Erfahrungs- und Forschungsbericht 2012 - Ensi

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Erfahrungs- und Forschungsbericht 2012 - Ensi

een irradiated in KKL Leibstadt to a burn-up of

73 MWd/kgU. The experimental conditions were

the same as those of IFA-650.12 except for the important

difference that the rod was designed to fail.

The experiment was again prepared based on thorough

design and test execution calculations by PSI.

As indicated by the rod pressure measurement, the

rod ballooned and failed at 827 °C. A peak cladding

temperature of 861 °C was reached. There

was no evidence of gross fuel relocation from the

temperature readings. Gamma scanning after unloading

showed a clear ballooning and only small

amounts of fuel (fragments) fallen to the bottom of

the pressure flask.

The in-pile corrosion and hydriding behaviour of

modern Zircaloy-based PWR cladding materials is

studied in aggressive water chemistry and thermal

hydraulic conditions exceeding those currently allowable

in operating PWRs. The materials were

supplied by Westinghouse (USA/Sweden), AREVA

(France) and Japanese industry organisations. The

assembly contains six test rods, each made up of

four sub-segments. The second interim inspection

was completed in May 2012 after about 320 full

power days (assembly burnup: 22 MWd/kg UO 2 ).

The oxide thicknesses of the different cladding

materials varied between 7.5–13 µm and between

10–16 µm, depending on position and in good

agreement with the flux profile.

The benefits of hydrogen water chemistry in mitigating

the initiation of cracks in irradiated (about

13 dpa) 304L SS tensile test specimens is studied

with 18 specimens, 9 in high flux and 9 in low flux

positions. The results are compared with specimen

failures occurring in normal water chemistry. The

load is set to 75 and 95% of yield stress and cycled

(20% reduction) once a day. Failed samples were

removed and replaced with dummies, and the fracture

surfaces were investigated using SEM. Both

fully ductile failure and partial intergranular cracking

were observed. An approximate crack growth

rate of 2.7×10 –6 mm/s is calculated for the intergranular

crack.

A long-term creep and stress relaxation study includes

thirty tensile specimens. Twelve of them are instrumented

and prepared from Alloy 718, CW 316

SS, CW316 Nlot, CW316LN and SA 304L SS. The

uninstrumented specimen matrix comprises 6 Alloy

718, 6 CW 316 SS and 6 SA 304 SS samples. The specimens

are being irradiated at temperatures ranging

from 290 to 390 °C. For the CW 316 SS speci mens,

irradiation creep and stress relaxation data have

been found to be consistent. The SA 304L and the

CW 316LN (low SFE) samples show more creep/

stress relaxation resistance than the CW 316 SS.

The aged Alloy 718 specimens exhibit significantly

higher stress relaxation than the CW 316 SS specimens.

For the CW 316 SS specimens, irradiation creep

and stress relaxation data were found to be consist

ent, and steady state creep rates are in agreement

with previous fast reactor pressurised tube tests.

The test will continue to a dose of 2 dpa.

On-line instrumentation is of key importance for

the in-pile tests performed in the Halden reactor.

Although the instruments perform well, there

are continuous efforts to improve their accuracy,

to obtain more compact designs and to enhance

their measurement range. In addition, new types

of experiments sometimes necessitate the development

of new types of instruments. Efforts in 2012

concentrated on further improving the iron/ironoxide

reference electrodes for measuring the electrochemical

potential, and the in-core testing of online

corrosion measurement. Two methods were

tried, namely Electrochemical Impedance Spectroscopy

(EIS) and Potential Drop (PD) measurements.

A first data evaluation gave promising results. After

discharge, the oxide layer thicknesses on the test

rods will be determined by PIE for comparison/calibration

against the in-core data.

Man-Technology-Organisation (MTO)

research

The MTO research carried out at the Halden Project

is based on the Halden Man-Machine Laboratory

(HAMMLAB), a world-wide reference facility

for human factor studies and advice on control

room engineering. It provides the basis for studies

on the performance of control room operators in

complex and automated environments. HAMMLAB

is complemented by the Virtual Reality Laboratory,

a facility for rapid, interactive, high quality design

of control rooms. Tools to assist in verification

and validation of such designs as well as tools for

maintenance training have been developed. During

2012 a new FutureLab has been established for

early prototyping of operational concepts in highly

automated plants.

Highlights of the work in the MTO area performed

in 2012 are given below.

Human Performance

Past accidents and incidents have underscored the

influence of human performance on the safety of

nuclear power plants. In upgrades of existing plants

or in advanced reactors, the quality and reliability

ENSI Erfahrungs- und Forschungsbericht 2012 109

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