ML24215A075
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Response to SDAA Audit Question Question Number: A-3.11-4 Receipt Date: 11/06/2023 Question:
This item is a follow-on from item A-3.11-1.
In the response to A-3.11-1, part of NuScales justification for the 720 hour0.00833 days <br />0.2 hours <br />0.00119 weeks <br />2.7396e-4 months <br /> equipment qualification timeframe for Type C variables is that NuScale calculates that they will reach a stable state within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after a core damage accident. In the response, they also propose including a few sentences in a note to FSAR Table 3C-4 indicating that since the core reaches a stable state within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> post core damage, that 720 hours0.00833 days <br />0.2 hours <br />0.00119 weeks <br />2.7396e-4 months <br /> is sufficient for the qualification time for Type C variables. However, for the NuScale design, the EQ program is designed to prevent core damage and under the EQ program for NuScale equipment is not qualified to core damage conditions. This was discussed in our SECY-19-0079. Therefore, core damage shouldnt be relevant to Section 3.11 EQ. Since equipment in the Section 3.11 EQ program are not qualified to core damage conditions, it is unclear why information related to the timeframe for being in a stable state post core damage would be part of the basis for Section 3.11 EQ qualification times. Please justify.
Response
This response supplements the response to Audit Question A-3.11-1 to provide additional justification for assigning a 720 hour0.00833 days <br />0.2 hours <br />0.00119 weeks <br />2.7396e-4 months <br /> post-accident operating time to RG 1.97 Type C variables.
Type C variables provide primary information to the control room operators to indicate the potential for breach or the actual breach of fission product barriers; fuel cladding, reactor coolant pressure boundary, and containment pressure boundary.
The 720 hour0.00833 days <br />0.2 hours <br />0.00119 weeks <br />2.7396e-4 months <br /> extended term post-accident operating time in FSAR Table 3C-4 is applied to Type C variables to ensure monitoring of fission product barrier integrity for design basis accidents addressed by EQ Program as discussed in FSAR Section 3C.4.2.4.
NuScale Nonproprietary NuScale Nonproprietary
The 720 hour0.00833 days <br />0.2 hours <br />0.00119 weeks <br />2.7396e-4 months <br /> extended term post-accident operating time is consistent with the analytical approach used to define the radiological consequences of the iodine spike design basis source term in TR-0915-17565-P-A, Revision 4, Accident Source Term Methodology. In alignment with the guidance in RG 1.183 Revision 0, the iodine spike design basis source term is used in the EQ Program as a bounding surrogate for the radiological consequences of DBEs that result in primary coolant entering the containment. The 720 hour0.00833 days <br />0.2 hours <br />0.00119 weeks <br />2.7396e-4 months <br /> extended term post-accident operating time is also bounding compared to the following:
a)
The emergency core cooling system is analyzed for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> post-accident.
b)
The long term high energy line break cases are run for up to 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> post-accident. After which, the passive cooling analysis becomes dominant.
c)
The passive cooling analysis for the reactor building and control building stabilizes within 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> post-accident.
d)
Control room habitability system has a 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> duration of supply air for breathing and pressurization.
NuScale revises Note 4 of FSAR Table 3C-4 to provide additional bases for the Type C variable 720 hour0.00833 days <br />0.2 hours <br />0.00119 weeks <br />2.7396e-4 months <br /> extended term operating time and to remove the discussion incorporated into Note 4 in response to Audit Question A-3.11-1.
Markups of the affected changes, as described in the response, are provided below:
NuScale Nonproprietary NuScale Nonproprietary
NuScale Final Safety Analysis Report Methodology for Environmental Qualification of Electrical and Mechanical Equipment NuScale US460 SDAA 3C-20 Draft Revision 2 Audit Question A-3.11-1, A-3.11-4 Table 3C-4: Equipment Post-Accident Operating Times Description Time Frame (hours)
Actions Accomplished Basis Short Term (ST) 1
- Event detection
- Initiation of trip and engineered safety features actuation
- Achievement of hot shutdown Note 1 Intermediate Term (IT)
- Achievement of safe shutdown
- RCS depressurization and cooldown
- Maintain fission product barrier integrity Note 2 Long Term (LT)
IT LT 72
- Maintaining safe shutdown
- Maintain fission product barrier integrity Note 3 Extended Term (ET)
LT ET 720
- Maintaining safe shutdown
- Maintain fission product barrier integrity
- Monitoring of fission product barrier integrity Note 4 Notes:
1.
The short term post-accident operating time is assigned to components associated with event detection, reactor trip initiation, or engineered safety features actuation that occur very early in the accident sequence. This includes the module protection system initiation of reactor trip.
containment isolation.
decay heat removal system actuation, emergency core cooling system actuation.
de-energizing the pressurizer heaters.
isolation of demineralized water.
Short term actions are also associated with the achievement of hot shutdown.
2.
Intermediate term actions are associated with the achievement of safe shutdown using decay heat removal system. The intermediate term time frame extends to 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> and is used to qualify equipment that is relied upon to support the emergency core cooling system hold for up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
Examples of equipment assigned an intermediate term post-accident operating time includes:
reactor vent valves reactor recirculation valves 3.
The long term time frame extends to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. This category is considered the maximum post-accident operating time for HELB and MELB events outside containment in areas that are readily accessible after break termination or isolation.
Examples of equipment assigned to this category includes the following.
Equipment that is relied upon to mitigate a HELB or MELB outside containment that are located in the top of module area (outside containment and under bioshield).
Augmented DC power system batteries for separation groups B and C which are sized to support an extended loss of AC power for up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
4.
The extended time frame of 720 hours0.00833 days <br />0.2 hours <br />0.00119 weeks <br />2.7396e-4 months <br /> represents the maximum post-accident operating time used to analyze the design basis accidents addressed by the Chapter 3.11 EQ program and qualify equipment that is relied upon to maintain a safe shutdown condition following a design basis accident. Equipment assigned to this post-accident operating time category are typically located inside the CNV, or in an inaccessible area outside of containment, such as under the bioshield, or are identified as PAM type B, C, or D variables.