But after more than 20 years battling on test veterans' behalf, he is cynical.
"I hope the panel will take a fresh look. But I've become a little immune to politicians and bureaucrats. I want to see actions, not words."
More than 1000 New Zealand service personnel have witnessed nuclear tests.
Mr Sefton (70), of Palmerston North, was one of 551 New Zealand sailors involved with Operation Grapple in the late 1950s, and about the same number watched nuclear testing at Mururoa Atoll in 1973.
Fewer than 15% of that total receive war pensions.
More than 400 Operation Grapple veterans have died already, most in their 50s, from cancer.
Mr Sefton says "good headway" has been made since the New Zealand Nuclear Test Veterans Association, of which he is president, was formed in 1975.
Now several cancers are accepted as presumptive conditions.
That means if test veterans are diagnosed with a listed cancer it is assumed their illness is attributable to radiation exposure and they are eligible for a war pension.
However, that ruling does not always seem to filter down to Veteran Affairs, Mr Sefton says.
He maintains the department is inconsistent in its rulings on pension levels, pressures "stressed, fatigued and frightened veterans" with a complicated and prolonged application process and generally treats veterans "callously".
Test veterans deserve better, he says.
After all, formerly top-secret information confirms sailors were ordered above decks to witness atomic detonations so the effect on people and equipment "both protected and unprotected" could be monitored.
In other words, they were unwitting guinea pigs.
Mr Sefton was only 17 when he witnessed his first test, dressed in combat gear, thick protective goggles and a hood. He watched five in all.
By the time the fifth test came round he and his companions were more casual about safety.
"I don't think the implications of radiation were well explained to us at all.
"I remember for [that] test I was standing on the deck with my hands in my pockets, bare-headed, bare-chested and wearing a pair of shorts and sandals.
"We turned our backs for about 10 seconds as the blast went off, then turned round and watched the mushroom cloud rise into the air."
The mushroom looked unusual that day.
Mr Sefton later found out the atomic bomb had exploded too close to the ground.
It sucked up sand and sea water, which it spewed out in a radioactive rain over many square kilometres.
Mr Sefton left the navy when he was 30.
By his mid-30s the artist and musician was so ill he was in "horrific" pain and unable to work.
Specialists eventually diagnosed him with post-traumatic stress disorder which was sending his muscles into spasms.
He later learnt most test veterans were stressed to a lesser or greater degree - so worried their exposure to radiation might cause them to get cancer that they got sick, even when they didn't have cancer.
That theory was confirmed in the early 2000s in a study carried out by Massey University molecular scientist Dr Al Rowland which showed 50 Operation Grapple veterans suffered much greater psychological damage than a control group of 50 men of similar age and background.
A second study on the same groups showed the veterans also had extreme genetic damage compared with the control group - even higher levels of damage than the people involved in the Chernobyl nuclear power plant disaster clean-up.
Genetic damage is known to increase the chances of a variety of illnesses, including cataracts, skin problems, chronic arthritis, blood cancers and premature ageing.
It can also be passed down to subsequent generations.
He says his association will be first on the list for time with the expert panel on veterans' health, with a view to getting a quicker and more consistent outcome for test veterans applying for pensions.