Numerical Advisory Solutions
Thermal Hydraulic Analysis

Thermal-Hydraulic Analysis

Our thermal-hydraulic analysis experience has developed from performing a wide variety of nuclear safety and transient analyses for nuclear utilities and vendors. These analyses include but are not limited to design basis transients, operational transients, small and large break LOCAs, anticipated transients without scram, stability, and post-incident evaluation. Our staff can help prepare the code input, select modeling options and make sure all components are simulated correctly. To address NRC concerns, an analysis needs to be defensible beginning with the code input preparation and ending with the analysis results. We can provide training or perform independent reviews to verify the analysis was done properly.
Transient and LOCA Analysis
NAS personnel have developed transient analysis, Chapter 15 safety and radiological analysis, mass and energy releases (including the changes due to steam generator replacements and extended power uprates) and simulator validation. In addition, NAS personnel have developed deterministic and best-estimate analytical methods for small and large break LOCA events. Other projects include use of containment deterministic methods, SMR transient and LOCA methods as well as naval reactor methods. We develop and maintain GOTHIC, RETRAN and VIPRE codes which are used for these specific applications. Moreover, we have used COBRA, RELAP and other codes to model PWR, BWR and fuel vendor transient and LOCA applications.
Containment Response
NAS staff have created GOTHIC and other software models for PWRs, BWRs and new reactor designs for use in containment response analyses. Each model represents the individual plant and has been developed with enough detail to support the requested results such as containment atmosphere pressure and temperature, sump temperature, containment liner temperature and net positive suction head (NPSH) results. GOTHIC has been is approved by the NRC for long term LOCA Mass and Energy release to containment. As a developer and maintainer of GOTHIC, NAS is best positioned to provide guidelines and support for current and future modifications and developments of containment models. Models have been created to support GSI-191 issues and to support submittals to the NRC. We have also evaluated containment mixing, crediting of containment sprays, ice condenser designs and hydrogen management strategies, including the optimization of placement of ignitors and passive autocatalytic recombiners (PARs).

Internal Flooding
We have used GOTHIC to evaluate flooding in buildings caused by a pipe rupture or other liquid intrusion through openings in the walls. A building model can be constructed with sufficient detail to allow evaluation of fluid progression through the building. The water level can be tracked in each room as it builds up on the floor, and drains to rooms on lower elevations through drains, openings, and over curbs. The results can be used to better inform the Probabilistic Risk Assessment (PRA).

Severe Accident Analysis
NAS has analytical experience supporting Fukushima initiatives and other severe accident analyses. Previous work includes but is not limited to a GOTHIC model to evaluate critical rooms for Fukushima Near-Term Task Force (NTTF) issues (EPRI Product 3002005295), portable equipment evaluations (FLEX/ELAP) , and GOTHIC models used to perform a Main Steam Valve Building temperature habitability analyses.
Environmental Qualification
NAS has developed GOTHIC models that have been used to perform environmental qualification analyses. Information pertaining to temperatures and other environmental conditions (such as humidity, hydrogen concentration, habitability issues, etc.) in various buildings of different power plants were evaluated as a consequence of a HELB, ELAP, or LOCA. Results were used to assess HVAC operability, personnel habitation and equipment functional limitations. Analyses were performed for PWRs, BWRs and small modular reactors (SMRs).
Building and Room Heatup
NAS personnel have performed room heat-up calculations to address operability, PSA and Fire Protection requirements. Previous projects have developed temperature profiles of affected rooms following a loss of coolant accident (LOCA), loss of HVAC, loss of off-site power (LOOP) extended loss of AC power (ELAP), and Station Blackout (SBO). Other room analyses consist of charging pump rooms not functioning properly (i.e. cooling water tripping), diesel compartment heat up due to a failure of cooling fans and other room heat-up analyses specific to individual plant scenarios. We have also performed loss of HVAC analyses to assess impacts on diesel, switchgear, cable spreading and control rooms as well as chiller areas.
High Energy Line Break (HELB)
NAS has used GOTHIC to perform many HELB calculations for various nuclear plants. A HELB in one part of the plant has potential impacts on other parts of the plant. Previous analyses evaluated environmental HELB consequences, mass and energy release profiles for multiple line breaks, and designs for small modular reactors (SMRs).
RELAP Experience
While well-known for our GOTHIC, RETRAN, VIPRE and PROTO Tools development, maintenance and applications, NAS has significant experience both applying and developing RELAP. We have over 250 person-years of RELAP experience, including RELAP5/mod3.3, RELAP5-3D and our client's in-house versions. Our staff has constructed RELAP models for 62 PWRs and 8 BWRs and have supported many new reactor concepts using RELAP. We have provided RELAP user support and supported testing, qualification and commercial grade dedication of RELAP. Additionally, we have extensive experience modifying and improving various versions of RELAP to support reactor vendors, international clients and government agencies. NAS personnel have added new features, modified existing capabilities, coupled RELAP to GOTHIC and updated documentation to be compliant with Reg. Guide 1.203.