Lawrence Livermore and

Sandia National Laboratories

Nathaniel BowdenAdvanced Detectors Group

Lawrence Livermore National Laboratory

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory in part under Contract W-7405-Eng-48 and in part under Contract DE-AC52-07NA27344.Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,

for the United States Department of Energy under contract DE-AC04-94AL85000

Status of Recent Detector Deployment(s) at SONGS

December 14, 2007

2

Introduction

Since 2003 a small detector based on Gd loaded liquid scintillator has been deployed at a commercial plant in the US (SONGS)

This relatively simple and non-invasive design has demonstrated remote and unattended monitoring of:• reactor state (power level, trips)• reactor fuel evolution (burnup)

Recently, we have been investigating several paths to more deployable detectors• Use of doped water Cerenkov detectors instead of scintillator• Use of less flammable and combustible, more robust, plastic

scintillator

3

Constant(Geometry,Detector EfficiencyDetector mass)

• ~ 6 Antineutrinos are produced by each fission:

• Antineutrinos interact so weakly that they cannot be shielded, but small detectors have useful interaction rates

• 0.64 ton detector, 24.5 m from 3.46 GW reactor core

• 3800 events/day for a 100% efficient detector

• Rate is sensitive to the isotopic composition of the core• e.g. for a PLWR, antineutrino rate change of about 10% through a 500 day

PLWR fuel cycle, caused by Pu ingrowth

thPN

thPkN )1( Fuel composition dependentSum over fissioning isotopes, Integral over energy dependent cross section, energy spectrum, detector efficiency

Reactors Produce Antineutrinos in Large Quantities

4

The Antineutrino Production Rate varies with Fissioning Isotope: PLWR Example

Days into Cycle0 150 300 450 600F

ract

ion

of

To

tal

Fis

sio

ns

0.0

0.2

0.4

0.6

0.8

1.0235U239Pu238U241Pu

The fuel of a PLWR evolves under irradiation: 235U is consumed and

239Pu is produced

Energy (MeV)

The energy spectrum and integral rate produced by each fissioning isotope is different

5

Prediction for a PLWR

Rea

cto

r P

ow

er (

%)

-20

0

20

40

60

80

100

Date

06/2005 10/2005 02/2006 06/2006 10/2006

Det

ecte

d A

nti

neu

trin

os

per

day

0

100

200

300

400

500

Predicted rate Reported power

Cycle 13Outage

Cycle 14Cycle 13

thPkN )1(

Non-neutrino background

6

LLNL/Sandia Antineutrino Detector “SONGS1” (2004-2006)

Detector system is…

• ~1 m3 Gd doped liquid scintillator readout by 8x 8” PMT

• 6-sided water shield

• 5-sided active muon veto

see NIM A 572 (2007) 985

7

Tendon gallery is ideal location

• Rarely accessed for plant operation

• As close to reactor as you can get while being outside containment

• Provides ~20 mwe overburden

3.4 GWth => ~ 1021 / s

In tendon gallery ~1017 / s per m2

Around 3800 interactions expected per day (~ 10-2 / s)

SONGS Unit 2 Tendon Gallery

~25 m

8

Short Term monitoring – Reactor Scram

With a one hour integration time, sudden power changes can be seen

In this case, a scram is “detected” via SPRT with 99.9% confidence after 5 hours

Manuscript accepted by JAP

9

Relative Power Monitoring Precision

Weekly average 3% relative uncertaintyin thermal power estimate (normalized to 30 day avg.)

Daily average 8 % relative uncertaintyin thermal power estimate (normalized to 30 day avg.)

Manuscript accepted by JAP

10

Rea

cto

r P

ow

er (

%)

-20

0

20

40

60

80

100

Date

06/2005 10/2005 02/2006 06/2006 10/2006

Det

ecte

d A

nti

neu

trin

os

per

day

0

100

200

300

400

500

Predicted rate Reported powerObserved rate, 30 day average

Cycle 14Cycle 13outage

Cycle 13

SONGS1 Fuel Burnup Measurement Removal of 250 kg

239Pu, replacement with 1.5 tons of fresh 235U fuel

11

SONGS1 was very successful, but….

The liquid scintillator used is somewhat flammable, rather combustible, can spill

LS must be transported as a hazardous material, and is transferred onsite into the detector

With the SONGS1 run completed, we are leveraging the installed infrastructure to investigate several paths to more deployable detectors• Use of doped water Cerenkov detectors instead of scintillator• Use of less flammable and combustible, more robust, plastic

scintillator

12

Solid, non-flammable, less combustible, Plastic detector

Replace half of liquid scintillator with plastic scintillator (PS):• Must retain neutron capture capability, ideally on Gd - commercial

neutron capture PS not suitable/available (e.g. Boron loaded BC-454)

• Final design: 2 cm slabs of BC-408 PS, interleaved with mylar sheets coated in Gd loaded paint

13

Such a design is a trade off:

Reactor Operator/ Safeguards Agency

Reduction in combustible inventory of ~ 40%

No leakage or flammable vapour concerns

No transportation of hazardous material required

Preassembled

Physics

XX Lower neutron capture efficiency on Gd

(LS: 80% / 20% Gd/H

PS: 60% / 40% Gd/H)

XX ~ 10% fewer protons/cc

XX Dead material in main volume

14

Design Optimization: Gd loading/PS thickness

Use a Geant4 simulation to explore the effect on neutron capture of varying:• Plastic slab thickness• Gd loading

Use 2 cm thickness, 20 mg/cm2 loading

0

20

40

60

80

100

0.01

0.1

1

10

100

0.40.6

0.81.01.21.41.61.82.0

% c

aptu

res

on G

d

Gd

area

l den

sity

(mg/

cm2 )

Plastic pitch (cm)

0 20 40 60 80 100

Capture fraction, 2cm pitch

Gd areal density (mg/cm2)

0.01 0.1 1 10 100

% c

aptu

res

0

20

40

60

80

100

GdPVT

15

Design Optimization: Optical Modeling

Investigate several readout configurations to optimise position uniformity

y=100

x (mm)

-400 -200 0 200 400

z (m

m)

-300

-200

-100

0

100

200

300

16 18 20 22 24

y=0

x (mm)

-400 -200 0 200 400

z (m

m)

-300

-200

-100

0

100

200

300

16

18

20

22

24

y=100

x (mm)

-300 -200 -100 0 100 200 300

z (m

m)

-400

-200

0

200

400

10 12 14 16 18 20 22

y=0

x (mm)

-300 -200 -100 0 100 200 300

z (m

m)

-400

-200

0

200

40010 12 14 16 18 20 22

16

Construction

17

Installation at SONGS

18

Initial Plastic Data

Response to AmBe neutron source

Response to background at

SONGS

Energy

The plastic detector responds to neutrons in the expected fashion: neutron captures on Gd are observed, as well as correlated (gamma,neutron) events from an AmBe neutron source

Inter-event time

Correlated events

19

Deployment Status

The plastic detector were successfully inserted into the SONGS Unit 2 Tendon Gallery during a two week campaign in August• The removal of liquid scintillator reduced the

combustible inventory in the gallery by almost 40% Neutron captures and correlated events are observed We use a scheduled reactor outage beginning Nov. 27

to observe the detector antineutrino sensitivity……

STOP PRESS!

20

Interevent Time (s)0 50 100 150 200

Co

un

ts

500

750

1000

Plastic detector outage data

Interevent Time (s)0 50 100 150 200

Co

un

ts

500

750

1000

Reactor OnReactor Off

21

Pow

er (

%)

-50

0

50

100

Date

Sep 17 Oct 01 Oct 15 Oct 29 Nov 12 Nov 26

Cou

nts

per

day

0

50

100

150

200

250

300

PredictedObservedReactor Power

Plastic detector outage data

22

Conclusion

A robust antineutrino detector based on a large volume of commercial plastic scintillator has been designed, constructed and deployed

This device has several important advantages over the liquid scintillator that it replaces in a commercial reactor environment:• Non-flammable, non-hazardous, and no possibility of

liquid spillage• Near complete preassembly is relatively simple

The device clearly observes reactor antineutrinos, i.e. can monitor reactor state

Forthcoming work will focus on detector stability and calibration, with a view to observing fuel burnup

23

24

Test of compact steel shielding

Low density shielding is the bulk of the detector volume Replace 60cm water shield with 10 cm steel and measure:• Change in gamma bkg - should be unchanged• Change in correlated bkg (antineutrino like) due to:

Neutrons not attenuated by the steel Neutrons produced in the steel by cosmic ray muons

25

Steel installation in Jan ‘07

26

Steel results

We compare detector halves near and far from steel wall

Near

Before

Near After

Near Ratio

Far

Before

Far

AfterFar

ratio

e+/gamma events /day

149,500 150,500 1.0 166,000 166,000 1.0

Neutron events/day

5,900 7,100 1.2 6,200 6,200 1.0

Correlated events/day

280 360 1.3 280 280 1.0

Correlated bkg events/day

60 140 2.3 70 70 1.0

As expected, gamma ray background is unchanged, but more neutrons get through, producing more correlated background

27

Unscheduled SONGS Unit 2 outage

Unit 2 went down for one week in late October for unscheduled maintenance• Coincidently, wildfires came near the plant a few days

later!

28

Antineutrino Detection

We use the same antineutrino detection technique used to first detect (anti)neutrinos:

e + p e+ + n• inverse beta-decay produces a pair of correlated events in the detector

– very effective background suppression Gd loaded into liquid scintillator captures the resulting neutron after a

relatively short time

Positron• Immediate• 1- 8 MeV (incl 511 keV s)

Neutron• Delayed (= 28 s)• ~ 8 MeV gamma shower(200 s and 2.2 MeV for H capture)

n

ep

~ 8 MeV

511 keV

511 keV e+

Gd

~ 30 s

prompt signal + n capture on Gd

29

Acknowledgements and Project Team

Nathaniel Bowden (PI)

Adam Bernstein

Steven Dazeley

Bob Svoboda

David Reyna (PI)

Lorraine Sadler

Jim Lund

Many thanks to the San Onofre Nuclear Generating Station

Alex Misner

Prof. Todd Palmer

Lawrence Livermore National Laboratory