FRAPCON/FRAPTRAN Code Users Group Meeting Effect of additional He production

1. FRAPCON/FRAPTRAN Code Users Group Meeting Effect of additional He production From B10 mixed into the fuel Ulsan National Institute of Science and Technology Westin Charlotte Hotel, Charlotte September, 2013

2. I. INTRODUCTION Current Burnable Absorbers: mostly integrated into fuel • Gd2O3, ZrB2 coated on fuel surface Concern over timely supply of Gd Development of B burnable absorber mixed in the fuel Use of B absorber in UO2 fuel • Preservation of B contents during sintering: BN : relatively good stability until the completion of sintering • Generation of He & Li by the absorption of neutron: affect the fuel performance 10B + n 7Li + 4He

3. II. Evaluation Methods In GASPRO, He production from U fission (hmgp) is calculated as:(cumulative amount if the fuel is burnt until time t with the heat flux qc) where hmgp(t) = The amount of He produced from fission at time t [moles] qc = Heat flux at the time t ProblemTime(t) = Cumulative time at the time t dco = outer diameter of cladding [ft] deltaz = length of axial node [ft]

4. II. Evaluation Methods In subroutine “gaspro”, effective helium production at the beginning of the time step and at the end of the time step (using the total time to this point and the local power) are calculated. The actual production ina timestepis calculated as the production from the previous time step plus the difference of the two previous quantities.

5. II. Evaluation Methods He Production from the absorption of neutron by B10 where HeProd(t) = The amount of He produced from added B10at time t = Boron moles at initial time [moles] BU(t) = the burnup until the time t [GWD/MTU] = the enrichment of the fuel a,b,c= constants The amount of He produced at time ‘t’ can be calculated as a function of BU(t) (Chungchan Lee)

6. II. Evaluation method To sum-up hmgp(t) and Heprod(t), burnup of each axial node in Heprod(t) is simply calculated by using local power and uranium fuel mass ,like hmgp calculation. The He produced in the time step is calculated as hmgp(end of time step) – hmgp(beginning of step) : calculated in TOTGAS subroutine

7. II. Evaluation Methods The actual cumulative production (hmgpt) is calculated at the production from the previous time step plus the difference of the two previous quantities. He Production from fission

8. He Production and B10 depletion • He production by B10 is added to the He from fission of U • : GASPRO & TOTGAS subroutines in FRAPCON • Total cumulative He production(hmgpt) is calculated in subroutine TOTGAS

9. The total He production (both from fission and B10) is calculated in GASPRO as the sum of hmgp and Heprod as follows: Current total He production is calculated as the Hmgpt (total He) = hmgpt(prev. step) + [ hmgp(End of current step) – hmgp(Beginning of current step)] Total He production from fission and B10

10. (i+1)th time step (i-1)th time step ORIGINAL FRAPCON GASPRO subroutine hmgp(Beg.) hmgp(End) hmgp(End) FRAPCON-UNI GASPRO subroutine hmgp(Beg.)= hmgp(Beg.)+Heprod(Beg.) hmgp(End)= hmgp(End)+Heprod(End) hmgp(Beg.) Heprod(Beg.) Heprod(End) (i)th time step TOTGAS subroutine hmgpt(i) = hmgpt(i-1) +[hmgp(End) – hmgp(Beg.)] Beginning(Beg.) End

11. He release to the gap : Booth model : FRAPCON recommendation Fission gases release : F-M model with PNNL modification Total amount of He released

12. II. Evaluation Methods Input description :PWR, UO2 fuel 6 cycle irradiated high BU rod : ~ 70 GWD/MTU : N05

13. III. Results and Discussion The total He : both from B10 and U fission. 300, 450, and 500 ppm boron by modified FRAPCON code, and compared with original UO2 fuel (0 boron). • Fission gas release: rapidly • increases after ~36 GWD/MTU, • He release: continuous increase

14. III. Results and Discussion Rod Internal Pressure • minor influence of boron addition • up to 500ppm Possible reasons The less-than-expected release fraction of He compared with that of fission gas The smaller production of He (by boron addition) compared with that of fission gas in the fuel rod The difference in the release calculation models for He and fission gases

15. III. Results and Discussion Most of the He is generated until early stage of the burnup and then stays the same, while fission gas productions are continuously increasing. The cumulative amount of the production of He is about 1/10 of fission gases Gas Production

16. III. Results and Discussion Until medium burnup level(~37GWD/MTU), the RF of Xe is much less than that of He, but rapidly increase after that BU. The RF of He is higher than those of other fission gases, but still in the 1~2.5 % range. Cumulative release fraction (RF)

17. Conclusion Considering the additional helium generated by neutron absorption of B10, the helium production terms in FRAPCON-UNI are modified well. Based on booth model, helium release fraction should be higher than those of fission gases considering diffusivity , but at the end of life, fission gas(Xe) show a relatively higher release fraction than that of helium. Like fission gases release, Forsberg-Massih model might be applied for evaluating helium release in the future.

18. Thank you for your kind attention!