ML22154A173
| ML22154A173 | |
| Person / Time | |
|---|---|
| Issue date: | 10/06/2017 |
| From: | Hossein Esmaili NRC/RES/DSA |
| To: | |
| Esmaili H | |
| References | |
| Download: ML22154A173 (2) | |
Text
Guidance for Performing a Spent Fuel Assembly Adiabatic Heatup Calculation (October 6, 2017)
Introduction and Objectives In the draft regulatory basis, Regulatory Improvements for Power Reactors Transitioning to Decommissioning, (ML16309A332), the staff proposed providing licensees the option of submitting a site-specific analysis. However, currently no guidance exists for performing a spent fuel assembly adiabatic heatup analysis to a limiting condition of 900 oC. The objective of this guidance is to provide a procedure for performing the heatup calculation informed by the analysis documented in Reference [1].
Specifically, The guidance includes a list of assumptions, initial conditions, and acceptable calculation methods necessary to perform an analysis of the cooling time needed after permanent cessation of operations such that spent fuel in the spent fuel pool will not reach the limiting temperature condition of 900 oC within 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />.
BWR/PWR specific guidance is provided as needed.
Considerations for taking the mass of the racks and fuel assembly loading patterns into account should also be provided.
Technical Procedure The steps in performing the heatup calculations are given below and follow the procedure in Reference
[1].
- 1. The adiabatic heatup calculation should be performed based on the decay heat of the hottest assembly discharged from the reactor by considering the burnup and the cooling time discussed in NUREG/CR-7227 [2]. For BWR assemblies, Figure 21 and Table A.3 in Reference [2] provide the decay heat based on 1 metric ton of initial heavy metal loading (MTHM)1. Figure 22 and Table B.3 in Reference [2] provide the data for PWR assemblies, and corresponding results for MOX assemblies are given in Figure 23 and Table C.3 [2]. The decay heat scaling factors in Table D.2 of Reference [2]
should be applied to the decay heat powers discussed above to obtain the data for the hottest assembly.
- 2. The normal operating pool temperature can be used as the initial condition for the fuel assembly (assumed 30°C in Reference [1]).
- 3. The adiabatic heatup of an assembly should be calculated based on Equation (1) in Reference [1]
which was benchmarked against MELCOR calculations using adiabatic boundary conditions.
1 The mass unit MTU is interchangeable with MTHM in the context of UO2 fuel. These results can be converted to an assembly basis by multiplying the quantities by the actual initial loading of uranium or heavy metal of a given assembly [2].
The input decay heat is obtained from step 1 above.
The mass of the fuel rods (UO2, Zr) as well as the rack should be taken into account. The mass of the poison materials should be neglected due to possible degradation and melting at low temperatures.
The MELCOR calculations as well as experimental data (see NUREG/CR-7215) suggest that both fuel rods and the racks heatup together with only a slight temperature difference between them as long as adiabatic boundary conditions are imposed. Therefore, the use of a single temperature for all components is justified.
The specific heat as a function of temperature should be specified and used in the heat up calculation considering the variation with temperature of different components. The inclusion of a temperature dependent specific heat is straightforward in Equation (1) of Reference [1]. The values use in Reference [1] were based on the MELCOR code Reference manual [3].
References
- 1. H. Esmaili, Spent Fuel Assembly Heat Up Calculations in Support of Task 2 of User Need NSIR-2015-001, April 2016 (ADAMS Accession Number ML16110A431).
- 2. J. Hu, et al. US Commercial Spent Nuclear Fuel Assembly Characteristics: 1968-2013, NUREG/CR-7227, ORNL/TM-2015/619, September 2016.
- 3. MELCOR Computer Code Manuals, Vol. 2: Reference Manual, Version 2.2.9541, SAND 2017-0876 O, Sandia National Laboratories, January 2017 (ADAMS Accession No. ML17040A420).