radiological Emergency Response Plans and Preparedness dated December 2019. The RERP is not itself an analysis, but rather a response plan that provides the FAA assurance that the applicant and involved government entities are prepared to respond in the event of a radiological emergency. RERPs contain contingencies to address scenarios addressing fixed facilities where a member of the public may be exposed to ionizing radiation, as identified in the RHA, HFRSA and criticality safety analysis if applicable. Thus, while the RMR determines whether an RERP is needed, the subsequent analyses may need to be completed before the RERP can be completed.
Launch and Reentry of Space Nuclear Systems AC 450.45-1 51 A.9.6 RERPs for SNS that will operate or linger in Earth orbit include how the radiological risks have been discussed with other nations, and the procedures and governmental collaboration that will be used to recover, mitigate, and decontaminate the area if a SNS has an uncontrolled reentry in another nation.
A.9.7 RERPs can be incorporated in an applicant’s overall mishap plan as required by § 450.173.
A.10 TIER LEVEL DETERMINATION.
After the HFRSA process is complete, the final Tier level of the SNS can be determined, unless it was previously determined due to satisfying automatic criteria.
The applicant will utilize the results of their HFRSA to determine the Tier level, and the FAA will evaluate both the analysis and the final Tier level conclusion.
A.11 SAFETY ANALYSIS REPORT.
An application for launch or reentry of an SNS requires a SAR (NSPM-20 2019). The SAR provides sufficiently detailed and complete enough documentation to support the FAA’s evaluation of the applicant’s safety analysis as applicable for that SNS. The SAR documents the detailed and complete results of all analysis performed to assess the safety of the SNS and elaborates on the comparison to existing analyses for the SNS that are assessed using this method. Additional information might be warranted in the SAR as determined by SNS mission parameters on a case-by-case basis. Creating the SAR provides the applicant an opportunity to communicate to the FAA how the risks of the SNS are being properly assessed and addressed to protect public health and safety and the national security and foreign policy interests of the United States. A SAR should include the following:
• Evidence of technical peer review for all hazard analyses and safety analyses;
• A concise, high-level summary of key risk information:
a. The likelihood of an accident resulting in an exposure more than 5 rem TED to any member of the public;
b. The number of individuals who might receive exposure more than 5 rem TED in an accident scenario;
c. Comparisons of the potential exposure levels to other meaningful measures:
i. Space nuclear system launch safety guidelines;
ii. Average public exposure from natural and human made sources; and iii. Other relevant public safety standards.
Launch and Reentry of Space Nuclear Systems AC 450.45-1 52 A.11.1 In some cases, it may be appropriate to include a system-specific SAR within a mission SAR. This could be advantageous when multiple launches of the same space nuclear system are planned, as the first system-specific SAR could specify the safety basis envelope for the system. The safety basis envelope would set the conditions under which the nuclear safety analyses are valid and provide assurance of safe operation of the SNS. This would limit the scope of the applicant produced nuclear safety analysis for future missions with the same SNS. If a system-specific SAR is used, the mission SAR either:
1. Demonstrates that the mission is within the safety basis envelope established in the system-specific SAR.
a. No additional safety analysis is required for the space nuclear system in this case because the safety of the system has already been established within the safety basis envelope.
2. Includes supplemental safety analysis for deviations outside the established safety basis envelope where safety has not yet been demonstrated.
a. Additional analysis is required to ensure public safety is not adversely impacted by the planned operations outside the initial safety basis envelope.
Launch and Reentry of Space Nuclear Systems AC 450.45-1 53 Appendix B. Guideline Safety Recommendations B.1 SCOPE.
This appendix provides recommendations for an applicant to consider to minimize the public safety risk of an SNS. This appendix also provides recommendations to applicants that, if incorporated, will increase the likelihood that the FAA will be able to issue a safety approval or a favorable payload determination.
B.2 NUCLEAR SAFETY THEMES.
B.2.1.1 From the comprehensive reviews performed to develop this AC, several overarching themes emerged for commercial SNS safety including but not limited to:
• Sustained successful use of nuclear technology requires a license applicant to have a strong safety culture developed in their organization;
• Preventing failure of an SNS does more to protect the public than responding to failures;
• The risk to the public increases if the radioactive material escapes from the SNS;
• The larger the ionizing radiation potential from an SNS, the less likely failures must be to achieve an acceptable overall risk to the public;
• The initial design of the SNS determines the baseline radiation exposure risk that an SNS can pose to the public;
• SNS may increase the risk to the public above the baseline radiation exposure risk any time there is potential for an SNS to return to Earth, including launch, orbit, reentry, and Earth flyby.
• Spacecraft maneuvers can change the risk of the SNS to the public relative to the baseline radiation exposure risk;
• Operation of the SNS can increase the risk to the public from the baseline radiation exposure risk, sometimes significantly;
• The risk to the public increases as the operating time increases for a fission based SNS;
• The risk to the public for any SNS is much higher when a critical chain reaction is in progress than when the chain reaction is sub-critical;
• The uncontrolled reentry of a fission reactor with a critical chain reaction in progress poses a significant risk to the public;
• The risk to the public increases the closer the SNS operates to Earth; and
• EOM disposal decisions can change the risk of the SNS to the public.
Launch and Reentry of Space Nuclear Systems AC 450.45-1 54 B.2.1.2 From reviewing the designs, licensing requirements, and standards that were in place for terrestrial nuclear reactors, it became clear that SNS have unique characteristics that will require additional consideration beyond what has been developed to this point. For example, the sophisticated computer models for analyzing terrestrial nuclear accidents currently lack the flexibility to analyze a radioactive release that begins in orbit and results in an uncontrolled reentry, which will make reactor accident analysis for on-orbit SNS challenging (Nuclear Regulatory Commission 2017), (Sandia National Laboratories 2021). The guidelines in this appendix were developed to help bridge those gaps.
B.2.1.3 These guidelines are intended to reduce the public safety risk of all SNS. The guidelines outlined in this appendix use an engineering approach without biases, and a narrow focus for each guideline, which can lead to apparent redundancy for mission concepts that include multiple guideline categories. Collectively, the guidelines in this appendix provide useful direction for a wide variety of nuclear technologies. In some instances, specific guidelines are applicable only to a specific technology or operational concept to address specific identified vulnerabilities. Applicants should use their judgement to identify the guidelines that do not apply to their SNS or mission. Applicants should also use sound engineering judgement and risk mitigation for their mission and implement these guidelines in a manner that reduces the overall public safety risk of the SNS mission.
B.2.2 Minimizing Public Safety Risks.
B.2.2.1 SNS pose a radiological risk to the public any time there is potential for an SNS to return to Earth, this includes launch, orbit, reentry, and Earth flyby. During the development of this AC, the FAA identified topics that each had the ability to significantly increase the overall risk of the system. Summarized below are vulnerabilities in the form of guidelines, recommending selection of lower risk alternatives, with rationale in italics. Some of the guidelines focus on reducing the mission risk, while others focus on reducing the SNS risk.
B.2.2.2 When assessing the risk of an SNS, operators should consider the risks of the system itself, and how the risks of the overall mission impact the risk of the SNS. This is because the public safety impact of an SNS depends not only on the potential failures, but also on the potential locations and interactions of those failures.
B.2.2.3 The overall risk of radiation exposure to the public is a combination of both risks, taking into consideration that the failure of either the SNS or the spacecraft may induce a subsequent failure in the other component. To stay within public risk range requires using lower risk SNS for higher risk missions or performing lower risk missions for higher risk SNS. The guidelines in this appendix address both the mission risk and the SNS risk to aid applicants in staying below the maximum risk threshold regardless of whether the mission development process is started from the perspective of fulfilling a specific mission (fixed initial mission risk) or using a specific SNS (fixed initial SNS risk).
Launch and Reentry of Space Nuclear Systems AC 450.45-1 B.2.2.4 Figure 5 of this AC was developed to aid applicants in understanding the different risk drivers for both mission and SNS risk. The colors assigned to various options are indicators of relative risk within that column, and not indicators of absolute risk, or relative risk between columns. For example, the relative risk between disposal on Earth and a fission system operating close to material limits cannot be definitively stated without knowing additional information about the SNS and the mission. Likewise, the absolute risk for disposal on Earth and operating close to material limits cannot be quantified without additional information about the SNS and mission. What can be definitively stated is that disposal on Earth is riskier than disposal in interplanetary space with no free return trajectory to Earth, and that operating with significant margin to material limits reduces risk compared to operating at material limits.
SNS Design SNS Mission Planning SNS Operations Analysis, Any SNS Cybersecurity Verification Launch Operations EOM Launch Operations EOM and Testing Operating Close Fission System to Material Limits Updated Over Static, Not At Rated Power Critical Testing 1, 2 Populated Areas Overflight of a Densely Planned Lingering in Congested Planned Orbits Planned De-orbit Offshore Winds in the Potential Debris Area Blowing Collision Risk in Exceeds 1x10€ Earth Orbit Disposal on Earth 1,2 1,2 Afterthought 1 Populated Areas Towards Analysis Relies on Novel Increasing Risk Become Critical SNS That May in Accident Conditions 1,2 Meets Generally Cybersecurity Accepted Approaches and Verification and Assumptions Minimal Testing Planned for a Novel Launch Non-Optimal Vehicle and Launch Site Movements to Lower Orbits Planned with SNS Onboard 1 Sufficiently High Disposal in a Planned Orbit Launch Window Second Launch Safe at One- Intervals Orbits with SNS Towards Lower Maneuvers Onboard Sufficiently High Disposal in a Orbit Increasing RIsk Standards and Best Practices at Time of Launch with High Safety Several Barriers Novel Designs Factors and to Release Analysis Based on Accepted Approaches Rigorous Optimal Launch Novel Launch Planned for a Vehicle and Maneuverable Planned on a Beyond GEO Spacecraft Highly Lagrange Point Disposal at a Planned 1 Launch Intervals Launch Window Shown Safe at Sub-Second Gravity Assist Collision Risk Fly-By with Lagrange Point Disposal at a Integrall Site Below 1x10-6 1,2 Designed Quantum-Proof Methods Protect SNS, Planned for a P anned Tor Planned of a Radioactive Natural Decay Host Spacecraft, Up/Downlinks Robust Analysis Rigorous Testing Proven Launch Vehicle and Interplanetary Space with No Interplanetary Disposal in SNS Loaded Late in Launch Interplanetary Disposal in Isotope in a and Ground and Verification Optimal Launch Earth Orbit Space with ivo Countdown Permanent Space with No Robust Package 1, 2 Stations Intersectons Intersections Earth Orbit 1 Departure from Earth's Gravity Intersections Earth Orbit
1. Assessed by FAA Prior to Launch
2. Nuclear Regulator License(s) Required Figure 5 - SINS Mission Risk Drivers B.2.2.5 The risk drivers, and guidelines to minimize risk, fall into these broad categories:
• SNS Design
• Any SNS, appendix B.2.3;
• SNS with Potential to Return to Earth, appendix B.2.4;
o Fission-Based SNS, appendix B.2.5;
• SNS Host Spacecraft, appendix B.2.6;
Launch and Reentry of Space Nuclear Systems AC 450.45-1 56 o SNS Cybersecurity, appendix B.2.7;
o SNS Analysis, appendix B.2.8; and o SNS Validation, Verification and Testing, appendix B.2.9.
• SNS Mission Planning o Launch and Launch Sites, appendix B.2.10;
o Operations, appendix B.2.11; and o EOM, appendix B.2.12.
• SNS Operations o Launch, appendix B.2.13;
o Operations, appendix B.2.14; and o EOM, appendix B.2.15.
B.2.2.6 These guidelines are not requirements or licensing criteria, as it may be possible to design a system that disregards one or more of these guidelines while still meeting an acceptable overall risk level for licensing. Rather, these guidelines give ways to minimize the overall risk to the public from any given SNS and aid applicants who are unfamiliar with either the risks of radioactive material, commercial space operations, or both.
B.2.3 Guidelines Applicable to All SNS Designs.
B.2.3.1 All SNS should be designed to survive the uniquely challenging space environment, including the conditions identified in Table 8 of this AC. SNS should be designed to have a low probability of releasing radionuclides in the event of a launch mishap, in space collision, or uncontrolled reentry impact. To meet this objective, designs should use materials that are able to withstand the operating environmental conditions without failure. Material failure can create a direct path for radioactive material release to the environment or lead to a subsequent SNS or space vehicle failure that results in a direct path for radioactive release to the environment. Of note, the FAA does not regulate SNS designs. Per the Atomic Energy Act of 1954 and the Energy Reorganization Act of 1974, the commercial use of nuclear material in the U.S. is regulated under the authority of the NRC (Atomic Energy Act of 1954, as amended 2021), (Energy Reorganization Act 1974).