ML12124A078

Power Point Presentation: Peach Bottom - Timing and Criteria for RCS Failure

ML12124A078
Person / Time
Site:	Peach Bottom
Issue date:	04/26/2012
From:	- No Known Affiliation
To:	Office of Information Services
References
FOIA/PA-2011-0083
Download: ML12124A078 (15)

Text

Peach Bottom - Timing and Criteria for RCS Failure

Background:

- Multiple natural mechanisms for early RCS failure are represented in the Peach Bottom MELCOR model

• Stochastic failure of a cycling SRV to re-close

" Thermal seizure of an SRV in the open position

• Steam line or nozzle creep rupture

- SOARCA baseline calculations - SRV thermal failure was the 'lead' or first mechanism to occur Peer reviewers seemed to generally agree with our approach, but questioned the sensitivity of the results to this modeling

Stochastic vs Thermal SRV Failure in Baseline LTSBO U-'

0 0~

rn-I a)

L.

00a)

I.-0~

1400 1200 1000 800 600 400 200 0

2500 2000 1500 CL 1000 500 0

0 2

4 6

8 10 12 14 16 8

9 10 11 12 13 14 15 16 time [hr]

0 6z 600 500 400 300 200 100 0

100 75 50 0

U-25 0

0 2

4 6

8 10 12 14 16 time [hr]

8 9

10 11 12 13 14 15 16 time [hr]

Stochastic Thermal 2

Sensitivity Calculations for Peer Review

" Thermal seizure in half-open position.

Work continues to explain long-term Cs release for this case

" Earlier (stochastic) failure to reclose (level @ TAF)

Failure at -70% confidence level No SRV failure to reclose, main steam line (MSL) creep rupture Represents lower likelihood case No depressurization (ignores predicted SRV seizure or creep rupture)

Not judged a credible case, but examined in response to peer review request 1400

-- No SO-SRV 1000 Operator manually

-Early SO-SRV opens 1 SRV

.MSL creep 900

-NoSO-SRV 1200

-SO-SRV 1/2area

-EarlySO-SR

-Base Case 800

-" -MSL Creep

-B----ea-Base Case 1000 wn 700 MSL creep

)

700-C.

rupture I

II

>% 600 2

800 SRV seizes open 0

RV sei r 600

,O i

Batteries exhaust, I------

-SRVrecloses I

400 A.

.Low er head Z

300 ---- ---

/,

,failure 200-0 0I I

0 2

4 6

8 10 12 14 16 18 20 22 24 0

2 4

6 8

10 12 14 16 18 20 22 24 time [hr]

time [hr]

3

Impact of MSL Creep Rupture vs.

SRV Seizure on Containment Pressure 160 140 120 100 80 60 CL 0)

U)

(L 40 20 0

0 2

4 6

8 10 12 14 16 18 20 22 24 time [hr]

4

Effects of SRV Failure Criteria on Environmental Source Term 0

0 r-0 I..

0.2 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0

MSL creep No SO-SRV Base Case SO-SRV 1/2 area Early SO-SRV 0

7V-0 C

0 LL 0.2 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0

- JNoSO-SRV S.

SO-SRV 1/2 area MSL creep Case i-Early SO-SRV 36 48 0

12 24 time [hr]

36 48 0

12 24 time [hr]

5

Status

• Additional information provided by peer reviewer at 3rd peer review meeting suggests that a purely stochastic SRV failure may be less likely However, early SRV failure may be more likely due to combination of large number of lifts and modest heating above design

• Examination of material properties suggests SRV thermal failure modeling approach (fails after 10 lifts after reaching 1000K) is not best estimate

- Valve may be weaker thermally than currently modeled

• Examination of valve material properties indicates dramatic decrease in spring constant with temperature well below 1000K

- Considering side calculations (ABACUS) using MELCOR thermal hydraulic predictions to develop more realistic estimate of time of SRV thermal failure, and feed that back into MELCOR 6

Surry - Uncertainties in Hydrogen Combustion in the Mitigated STSBO Long-standing issue (SAMGs) - containment spray recovery following core damage and potentially high hydrogen concentrations SOARCA mitigated STSBO sequence assumes emergency containment Containment Pressure STSBO - Mitigation with Portable Equipment spray established after 8 hrs 1

145 Large seismic event slows 0.9-------------...

131 mitigation efforts 0.8 0.7 -- -- - - -- - -- - - -- - -- - - -- -.-- - -..

10 2 Uncertainties in the 0-0

-high timing and severity of the 5--

=* 0.5 73 hydrogen combustion t* 0.$0

'="'*-SPraYS N

58 a

O.

on t* 3..

44 1 0.2

- - 29 I

I 0.1 Spray*

H2 burns Time (days) 7

Investigating Uncertainties in Hydrogen Combustion Element of investigation

- Assessed potential and consequences of high temperature auto or jet ignition at hot leg rupture and vessel failure Performed sensitivity studies using MELCOR to investigate the consequences of delayed combustion Hand calculations

" Maximum deflagration pressure (AICC)

• Detonation pressure (CJ) 8

Analysis of Auto and Jet Ignition

• Two time frames examined Hot leg creep rupture (high temperature, hydrogen rich gas jet)

Vessel failure (high temperature core debris)

• Hot leg creep rupture findings

- Jet combustion is likely with minor pre rization High temperature jet at --1300 K Xh2, jet 0.20,Xoo 2

0.10, and 0.35:< Xh2o <0.50

• Blowdown done in minutes

• Containment is steam inerted after accumulators dump (Xh 2o > 0.65) 9

Analysis of Auto and Jet Ignition Hot leg creep rupture findings (cont)

Occurs after only 140 kg in-vessel hydrogen production

-140 kg (-70 kg created during the ContainmentPressure Response blowdown)

Mitigated Surry STSBO - Delayed Hydrogen Burn Conclusions 1.0 100 0.9 90-0 "Small" burn likely 0.8 Increased Containment Leakage 800

" No risk of increased containment leakage 0.7

.700.

4 0

• Burn would terminate 0.6

" 600 when accumulator 0.5 iydgen-

.-, 500'2 water cools the jet bur 400 0,*.4 400 and steam inerts the Hot 2

containm ent 0.3

.... (z.

a y.------

failur 300 "0

0.2 ves el-------------

2-0.1 100 0.0 0

0 4

8 12 16 Time (hr) 10

Analysis of Auto and Jet Ignition Vessel failure findings High temperature ignition source

• Debris is >1700 K Auto combustion is unlikely

• Locally and globally steam inerted (>65%)

• Earlier spray operation would reduce steam concentration and make auto combustion more likely Water covers the debris

• Water sources Seal leakage PRT rupture Condensation

• Water boils to keep the cavity (and

.*w containment) highly steam inerted CV55 V's 3 0, CV50 CV41 C,1I

,CV5.

11

Analysis of Delayed Ignition

• MELCOR sensitivity study on delayed ignition

• Assumptions Containment Pressure Response Ignored beneficial ignition Mitigated Surry STSBO - Delayed Hydrogen Burn at hot leg and vessel failure 1.0 Delayed ignition until 0.9 0

containment spray 0.8 Increased Containment Leakage ---....-..................

800 te rm in a tio n (1 5 h o u rs )

'.a 0. -:

Ignited all CVs 0.0.

0 simultaneously Delaye XH2 ~ 0. 2 0 hydrogen

• R esu lts

0.

failu re,,.*..

30-"

Potential for increased 0.2 V

---

2..00 containment~

~

~

~~Ho leegg.1

.. -o Predicted failure area of 0.0 0

square inches 0

4 8

12 16 Burn is oxygen limited Time (hr)

(incomplete combustion) 12

Analysis of Delayed Ignition Sprays create combustible conditions but also knockdown airborne fission products Comparison ofAirbone radionuclides in the Containment versus Hydrogen Concentration

• Results Airborne aerosol fission product concentration is negligible after -1 hour Additional fission product release due to increased containment leakage would consist only of noble gases Base case judged as reasonable

" Bounding cases do not increase the source term

• Bounding cases require many conservative and some non-physical assumptions 1.0 0.25 0.20 0

0 4--

I.-

o-0 0

C 0.10 C5 M-0 L0 0.05 0.00 0

5 10 Time (hr) 15 13

Analysis of Bounding Combustion Conservative methods Adiabatic, isochoric, complete combustion (AICC)

• No heat transfer C

XH 2 ~0.20 Surr)

XCO 0.15 15[

ontainment Pressure Response

, STSBO - Delayed Hydrogen Burn f

• Results Potential for increased containment leakage

• Just H2, AICC at 20%

" CO+ H2, AICC at 24%

o

>X 0 2 - 0.12

- Conservatism

• No heat transfer

• CJ (Detonation) o AICCat24%

• AICCat20%

- - Increased Containment Leakage

-MELCOR-Dome U

9 0-0*

1=

L1.

10 AICC Peak -..

Pressure

.4 rt 5t---------*-

Default MELCOR deflagration response moel after sprays complete U-0 0

4 8

Time (hr) 12 16 14

Status

" Results indicate that containment not likely to be deinerted at the same time there are significant fission products airborne Planning additional sensitivity calculations to confirm

- Vary spray start time (6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />)

- Vary ignition time

• Current sensitivities for delayed ignition do not take credit for burn when hot leg ruptures Plan to credit in any additional calculations

" Issue of whether operators would turn on sprays if suspected there was very high concentration of H2 and CO Highlight issue.when requesting Surry perform fact check in April 15