# Presentation: 218555

## Development of a RELAP5-3D thermal-hydraulic model for a Gas Cooled Fast Reactor 

**D. Castelliti, **_**C. Parisi**_**, G. M. Galassi, N. Cerullo**** **
**(*****San Piero A Grado Nuclear Research Group**** ***)**
**DIMNP – University of Pisa - ITALY**

***2006 RELAP5-3D******©****** Users Seminar  ***
***Holiday Inn SunSpree Resort – West Yellowstone – USA***
***16 – 18 August 2006***

## Contents

**Introduction**
**ETDR Thermal-Hydraulic Nodalization**
**Main Results**
**Steady State **
**Transient**
**Conclusions**

## Introduction [1/3]

- GCFR**, ****a Gen IV system developed by a wide international consortium (NNC, CEA, CIRTEN, Framatome, JRC-IE, NRG, PSI, Univ. of Delft, etc.)**
**Huge efforts required for testing materials, component, plants layout**
**Need to have a testing facility ******** ETDR**
** **
**Need to have ****numerical tool**** and a ****model**** for proposed experimental analyses**

## Introduction [2/3]

**Different features of GCFR system *****vs.***** present NPPs technology**
**Helium coolant**
**Direct Brayton cycle**
**Fast Neutron Flux**
**Fuel geometry**

- Needs
- to have a **reliable**
-  and **flexible**
- system code
- for _experiments _
- _planning and analyses_

**RELAP5-3D****©**

## Introduction [3/3]

**Proposed ETDR layout as testing facility for GCFR system:**
**Testing **start-up **and **demo** **cores** (different temperatures ranges)**
**Testing fuel and structural materials**
**Analyzing system dynamic behavior**
**Asses Codes Qualification**

**Notes:**
Start Up: 260/560 ° C (500/1040 °F)

## ETDR TH Nodalization [1/2]

** ****722** Nodes
** ****836** Junctions
** ****401** Heat Structures
** ****4635** Mesh Points

## ETDR TH Nodalization [2/2]

**Core modeled by two hydraulic channels**
**Average channel**
**Hot channel**
**MULTID component used for MHX for an improved estimation of Heat Transfer Coefficient (HTC ****not**** imposed)**
**Blower modeled by PUMP component******** use of  benchmark homologous curves**
**Heat structures simulated for all components**
**Model qualified according to benchmark data**

## Qualification [1/2] - Volume-Height Curve

## Qualification [2/2] - Steady State Results

| Parameter | Value | Reference | Error |
| --- | --- | --- | --- |
| System flow rate | 32.18 Kg/s | 32.00 Kg/s |  0.56 % |
| Average channel flow rate | 0.60 Kg/s | N/A | N/A |
| Hot channel flow rate | 0.58 Kg/s | N/A | N/A |
| Pressure (top of the vessel) | 6.92 MPa | 7.00 MPa | 1.14 % |
| Total mass of coolant | 450.28 Kg | N/A | N/A |
| Total mass of coolant without DHR | 351.60 Kg | N/A | N/A |
| Core inlet temperature | 262.5 °C | 260.0 °C | 0.96 % |
| Core average exit temperature | 561.7 °C | 560.0 °C | 0.30 % |
| Exit temp. In average channel | 560.6 °C | N/A | N/A |
| Exit temp. In hot channel | 613.2 °C | N/A | N/A |
| Maximum clad temp. In avg. channel | 623.0 °C | N/A | N/A |
| Maximum clad temp. In hot channel | 685.0 °C | N/A | N/A |
| Maximum fuel temp. In avg. channel | 944.0 °C | N/A | N/A |
| Maximum fuel temp. In hot channel | 1067.0 °C | N/A | N/A |
| Main blower head | 8399 m2/s2 | 8565 m2/s2 | 1.94 % |
| Main blower torque | -2025.5 Nm | -2036.4 Nm | 0.53 % |
| Main heat exchanger heat transfer area | 157.32 m2 | 157.00 m2 | 0.2 % |
| Main heat exchanger heat transfer coefficient | 2261.8 W/(m2 K) | 1648.0 W/(m2 K)  | 37.2 % |
| Reactor power | 50 MW | 50 MW | 0 % |
| Core pressure drop | -0.42 bar | -0.41 bar | 2.44 % |
| Main blower pressure drop | 0.5147 bar | N/A | N/A |

## LOFA Results [1/7] - Blower Velocity

## LOFA Results [2/7] - Primary pressure

## LOFA Results [3/7] - DHR mass flow - helium side

**Open DHR valves**

## LOFA Results [4/7] – DHR mass flow – water side

## LOFA Results [5/7] - Hot channel Clad temperature

## LOFA Results [6/7] - Power trend in DHR HX (provided run-down curve)

## LOFA Results [7/7]

** **Two** transient-cases analyzed**
- provided run-down curve
- calculated run-down curve
**DHR Valves open in ****170 s**** from LOFA in 1****st****  case, and in ****600 s**** in 2****nd****  case**
**Second transient **_**less severe**_** than first one**
**lower pressure peak **
**lower cladding temperature peak **
** ****Natural Circulation**** occurs at:**
**370 s first case**
**870 s in second case (from LOFA)**
**No differences can be found after 1700 s from LOFA for both transients**
**Equilibrium conditions reached after 2600 s from LOFA**

## Conclusions

**RELAP5-3D****©**** confirmed to be a valid and a reliable tool for the development of GCFR technology**
**Model developed can be applied and tested for other transients**
**Further data needed for extensive qualification**
**Future works:**
**Improvements of MHX model using cylindrical geometry MULTID**
**Add 0D and 3D NK feedback**